StLouis Renewable Energy: Eco Friendly Roofs
Showing posts with label Eco Friendly Roofs. Show all posts
Showing posts with label Eco Friendly Roofs. Show all posts

StLouis White TPO Roof Project CAD Detail

StLouis, MO St. Louis, MO, USA Links to this post
CAD Detail No: 9821 White TPO Flat Roof Replacement Detail using Structodeck.

CAD Detail White Roof Install Masonry Building StLouis Investment Property
CAD Detail No: 9821 White TPO Flat Roof Replacement Detail using Structodeck
  • I've found that making a simple and quick graphic image to use as a visual tool to explain a building system repair to a client is easier when I provide a "non technical" image of the proposed work to be done.
  • Why GAF EverGuard® TPO
    • Outperforms standard TPO in heat aging and UV tests—the best predictors of TPO performance
      - Independent TPO Study proves EverGuard® TPO 60 mil Membrane is the best standard TPO in accelerated aging. View the key findings and full study here.
      - After accelerated heat aging at 275°F (135°C) for 112 days, EverGuard® TPO showed no cracking—while every one of the competitors’ samples had failed!
      - UV testing—Greater than 2.5 times the industry standard (ASTM D6878 weather resistance test)
    • Guarantees are available up to 25 years when using EverGuard® TPO 60 mil Membrane.*
    • Easier to install due to:
      - Large welding window
      - Most complete line of accessories
      - 10' (3.05 m) wide sheets



  • DESCRIPTION STRUCTODEK HD is not only an integral roofing system component; it also makes roofing easier with physical properties that generate structural rigidity and dimensional stability. The wood fiberboard composition of STRUCTODEK HD possesses natural bonding qualities, resulting in superior adhesion capabilities. Adhesive tightly grasps the fibers of STRUCTODEK HD without causing excess absorption, providing a solid and secure roof system which bonds very well with many asphalt, coal tar, and cold-process adhesive products. The lightweight nature of STRUCTODEK HD is better than heavier alternatives and will keep the roof load below the specified maximum weight. Source




  • Below photo prior jobsite building photo after barrel tile roof removal replaced with asphalt shingles.


    Kevin at Travis Roofing Supply was a great help in outlining the proper materials and needed prep to ensure the TPO roofing will meet and exceed the expectations of the Investment Property Owner plus the 25 year product guarranty. 

    Travis Roofing Supply is located just north of the Vandeventer/44 in the old RSG Roofing Building 


    Thank You for stopping by the Green Blog. If additional information in needed or you have a question let me know by posting a question or comment. Together we can make a difference and create a future that will benefit everyone.
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    Porch Roof Replacement

    StLouis, MO St Louis, MO 63109, USA Links to this post
    Photos and Project Descriptions of Roof Replacement on Front Porch of Investment Property in South St Louis MO
    • CertainTeed Ashphalt Shingles, Drip Edge, Lumber, and Misc Materials

    Porch Roof Replacement (6 Square Roof)
    Scotts Contracting-Porch Roof Replacement

    Radiant Barriers

    StLouis, MO St Louis, MO 63109, USA Links to this post
    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

    Residential Green Roofs

    Links to this post

    Scotts Contracting is available for the building of your Green Roof.  Scotty is available to supply a Free Green Estimate for your Roofing Projects- large or small.  With more than 50 different Green Roofing options available at my preferred Roofing Supplier, RSG- Roofing Supply Group, in St Louis.  I can build a Green Roof on most every budget.

    Green House

    Green is a great in commercial roofing, but what about for residential roofing?


    Read more articles related to:


    Brett Hall/Joe Hall Roofing
    Source: REPLACEMENT CONTRACTOR Magazine
    Publication date: May 12, 2010

    By Jim Cory
    Ask a roofer what a green roof on a commercial building is and he probably has a clear idea of the options. It could be a vegetation roof installed on top of a water-proofing system or a roofing system designed to save on the cost of heating and cooling the building. Or it could be both. Many such systems exist because there's a market for them. Commercial building owners budget to replace their roofs on a regular basis, and reducing energy consumption, as well as prolonging the life of the roof and thus of the building, is always a goal.

