10/29/2010

Using science, not garlic, to fight energy vampires

Information Provided by:Scotty,Scott's Contracting GREEN BUILDER, St Louis "Renewable Energy" Missouri for additional information or to Schedule a "Free Green Site Evaluation" Home Repair and Green Building Specialist!!!

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Scientists collaborating on the project will apply their expertise and research to tunnel field effect transistors and semiconducting nanowires to improve the efficient use of energy in electronics.

To explain the challenge, consider a leaky water faucet — even after closing the valve as far as possible water continues to drip — this is similar to today’s transistor, in that energy is constantly "leaking" or being lost or wasted in the off-state.

In Steeper, scientists not only hope to contain the leak by using a new method to close the valve or gate of the transistor more tightly, but also open and close the gate for maximum current flow with less turns, i.e. less voltage for maximum efficiency.

According to the International Energy Agency, electronic devices currently account for 15 percent of household electricity consumption, and energy consumed by information and communications technologies as well as consumer electronics will double by 2022 and triple by 2030 to 1,700 TWh — this is equal to entire total residential electricity consumption of the in U.S. and Japan in 2009.

Particularly wasteful is the enormous amount of standby consumption. In the European Union it is estimated that standby power already accounts for about 10 percent of the electricity use in homes and offices of the member States.

By 2020 it is expected that electricity consumption in standby/off-mode will rise to 49 TWh per year — nearly equivalent to the annual electricity consumption for Austria, Czech Republic and Portugal combined.
“Our vision is to share this research to enable manufacturers to build the Holy Grail in electronics, a computer that utilizes negligible energy when it’s in sleep mode, which we call the zero-watt PC,” said Prof. Adrian M. Ionescu, Nanolab, Ecole Polytechnique Federale de Lausanne, who is coordinating the project. 


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Part 8: 1st Floor Weatherization

Part 9: See the Difference a Little White Paint Makes

Part 10: Interior Framing-Plumbing-Laundry Room

Part 11: Kitchen Framing Tip #36-Benton Rehab Project

Part 12: Water Main Repair- Benton Rehab

Part 13: Benton Rehab Project Drywall Installation and Tip: Number 1172

Which Kind Of Insulation Is Best?

Email: Scotts Contracting to Schedule a Green Proposal

for Your Next Project 

Scotts Contracting Offers Green Insulation Installs for the St Louis Area




Contents:

Introduction
  • Why Insulate Your House?
  • How Insulation Works
Which Kind of Insulation is Best?
  • What Is an R-Value?
  • Reading the Label
  • Insulation Product Types
Insulating a New House
  • Where and How Much
  • Air Sealing
  • Moisture Control and Ventilation
  • Installation Issues
    • Precautions
    • Attics
    • Walls
  • Design Options
    • Crawlspaces and Slabs
    • Advanced Wall Framing
    • Metal Framing
    • Insulating Concrete Forms
    • Massive Walls
    • Structural Insulated Panels
    • External Insulation Finish System
    • Attic Ventilation or a Cathedralized Attic
Adding Insulation to an Existing House
  • Where and How Much
  • How Much Insulation Do I Already Have?
  • Air Sealing
  • Moisture Control and Ventilation
  • Insulation Installation, the Retrofit Challenge
    • Precautions
    • Attics
    • Walls
    • Basement Walls
    • Floors and Crawlspaces
Resources and Links
About This Fact Sheet



Which Kind Of Insulation Is Best?


Based on our email, this is one of the most popular questions homeowners ask before buying insulation. The answer is that the 'best' type of insulation depends on:
  • how much insulation is needed,
  • the accessibility of the insulation location,
  • the space available for the insulation,
  • local availability and price of insulation, and
  • other considerations unique to each purchaser.
Whenever you compare insulation products, it is critical that you base your comparison on equal R-values.

What Is an R-Value?
Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the greater the insulating effectiveness. The R-value of thermal insulation depends on the type of material, its thickness, and its density. In calculating the R-value of a multi-layered installation, the R-values of the individual layers are added.


The effectiveness of an insulated ceiling, wall or floor depends on how and where the insulation is installed.
  • Insulation which is compressed will not give you its full rated R-value. This can happen if you add denser insulation on top of lighter insulation in an attic. It also happens if you place batts rated for one thickness into a thinner cavity, such as placing R-19 insulation rated for 6 1/4 inches into a 5 1/2 inch wall cavity.
  • Insulation placed between joists, rafters, and studs does not retard heat flow through those joists or studs. This heat flow is called thermal bridging. So, the overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself. That is why it is important that attic insulation cover the tops of the joists and that is also why we often recommend the use of insulative sheathing on walls. The short-circuiting through metal framing is much greater than that through wood-framed walls; sometimes the insulated metal wall's overall R-value can be as low as half the insulation's R-value.
Reading the Label
No matter what kind of insulation you buy, check the information on the product label to make sure that the product is suitable for the intended application. To protect consumers, the Federal Trade Commission has very clear rules about the R-value label that must be placed on all residential insulation products, whether they are installed by professionals, or whether they are purchased at a local supply store. These labels include a clearly stated R-value and information about health, safety, and fire-hazard issues. Take time to read the label BEFORE installing the insulation. Insist that any contractor installing insulation provide the product labels from EACH package (which will also tell you how many packages were used). Many special products have been developed to give higher R-values with less thickness. On the other hand, some materials require a greater initial thickness to offset eventual settling or to ensure that you get the rated R-value under a range of temperature conditions.

Insulation Product Types
Some types of insulation require professional installation, and others you can install yourself. You should consider the several forms of insulation available, their R-values, and the thickness needed. The type of insulation you use will be determined by the nature of the spaces in the house that you plan to insulate. For example, since you cannot conveniently "pour" insulation into an overhead space, blankets, spray-foam, board products, or reflective systems are used between the joists of an unfinished basement ceiling. The most economical way to fill closed cavities in finished walls is with blown-in insulation applied with pneumatic equipment or with sprayed-in-place foam insulation.
The different forms of insulation can be used together. For example, you can add batt or roll insulation over loose-fill insulation, or vice-versa. Usually, material of higher density (weight per unit volume) should not be placed on top of lower density insulation that is easily compressed. Doing so will reduce the thickness of the material underneath and thereby lower its R-value. There is one exception to this general rule: When attic temperatures drop below 0°F, some low-density, fiberglass, loose-fill insulation installations may allow air to circulate between the top of your ceiling and the attic, decreasing the effectiveness of the insulation. You can eliminate this air circulation by covering the low-density, loose-fill insulation with a blanket insulation product or with a higher density loose-fill insulation.
Blankets, in the form of batts or rolls, are flexible products made from mineral fibers, including fiberglass or rock wool. They are available in widths suited to standard spacings of wall studs and attic or floor joists. They must be hand-cut and trimmed to fit wherever the joist spacing is non-standard (such as near windows, doors, or corners), or where there are obstructions in the walls (such as wires, electrical outlet boxes, or pipes). Batts can be installed by homeowners or professionals. They are available with or without vapor-retarder facings. Batts with a special flame-resistant facing are available in various widths for basement walls where the insulation will be left exposed.
Blown-in loose-fill insulation includes cellulose, fiberglass, or rock wool in the form of loose fibers or fiber pellets that are blown using pneumatic equipment, usually by professional installers. This form of insulation can be used in wall cavities. It is also appropriate for unfinished attic floors, for irregularly shaped areas, and for filling in around obstructions.
In the open wall cavities of a new house, cellulose and fiberglass fibers can also be sprayed after mixing the fibers with an adhesive or foam to make them resistant to settling.
Foam insulation can be applied by a professional using special equipment to meter, mix, and spray the foam into place. Polyisocyanurate and polyurethane foam insulation can be produced in two forms: open-cell and closed-cell. In general, open-celled foam allows water vapor to move through the material more easily than closed-cell foam. However, open-celled foams usually have a lower R-value for a given thickness compared to closed-cell foams. So, some of the closed-cell foams are able to provide a greater R-value where space is limited.
Rigid insulation is made from fibrous materials or plastic foams and is produced in board-like forms and molded pipe coverings. These provide full coverage with few heat loss paths and are often able to provide a greater R-value where space is limited. Such boards may be faced with a reflective foil that reduces heat flow when next to an air space. Rigid insulation is often used for foundations and as an insulative wall sheathing.
Reflective insulation systems are fabricated from aluminum foils with a variety of backings such as kraft paper, plastic film, polyethylene bubbles, or cardboard. The resistance to heat flow depends on the heat flow direction, and this type of insulation is most effective in reducing downward heat flow. Reflective systems are typically located between roof rafters, floor joists, or wall studs. If a single reflective surface is used alone and faces an open space, such as an attic, it is called a radiant barrier.
Radiant barriers are installed in buildings to reduce summer heat gain and winter heat loss. In new buildings, you can select foil-faced wood products for your roof sheathing (installed with the foil facing down into the attic) or other locations to provide the radiant barrier as an integral part of the structure. For existing buildings, the radiant barrier is typically fastened across the bottom of joists, as shown in this drawing. All radiant barriers must have a low emittance (0.1 or less) and high reflectance (0.9 or more).

