Implementing Green Sustainable Building Design in Malaysia One of the strategies of the energy sector as mentioned in the 9th Malaysia Plan is “intensifying energy efficiency initiatives in the industrial, transport and commercial sectors as well as in government buildings”. The implementation of energy efficiency (EE) program will focus on energy saving features in the industrial and commercial sectors. In this regard, EE features such as efficient lighting and air conditioning systems as well as establishing a comprehensive energy management system will be encouraged. Malaysia Green Building Index The Green Building Index (GBI) is Malaysia’s industry recognized green rating tool for buildings to promote sustainability in the built environment and raise awareness among Developers, Architects, Engineers, Planners, Designers, Contractors and the Public about environmental issues and our responsibility to the future generations. The GBI rating tool provides an opportunity for developers and building owners to design and construct green, sustainable buildings that can provide energy savings, water savings, a healthier indoor environment, better connectivity to public transport and the adoption of recycling and greenery for their projects and reduce our impact on the environment. (PDF 64Kb) PTM ZEO Project type : Building Integrated PV (BIPV) - SHOWCASE PROJECT: 92 kWp BIPV SYSTEMS  Building Energy Indices Before going into details of the factors affecting energy use, some method of comparing energy use - the energy use indices – will be explained. The index selected would depend on the intended application of the index and the normalizing factor. Among Architects the normalizing factor for comparing buildings is the gross floor area. The most commonly used index for comparing energy use in buildings is therefore the Building Energy Use Index - BEI. This is usually expressed as kWh/m2/year which measure the total energy used in a building for one year in kilowatts hours divided by the gross floor area of the building in square meters.
GREEN BUILDING INDEX – MS1525 Green Building Congress Malaysia 2010 - ARCHITECTURAL AND PASSIVE DESIGN.
This means that whenever possible, orientate the building to have most of the windows facing either north or south. East and west facing windows in Malaysia get direct sunlight into the building and this can easily increase building energy consumption by 20% or more. For example, we are on the equator. The sun goes from east to west. If you have a thin vertical building, a good part of the sides are heated up in the morning and evenings. So let’s say you shape your building in a more horizontal or broad approach (with plenty of roof area), the sun only heats up at the sides (smaller area). That means this (broad) building does not get so hot. So it is easier to air-condition because it is cooler. But the worst is a diagonally-shaped building, because that means the top and sides all get heated up (throughout the day). Now, let’s say for a house. You shade one side to keep the sun out, but half the day the sun is at the top. In a terrace house, the roof gets very hot. So you need to insulate it. For instance, if you start putting trees at the sides of the house, then trees provide shade to the house. One of the best measures for keeping solar heat out of buildings is simply to use reflective roofing materials. (PDF 851Kb) Then, the sun's radiant energy is simply reflected back toward the sky from which it came. In fact, reflective materials also help keep the building's environment (i.e., the city) cool, by reflecting sun's radiant energy back out into space, before it penetrates into the interior of the building.
For example, black color absorbs heat. Instead of reflecting heat, you are absorbing the heat. Conventional white materials and coatings are rather good from this standpoint. Besides high solar reflectance, a high infrared emittance is also desirable. Infrared emittance is a measure of the ability of a surface to emit its energy in the form of heat radiation. Fortunately, most roofing materials (excepting bare metals) have a high infrared emittance. Also desirable is good convective heat transfer: as the roof heats in the sun some of the heat can be carried away by the outside air. In some roofing systems air can circulate underneath the outer roofing material (e.g., tile and wood shake systems). Attic venting also can be used to intercept heat before it penetrates into the conditioned space. Finally, of course, thermal insulation is effective in reducing, but not eliminating, the flow of unwanted heat. Building materials are constantly being researched into to find the best thermal performance. But no matter what the materials seem to be, any direct sunlight into the house would defeat the purpose of having a good thermal performance material. (PDF 1.65MB) Whatever material used for the building envelope it should be supplemented with efforts to reduce radiant heat by the design of building such as the shape and orientation, roof shape and roof pitch, sun-shadings of all sorts, roof and wall sprays, reflective materials including white paint and insulation materials. (PDF 1.61MB)
Once the building fabric is prevented from heat gain at the same time there must be efforts to encourage air movement inside the building. Such initiatives are like having wind deflectors, shape and orient the building shell to maximize exposure to the prevailing wind, open plan, air shafts to encourage stack effect, double wall and double roof and lots of fenestration's. While the cool roofing materials address on the important issue of keeping the building cool, one should not overlook the fact that the primary function of a roof is to keep out all the elements of the weather! A roof must last for decades, with minimal maintenance, and at a reasonable cost. Factors which can shorten the lifetime of a roof include ultraviolet radiation from the sun, freeze-thaw cycles, wind, rain, damage from foot traffic, biological growth, chemical reactions with air pollutants, thermal expansion stresses due to temperature changes, poor installation, etc. Thus, if a cooler material is inferior from a cost or lifetime point of view compared to a warmer material, it's not a good deal. It's important to find a contractor or supplier who has experience with the materials to be used, and who will stand behind the quality of the work. Solar Reflectance and Thermal Emittance values of the roof surface help determine its temperature. (PDF 1.46MB) Most roofs are not washed frequently, so we recommend using aged values to predict energy savings. If aged values for your roof are unknown, you can estimate the aged solar reflectance based on the initial solar reflectance by using this formula: Aged Reflectance = 0.7 x (Initial Reflectance – 0.2) + 0.2 Some materials retain solar reflectance better than others, so use measured aged values whenever possible. Using initial values for thermal emittance is fine, since these values tend to change less over time. A common theme in green design is the importance of building components with a high solar reflective value. Solar reflectance or reflectivity is the fraction of energy reflected over energy incident on the surface. It is the deflection of solar energy from a surface. The greater the amount of solar energy reflected from a surface, the less energy the building will need to cool down. (PDF 998 Kb)
Passive Design Factors affecting Energy use in Buildings
The difference between a passive solar home and a conventional home is design. Passive solar homes and other buildings are designed to take advantage of the local climate. Passive solar design—also known as climatic design—involves using a building's windows, walls, and floors to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. (PDF 42Kb) The building layout, planning, design, shape, fabric and construction cover a wide number of variables that affect building energy requirements. This is the area where the basic decisions of the architect will have the most influence on the building’s energy use. How much then does the designer have? The following sets of estimates by Givoni should serve to illustrate a building’s influence on its indoor environment and thus air conditioning or heating requirement. Depending on the design
The building related factors influencing energy requirements are numerous and complex.