    Residential Green

    But for residential steep-slope roofs, where exactly does green fit in? Obviously no one is going to plant a garden on a gable roof, since it would all slide off in the first hard rain. So is the concept of green roofing restricted to commercial roofing applications?
    In Naples, Fla., roofer Ken Kelly, president of Kelly Roofing, doesn't think so. He is convinced that green is the way to go with residential roofing customers, so much so that he puts green roofing front and center on the company website. "Commercial customers are the ones with the deep pockets," he says. "They can afford the $500,000 photovoltaic system or the 5,000-square-foot roof garden. But green is as big an issue in residential as it is in commercial roofing. Homeowners are asking more questions about green than our commercial customers." Driven by changes in the Florida building code and a desire to save on air conditioning bills, Kelly Roofing customers are amenable to suggestions that green products such as solar-powered attic fans be included in their re-roofing jobs.

    Interest, Awareness Vary by Market

    For those working on residential roofs, green means a new roof installed with attention paid to emissivity - the degree to which the roof reflects heat and sunlight away from the building - reduced energy consumption, and the recycling of tear-off materials. Different products, different practices. Once incorporated into a company's procedures, customers are often open to these. But cost remains an issue, and not all homeowners are open to green roofing or green roofing products.
    Roofers who attend trade shows and read trade magazines may know about green roofing products, but homeowners generally know little. "It hasn't taken off like it has in commercial," says Chris Kamis, owner of Absolute Roofing & Construction, in Parma, Ohio, which divides its business about evenly between commercial and residential jobs. Other companies find similar.
    "The customer never brings it up," notes Brett Hall, president of Joe Hall Roofing, a Pantego, Texas, company that also does both commercial and residential roofs. Hall says that it's up to him to introduce homeowners to the subject of cooling the roof with enhanced ventilation and different shingle colors. And if people are getting a new roof because they're planning to move, as is often the case, "it's not that popular a subject. Why invest in something when they can never recoup the cost?"

    Demonstrate by Example

    Customers may not know that much about the subject, but Absolute Roofing is no stranger to green. Five years ago the company installed the roofing, siding, and gutters at Eco-Village, a 20-townhouse pilot project sponsored by the city of Cleveland and partly funded with federal money. In that case, the cost of using green products was a factor in landing the company the job, but not the only factor.
    What was more important were LEED points earned by the builder/designer. And a year ago Absolute Roofing won the business of a Cleveland-area homeowner who required the bidders to show that they would recycle roofing tear-off. Absolute Roofing & Construction did so and won the job. But projects like these are rare. In many residential jobs, which make up 50% of the company's business, green for Absolute Roofing means installing shingles that absorb heat and are eligible for tax credits under the 2009-2010 American Recovery and Reinvestment Act.
    Kamis notes that one popular request in the green building line is rain barrels, which capture rainwater run-off and store it for reuse. Solar would be on the agenda, if the price put it within the average homeowner's reach. "Some people are a lot more sensitive about it than others," says Rod Menzel, co-owner of GreatWay Roofing, in Moorpark, Calif. "Some have the money to be environmentally friendly and green, and others don't."
    Kelly Roofing found that the suggestion of switching from a shingle to a metal or tile roof in a re-roofing job — the metal product the company installs qualifies for tax credits — met with great receptivity from homeowners once the cost of installing a roof with any of those materials became relatively similar. Because green is all over Kelly Roofing's website, "our customers are expecting us to mention green in our presentation and to follow that up with some sort of green product," Kelly says. The company, which does business in a market where failure to recycle shingle tear-off results in a $500 fine, has "Follow Me To The Recycling Center" painted on the back of all its trucks.

    Green in Increments

    Other green products popular with roofing and home improvement contractors include radiant heat barriers, which reduce heat transfer through the attic by as much as 95%. Menzel says that there are a number of roofing systems his company uses to reduce heating and cooling costs in commercial products ? far fewer in residential. "We use the Solaris shingle by CertainTeed," he says — an Energy Star-qualified product that meets both emissivity and reflectivity standards. GreatWay Roofing has also seen strong demand for those same solar-powered attic fans, a hot product at this year's International Roofing Expo in New Orleans. But when it comes to big-ticket green items — say renewable energy projects such as solar systems to power the house — most residential roofers hang back. "There are some awesome ideas out there," Kamis says. "But there's not enough interest to make them practical and affordable in the market."Other home improvement companies are looking at eco-friendly roofing products that can be installed without committing to the cost of a totally green roof. Matt Weiner, general manager of Moonworks, in Rhode Island, says that his company is looking at products such as reflective shingles, although "in the Northeast it doesn't make that much difference." What does intrigue him, he says, are photovoltaic cells that can be integrated into an asphalt shingle roof. "It's a way to bring a greener product to the marketplace and differentiate us," he says. And in the end, a means to greater profitability and a higher close rate.