Adding Insulation to an Existing House (Smart Approaches)

[Where and How Much] [How Much Insulation Do I Already Have?] [Air Sealing] [Moisture Control and Ventilation] [Insulation Installation, the Retrofit Challenge]

Does your home need more insulation? Unless your home was constructed with special attention to energy efficiency, adding insulation will probably reduce your utility bills. Much of the existing housing stock in the United States was not insulated to the levels used today. Older homes are likely to use more energy than newer homes, leading to higher heating and air-conditioning bills.

Where and How Much
Adding more insulation where you already have some, such as in an attic, will save energy. You can save even greater amounts of energy if you install insulation into places in your home that have never been insulated. Figure 1 shows which building spaces should be insulated. These might include an uninsulated floor over a garage or crawlspace, or a wall that separates a room from the attic. Figure 3 can give you general guidance regarding the appropriate amount of insulation you should add to your home, and the rest of this page will provide more specific information.
A qualified home energy auditor will include an insulation check as a routine part of an energy audit. For information about home energy audits, call your local utility company. State energy offices are another valuable resource for information. An energy audit of your house will identify the amount of insulation you have and need, and will likely recommend other improvements as well. If you don't have someone inspect your home, you'll need to find out how much insulation you already have.

After you find out how much you have, you can use the ZipCode tool to find out how much you should add. This recommendation balances future utility bill savings against the current cost of installing insulation. So the amount of insulation you need depends on your climate and heating fuel(gas, oil, electricity), and whether or not you have an air conditioner. The program is called the ZipCode because it includes weather and cost information for local regions defined by the first three digits of each postal service zip code. The program also allows you to define your own local costs and to input certain facts about your house to improve the accuracy of the recommendations. However, some personal computer security systems won't allow Java programs to run properly. The recommended R-values table can be helpful in those cases, because it will provide recommendations based on insulation and energy costs for your local area.

 
Look into your attic. We start with the attic because it is usually easy to add insulation to an attic. This table will help you figure out what kind of insulation you have and what its R-value is.

Look into your walls. It is difficult to add insulation to existing walls unless:
  • You are planning to add new siding to your house, or
  • You plan to finish unfinished space (like a basement or bonus room).
If so, you need to know whether the exterior walls are already insulated or not. One method is to use an electrical outlet on the wall, but first be sure to turn off the power to the outlet. Then remove the cover plate and shine a flashlight into the crack around the outlet box. You should be able to see whether or not insulation is in the wall. Also, you should check separate outlets on the first and second floor, and in old and new parts of the house, because wall insulation in one wall doesn't necessarily mean that it's everywhere in the house. An alternative to checking through electrical outlets is to remove and then replace a small section of the exterior siding.

Look under your floors. Look at the underside of any floor over an unheated space like a garage, basement, or crawlspace. Inspect and measure the thickness of any insulation you find there. It will most likely be a fiberglass batt, so multiply the thickness in inches by 3.2 to find out the R-value (or the R-value might be visible on a product label). If the insulation is a foam board or sprayed-on foam, use any visible label information or multiply the thickness in inches by 5 to estimate the R-value.

Look at your ductwork. Don't overlook another area in your home where energy can be saved - the ductwork of the heating and air- conditioning system. If the ducts of your heating or air-conditioning system run through unheated or uncooled spaces in your home, such as attic or crawlspaces, then the ducts should be insulated. First check the ductwork for air leaks. Repair leaking joints first with mechanical fasteners, then seal any remaining leaks with water-soluble mastic and embedded fiber glass mesh. Never use gray cloth duct tape because it degrades, cracks, and loses its bond with age. If a joint has to be accessible for future maintenance, use pressure- or heat-sensitive aluminum foil tape. Then wrap the ducts with duct wrap insulation of R-6 with a vapor retarder facing on the outer side. All joints where sections of insulation meet should have overlapped facings and be tightly sealed with fiber glass tape; but avoid compressing the insulation, thus reducing its thickness and R-value.

Return air ducts are often located inside the heated portion of the house where they don't need to be insulated, but they should still be sealed off from air passageways that connect to unheated areas. Drywall- to-ductwork connections should be inspected because they are often poor (or nonexistent) and lead to unwanted air flows through wall cavities. If the return air ducts are located in an unconditioned part of the building, they should be insulated.

Look at your pipes. If water pipes run through unheated or uncooled spaces in your home, such as attic or crawlspaces, then the pipes should be insulated.

 
Air sealing is important, not only because drafts are uncomfortable, but also because air leaks carry both moisture and energy, usually in the direction you don't want. For example, air leaks can carry hot humid outdoor air into your house in the summer, or can carry warm moist air from a bathroom into the attic in the winter.

Most homeowners are aware that air leaks into and out of their houses through small openings around doors and window frames and through fireplaces and chimneys. Air also enters the living space from other unheated parts of the house, such as attics, basements, or crawlspaces. The air travels through:
  • any openings or cracks where two walls meet, where the wall meets the ceiling, or near interior door frames;
  • gaps around electrical outlets, switch boxes, and recessed fixtures;
  • gaps behind recessed cabinets, and furred or false ceilings such as kitchen or bathroom soffits;
  • gaps around attic access hatches and pull-down stairs;
  • behind bath tubs and shower stall units;
  • through floor cavities of finished attics adjacent to unconditioned attic spaces;
  • utiltity chaseways for ducts, etc., and
  • plumbing and electrical wiring penetrations.
These leaks between the living space and other parts of the house are often much greater than the obvious leaks around windows and doors. Since many of these leakage paths are driven by the tendency for warm air to rise and cool air to fall, the attic is often the best place to stop them. It's important to stop these leaks before adding attic insulation because the insulation may hide them and make them less accessible. Usually, the attic insulation itself will not stop these leaks and you won't save as much as you expect because of the air flowing through or around the insulation. There are many fact sheets that will help you stop these air leaks:
Moisture Control and Ventilation
We talk about moisture control in an insulation fact sheet because wet insulation doesn't work well. Also, insulation is an important part of your building envelope system, and all parts of that system must work together to keep moisture from causing damage to the structure or being health hazards to the occupants. For example, mold and mildew grow in moist areas, causing allergic reactions and damaging buildings.
When Is Moisture a Problem?


When moist air touches a cold surface, some of the moisture may leave the air and condense, or become liquid. If moisture condenses inside a wall, or in your attic, you will not be able to see the water, but it can cause a number of problems. Adding insulation can either cause or cure a moisture problem. When you insulate a wall, you change the temperature inside the wall. That can mean that a surface inside the wall, such as the sheathing behind your siding, will be much colder in the winter than it was before you insulated. This cold surface could become a place where water vapor traveling through the wall condenses and leads to trouble. The same thing can happen within your attic or under your house. On the other hand, the new temperature profile could prevent condensation and help keep your walls or attic drier than they would have been.
Four Things You Can Do to Avoid Moisture Problems:

1. Control liquid water. Rain coming through a wall, especially a basement or crawlspace wall, may be less apparent than a roof leak, especially if it is a relatively small leak and the water remains inside the wall cavity. Stop all rain-water paths into your home by:
  • making sure your roof is in good condition,
  • caulking around all your windows and doors, and
  • keeping your gutters clean - and be sure the gutter drainage flows away from your house.
  • If you replace your gutters, choose larger gutters and gutter guards to help keep rain from dripping onto the ground near the house.
Be sure that the condensate from your air conditioner is properly drained away from your house. You should also be careful that watering systems for your lawn or flower beds do not spray water on the side of your house or saturate the ground near the house. It is also a good idea to check the caulking around your tub or shower to make sure that water is not leaking into your walls or floors. You can place thick plastic sheets on the floor of your crawlspace to keep any moisture in the ground from getting into the crawlspace air, and then into your house.