They can be classified under the following headings.
Size and Shape – Generally, a larger building will require more energy to cool than a smaller building because of the larger of space to be cooled. This is widely accepted. The question of whether a building needs less energy per unit volume or floor area is however a more complex one and still not completely resolved. (PDF 193Kb) Many theoretical researchers take the view that larger buildings need less energy per unit size because of their smaller surface area per unit size and thus lower heat gain per unit size. Based on this theory they say “ The larger a building, and the nearer to spherical in shape, the less are its energy needs because of the simple reduction in the ration of surface area to volume”. They conclude that “The architectural fad for angular protrusions of buildings is an energy wasting form”.
The Building Research Unit however found from field data that compact buildings cost more to erect and had higher energy running costs than sprawling ones. These empirical findings were contrary to the Unit’s theoretical predictions. They concluded that the quality of “compactness” in layout is one which cannot, on present evidence, be shown to be of paramount importance. Stein reach conclusions similar to the BPRU ( Building Performance Research Unit ) “ …the maximum volume, minimum perimeter building will not be the most energy conservative and because of the mechanical systems required to provide interior comfort conditions at all times, may not even be the least expensive.” Building Orientation Building orientation affects the air conditioning / heating energy requirements in two respects by its regulation of then influence of two distinct climatic factors. (PDF11.7MB)
The table below compares the approximate daily solar gain for some typical Malaysian housing types. SOLAR HEAT GAINS IN TYPICAL MALAYSIAN HOUSING
For an intermediate single storey terraced houses, where the roof makes up nearly 70% of the building envelope exposed to the sun, roof insulation becomes all important to keep the home cool. Orientation has less of an effect the difference in solar radiation for a north-south and east-west facing being only about 14%.  An intermediate double storey terrace house however has significantly more wall area and orientation will have a significant effect on the solar gain, being nearly 30% more for an east-west facing house. For flats and apartments, depending on the aspect ratio and height of the building, an east west facing building can have 16% to 40% more solar gain than a north-south facing block. What can the Architect do to reduce this solar heat gain? The following are some suggested ideas.
Roof System The typical Malaysian terraced house receives most of its solar heat gain from the roof. This is because the horizontal surface receives the highest solar radiation, peaking at about 350 Wh/m2 at mid-day in the tropical sun and it continues to receive the highest solar radiation level throughout the day. Add to that the higher ratio of roof to building envelope area; the typical roof receives from 50% to 85% of the total solar radiation as shown in the table below.
Reducing the solar heat gain through the roof should therefore be the first priority for keeping the home cool. Measurements by “Lafarge Roofing” have found peak temperatures differences between a roof insulated and an not insulated to be as much as 4.5°C. For sloping roofs the following if implemented correctly can reduce inside temperatures by as much as 4°C centigrade.
 Planning and Layout – It is not possible to generalize or quantify the complex implications that planning and layout of spaces will have on air conditioning and lighting requirements. Some areas where the layout will influence are listed below.
Thermo Physical Properties – The properties of materials which affect the rate of heat transfer in and out of a building, and consequently the air conditioning or heating energy requirements are.
Window Systems The size, location, shape and orientation of glazed areas in a building will have a critical effect on both the heat gains and solar gains of a building because glazed areas have the highest hat gain per unit area and the major proportion of solar gains are also through windows.
The importance of this factor is indicated by Stein’s finds that the school with the highest energy use per square foot in New York City was a completely sealed building with windowless classrooms. The amount of heat gains will also be influenced by
For tropical climates, external shading devices or recessed windows have been found to be the most effective method of reducing solar heat gains through windows without losing the significant benefits of day lighting. (PDF1.02MB) The recommendations by Assoc Prof Dr Ku Azhar Ku Hassan of University Science Malaysia should serve as a useful guide to Architects.
Construction Detailing – This will influence air conditioning loads in the following areas.