    Not For the Faint of Heart

    Hall brings up the subject of green roofing to let prospects know what kind of upgrade options are available when buying a new roof. "When we're talking about green, we're talking about ways to conserve energy in your home that relate to roofing," he says. It's as simple as that. And in Texas, where shingle recycling facilities are few, if they exist at all, the major opportunity for green roofing is in increasing emissivity and energy loss, which is chiefly caused by the roof baking away while air conditioning bills go up, up, up. "In Texas, green is emissivity. That's where they start having some return on investment," Hall says.
    To prove the point, the president of Joe Hall Roofing decided to design the new home he is moving into this August with the greenest possible roof. That roof material is standing seam metal painted with a cool pigment. Underneath it is ice-and-water shield covering all the decking. Key to keeping the roof much cooler is the 1-inch pocket of air between that OSB decking and the 1-inch polyiso insulation panel. The roof system is fully vented, with removable soffit vents, for cleaning. The next step: a photovoltaic array on the roof.
    Besides radically reducing what would typically be a $1,000 a month air conditioning bill during the summer, Hall will use the house to show prospects what green roofing looks like, what it feels like, and how well it works.
    —Jim Cory, editor, REPLACEMENT CONTRACTOR.


    --
    Scott's Contracting
    scottscontracting@gmail.com
    http://stlouisrenewableenergy.blogspot.com
    http://www.stlouisrenewableenergy.com

    Cool Roofs-Materials, Options, Insulation, Photos

    StLouis, MO St Louis, MO 63109, USA Links to this post

    Cool Roofs for Hot Climates

    Lighten the loads on home air conditioners with reflective roofing, radiant barriers, or better insulation and ventilation



    Steven Spencer, FSEC

    Even in hot, sunny climates, it's common to see dark shingle roofs. That heat-absorbing choice carries a significant energy penalty: In sunny climates, heat gain through the roof makes up a major share of a house's cooling load.

    People try different strategies to limit heat gain through the roof. Extra ceiling insulation, extra ventilation, under-roof radiant barriers, and sealed attics with insulated roof decks can all help in certain circumstances. But research shows that the single most effective way to cut the cooling loads from a hot-climate roof is to make the roof reflective. There's a reason all those quaint little cottages in Bermuda have white roofs -- they work.

    Reflective roofs work because they stop the rooftop heat before it ever gets going. The sun's rays hit the roof at the speed of light, and at the speed of light they bounce back into space. White or light-colored materials work best, but some new dark pigments reflect enough invisible infrared radiation to reject a lot of solar energy. And whether you're applying tile, metal, membranes, or even asphalt shingles, choosing a more reflective version seldom adds cost.

    Let's look first at reflective roofs, then consider some of the other options for cutting heat gain through the roof.


    Reflective Roofing
    It's well established that reflective roofing materials can lighten the load on home air conditioners. When researchers at the Florida Solar Energy Center (FSEC), where I am a principal scientist, whitened the roofs of nine occupied homes in the summer of 1994, air-conditioning savings averaged 19%. We got even better information by comparing seven otherwise identical new homes with various roof types in a study sponsored by Florida Power & Light (FPL) during the summer of 2000 (see Figure 1). All these homes had R-19 ceiling insulation, but each had a different roof covering. Clearly, reflective roofing made a huge difference.


    Reflective Roof Savings
    0603PAchart_r2
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    Figure 1. Florida Solar Energy Center researchers compared the air-conditioning power use of seven identically built houses with different roof coverings. Reflective roofing dramatically reduced total power use (bottom chart) and had an even greater effect on peak A/C power demand (middle chart). Insulating the roof deck and sealing the attic, without using a reflective roof, cut total energy use somewhat but did not reduce peak cooling loads noticeably.

    One house of the seven had an insulated roof deck, to keep the ductwork within the sealed, conditioned attic. That modification did save energy on average, but not as much as the reflective roofs -- and it had little effect on peak loads.

    Cool colors. Until recently, a roof had to be white to have high solar reflectance -- something not every customer wants. But we now have tile and metal roofing systems made with "spectrally selective" paints, which absorb some colors of light in the visible range but reflect rays in the infrared and ultraviolet spectra that account for much of the sun's heat. These colors give designers more choices, while still saving considerable energy (Figure 2).

    0503PA2Musjls 0503PA2Darkjlc 0503PA2Tilejlc 0503PA2Fairjlc
    0503PA2Ajlc
    Figure 2. Kynar roof coatings using spectrally selective pigments from Ferro Corporation allow Classic Roofs to produce aluminum and steel shingles in several dark colors that meet Energy Star minimums with solar reflectances better than white asphalt shingles. Tests indicate that the colors will sharply reduce solar heat gain through the roof.