2. Ventilate. You need to ventilate your home because you and your family generate moisture when you cook, shower, do laundry, and even when you breathe. More than 99% of the water used to water plants eventually enters the air. If you use an unvented natural gas, propane, or kerosene space heater, all the products of combustion, including water vapor, are exhausted directly into your living space. This water vapor can add 5 to 15 gallons of water per day to the air inside your home. If your clothes dryer is not vented to the outside, or if the outdoor vent is closed off or clogged, all that moisture will enter your living space. Just by breathing and perspiring, a typical family adds about 3 gallons of water per day to their indoor air. You especially need to vent your kitchen and bathrooms. Be sure that these vents go directly outside, and not to your attic, where the moisture can cause problems. Remember that a vent does not work unless you turn it on; so if you have a vent you are not using because it is too noisy, replace it with a quieter model. If your attic is ventilated, it is important that you never cover or block attic vents with insulation. Take care to prevent loose-fill insulation from clogging attic vents by using baffles or rafter vents. When you think about venting to remove moisture, you should also think about where the replacement air will come from, and how it will get into your house. When natural ventilation has been sharply reduced with extra air-sealing efforts, it may be necessary to provide fresh air ventilation to avoid build-up of stale air and indoor air pollutants. Special air-to-air heat exchangers, or heat- recovery ventilators, are available for this purpose. For more information about controlled ventilation, see the Whole-House Ventilation Systems Technology Fact Sheet.

3. Stop Air Leaks. It is very important to seal up all air-leakage paths between your living spaces and other parts of your building structure. Measurements have shown that air leaking into walls and attics carries significant amounts of moisture. Remember that if any air is leaking through electrical outlets or around plumbing connections into your wall cavities, moisture is carried along the same path. The same holds true for air moving through any leaks between your home and the attic, crawlspace, or garage. Even very small leaks in duct work can carry large amounts of moisture, because the airflow in your ducts is much greater than other airflows in your home. This is especially a problem if your ducts travel through a crawlspace or attic, so be sure to seal these ducts properly (and keep them sealed!). Return ducts are even more likely to be leaky, because they often involve joints between drywall and ductwork that may be poorly sealed, or even not sealed at all.

4. Plan a moisture escape path. Typical attic ventilation arrangements are one example of a planned escape path for moisture that has traveled from your home's interior into the attic space. Cold air almost always contains less water than hot air, so diffusion usually carries moisture from a warm place to a cold place. You can let moisture escape from a wall cavity to the dry outdoors during the winter, or to the dry indoors during the summer, by avoiding the use of vinyl wall coverings or low-perm paint. You can also use a dehumidifier to reduce moisture levels in your home, but it will increase your energy use and you must be sure to keep it clean to avoid mold growth. If you use a humidifier for comfort during the winter months, be sure that there are no closed-off rooms where the humidity level is too high.
Insulation Installation, the Retrofit Challenges


Whether you install the insulation yourself or have it done by a contractor, it is a good idea to educate yourself about proper installation methods because an improper installation can reduce your energy savings.
Also, if your house is very old, you may want to have an electrician check to see if:
  • the electrical insulation on your wiring is degraded,
  • the wires are overloaded, or
  • knob and tube wiring was used (often found in homes built before 1940).
If any of these wiring situations exists in your house, it may be hazardous to add thermal insulation within a closed cavity around the wires because that could cause the wires to overheat. THIS IS FOR FIRE SAFETY. The National Electric Code forbids the installation of loose, rolled, or foam-in-place insulation around knob and tube wiring. Adding thermal insulation to the ceiling or walls of a mobile home is complex and usually requires installation by specialists.

If adding insulation over existing insulation, do NOT use a vapor barrier between the two layers!


Attics
On unfinished attic floors, work from the perimeter toward the attic door. Be careful about where you step in the attic. Walk only on the joists so that you won't fall through the drywall ceiling. You may need to place walking boards across the tops of the joists to make the job easier. Remember that it is important to seal up air leaks between your living space and the attic before adding insulation in your attic.
Installing batts and rolls in attics is fairly easy, but doing it right is very important. Use unfaced batts, especially if reinsulating over existing insulation. If there is not any insulation in your attic, fit the insulation between the joists. If the existing insulation is near or above the top of the joists, it is a good idea to place the new batts perpendicular to the old ones because that will help to cover the tops of the joists themselves and reduce thermal bridging through the frame. Also, be sure to insulate the trap or access door. Although the area of the door is small, an uninsulated attic door will reduce energy savings substantially.

In some houses, it is easier to get complete coverage of the attic floor with blown-in loose-fill insulation. It is best to hire an insulation contractor for this job. Loose-fill insulation must be prevented from shifting into vents or from contacting heat-producing equipment (such as recessed lighting fixtures). Block off those areas with baffles or retainers to hold the loose-fill insulation in place.
When you stack new insulation on top of existing attic insulation, the existing insulation is compressed a small amount. This will slightly decrease the R-value of the existing insulation. This effect is most important if the new insulation is more dense than the old insulation. You can compensate for this stacking effect and achieve the desired total R-value by adding about one extra inch of insulation if the old insulation is fiber glass, or about 1/2 inch if the old insulation is rock wool or cellulose.
Reflective Systems are installed in a manner similar to placing batts and blankets. Proper installation is very important if the insulation is to be effective. Study and follow the manufacturer's instructions. Often, reflective insulation materials have flanges that are to be stapled to joists. Since reflective foil will conduct electricity, avoid making contact with any bare electrical wiring.

Radiant barriers may be installed in attics in several configurations. The radiant barrier is most often attached near the roof, to the bottom surface of the attic truss chords or to the rafter framing. Do not lay a radiant barrier on top of your insulation or on the attic floor because it will soon be covered with dust and will not work. A separate DOE fact sheet is available for radiant barriers to show which parts of the country are most likely to benefit from this type of system.

If your attic has NO insulation, you may decide to insulate the underside of the roof instead of the attic floor. (This option is more often used in new houses and is described in Design Option: ATTIC VENTILATION OR A CATHEDRALIZED ATTIC). If you choose the cathedralized attic approach, all attic vents must be sealed. Spray-foam is then often used to insulate the underside of the roof sheathing. If batts are used for this purpose, they must be secured in a manner similar to that described below for insulating under floors. It is best to hire an insulation contractor with experience in this type of installation for this job.

Walls
Installing insulation in the cavity of exterior walls is difficult. However, when new siding is to be installed, it is a good idea to consider adding thermal insulation under the new siding. The Retrofit Best Practices Guide provides useful information about adding insulation when you remodel the outside of your house. It usually requires the services of a contractor who has special equipment for blowing loose-fill insulation into the cavity through small holes cut through the sidewall, which later are closed. It is sometimes feasible to install rigid insulation on the outdoor side of masonry sidewalls such as concrete block or poured concrete. However, if that is not an option, you can use rigid insulation boards or batts to insulate the interior of masonry walls. To install boards, wood furring strips should be fastened to the wall first. These strips provide a nailing base for attaching interior finishes over the insulation. Fire safety codes require that a gypsum board finish, at least 1/2 inch thick, be placed over plastic foam insulation. The gypsum board must be attached to the wood furring strips or underlying masonry using nails or screws.
The first-floor band joist may be accessible from the basement or crawlspace. Make sure it is properly insulated as shown in Figure 1. More detailed drawings and insulation techniques for the band joist are shown in the Wall Insulation Technology Fact Sheet.
Basement Walls
When using batt or rigid insulation to insulate the inside of concrete basement walls, it is necessary to attach wood furring strips to the walls by nailing or bonding, or to build an interior stud-wall assembly on which the interior finish can be attached after the insulation is installed. The cavity created by the added framing should be thick enough for the desired insulation R-value.

The kraft paper or standard foil vapor retarder facings on many blanket insulation products must be covered with gypsum or interior paneling because of fire considerations. Some blanket products are available without these facings or with a special flame resistant facing (labeled FS25 - or flame spread index 25) for places where the facing would not be covered. Sometimes the flame-resistant cover can be purchased separately from the insulation. Also, there are special fiber glass blanket products available for basement walls that require less framing and can be left exposed. These blankets have a flame-resistant facing and are labeled to show that they comply with ASTM C 665, Type II, Class A.