Green building Construction and day lighting Passive Solar Home Design - Roof Overhangs In passive solar home design, exterior roof overhangs provide a practical method for shading building elements such as windows, doors, and walls. (PDF 598Kb)
How They Work Overhangs are most effective for south facing elements (in the northern hemisphere) and at midday. If the building element bears more than about 30° off true south, the effectiveness of an overhang, as with any solar feature, begins to decrease significantly. Overhangs usually only affect the amount of direct solar radiation that strikes a surface. Diffuse sky and reflected radiation gains are not often directly affected by overhangs. The higher overhead the sun is, the shorter the shadow a person will cast on the ground. However, the short brim of a baseball cap can create a long shadow across the body of a standing person. The same concept applies in designing overhangs for buildings. The higher, or more vertical, the arc of the sun, the longer the shadow that the building overhang generates along the face of the wall. Summer shadows extend down walls the furthest, winter shadows the least. Sites closer to the equatorial path of the sun have deeper-extending wall shadows than ones farther from the equator, assuming the same overhang length. Types of Overhangs
Overhangs may be solid, louvered, vegetation-supporting, or a combination of all of these aspects. Some shutters, eaves, trellises, light shelves, and awnings serve the same purpose as an overhang. Overhangs may also be fixed, operable, and/or removable. Examples include roof eaves, awnings, and top-hinged louvered shutters typically propped open with wooden dowels respectively. Fixed overhangs offer perceived longevity and low maintenance at the expense of flexibility or the ability to adjust to site-specific factors. Although adjustable devices allow the user to fine tune the amount of shade or direct sunlight, they require more maintenance. Removable fixtures generally provide flexibility and longevity plus some personal involvement with installation and removal. Window Blinds Window blinds—vertical or horizontal slat-type—are more effective at reducing summer heat gain than winter heat loss. (PDF 5.56MB) Interior Blinds Because of the numerous openings between the slats, it's difficult to control heat loss through interior window blinds, but the slats offer flexibility in the summer. Unlike shades, you can adjust the slats to control light and ventilation. For example, when completely closed and lowered on a sunny window, highly reflective blinds can reduce heat gain by around 45%. They can also be adjusted to block and reflect direct sunlight onto a light-colored ceiling. A light-colored ceiling will diffuse the light without much heat or glare. Exterior Blinds Exterior roller blinds are usually made of wood, steel, aluminum, or vinyl. They're mounted above the window. Side channels guide them as they're lowered and raised. When you lower these blinds completely, their slats meet and provide shade. If partially raised, the blinds allow some air and daylight to enter through windows. Window Awnings Window awnings can reduce solar heat gain in the summer by up to 65% on south-facing windows and 77% on west-facing windows. You can use an awning to shade one window or have an awning custom-made to shade the entire side of your house. (PDF 2.62MB) In the past, most awnings were made of metal or canvas, which need to be re-covered every five to seven years. Today, awnings are made from synthetic fabrics — such as acrylic and polyvinyl laminates — that are water-repellent and treated to resist mildew and fading. Whatever the fabric, you should choose one that is opaque and tightly woven. A light-colored awning will reflect more sunlight. Awnings require ventilation to keep hot air from becoming trapped around the window. Grommets (eyelets) or other openings along the tops and sides of an awning can provide ventilation. The awning may also open to the sides or top to vent hot air. A small, horizontal awning will completely shade a south-facing window during the summer. An east- or west-facing window needs an awning that extends down to cover a large percentage of the window. Side less awnings, called Venetian awnings, can be adjusted as the angle of the sun changes. Venetian awnings, however, are usually not effective at blocking direct sunlight on south-facing windows. Hood awnings with sides added to block out additional sun are more effective. Hip awnings project out and down to accommodate casement windows that open outward. You can roll up adjustable or retractable awnings in the winter to let the sun warm the house. New hardware, such as lateral arms, makes the rolling up process quite easy. Passive Solar Window Design
Properly designed, energy efficient windows represent a cost-effective way to use solar energy for heating. Windows are an important element in passive solar home designs, which can reduce heating, cooling, and lighting needs in a house. Passive solar design strategies vary by building location and regional climate. The basic techniques involving windows remain the same—select, orient, and size glass to control solar heat gain along with different glazing usually selected for different sides of the house (exposures or orientations). Heating-Dominated Climates In heating-dominated climates, major glazing areas should generally face south to collect solar heat during the winter when the sun is low in the sky. In the summer, when the sun is high overhead, overhangs or other shading devices (e.g., awnings) prevent excessive heat gain. To be effective, south-facing windows usually must have a solar heat gain coefficient (SHGC) of greater than 0.6 to maximize solar heat gain during the winter, a U-factor of 0.35 or less to reduce conductive heat transfer, and a high visible transmittance (VT) for good visible light transfer. Windows on east-, west-, and north-facing walls are reduced in heating climates, while still allowing for adequate daylight. East- and west-facing windows are limited because it is difficult to effectively control the heat and penetrating rays of the sun when it is low in the sky. These windows should have a low SHGC and/or be shaded. North-facing windows collect little solar heat, so they are used just to provide useful lighting. Low-emissivity window glazing can help control solar heat gain and loss in heating climates. Cooling-Dominated Climates In cooling climates, particularly effective strategies include preferential use of north-facing windows and generously shaded south-facing windows. Windows with low SHGCs are more effective at reducing cooling loads. The following types of glazing help reduce solar heat gain, lowering a window's SHGC:
Most of these glazing types, except for spectrally selective, also help lower a window's VT. Low-Emissivity Window Glazing or Glass Low-emissivity (Low-E) coatings on glazing or glass control heat transfer through windows with insulated glazing. Windows manufactured with Low-E coatings typically cost about 10%–15% more than regular windows, but they reduce energy loss by as much as 30%–50%. A Low-E coating is a microscopically thin, virtually invisible, metal or metallic oxide layer deposited directly on the surface of one or more of the panes of glass. (PDF 175Kb) The Low-E coating reduces the infrared radiation from a warm pane of glass to a cooler pane, thereby lowering the U-factor of the window. Different types of Low-E coatings have been designed to allow for high solar gain, moderate solar gain, or low solar gain.