    BASF Corporation's ULTRA-Cool metal-roof coatings (800/669-2273, www.basf.com), which use spectrally selective pigments from Ferro Corporation (216/641-8580, www.ferro.com), have a 38% reflectivity in colors that achieve only 25% reflectivity when made with standard pigments. And at least two companies, Classic Products (800/543-8938, www.classicroof.com) and MCA Tile (800/736-6221, www.mca-tile.com) now supply metal or clay tile in a range of colors with solar reflectance around 30%. Classic's "Musket Brown," for instance, reflects 31% -- quite a bit better than a white shingle -- while the same color in traditional paint would reflect only 8%.

    Bare metal roofs. Unfinished galvanized or "tin" roofs are still fairly common in the hot Southeast. Galvanized steel is highly reflective when new, but its reflectivity soon drops as the zinc oxidizes; and the material also has low infrared emittance. The high absorptance and low emittance can combine to keep the roof blazing hot.

    When FSEC researchers put a white coating on the ten-year-old galvanized steel roof of a retail strip mall, the roof's reflectance went from 30% to 77%. The average air-conditioning reduction in seven monitored shops was more than 24% (Figure 3).

    0503PA3Cjlc
    0503PA3Ajlc
    0503PA3Bjlc
    Figure 3. Unfinished galvanized steel roofs may look shiny when new, but they age quickly to become very nonreflective. The infrared thermal scan (top) shows the drop ceiling (middle) at a radiant temperature of almost 90°F under the metal roof of a strip mall building, despite insulation below the roofing. When FSEC researchers applied a reflective coating (bottom), the building's air-conditioning power use dropped 16%, and tenants reported improved comfort. One tenant even called to thank the landlord for fixing the air conditioner. (He hadn't.)

    If you want unfinished metal roofing, Galvalume (an alloy of aluminum and zinc) is a much better cool-roof choice than galvanized steel, especially in mixed heating and cooling climates. Galvalume maintains its reflectance as it ages, and its low emissivity means it holds heat well in winter even though it reflects well in summer.

    Tile Roofing
    It's conventional wisdom that tile roofs are cooler than shingle roofs. To a small extent, that's true: S-tiles permit cooling airflow between the tile and the roof deck, and their thermal mass stores energy during the day and re-radiates it at night, instead of passing it all through to the attic.

    But the color of the tile matters. For instance, we painted some dark gray tiles bright white at midsummer in central Florida in 1996, and we measured an 18% drop in space-cooling energy.

    Shape appears to be far less important than color. In the seven-home side-by-side study for Florida Power & Light, one of the homes had flat white tile, and another had white S-tile. We didn't see much difference -- both roofs did about 20% better than the asphalt shingle roof. An S-shaped red tile roof in the same study was only 3% better than dark asphalt shingles.

    In general, light-colored metal roofs will outperform tile in a hot climate like Florida's. At night, they actually radiate attic heat upward into the night sky, cooling the attic to below the ambient air temperature. The thermal mass of tile will not let attic heat escape so readily.

    Radiant Barrier Systems
    When a house has a dark, sun-absorbing roof, radiant barriers in the attic can cut heat gain and save energy. But they don't necessarily work in every case, and they're not always the best solution.

    The basic radiant barrier is a layer of aluminum foil placed with its shiny side facing a clear air space. Placed under the rafters, aluminum's low emissivity prevents heat from radiating off the shiny surface onto the insulation below (Figure 4). If the surface gets dirty, it won't work as well; that's why radiant barriers placed shiny side down, so dust can't collect, work better than radiant reflective material placed facing up.

    0503PA4Ajlc
    FI-Foil Corp.
    Solec, Inc.
    Figure 4. Radiant barrier foil under the rafters stops heat from radiating into the attic, because the foil will not emit heat radiation even when it's hot (top and middle, before and after). Lo/Mit low-emissivity silicone coating spray-applied to the roof underside (bottom) is a cost-effective alternative method.

    There's now a range of material choices for attic radiant barriers, including radiant-barrier sheathing, spray-applied low-emissivity coatings, and a wide variety of foil products. Homes with complex attic geometry and poor access to the space are not great candidates for a foil application, but a radiant barrier sheathing is easy to apply to any new house, and a spray-applied low-e coating such as Lo/Mit from Solec, Inc. (www.solec.org) makes a practical retrofit.