Floors and Crawlspaces
If you have a floor over a crawlspace, you can EITHER:
  • Insulate the underside of the floor and ventilate the crawlspace, OR
  • Leave the floor uninsulated and insulate the walls of an unventilated crawlspace.
When batts or rolls are used on the underside of a floor above an unheated crawlspace or basement, fit the insulation between the beams or joists and push it up against the floor overhead as securely as possible without excessive compaction of the insulation. The insulation can be held in place, either by tacking chicken wire (poultry netting) to the edges of the joist, or with snap-in wire holders. Batts and rolls must be cut and fit around cross-bracing between floor joists or any other obstructions. Strips of insulation may be cut off and stuffed into tight spaces by hand. Don't forget to place insulation against the perimeter that rests on the sill plate. If you insulate above an unheated crawlspace or basement, you will also need to insulate any ducts or pipes running through this space. Otherwise, pipes could freeze and burst during cold weather.

Reflective Systems are installed in a manner similar to placing batts. Proper installation is very important if the insulation is to be effective. Study and follow the manufacturer's instructions. Often, reflective insulation materials have flanges that are to be stapled to floor joists. Since reflective foil will conduct electricity, one must avoid making contact with any bare electrical wiring.

Spray-foam can be used to insulate the underside of a floor. The spray foam can do a good job of filling in the space around wires and other obstructions and in filling any oddly-shaped areas. It is best to hire an insulation contractor with experience in this type of installation.

When a fiberglass blanket is used to insulate the walls of an unventilated crawlspace, it is sometimes necessary to attach wood furring strips to the walls by nailing or bonding. The insulation can then be stapled or tacked into place. Alternatively, the insulation can be fastened to the sill plate and draped down the wall. You should continue the insulation over the floor of the crawl space for about two feet on top of the required ground vapor retarder. Because the insulation will be exposed, be sure to use either an unfaced product or one with the appropriate flame spread rating. When rigid foam insulation boards are used to insulate the walls of an unventilated crawlspace, they can be bonded to the wall using recommended adhesives. Because the insulation will be exposed, be sure to check the local fire codes and the flame-spread rating of the insulation product. If you live in an area prone to termite damage, check with a pest control professional to see if you need to provide for termite inspections.

 Article Provided by: http://www.ornl.gov/sci/roofs+walls/insulation/ins_06.html
--
Scott's Contracting
scottscontracting@gmail.com
http://stlouisrenewableenergy.blogspot.com

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Radiant Barriers

Information Provided by:Scotty,Scott's Contracting GREEN BUILDER, St Louis "Renewable Energy" Missouri; http://stlouisrenewableenergy.blogspot.com; contact scottscontracting@gmail.com for additional information or to Schedule a "Free Green Site Evaluation"

Scotts Contracting Home Repair and Green Building Entrepreneur

Posting is Follow up on Radiant Barrier Issues:  http://stlouisrenewableenergy.blogspot.com/2010/06/cool-roofs-materials-options-insulation.html

August 2000-From Journal of Light Construction Radiant Heat Barriers


Q. I have seen many ads for radiant barriers designed to save energy. Is there any evidence that these radiant barriers can reduce home energy costs? If so, in what climates are they most effective? How should they be installed?

A. David Beal, building scientist at the Florida Solar Energy Center, responds: In cooling climates, radiant barriers can and do save cooling energy. Testing at the Florida Solar Energy Center and other laboratories have consistently shown that a radiant barrier can reduce the amount of heat entering a home through the ceiling by 25 to 40 percent. The amount of energy saved depends on the level of conventional insulation in the attic. For those with a thick layer of attic insulation, a 40% reduction in the small amount of heat coming through the ceiling is correspondingly small. For those with minimal attic insulation, on the other hand, a 40% reduction in heat flow through the ceiling is a much larger amount.
Two rules of thumb:
  • If you have R-30 or better attic insulation, the payback period for the installation of a radiant barrier may be long, although it will save energy.
  • In a cooling climate, a house with a radiant barrier and R-19 attic insulation, compared to R-19 with no radiant barrier, should see a reduction in cooling energy requirements of about 10 to 12 percent.
Radiant barriers are not recommended in heating-dominated climates. To my knowledge, there has been no testing of radiant barriers in a heating climate. 

The easiest and cheapest way to install a radiant barrier in new construction is to install roof sheathing with a radiant barrier. Several manufacturers now offer OSB or plywood roof sheathing with a laminated radiant barrier. A radiant barrier system can also be installed under the bottom of the top chord of a roof truss, or to the bottom edge of rafters. Installing a radiant barrier on an attic floor is not recommended, since such barriers easily get dirty, reducing the performance of the radiant barrier significantly. For more information, contact the Florida Solar Energy Center at 407/638-1000. 

Another Article from JLC
October 1992 Do radiant barriers save energy?
Steve Andrews responds: Yes, radiant barriers in vented attics can cut cooling bills by about 10%. They achieve this by reducing heat flow down through the ceiling by 40% or more. But the better question is: Are radiant barriers cost-effective? The answer is also yes, but only in the right climates, only when properly installed, and only at the right price (see map).
Here�s a summary of the latest information:

Climate. The NAHB Research Center�s study (funded by Eagle Shield) promised to yield good information on radiant barrier performance in cold climates, but it has hit contractual snags. So climate-related advice hasn�t changed: Radiant barriers in attics make the most sense in locations where there are 2,000 cooling degree days or more (see map at right). They may also make sense in more moderate climates where annual cooling bills still exceed annual heating bills (excluding mild sections of the West Coast). In cold climates, radiant barriers can make sense in a crawlspace, but this remains unproven for attics.

Properly installed. For attics, staple the barrier beneath the rafters, drape it over the roof trusses before the decking goes on, or staple it directly to the bottom of the roof decking � shiny side down in all cases (see illustration at left). Make sure you vent the attic, since this is the best way to cool this space. Research shows that laying a radiant barrier flat over horizontal attic insulation can cut radiant barrier performance by up to 50% after five years due to dust buildup.

Cost. If you buy material directly from a manufacturer, expect to pay between 7� and 15� per square foot, depending on the quality of paper backing and fiber mesh reinforcement. These two features can dramatically reduce tearing during installation; test this by ripping up samples before you buy. According to the Florida Solar Energy Center, if a homeowner pays about 20� per square foot for the installed barrier, the simple payback will be as little as five years in a cooling climate (based on electricity costs of 8� per Kwh). The greater the cooling load and utility costs, the faster the payback will be.

Steve Andrews is a residential energy consultant and freelance writer in Denver, Colo.

In attics, staple the radiant barrier beneath the rafters, drape it over the roof trusses, or staple it to the bottom of roof decking. In all cases, install the foil shiny side down and vent the roof. 

Radiant barriers make the most economic sense in the deep South. 



Radiant Barrier Information provided by: http://www.ornl.gov/sci/roofs+walls/radiant/rb_01.html

  

DOE/CE-0335P
June 1991


Department of Energy
Assistant Secretary
Energy Efficiency and Renewable Energy 

Building Envelope Research
Oak Ridge National Laboratory

For more information, contact the program manager for Building Envelope Research:
André O. Desjarlais
Oak Ridge National Laboratory
P. O. Box 2008, MS 6070
Oak Ridge, TN 37831-6070

E-mail Andre Desjarlais


Contents:

Introduction
Effect of Radiant Barrier on Heating and Cooling Bills
Important Non-Energy Considerations
Installation Procedures
Appendix
Key to Abbreviations
Information Services
About This Fact Sheet