A Low-E coating can also reduce a window's visible transmittance unless you use one that's spectrally selective. To keep the sun's heat out of the house (for hot climates, east and west-facing windows, and unshaded south-facing windows), the Low-E coating should be applied to the outside pane of glass. If the windows are designed to provide heat energy in the winter and keep heat inside the house (typical of cold climates), the Low-E coating should be applied to the inside pane of glass. Window manufacturers apply Low-E coatings in either soft or hard coats. Soft Low-E coatings degrade when exposed to air and moisture, are easily damaged, and have a limited shelf life. Therefore, manufacturers carefully apply them in insulated multiple-pane windows. Hard Low-E coatings, on the other hand, are more durable and can be used in add-on (retrofit) applications. The energy performance of hard-coat, Low-E films is slightly poorer than that of soft-coat films. Although Low-E coatings are usually applied during manufacturing, some are available for do-it-yourselfers. These films are inexpensive compared to total window replacements, last 10–15 years without peeling, save energy, reduce fabric fading, and increase comfort. Heat-Absorbing, Tinted Window Glazing or Glass Heat-absorbing window glazing contains special tints that change the color of the glass. Tinted glass absorbs a large fraction of the incoming solar radiation through a window. This reduces the solar heat gain coefficient, visible transmittance, and glare. (PDF 2.37MB)
Some heat, however, continues to pass through tinted windows by conduction and re-radiation. Therefore, the tint doesn't lower a window's U-factor. However, inner layers of clear glass or spectrally selective coatings can be applied on insulated glazing to help reduce these types of heat transfer. Gray-and bronze-tinted windows—the most common—reduce the penetration of both light and heat into buildings in equal amounts (i.e., not spectrally selective). Blue-and green-tinted windows offer greater penetration of visible light and slightly reduced heat transfer compared with other colors of tinted glass. In hot climates, black-tinted glass should be avoided because it absorbs more light than heat. Tinted, heat-absorbing glass reflects only a small percentage of light, so it does not have the mirror-like appearance of reflective glass. Note: when windows transmit less than 70% of visible light, indoor plants can die or grow more slowly. Reflective Window Glazing or Glass Reflective coatings on window glazing or glass reduce the transmission of solar radiation, blocking more light than heat. Therefore, they greatly reduce a window's visible transmittance (VT) and glare, but they also reduce a window's solar heat gain coefficient (SHGC). See Building Codes and Green Standards - energy performance ratings for windows, doors, and skylights for more information on these terms. (PDF 5.7MB) Reflective coatings usually consist of thin, metallic layers. They come in a variety of metallic colors, including silver, gold, and bronze. Reflective window glazing is commonly used in hot climates where solar heat gain control is critical. However, the reduced cooling energy demands they achieve can be offset by the resulting need for additional electrical lighting, so reflective glass is mostly used just for special applications. Spectrally Selective Window Glazing or Glass
A special type of low-emissivity coating is spectrally selective. Spectrally selective coatings filter out 40%–70% of the heat normally transmitted through insulated window glass or glazing, while allowing the full amount of light to be transmitted. Spectrally selective coatings are optically designed to reflect particular wavelengths but remain transparent to others. Such coatings are commonly used to reflect the infrared (heat) portion of the solar spectrum while admitting a higher portion of visible light. They help create a window with a low U-factor and solar heat gain coefficient but a high visible transmittance. See energy performance ratings for windows, doors, and skylights for more information on these terms. (PDF 1.56MB) Spectrally selective coatings can be applied on various types of tinted glass to produce "customized" glazing systems capable of either increasing or decreasing solar gains according to the aesthetic and climatic effects desired. Computer simulations have shown that advanced window glazing with spectrally selective coatings can reduce the electric space cooling requirements of new homes in hot climates by more than 40%. How should one choose glazing for green, low energy commercial buildings? Guidelines for Selecting Cool Roofs Cool roofs can help many building owners save money while protecting the environment. If you are planning a new building or replacing or restoring an existing roof, cool roofs should be considered as an energy efficiency option. Cool roof products exist for virtually every kind of roof. (PDF 330Kb)
Just as wearing light-colored clothing can help keep a person cool on a sunny day, cool roofs use solar-reflective surfaces to maintain lower roof temperatures. Traditional dark roofs can reach temperatures of 150ºF (66ºC) or more in the summer sun. A cool roof under the same conditions could stay more than 50°F (28ºC) cooler. Why Use Cool Roofs A cool roof can be desirable to a building owner for several reasons. Cool roofs can
In many cases, cool roofs cost about the same as non-cool alternatives. The energy cost savings you can realize from a cool roof depends on many factors, including local climate; the amount of insulation in your roof; how your building is used; energy prices; and the type and efficiency of your heating and cooling systems. Cool roofs can also benefit the environment, and policymakers may issue cool roof regulations to provide these benefits to society. Cool roofs can
What Is a Cool Roof Cool roofs are roofs that are designed to maintain a lower roof temperature than traditional roofs while the sun is shining. Sunlight is the primary factor that causes roofs to become very hot. How Cool Roofs Work
Cool roofs have surfaces that reflect sunlight and emit heat more efficiently than hot or dark roofs, keeping them cooler in the sun. In contrast, hot roofs absorb much more solar energy than cool roofs, making them hotter. Solar reflectance and thermal emittance are the two key material surface properties that determine a roof’s temperature, and they each range on a scale from 0 to 1. The larger these two values are, the cooler the roof will remain in the sun. Since most dark roofs absorb 90% or more of the incoming solar energy, the roof can reach temperatures higher than 150°F (66ºC) when it’s warm and sunny. Higher roof temperatures increase the heat flow into the building, causing the air conditioning system to work harder and use more energy in summertime. In contrast, light-colored roofs absorb less than 50% of the solar energy, reducing the roof temperature and decreasing air conditioning energy use. Reducing the roof’s temperature with a cool roof can also increase the need for heating during heating seasons. Later sections of this report show you how to evaluate the resulting cost savings for your building. Solar Reflectance is the fraction of sunlight that a surface reflects. Sunlight that is not reflected is absorbed as heat. Solar reflectance is measured on a scale of 0 to 1. For example, a surface that reflects 55% of sunlight has a solar reflectance of 0.55. Most dark roof materials reflect 5 to 20% of incoming sunlight, while light-colored roof materials typically reflect 55 to 90%.