    Energy savings. Radiant barriers are effective. Our research indicates that under-roof foil barriers reduce heat flow through the ceiling by 30% to 50% and can bring annual cooling electricity savings of 7% to 10% in the Southeast climate.

    Radiant barriers also have a strong effect on peak loads for the air conditioner. A nine-home retrofit study we conducted for Florida Power Corporation found that radiant barriers reduced air-conditioning power use by 9% and cut afternoon air-conditioning peak loads by 16%. In a six-ton system, that's a ton of cooling. Attic temperature peaks dropped by about 8°F. Perhaps most important, indoor temperatures fell by an average 2°F -- a boost for homeowner comfort.

    But that was in the South. In colder climates, radiant barriers may create a risk of wintertime condensation, because some foil products also act as vapor barriers. For cool-climate homes, it's wise to search out a product that has high permeability as well as low emissivity (manufacturers can supply data sheets with perm ratings, emissivity ratings, and other useful information).

    And be aware that if you have a reflective roof to begin with, a radiant barrier is overkill -- and may even be counterproductive. Since the underside of a reflective roof does not get hot, a radiant barrier under the roof adds little benefit. On the other hand, by reflecting heat inward, the radiant barrier will impede the ability of the attic to radiate excess heat to the night sky.

    Another word of caution: We installed our test radiant barriers in midsummer, so we could immediately measure the benefit. But the attics we worked in were dangerously hot -- one of our people actually had to stop and get medical attention. It's much safer to install attic radiant barriers in the cool season, or at least during the early morning before the attic is baking hot.

    Boosting Attic Ventilation
    If the attic is too hot, is more ventilation a good idea? Maybe, but maybe not. Increasing the roof's passive air vents can reduce the cooling load, but it is usually one of the least effective options. The incoming ventilation air is hottest just when you need the cooling.

    In retrofit work, we have seen increased ventilation bring a 5% reduction in building cooling loads. But in humid or coastal locations, it can also create problems: At night, the vents bring in moist outside air that may condense on duct systems.

    Since passive vents work inconsistently, some people recommend powered ventilation fans. But the electric power used to operate the fan usually outweighs the air-conditioning savings. And there's another drawback: Power attic ventilation can depressurize the house and cause gas water heaters to backdraft. It may also draw conditioned air out of the house into the attic, creating a further energy penalty.

    We've conducted tests of photovoltaic solar-powered attic fans in Florida. They run whenever the sun is shining, and we found savings of about 6% on electric bills. But at around $600 for the solar panels plus the fan, the savings don't really justify the cost in simple financial terms.

    Added Insulation
    Added insulation is another option for cutting heat gain through the roof. It certainly works: One of our studies for a Florida utility showed that boosting ceiling insulation from R-19 to R-30 cut space cooling by about 9% in summer.

    But your mileage may vary. Duct systems in many homes run through the hot attic and may be insulated to only R-4 or R-6. So the air conditioner is sending 55°F air into the duct in a space that can reach 130°F on a hot day. That's a temperature difference of 75°F, across just an R-6 insulated duct wall -- much greater than the 20°F difference you might see from indoors to outdoors across an R-11 or R-19 building wall. And duct surface area is much greater than you might think -- often as much as 25% of the house floor area. During the hottest hours, as much as 30% of the cooling system's capacity can be lost to heat gains in the duct system. Besides the wasted energy, this means it takes longer to cool down the house when the air conditioner kicks in.

    Unlike a reflective roof or attic radiant barrier, ceiling insulation does little to address duct system losses. So if your design relies on ceiling insulation to limit roof-related cooling loads, try to locate the duct system within the thermal envelope, below the insulated ceiling. Even running the ducts through the crawlspace, though they might be exposed to outdoor air temperatures, will add less to the load than running them through the solar-heated attic.

    Insulated Roof Deck With Sealed Attic
    Sealing the attic and insulating the roof deck is another way to get the duct system into a more friendly environment. Some code officials may not like this roof design, and researchers don't recommend it in colder climates, but it does save energy. It also creates semi-conditioned storage space in the attic, reduces interior moisture loads in hot climates, and avoids the risk of condensation on air handlers and ducts.

    In our seven-home side-by-side comparison, the house with a sealed and insulated attic used 9% less energy than the base case house, even though both had dark shingles. Some of us were expecting a greater savings, but several factors limit the benefit of this method.

    The big advantage is that the ductwork is inside the thermal envelope. However, while a ventilated attic can flush some heat out through the vents, an insulated roof deck fights its whole battle at the roof surface. Also, the air conditioner has to treat the additional air volume of the attic space.