Introduction

What is a radiant barrier?
Radiant barriers are materials that are installed in buildings to reduce summer heat gain and winter heat loss, and hence to reduce building heating and cooling energy usage. The potential benefit of attic radiant barriers is primarily in reducing air-conditioning cooling loads in warm or hot climates. Radiant barriers usually consist of a thin sheet or coating of a highly reflective material, usually aluminum, applied to one or both sides of a number of substrate materials. These substrates include kraft paper, plastic films, cardboard, plywood sheathing, and air infiltration barrier material. Some products are fiber reinforced to increase the durability and ease of handling.
Radiant barriers can be used in residential, commercial, and industrial buildings. However, this fact sheet was developed only for applications of radiant barriers in ventilated attics of residential buildings. For information on other applications, see the references at the end of the Fact Sheet.
How are radiant barriers installed in a residential attic?
Radiant barriers may be installed in attics in several configurations. The simplest is to lay the radiant barrier directly on top of existing attic insulation, with the reflective side up. This is often called the attic floor application. Another way to install a radiant barrier is to attach it near the roof. The roof application has several variations. One variation is to attach the radiant barrier to the bottom surfaces of the attic truss chords or rafter framing. Another is to drape the radiant barrier over the tops of the rafters before the roof deck is applied. Still another variation is to attach the radiant barrier directly to the underside of the roof deck.
How do radiant barriers work?
Radiant barriers work by reducing heat transfer by thermal radiation across the air space between the roof deck and the attic floor, where conventional insulation is usually placed. All materials give off, or emit, energy by thermal radiation as a result of their temperature. The amount of energy emitted depends on the surface temperature and a property called the "emissivity" (also called the "emittance"). The emissivity is a number between zero (0) and one (1). The higher the emissivity, the greater the emitted radiation.
A closely related material property is the "reflectivity" (also called the "reflectance"). This is a measure of how much radiant heat is reflected by a material. The reflectivity is also a number between 0 and 1 (sometimes, it is given as a percentage, and then it is between 0 and 100%). For a material that is opaque (that is, it does not allow radiation to pass directly through it), when the emissivity and reflectivity are added together, the sum is one (1). Hence, a material with a high reflectivity has a low emissivity, and vice versa. Radiant barrier materials must have high reflectivity (usually 0.9, or 90%, or more) and low emissivity (usually 0.1 or less), and must face an open air space to perform properly.
On a sunny summer day, solar energy is absorbed by the roof, heating the roof sheathing and causing the underside of the sheathing and the roof framing to radiate heat downward toward the attic floor. When a radiant barrier is placed on the attic floor, much of the heat radiated from the hot roof is reflected back toward the roof. This makes the top surface of the insulation cooler than it would have been without a radiant barrier and thus reduces the amount of heat that moves through the insulation into the rooms below the ceiling.
Under the same conditions, a roof mounted radiant barrier works by reducing the amount of radiation incident on the insulation. Since the amount of radiation striking the top of the insulation is less than it would have been without a radiant barrier, the insulation surface temperature is lower and the heat flow through the insulation is reduced.
Radiant barriers can also reduce indoor heat losses through the ceiling in the winter. Radiant barriers reduce the amount of energy radiated from the top surface of the insulation, but can also reduce beneficial heat gains due to solar heating of the roof. The net benefits of radiant barriers for reducing winter heat losses are still being studied.
How does a radiant barrier differ from conventional attic insulation?
Radiant barriers perform a function that is similar to that of conventional insulation, in that they reduce the amount of heat that is transferred from the attic into the house. They differ in the way they reduce the heat flow. A radiant barrier reduces the amount of heat radiated across an air space that is adjacent to the radiant barrier. The primary function of conventional insulation is to trap still air within the insulation, and hence reduce heat transfer by air movement (convection). The insulation fibers or particles also partially block radiation heat transfer through the space occupied by the insulation.
Conventional insulations are usually rated by their R-value. Since the performance of radiant barriers depends on many variables, simple R-value ratings have not been developed for them.
What are the characteristics of a radiant barrier?
All radiant barriers have at least one reflective (or low emissivity) surface, usually a sheet or coating of aluminum. Some radiant barriers have a reflective surface on both sides. Both types work about equally well, but if a one-sided radiant barrier is used, the reflective surface must face the open air space. For example, if a one-sided radiant barrier is laid on top of the insulation with the reflective side facing down and touching the insulation, the radiant barrier will lose most of its effectiveness in reducing heating and cooling loads.
Emissivity is the property that determines how well a radiant barrier will perform. This property is a number between 0 and 1, with lower numbers indicating better potential for performance. The emissivity of typical, clean, unperforated radiant barriers is about 0.03 to 0.05. Hence they will have a reflectivity of 95 to 97 percent. Some materials may have higher emissivities. It is not always possible to judge the emissivity just by visual appearance. Measured emissivity values should be part of the information provided by the manufacturer.
A radiant barrier used in the attic floor application must allow water vapor to pass through it. This is necessary because, during the winter, if there is no effective vapor retarder at the ceiling, water vapor from the living space may condense and even freeze on the underside of a radiant barrier lying on the attic floor. In extremely cold climates or during prolonged periods of cold weather, a layer of condensed water could build up. In more moderate climates, the condensed water could evaporate and pass through the radiant barrier into the attic space. While most uniform aluminum coatings do not allow water vapor to pass through them, many radiant barrier materials do allow passage of water vapor. Some allow water vapor passage through holes or perforations, while others have substrates that naturally allow water vapor passage without requiring holes. However, excessively large holes will increase the emissivity and cause a reduction in the radiant barrier performance. The ability to allow water vapor to pass through radiant barrier materials is not needed for the roof applications.
What should a radiant barrier installation cost?
Costs for an attic radiant barrier will depend on several factors, including the following:
  • Whether the radiant barrier is installed by the homeowner or by a contractor.
  • Whether the radiant barrier will be installed in a new home (low cost) or in an existing home (possibly higher cost if done by a contractor).
  • What extra "features" are desired; e.g., a radiant barrier with perforations and reinforcements may be more expensive than a "basic" radiant barrier.
  • Any necessary retrofit measures such as adding venting (soffit, ridge, etc.)
  • Whether the radiant barrier is installed on the attic floor or on the rafters.
Radiant barrier costs vary widely. As with most purchases, some comparison shopping can save you money. A survey of nine radiant barrier manufacturers and contractors representing 14 products, taken by the Reflective Insulation Manufacturers Association (RIMA) in 1989, shows the installed costs of radiant barriers to range as shown in Table 1. In some cases, radiant barriers are included in a package of energy saving features sold to homeowners. When considering a "package deal", you may want to ask for an itemized list that includes material and installation costs for all measures included. Then shop around to see what each item would cost if purchased individually before you make a decision.
What should conventional insulation cost?
Heating and cooling bills can also be reduced by adding conventional attic insulation. So that you can have some basis for comparison shopping, typical installed costs for adding various levels of insulation are given in Table 2. These costs are typical for insulation installed by contractors. Actual insulation costs will vary from region to region of the country, will vary with the type of insulation selected (blown, or loose-fill, insulation is usually lower in price than "batt" insulation), and may vary from one local contractor to another. You can expect to deduct 20% to 50% for a do-it-yourself application.
You should always check with your local or state energy office or building code department for current insulation recommendations or see the DOE INSULATION FACT SHEET.







Effect of Radiant Barriers on Heating and Cooling Bills

Have heating and cooling effects been tested? At present, there is no standardized method for testing the effectiveness of radiant barriers in reducing heating and cooling bills. But numerous field tests have been performed that show, depending on the amount of existing conventional insulation and other factors, radiant barriers are effective in reducing cooling bills, and also possibly heating bills.

Most of these field tests have been performed in warm climates where a large amount of air-conditioning is used. The Florida Solar Energy Center (FSEC) at Cape Canaveral has performed tests for a number of years using attic test sections, and has also performed tests with full-size houses. A test using a duplex house in Ocala, Florida has been performed by the Mineral Insulation Manufacturers Association. The Tennessee Valley Authority has performed a number of winter and summer tests using small test cells in Chattanooga, Tennessee. The Oak Ridge National Laboratory (ORNL) has performed a series of tests using three full-size houses near Knoxville, Tennessee. The ORNL tests included summer and winter observations. So far, very little testing has been done in climates colder than that of Knoxville. Also, little testing has been done in hot, arid climates such as the southwestern United States.

The tests to date have shown that in attics with R-19 insulation, radiant barriers can reduce summer ceiling heat gains by about 16 to 42 percent compared to an attic with the same insulation level and no radiant barrier. These figures are for the average reduction in heat flow through the insulation path. They do not include effects of heat flow through the framing members. See Tables A1 and A2 in the Appendix for a comparison of measured performance.

THIS DOES NOT MEAN THAT A 16 TO 42 PERCENT SAVINGS IN UTILITY BILLS CAN BE EXPECTED. Since the ceiling heat gains represent about 15 to 25 percent of the total cooling load on the house, a radiant barrier would be expected to reduce the space cooling portion of summer utility bills by less than 15 to 25 percent. Multiplying this percentage (15 to 25 percent) by the percentage reduction in ceiling heat flow (16 to 42 percent) would result in a 2 to 10 percent reduction in the cooling portion of summer utility bills. However, under some conditions, the percentage reduction of the cooling portion of summer utility bills may be larger, perhaps as large as 17 percent. The percentage reduction in total summer utility bills, which also include costs for operating appliances, water heaters, etc., would be smaller. Tests have shown that the percentage reductions for winter heat losses are lower than those for summer heat gains.