Solar reflectance has the biggest effect on keeping your roof cool in the sun. Thermal Emittance describes how efficiently a surface cools itself by emitting thermal radiation. Thermal emittance is measured on a scale of 0 to 1, where a value of 1 indicates a perfectly efficient emitter. Nearly all nonmetallic surfaces, like the unwrapped potato, have high thermal emittance, usually between 0.80 and 0.95, that helps them cool down. Bare, shiny metal surfaces, like aluminum foil, have low thermal emittance, which helps them stay warm. A bare metal surface that reflects as much sunlight as a white surface will stay warmer in the sun because it emits less thermal radiation. Solar Reflectance Index (SRI) is another metric for comparing the “coolness” of roof surfaces. It is calculated from solar reflectance and thermal emittance values. The higher the SRI, the cooler the roof will be in the sun. For example, a clean black roof could have an SRI of 0, while a clean white roof could have an SRI of 100. Dark roofs usually have an SRI less than 20. The US Green Building Council and Energy Star have set a minimum Solar Reflectance Index (SRI) of 29 for roofing. The SRI is calculated from physical testing of solar reflectance and thermal emittance. An SRI of 29 or higher will save the building owner money by reducing energy costs associated with cooling and give longer AC Unit life, as a result of decreased air conditioning loads. In addition, cool roofs combat the urban heat island effect caused by roofs and other non-reflective surfaces absorbing and trapping solar radiation or heat. (PDF 5.36MB) What Qualifies as a Cool Roof Typical minimum cool roof requirements are shown in Table 1, and this is what we mean by “cool roof” throughout this document. A roof can qualify as cool in one of two ways. The first way is by meeting or exceeding both the minimum solar reflectance and thermal emittance values. The alternative way is to meet or exceed the minimum SRI requirement. This allows some roofs that have a low thermal emittance and a high solar reflectance (or vice versa) to still qualify as a cool roof. Table 1: Typical Minimum Cool Roof Requirements
Cool roof requirements depend on the roof’s slope. Low sloped roofs have a pitch of 9.5° or less (2:12 rise over run), while steep sloped roofs have a pitch greater than this. Requirements are usually less stringent for steep sloped roofs. Some heavier roofs – such as those with concrete pavers, ballast, or vegetation – also have less stringent cool roof standards. The weight of these roofs causes them to heat up more slowly, and during the night some of that stored heat is returned to the outdoor environment. Reading Cool Roof Product Labels To help consumers compare the cool aspects of roof materials and coatings, the Cool Roof Rating Council (CRRC) manages a system for independently evaluating and documenting their properties. Roof products that are tested to CRRC methods receive a performance label, showing the measured solar reflectance and thermal emittance values. NOTE: Any roofing product that is tested by a CRRC accredited laboratory can be listed in the CRRC directory. Being listed does not imply that a product is cool. Because roof material surface properties can change over time due to soiling and weathering, values are measured and reported for both initial and three-year weathered conditions. The label shows this product’s solar reflectance has dropped from 0.87 to 0.77 after three years. Most weathering or soiling occurs during the first year or two, and then values tend to stabilize. Tested product data are published online by the CRRC.
Not All Cool Roofs Are White Although white materials tend to be very good solar reflectors, colored roofing materials, can also be made to reflect more sunlight. More than half of the sunlight reaching the earth is invisible to the human eye, and this invisible sunlight heats the roof. A colored surface that reflects much of the invisible sunlight is a called a cool dark color, or cool color. A cool dark color reflects more sunlight than a similar-looking conventional dark color, but less than a light-colored surface. For example, a conventional dark colored surface might reflect 20% of incoming sunlight, a cool dark colored surface, 40%; and a light-colored surface, 80%.