    Beyond that, an insulated roof deck contributes more heat to the house than an insulated attic floor does. Heat transfer is proportional to the temperature difference, and also to the area of the surface. In a ventilated attic on a hot day, the top surface of the ceiling insulation may hit 130°F -- a 55°F difference with the 75°F interior. But the deck of an insulated roof in the direct sun may reach 170°F while the attic reaches 85°F, for a difference of 85°F across the insulation. That wider temperature gap drives faster heat gain. And that faster gain is multiplied by a greater area, since the roof area is anywhere from 5% to 40% greater than the ceiling area, depending on the pitch of the roof (not to mention the gable ends).

    So with an insulated roof deck and a sealed attic, it is very worthwhile to block that solar gain right off the bat: Use a lighter tile, white shingles, or a more reflective metal. In our study, the sealed system with dark shingles did about 9% better than a ventilated attic with dark shingles. With a reflective roof, the sealed attic would likely post savings of 25% or 30%. Even matched with white shingles (with a reflectance of 25%), we estimate that the insulated roof would have scored about a 13% savings compared to the dark shingles and vented attic. Also, it's worth noting that we carefully sealed the ductwork in all the test houses, to avoid confusing the results. If the ducts are leaky, the benefit of a sealed attic is much greater, because those leaks can't communicate with the outdoors.

    Options for Stopping Rooftop Heat Gain
    Field research at the Florida Solar Energy Center (FSEC) has found several effective ways to limit rooftop heat gain in sunny conditions. Using a highly reflective roofing material (top) is the simplest and most effective: It stops the sun's energy before any heat is absorbed, so that even the roof sheathing and framing stay cool. If the existing roof is dark colored or the customer prefers a darker roof, heat can still be blocked by adding a radiant barrier foil just below the roof deck (middle). Savings from this method are roughly comparable to the saving achieved with reflective roofing; however, some conductive heating of the attic space will still take place, and the roof deck and shingles will experience some increased heat stress. A third option is to increase the insulation between the attic and the living space below, and to run the hvac ductwork within the conditioned space rather than in the unconditioned attic. This method has a smaller effect on cooling loads than the reflective or radiant barrier roof systems but is effective at reducing heating loads as well as cooling loads, making it the most cost-effective option in mixed heating and cooling climates.

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    Smart Choices
    Good roof details can save energy anywhere in the country. But climate and other building details do affect the choices. Here's how to approach the decision:

    Northern climate options. If you build in the North, reflective roofing materials or radiant barriers bring only modest savings. Adding insulation in the attic is a much more cost-effective upgrade. Insulation cuts both heating and cooling costs; and the heating savings in northern winters add up to much more money. (For the full benefit, it's important to run ductwork within the insulated envelope -- winter or summer, ducts in the attic will bypass the ceiling insulation and reduce its effectiveness.)

    Not that cooling doesn't matter up north, however. In summer, attics get hot everywhere. So even in the North, reflective roofing or radiant barriers may be worth installing simply to improve summer comfort and to reduce peak loads on the air conditioner. But if you want a reflective roof in the North, look for a material like Galvalume that is both reflective and low-e: This conserves attic heat during the winter as well as providing a summer cooling benefit.

    Southern choices. Down south, reflective roofs are a no-brainer -- they're money in your pocket. Air conditioning is the big energy cost, and reflective roofs can cut it by a third in the hottest months. Increasing the attic insulation can't hurt, but reflective roofs are more cost effective, particularly if the ductwork runs through the attic.

    If you're stuck with a dark roof, attic radiant barriers can achieve savings comparable to a reflective roof's performance. But if you use radiant barriers under an asphalt shingle roof, you're wise to also choose white shingles, just so the shingles themselves won't get quite so hot.

    Good ductwork location and reflective or radiant-barrier roof construction bring independent benefits, but they also complement each other. If you have a dark roof and a hot attic, bringing the ductwork below the insulated ceiling will help quite a lot. If the ducts are in the attic, switching from a dark roof to a reflective roof can help. But combining the two tactics -- applying reflective roofing and bringing the ducts inside -- provides the greatest total benefit. In a hot climate like Florida's, your summer cooling loads could drop by as much as 40%.



    By Danny Parker ,Danny Parker is a senior research scientist with the Florida Solar Energy Center. Article Supplier: http://www.jlconline.com/cgi-bin/jlconline.storefront/4c224d630329c28327180a32100a05df/UserTemplate/69

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