Experiments with various levels of conventional insulation show that the percentage reduction in ceiling heat flow due to the addition of a radiant barrier is larger with lower amounts of insulation. Since the fraction of the whole-house heating and cooling load that comes from the ceiling is larger when the amount of insulation is small, radiant barriers produce the most energy savings when used in combination with lower levels of insulation. Similarly, radiant barriers produce significantly less energy savings when used in combination with high levels of insulation.

Most of the field tests have been done with clean radiant barriers. Laboratory measurements have shown that dust on the surface of aluminum foil increases the emissivity and decreases the reflectivity. This means that dust or other particles on the exposed surface of a radiant barrier will reduce its effectiveness. Radiant barriers installed in locations that collect dust or other surface contaminants will have a decreasing benefit to the homeowner over time.

The attic floor application is most susceptible to accumulation of dust, while downward facing reflective surfaces used with many roof applications are not likely to become dusty. When radiant barriers are newly installed, some testing shows that the attic floor application will work better than the roof applications. As dust accumulates on the attic floor application, its effectiveness will gradually decrease. After a long enough period of time, a dusty attic floor application will lose much of its effectiveness. Predictive modeling results, based on testing, suggest that a dusty attic floor application will lose about half of its effectiveness after about one to ten years.

Testing of radiant barriers has been primarily concerned with the effect of radiant barriers on the heat gains or losses through the ceiling. Another aspect of radiant barriers may be important when air-conditioning ducts are installed in the attic space. The roof applications of radiant barriers can result in lowered air temperatures within the attic space, which in turn can reduce heat gains by the air flowing through the ducts, thus increasing the efficiency of the air-conditioning system. These changes in heat gains to attic ducts have not been tested; however, computer models have been used to make estimates of the impact on cooling bills.
Not all field tests have been able to demonstrate that radiant barriers or even attic insulation are effective in reducing cooling bills. In a field test performed by ORNL in Tulsa, Oklahoma, using 19 full-sized, occupied houses, neither radiant barriers nor attic insulation produced air-conditioning electricity savings that could be measured. As in all field tests, these results are applicable only to houses with similar characteristics as those tested. Unique characteristics of the houses used in this field test included the facts that the houses were cooled by only one or two window air-conditioning units, that the units were able to cool only a portion of the house, and that the occupants chose to limit their use of the units (initial air-conditioning electricity consumption averaged 1664 kilowatt-hours per year or about $119 per year).

How much will I save on my heating and cooling bills?
Your savings on heating and cooling bills will vary, depending on many factors. Savings will depend on the type of radiant barrier application, the size of your house, whether it is a ranch style or a two story house, the amount of insulation in the attic, effectiveness of attic ventilation, the color of the roof, the thermostat settings, the tightness of the building envelope, the actual weather conditions, the efficiency of the heating and cooling equipment, and fuel prices.

Research on radiant barriers is not complete. Estimates of expected savings, however, have been made using a computer program that has been checked against some of the field test data that have been collected. These calculations used weather data from a number of locations to estimate the reductions in heating and cooling loads for a typical house. These load reductions were then converted to savings on fuel bills using average gas furnace and central air-conditioner efficiencies and national average prices for natural gas and electricity.
ASSUMPTIONS. For these calculations, the house thermostat settings were taken to be 78F in the summer and 70F in the winter. In the summer, it was assumed that windows would be opened when the outdoor temperature and humidity were low enough to take advantage of free cooling. Also, it was assumed that the roof shingles were dark, and that the roof was not shaded. The furnace efficiency used was 65 percent, and the air-conditioner coefficient of performance (COP) was 2.34. Fuel prices used were 52.7 cents per therm (hundred cubic feet) for natural gas and 7.86 cents per kilowatt-hour for electricity.

Factors that could make your savings larger than the ones calculated would be: a summer thermostat setting lower than 78F, a winter thermostat setting higher than 70F, keeping the windows closed at all times, lower efficiency furnace or air-conditioner, or higher fuel prices. Factors that could make your savings less than the ones calculated would be: a summer thermostat setting higher than 78F, a winter thermostat setting lower than 70F, light colored roof shingles, shading of the roof by trees or nearby structures, higher efficiency furnace or air-conditioner, and lower fuel prices.

A standard economic calculation was then performed that converts the dollar savings from periods in the future to a "present value". The dollar savings were also adjusted to account for estimates of how prices for natural gas and electricity are predicted to rise in future years. This calculation gives a "present value savings" in terms of dollars per square foot of ceiling area. When this value is multiplied by the total ceiling area, the result is a number that can be compared with the cost of installing a radiant barrier. If the present value savings for the whole ceiling is greater than the cost of a radiant barrier, then the radiant barrier will be "cost effective." A real discount rate of 7 percent, above and beyond inflation, and a life of 25 years were used in the calculations.

Tables 3, 4, and 5 give present value savings for radiant barriers based on average prices and equipment efficiencies. Table 3 applies to the attic floor application, where the effects of dust accumulation have been taken into account. Since dust will accumulate at different rates in different houses, and since the effect of dust on performance is not well known, ranges of values are given for this application. Table 4 applies to radiant barriers attached to the bottoms of the rafters, while Table 5 applies to radiant barriers either draped over the tops of the rafters or attached directly to the underside of the roof deck. For comparison purposes, the same computer program has also been used to estimate present value savings for putting additional insulation in the attic; these values are listed in Table 6. By examining several options, the consumer can compare the relative savings that may be obtained versus the cost of installing the option. Generally, the option with the largest net savings (that is, the present value savings minus the cost) would be the most desirable. However, personal preferences will also enter into a final decision.

If you want a better estimate based on your local fuel prices or other equipment efficiencies, you may use the worksheet in the Appendix. Local fuel prices may be obtained from your local utilities.

Examples of Use of Present Value Tables

Example 1
I live in Orlando, Florida in an 1800 square foot ranch style house. I have R-11 insulation in my attic, and the air-conditioning ducts are in the attic. A contractor has quoted a price for a radiant barrier installed on the bottoms of my rafters and on the gable ends for $400. Would this be a good investment?
For this type of radiant barrier, the appropriate table is Table 4. For Orlando with R-11 insulation, the present value savings is listed as $0.32 when the air-conditioning ducts are in the attic. Multiplying this value by 1800 square feet gives a total of $576. This value exceeds the quoted cost of the radiant barrier of $400, and thus this would be a good investment.

Example 2
I live in Minneapolis, Minnesota in a 2400 square foot two-story house. I have R-19 insulation in my attic, and have no air-conditioning ducts in the attic. A contractor has quoted a price for a radiant barrier installed on the bottoms of my rafters and on the gable ends for $250. Would this be a good investment? Would investment in another layer of R-19 insulation be a better investment? A contractor has quoted a price of $564 for adding this insulation.

For this type of radiant barrier, the appropriate table is Table 4. For Minneapolis with R-19 insulation, the present value savings is listed as $0.08 when there are no air-conditioning ducts in the attic. Since the house is two-story, the ceiling area is 1200 square feet. Multiplying $0.08 by 1200 gives a total of $96. This value is less than the quoted cost of the radiant barrier of $250 and thus this would not be a good investment.
For adding another layer of insulation, the appropriate table is Table 6. For Minneapolis, this table gives a present value savings of $0.57 for adding a layer of R-19 insulation to an existing layer of R-19 insulation. Multiplying this value by 1200 square feet gives a total of $684. This value exceeds the quoted cost of the insulation, and thus this would be a good investment.






Important Non-Energy Considerations

Potential for moisture condensation
Condensation of moisture can be a concern when a radiant barrier is installed on the attic floor directly on top of conventional insulation. During cold weather, water vapor from the interior of a house may move into the attic. In most cases, this water vapor will not cause any problem because attic ventilation will carry excess vapor away. During cold weather, a radiant barrier on top of the insulation could cause water vapor to condense on the barrier's underside.

Condensation of large amounts of water could lead to the following problems: 1) the existing insulation could become wet and lose some of its insulating value, 2) water spots could appear on the ceiling, and 3) under severe conditions, the ceiling framing could rot.