Heat Gains, Heat Losses, and Thermal Insulation Heat flows naturally from a warmer space to a colder space. Heat that flows into the building is called heat gain, while heat that flows out of the building is called heat loss. When too much heat gain (loss) occurs, your air conditioning system (heating system) operates to keep the space comfortable. A large amount of heat can be gained (or lost) through a building’s roof. Cool roofs reduce heat gains throughout the year. This can save you energy on cooling, but it can also increase the energy you need for heating. Often, the annual cooling energy cost savings is substantially higher than the heating penalty. Thermal insulation can greatly reduce the amount of heat lost or gained through a roof system. Even though cool roofs reduce solar heat gains, they are never a substitute for using sufficient thermal insulation. Insulation reduces heat losses and heat gains through the roof in ways a reflective surface cannot. For more information about the importance of thermal insulation, see these DOE resources: Residential Insulation Fact Sheet and Energy Savers Types of Cool Roofs
Roof systems are made of one or more material layers. The surface exposed to the sun is the one that determines if a roof is cool or not. Different roofing systems present different surface options. By selecting the right surface, you can usually make your new or existing roof cool. Here are some common roof systems along with a description of how their surfaces can be made cool. To learn more about these and other roof systems, check with the National Roofing Contractors Association. Cool Roof Coatings contain white or special reflective pigments that reflect sunlight. Coatings are like very thick paints that can protect the roof surface from ultra-violet (UV) light and chemical damage, and some offer water protection and restorative features as well. (PDF 1.78MB) Coatings can extend a roof’s service life as long as the roof is still in good condition. More than 500 different cool roof coatings are available, and products exist for most roof types. Manufacturers also coat some roof surfacing materials (membranes, metals, granules, etc.) at the factory to make them more reflective. Low Sloped Roofs Single-ply Membranes are pre-fabricated sheets that are rolled onto the roof and attached with mechanical fasteners, adhered with chemical adhesives, or held in place with ballast (gravel, stones, or pavers). Some kinds of membranes, like thermoplastic polyolefin (TPO) and polyvinyl chloride (PVC), are typically white and reflect sunlight well. Others, like (EPDM) ethylene propylene diene M-class, a kind of synthetic rubber, are typically black, and must be formulated differently or coated to make them reflective.  Built-Up Roofs consist of a base sheet, fabric reinforcement layers, and a protective surface layer that is traditionally dark. The surface layer can be made in a few different ways, and each has cool options. One way involves embedding mineral aggregate (gravel) in a flood coat of asphalt. By substituting reflective marble chips or gray slag for dark gravel you can make the roof cool. A second way built-up roofs are finished is with a mineral surfaced sheet. These can be made cool with reflective mineral granules or with a factory-applied coating. Another surface option involves coating the roof with a dark asphaltic emulsion. This type can be made cool by applying a cool coating directly on top of the dark emulsion. Modified Bitumen Sheet Membranes are composed of one or more layers of plastic or rubber material with reinforcing fabrics, and are surfaced with mineral granules or with a smooth finish. A modified bitumen sheet can also be used to surface a built-up roof, and this is called a “hybrid” roof. Modified bitumen surfaces can be pre-coated at the factory to make them cool. Spray Polyurethane Foam roofs are constructed by mixing two liquid chemicals together that react and expand to form one solid piece that adheres to the roof. (PDF 98.7Kb) Since foams are highly susceptible to mechanical, moisture, and UV damage, they rely on a protective coating. These coatings are traditionally reflective and offer cool roof performance. Steep Sloped Roofs Shingled Roofs consist of overlapping panels made from any of numerous materials. Fiberglass asphalt shingles, commonly used on homes, are coated with granules for protection. Cool asphalt shingles are use specially coated granules that provide better solar reflectance. While it is possible to coat existing asphalt shingles to make them cool, this is not normally recommended or approved by shingle manufacturers. Other shingles are made from wood, polymers, or metals and these can be coated at the factory or in the field to make them more reflective. Metal shingles are described in the Metal Roofs section that follows. Tile Roofs can be made of clay, slate, or concrete. Clay and slate tiles come from the ground, so their colors differ depending on the earth’s composition. Some varieties will naturally be reflective enough to achieve cool roof standards. Tiles can be also be glazed to provide waterproofing or coated to provide customized colors and surface properties. These surface treatments can transform tiles with low solar reflectance into cool roof tiles. Low and Steep Sloped Roofs
Metal Roofs are available with natural metallic finishes, oven-baked paint finishes, or granular coated surfaces. Usually, unpainted metals are good solar reflectors but poor thermal emitters so they rarely satisfy low slope cool roof requirements, though some may still have a high enough SRI to count as a cool roof. Paint applied at the factory or in the field can increase a metal roof’s solar reflectance and thermal emittance, allowing it to achieve cool roof status. Alternatively, cool reflective coatings can be applied as with low sloped metal roofs. Building green with metal roofs and walls. Cool Roof Selection and Applications
If you decide to consider a cool roof, these notes can help you select and install the right option for your building. The decision to make your existing roof a cool roof usually means deciding to coat the roof, replace the roof, or build another roof on top of the existing roof. If your roof is in good condition; has relatively few, easy-to-repair leaks; and has at least five years of expected service life, a cool coating may be a good option. Note that the main reason for coating a roof is to extend its service life, and the energy savings alone will not normally provide sufficient financial reason to coat a roof to make it cool. If your roof is in poor condition, or is approaching the end of its service life, a roof re-covering (adding a new membrane) or replacement (removal of the existing roof, and installation of a new one) is the likely option. Roof re-covering or replacement gives you the opportunity to select any kind of roofing system and cool roof option you desire. Above all, your roof must protect the building from the effects of weather, so be sure to select a roof system that will do this well. A durable roof is the result of the combined efforts of the building owner, specifier, manufacturer, and contractor. Insist that your installer follow all manufacturer installation procedures. Asking the right questions and being involved can help safeguard your investment. The following application notes will help guide you through this process. Built-Up Roofs can be surfaced in three ways, and each has a cool option. First, light-colored aggregate, such as marble chips, can replace the dark mineral aggregate commonly used with hot bituminous flood coat surfacing. It is usually impractical to coat a gravel-surfaced built-up roof with a cool coating. Doing so requires the removal of the non-embedded gravel, which may affect the roof’s fire safety rating. (PDF 2.45MB)
Second, reflective aluminum pigments can be added, at some cost, to an asphalt-coated smooth surface, however these have a low thermal emittance and are not cool. To make this surface cool requires an additional cool coating. Finally, cap sheets with white mineral granules can be substituted for those with dark mineral surface, also at a small premium. Modified Bitumen roofs should have protective coatings to provide heat resistance, ultraviolet resistance, and fire resistance. SBS modified roofs must be coated to prevent rapid ozone and UV degradation. Styrene Butadiene Styrene (SBS) modified bitumen roofs have a flexible, rubber-like quality. Atactic Polypropylene (APP) modified roofs may be left unsurfaced, but this is not recommended because irregular surface cracks can develop that lead to premature aging. The protective surfacing layer can be made of aggregate, mineral, metal foil laminate, or smooth surfaced with a liquid coating. If a large amount of protective granules fall off, recoating becomes necessary. Atactic Polypropylene (APP) modified bitumen roofs have a more rigid, plastic-like quality. Spray Polyurethane Foam roofs are typically coated and periodically re-coated with reflective coatings to protect the foam from UV and water damage. As with membrane roofs, there are many suitable cool roof coatings for spray foam roofs, with acrylic being the most common. Some slightly pitched foam roofs cannot be white according to building appearance ordinances, so gray or tan colors may be used instead. Asphalt shingles roofs are a very economic roofing choice, which have a large share of the market, including most houses with sloping roofs. From a reflectance point of view, they are very similar to rolled asphalt roofing, which is often used as the top layer of low slope roofing.
These materials are composed of asphalt saturated mats made from organic felts or fiberglass. The asphalt is protected from the sun's UV light by roofing granules pressed into the shingle while it is hot (and soft). The roofing granules are 1 millimeter-sized stones (e.g., of crushed granite), which are coated with an inorganic silicate material. The coating contains microscopic pigment particles, similar to those used in paint, to provide color. The solar reflectance of all commercial asphalt shingles is rather low. Premium white shingles are only about 30% reflective, and other colors reflect less. (Incidentally, white roofing materials usually contain additive to inhibit biological growth, to avoid roof discoloration.) The low solar reflectance can be attributed to several factors. First, there is a limited amount of pigment in the granule coating. Also, the roughness of the shingle contributes to multiple scattering of light and thus to increased absorption. Finally, the black asphalt substrate is not 100% covered, and reflects only about 5% of the light which strikes it. Roof Coatings, white roof coatings contain transparent polymeric materials, such as acrylic, and a white pigment, such as titanium dioxide (rutile), to make them opaque and reflective. Other white pigments sometimes used are the anatase form of titanium dioxide, and zinc oxide. These coatings typically reflect 70 to 80 % of the sun's energy. Despite the white appearance, these pigments strongly absorb the 5 % or so of the sun's energy which falls in the ultraviolet. Thus, the pigments help protect the polymer material and the substrate underneath from UV damage. These coatings are applied in thicknesses considerably greater than typical white paints, ranging up to about 1 mm.
Some of the Oak Ridge data in the table show how the reflectance increases with thickness. The substrate must be clean and compatible with the coating system. The achievement of the very highest reflectance values requires sufficient pigment and a smooth substrate. If the substrate is already light in color, it can be made highly reflective with less pigment (fewer coats). To help maintain the high reflectance of a freshly applied white coating, several issues are important. A completely horizontal roof, with ponding water after rain, is likely to become quickly soiled, with a corresponding loss in reflectance. Of course it is also very likely to fail by leaking! A mildewcide additive can retard biological growth with its resulting stains. There is some variation in how tightly dirt adheres to coatings. Roof Coatings can be rolled, brushed, or sprayed onto most kinds of roofs. Any leaks or problems with the roof membrane must be repaired before coating the roof. If you plan to coat your roof, selecting the right coating for your particular roof is the most important thing you can do – cool roof or not. NOTE: Roof coatings are not the same as exterior paints. Ordinary paints are not designed to last on roof surfaces and will not provide protection. Three major kinds of coatings include acrylic, silicone, and urethanes, and cool roof formulations, Table 2. Aluminized asphaltic emulsions provide a glossy finish for some roof types, but fall short of meeting cool roof standards for low sloped roofs. Coating quality varies widely by manufacturer. Improper coating installation can produce coatings that flake off or wear out faster than they should. Insist that the installer follow the manufacturer’s recommended installation procedures, especially regarding weather condition restrictions during application and minimum coating thickness. Table 2: Roof Coating Types Available in Cool Options
Tinted colored coatings, especially light colors, are usually produced by adding tints to white coatings. Thus white is usually the least expensive color. Usually, the tinting process greatly reduces the solar reflectance. Note that the color "raw cotton" is quite reflective. This is a light yellow similar in appearance to a manila folder. It is even more reflective than the color "white stucco," a thick white coating with a rough texture. The relatively dark red, green, and blue colors all have reflectance's below 20%.
Aluminum roof coatings generally employ an asphalt-type resin containing "leafing" aluminum flakes. The term leafing refers to the tendency of the aluminum flakes to accumulate at the exposed upper portion of the coating, which is accomplished with specialized coatings on the flakes. Thus the upper surface is a nearly continuous aluminum layer, which protects the asphalt material from the sun's ultraviolet rays. The aluminum flakes greatly enhance the solar reflectance over the 4 % value for bare asphalt, to above 50 % for the most reflective coatings. The industry regards a visible reflectance above 50 % as a bright coating. (For aluminum coatings, it happens that the visible reflectance is roughly equal to the solar reflectance. This is not true in general due to the fact that about 1/2 of the solar energy content is in the invisible near-infrared region.) While the 50 % solar reflectance of a bright aluminum roof coating is a great improvement over the performance of a black material, the aluminum content has the offsetting effect of lower infrared emittance. Roofing membranes are fabricated from strong, flexible, watertight. They may be applied in multiple layers, as in the venerable Built-Up Roof (BUR), or they may consist of a single-ply membrane. Roof membranes come in several types. Membranes usually contain a fabric made from felt, fiberglass, or polyester, for strength, which is laminated to or impregnated with a flexible polymeric material. The polymeric material may range from bituminous hydrocarbon materials such as asphalt, to synthetic rubber known as EPDM, to synthetic polymers such as polyvinyl chloride (PVC). The color of the polymer itself ranges from black to white, often depending on the amount of carbon black present. The upper surface of the membrane may be coated with a pigmented material which determines the color and solar reflectance, or it may simply be ballasted with roofing gravel. When a dark membrane is surfaced with roofing granules, the membrane has the appearance (and solar reflectance) of asphalt shingles.