Some testing has been performed to determine the potential for moisture condensation with perforated radiant barriers laid on top of the insulation. A test was conducted during the winter near Knoxville, Tennessee, using houses that were operated at much higher-than-normal indoor relative humidities. Since this testing did not reveal any significant moisture condensation problems, it is expected that moisture condensation will not be a problem in climates warmer than that of Knoxville. Further testing of radiant barriers is needed to determine if moisture condensation is a problem in climates colder than that of Knoxville.

One precaution for preventing potential moisture problems is the use of perforated or naturally permeable radiant barriers. The higher the perm rating, the less potential for problems. Avoiding high indoor relative humidities, sealing cracks and air leaks in the ceiling, using a vapor retarder below the attic insulation, and providing for adequate attic ventilation are additional precautions.

Attic ventilation
Attic ventilation is an important consideration. With adequate ventilation, radiant barriers will perform better in summer and excess water vapor will be removed in winter. Unfortunately, specific recommendations for the best type and amount of attic ventilation for use with radiant barriers are not available. Model building codes have established guidelines for the amount of attic ventilation area per square foot of attic floor area to minimize the occurrence of condensation. These guidelines specify one square foot of net free ventilation area for each 150 square feet of attic floor area. This ratio may be reduced to 1 to 300 if a ceiling vapor retarder is present or if high (for example, ridge or gable vents) and low (soffit vents) attic ventilation is used. Since part of the vent area is blocked by meshes or louvers, the net free area of a vent is smaller than its overall dimensions.

Effect of radiant barriers on roof temperatures
Field tests have shown that radiant barriers can cause a small increase in roof temperatures. Roof mounted radiant barriers may increase shingle temperatures by 2 to 10oF, while radiant barriers on the attic floor may cause smaller increases of 2F or less. The effects of these increased temperatures on roof life, if any, are not known.

Fire ratings
The fire ratings of radiant barriers are important because flame and smoke characteristics of materials exposed to ambient air are critical.
TO MEET CODE, A RADIANT BARRIER MUST BE RATED EITHER CLASS A BY THE NATIONAL FIRE PROTECTION ASSOCIATION (NFPA) OR CLASS I BY THE UNIFORM BUILDING CODE (UBC).
To obtain these ratings, a material must have an ASTM E-84 Flame Spread Index of 25 or less and a Smoke Developed Index of 450 or less. Look for these ratings either printed on the product, or listed on material data sheets provided by the manufacturer.
Previous Section - Effect of Radiant Barriers on Heating and Cooling BIlls
Next Section - Installation Procedure



Installation Procedures

Most residential roofs provide some type of attic or airspace that can accommodate an effective radiant barrier system. In new residential construction, it is fairly easy to install a radiant barrier system. The following images show five possible locations for the installation of an attic radiant barrier system.

Location 1 is a relatively new application, where the radiant barrier material is attached directly to the underside of the roof deck.

Location 2 may offer advantages to the builder during construction of a new house. Before the roof sheathing is applied, the radiant barrier is draped over the rafters or trusses in a way that allows the product to droop 1-1/2 to 3 inches between each rafter.
In Locations 3 and 4, the radiant barrier is attached to either the faces or bottoms of the rafters or top chords of the roof trusses. Locations 3 and 4 may be used with either new construction, or with retrofit of an existing house. With either Location 2, 3 or 4, the space between the roof sheathing and the radiant barrier provides a channel through which warm air can move freely, as shown in Figure 2.
In Location 5, the radiant barrier is laid out on the attic floor over the top of existing attic insulation. As discussed previously, this location is susceptible to the effects of dust accumulation. This location is not appropriate when a large part of the attic is used for storage, since the radiant barrier surface must be exposed to the attic space. Also, kitchen and bathroom vents and recessed lights should not be covered with the radiant barrier.

To obtain the best performance with radiant barriers installed in Locations 1 through 4, radiant barrier material should also be installed over the gable ends. For attics that are open to the space over garages or carports, the radiant barrier should extend eight feet or more into the garage or carport to achieve the same effect as installing a radiant barrier on the gable ends. It is not necessary to cover the gable ends with Location 5.
Radiant barriers that are reflective on one or both sides may be used with any of these locations. However, if the radiant barrier is reflective on only one side, the reflective side must face toward the main attic space for Locations 1 and 5. Since a surface facing downwards is less likely to have dust settle on it, it is also recommended that the reflective side face downwards toward the main attic space for Locations 2, 3, and 4.
Since proper attic venting is important to obtain the best performance of the radiant barrier, some modification in the attic vents may be required to achieve expected performance. Where no ridge or gable vents exist, it is recommended that one or the other be installed. Always check existing ridge vent systems to ensure that roofing paper is not blocking the vent opening, and check the soffit vents to ensure that they have not been covered with insulation.

When installing a radiant barrier, care should be taken not to compress existing insulation present in the attic. The effectiveness of the existing insulation is dependent upon its thickness, so if it is compressed, its R-value is decreased. For instance, an R-19 batt compressed to 3-1/2 inches (to top of 2X4 attic floor joists) would now be approximately an R-13 batt.

Safety considerations
  • The installer should wear proper clothing and equipment as recommended by the radiant barrier manufacturer. Handling conventional insulation may cause skin, eye, and respiratory system irritation. If in doubt about the effects of the insulation, protective clothing, gloves, eye protection, and breathing protection should be worn.
  • Be especially careful with electrical wiring, particularly around junction boxes and old wiring. Never staple through, near, or over electrical wiring. Repair any obvious frayed or defective wiring in advance of radiant barrier installation.
  • Work in the attic only when temperatures are reasonable.
  • Work with a partner. Not only does it make the job go faster, it also means that you'll have assistance should a problem occur.
  • If the attic is unfinished, watch where you walk. If you step in the wrong place, you could fall through the ceiling. Step and stand only on the attic joists or trusses or the center of a strong moveable working surface.
  • Watch your head. In most attics, roofing nails penetrate through the underside of the roof. A hard hat may be of some use.
  • Make sure that the attic space is well ventilated and lighted.
  • Do not cover any recessed lights or vents with radiant barrier material (attic floor application).


Appendix

Test Results
Most tests of radiant barriers have measured the reduction in heat flow through the ceiling caused by adding a radiant barrier. The test results are usually expressed in terms of a percentage ceiling heat flow reduction. Table A1 gives a summary of measured ceiling heat flow reductions for summer conditions when radiant barriers were added in various locations to existing R-19 conventional insulation. Table A2 gives a summary for winter conditions. Table A1 shows that, while there are some variations in the summer data, there is also a good amount of consistency. For winter conditions, there are wider variations in the data and less consistency, but the percentage reductions for winter are less than for summer. Tests by the Tennessee Valley Authority and the Mineral Insulation Manufacturers Association show that increasing the insulation level from R-19 to R-30 instead of installing a radiant barrier reduces the ceiling heat flow by 27 to 33 percent. REMEMBER THAT THE NUMBERS GIVEN IN THE TABLES ARE PERCENTAGE REDUCTIONS FOR THE HEAT FLOW THROUGH THE CEILING; THEY ARE NOT PERCENTAGE REDUCTIONS FOR TOTAL ENERGY USED BY THE AIR-CONDITIONING OR HEATING EQUIPMENT.


Energy Savings Worksheet
If you want a more accurate estimate of your energy savings than the ones given in Tables 3-6, you may use the Worksheet given in this Appendix. Step-by-step instructions are as follows:
  1. Examine air-conditioning unit, determine SEER (for a key to abbreviations, see page 24). Divide SEER by 3.413 to obtain efficiency or COP and enter result in Box A. Typical efficiencies are given in Table X. If SEER is unknown, enter 2.3 in Box A.
  2. Examine heating equipment. Determine whether it is a gas furnace, oil furnace, heat pump, electric furnace, or electric baseboard heating. Determine efficiency, and enter in Box B. Typical efficiencies are given in Table X. If efficiency is unknown, enter 0.65 in Box B.
  3. Obtain cost of electricity, either by examining your electric bills or by contacting your utility. Multiply the cost in cents per kilowatt-hour by 2.93 and enter result in Box C.
  4. Obtain cost of heating fuel, either by examining your fuel bills or by contacting your utility.
    If you heat with gas, multiply the cost in dollars per CCF (or therm) by 10 and enter result in Box D.
    If you heat with oil, multiply the cost in dollars per gallon by 7.15 and enter result in Box D.
    If you heat with electricity (including a heat pump), multiply the cost in cents per kilowatt-hour by 2.93 and enter result in Box D.
  5. Divide the value in Box C by the value in Box A and enter result in Box E.
  6. Divide the value in Box D by the value in Box B and enter result in Box F.
  7. Inspect your attic to determine the type and level of conventional attic insulation, the area of the ceiling, and whether or not the cooling ducts run through the attic. The level of insulation may be estimated with the following chart for insulation thickness (in inches) as a function of insulation type and level:
    Type of Insulation R-11 R-19 R-30 R-38
    Fiberglass batts
    Loose-fill fiberglass
    Loose-fill cellulose
    3.5"
    4.75"
    3.75"
    6.25"
    8.25"
    6.50"
    9.75"
    12.75"
    10.50"
    12.5"
    16"
    13"
    The area of the ceiling is determined by estimating the length and width (in feet) of the ceiling and multiplying these two values together. Enter this value in Box 1.
  8. a. If you plan to install a radiant barrier (RB)
    Go to Table Y1. Locate a city that is near your location and then read off the value for that city for the level of insulation in your attic. Then multiply this value by one of the following factors depending upon the type of radiant barrier you plan to install, and enter the result in Box 2:
    Radiant Barrier Description Configuration Factor
    For low range of values for dusty attic floor RB 0.16
    For high range of values for dusty attic floor RB 0.65
    For RB attached to rafter bottoms, and with no ducts in attic 0.78
    For RB attached to rafter bottoms, and with ducts in attic,
    - and with R-11 conventional attic insulation 0.98
    - or with R-19 conventional attic insulation 1.07
    - or with R-30 conventional attic insulation 1.15
    - or with R-38 conventional attic insulation 1.22
    For RB draped over tops of rafters or attached to roof deck,
    - and with no ducts in attic 0.68
    For RB draped over tops of rafters or attached to roof deck, and with ducts in attic,
    - and with R-11 conventional attic insulation 0.86
    - or with R-19 conventional attic insulation 0.93
    - or with R-30 conventional attic insulation 1.01
    - or with R-38 conventional attic insulation 1.07
    b. If you plan to install more insulation.
    Go to Table Y3. Locate a city near your location and read off the value for that city and for the initial and final levels of attic insulation. Note that values in the table may be added in steps. For example, if you start with R-11 insulation and want to go to the R-38 level, add the values for going from R-11 to R-19, for R-19 to R-30, and for R-30 to R-38. Enter the value in Box 2.
  9. a. If you plan to install a radiant barrier.
    Go to Table Y2. Locate the same city that you used for Step 8a and read off the value for that city for the level of insulation in your attic. Then multiply this value by one of the following factors depending upon the type of radiant barrier you plan to install, and enter the result in Box 3:
    RAdiant Barrier Description Configuration Factor
    For low range of values for dusty attic floor RB 0.24
    For high range of values for dusty attic floor RB 0.61
    For RB attached to rafter bottoms 0.88
    For RB draped over tops of rafters or attached to roof deck 0.82
    b. If you plan to install more insulation.
    Go to Table Y4. Locate the same city that you used for Step 8b and read off the value for that city and for the initial and final levels of attic insulation. Note that values in the table may be added in steps. For example, if you start with R-11 insulation and want to go to the R-38 level, add the values for going from R-11 to R-19, for R-19 to R-30, and for R-30 to R-38. Enter the value in Box 3.
  10. Multiply the values in Boxes 1, 2, and E together, and divide the result by 1,000,000. Enter the result in Box 4.
  11. Multiply the values in Boxes 1, 3, and F together, and divide the result by 1,000,000. Enter the result in Box 5.
  12. Add the values in Boxes 4 and 5 together, and enter the result in Box 6. This is the expected savings per year due to adding a radiant barrier or additional attic insulation.
  13. a. If you plan to install a radiant barrier
    Determine the estimated cost for installing a radiant barrier in your home. This may be from a quote, or you may estimate the cost by using the values in Table 1 along with your estimate of the ceiling area. Note that for radiant barriers installed on the rafters or on the roof deck, you will have to estimate the area of the roof and the areas of the gable ends. Enter the estimated cost in Box 7. b. If you plan to install additional attic insulation.
    Determine the estimated cost for installing more insulation in your home. This may be from a quote, or you may estimate the cost by using the values in Table 2 along with your estimate of the ceiling area. Enter the estimated cost in Box 7.
  14. Go to Table Z. Locate the census region where you live and read off the value for electricity. Enter this value in Box 8.
  15. Go to Table Z. Locate the census region where you live and read off the value for either electricity, oil, or natural gas, depending upon your heating fuel type. Enter this value in Box 9.
  16. Multiply the value in Box 4 by the value in Box 8. Enter the result in Box 10.
  17. Multiply the value in Box 5 by the value in Box 9. Enter the result in Box 11.
  18. Add the value in Box 10 to the value in Box 11 and enter the result in Box 12.
  19. Compare the value in Box 12 with the value in Box 7. If the value in Box 12 is greater than or equal to the value in Box 7, then the radiant barrier or additional insulation is an economical investment. If the value in Box 12 is less than the value in Box 7, then the radiant barrier or additional insulation is not an economical investment.
  20. A simple payback period may also be determined by dividing the value in Box 7 by the value in Box 6. The result will be the number of years that it takes for the energy savings with the radiant barrier or additional insulation to pay back its initial cost. Note that this procedure is not applicable to the radiant barrier on the attic floor, because the energy savings changes from year to year.
Note: If you are planning to install a radiant barrier on the attic floor on top of the existing attic insulation, you should go through the worksheet twice, using the two factors that are given in Steps 8a and 9a to obtain an estimate of the expected range of energy savings.
Example of Use of Worksheet
I live in Orlando, Florida in a one-level 1800 square foot house. I have a heat pump system that has medium efficiency. My electricity costs 8 cents per kilowatt hour. I have 3.5 inches of fiberglass batt insulation (R-11) in my attic and the air-conditioning ducts are in the attic. A contractor has quoted a price for a radiant barrier installed on the bottoms of my rafters and on the gable ends for $400. Would this be a good investment?
Following the steps outlined in the instructions, the worksheet is filled out. The total present value of energy savings given in Box 12 is $533.14. This value exceeds the quoted cost of the radiant barrier of $400, and thus this would be a good investment.




EXAMPLE



ENERGY SAVINGS ESTIMATE FOR RADIANT
BARRIERS OR ATTIC INSULATION
WORKSHEET
COST OF ENERGY FOR HEATING AND COOLING
Code: (A) (B) (C) (D) (E) (F)
Cooling Equipment Efficiency
(From Table X)
Heating Equipment Efficiency
(From Table X)
Cooling Fuel Price
$/Million BTU
Heating Fuel Price
$/Million BTU
Cooling Energy Cost
$/Million BTU
[C÷A]
Heating Energy Cost
$/Million BTU
[D÷B]
2.6 1.9 8x2.93=
23.44
8x2.93=
23.44
9.02 12.34
For fuel prices:
Electricity: $/million BTU = ¢/KWH x 2.93
Natural Gas: $/million BTU = ($/therm or $/CCF) x 10
Fuel Oil: $/million BTU = $/gal. x 7.15


ESTIMATED ENERGY SAVINGS
Code: (1) (2) (3) (4) (5) (6) (7)
Ceiling Area, Square Feet Cooling Load Factor
(From Table Y)
Heating Load Factor
(From Table Y)
Annual Cooling Savings, $/yr
[(1) x (2) x E] ÷ 1,000,000
Annual Heating Savings, $/yr
[(1) x (3) x F]÷ 1,000,000
Total Energy Savings, $/yr
[(4)+(5)]
Cost for RB or Insulation, $
1800 2575x0.98=
2524
275x0.88=
242
40.98 5.38 46.36 400



ESTIMATED LIFE CYCLE PRESENT VALUE SAVINGS

Code: (8) (9) (10) (11) (12)
Cooling Discount Factor
(From Table Z)
Heating Discount Factor
(From Table Z)
Present Value Cooling Savings, $
[(4) x (8)]
Present Value Heating Savings, $
[(5) x (9)]
Total Present Value Energy Savings, $
[(10) + (11)]
11.50 11.50 471.27 61.87 533.14

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