PVC membranes are usually white and reflective, and do not require additional formulations or cool coatings. EPDM membranes are black, but can also be produced in white or cool colors. Durable cool EPDM options use black EPDM that is pre-coated with a reflective coating or laminated with a reflective material. The designer should consider membrane durability, since all membranes are not equally durable. Roof membranes that are attached with chemical adhesives must reach and maintain a minimum temperature to bond properly. To compensate for reduced surface temperatures, cool roofs that are chemically adhered might require warmer outdoor temperatures during installation to bond properly. Make sure your contractor follows the recommended installation procedures. Metal roofing is mostly steel or aluminum, although copper and other metals are sometimes used. Steel is invariably galvanized by the application of a zinc or zinc/aluminum coating, which greatly reduces the rate of corrosion. Metal Roofs are often coated with Fluoropolymer or Silicone-Polyester based paints, and many colors can achieve cool roof performance. (PDF 424Kb) Some manufacturers offer cool colors almost exclusively, since lower surface temperatures reduce color fading and cost premiums for the reflective pigments are modest. Unpainted metal roofs tend to have a high reflectance but a low thermal emittance, which prevents them from being considered cool in low slope applications. Metal roofing is available with pigmented polymeric coatings, similar to paint, that are factory applied. These coatings are used to protect the metal panels, and for appearance's sake; they can also keep the roof cooler. Roofing tiles can be ceramic (e.g., clay fired at a high temperature) or fabricated from cement concrete. Some of the lighter types use fibers (e.g., cellulose) added for strength. The color of a tile may be dispersed throughout, or it may be applied in the form of a coating. (PDF 17Kb) Tile Roofs may retain their color or not with aging depending on the type of tile. The color of clay tiles depends on naturally occurring chemicals and minerals in the clay. The surface of clay tiles may be altered by glazing the tiles during the manufacturing process. Concrete tiles can receive a surface coating after being produced, or color can be dispersed throughout the tile as it is produced (color through). The color of roofing slate depends on its chemical and mineral makeup. Weathering slate exhibits color changes as it weathers, while permanent or unfading slate retains its color with weathering. Selecting cool roof tiles that retain their surface properties can yield better lifetime energy savings. Roofing tiles are available in a wide range of colors; more data on the solar reflectance properties is needed. A starting point for the estimation of the solar reflectance would be to use the reflectance of a paint coating of similar color. Advantages of tile include fire safety, as they are non-combustible, and durability. Disadvantages include increased weight and cost compared with low-cost asphalt shingle roofs. Tile roofs often have enhanced air circulation compared to other roofing types because ambient air can circulate below as well as above the tile. (Wood roofs also have provision for air circulation below the roof, to make sure they always remain dry.) This enhanced air circulation helps the roof shed solar heat more readily. Cool Roof Maintenance
As a cool roof becomes dirty from pollution, foot traffic, wind-deposited debris, ponded water, and mold or algae growth, its reflectance will decrease, leading to higher temperatures. Especially dirty roofs may perform substantially worse than product labels indicate. Dirt from foot traffic may be minimized by specifying designated walkways or by limiting access to the roof. Steep sloped roofs have less of a problem with dirt accumulation because rainwater can more easily wash away dirt and debris. Some cool roof surfaces are “self-cleaning” which means they shed dirt more easily and may better retain their reflectance. Cleaning a cool roof can restore solar reflectance close to its installed condition. Always check with your roof manufacturer for the proper cleaning procedure, as some methods may damage your roof. While it is generally not cost effective to clean a roof just for the energy savings, roof cleaning can be integrated as one component of your roof’s routine maintenance program. It is therefore best to estimate energy savings based on weathered solar reflectance values rather than clean roof values. Precautions & Considerations Although cool roofs have been used successfully for many years, their use is growing and cool roofs are now being installed in a wider range of climates. There are some important questions about the durability of cool roof systems in certain applications. Condensation, Moisture, and Ice
Designing a roof that can withstand and control moisture is essential since uncontrolled moisture could cause damage to the roof or the building. The following considerations illustrate how cool roofs handle moisture differently than dark roofs. Ponding occurs when water, typically from rain, accumulates in pools on the roof. This happens when a roof has insufficient slope (caused by poor design or damage) or drain blockage. It takes longer for ponded water to evaporate from a cool roof due to its lower temperature. If your cool roof cannot tolerate ponding, it may be necessary to inspect the roof more frequently to prevent damage or leaks. Moisture from the indoor air can also condense within roof materials. If allowed to accumulate over months or years, moisture could damage those materials. Ordinarily, heat from the sun dries out building materials during the daytime and throughout the summer. Without proper design, both dark and cool roofs can accumulate moisture in colder climates. Cool roofs maintain lower temperatures than dark roofs, and so they may provide less heat to dry out moisture. Potentially, this could make a cool roof more susceptible to moisture accumulation when used in colder climates. While this issue has been observed in both cool and dark roofs in cold climates, the authors are not aware of any data that clearly demonstrate a higher occurrence in cool roofs. The potential for persistent moisture levels to arise in different roof designs and climates is the subject of ongoing research. The building envelope, or exterior shell, includes the façade (walls, windows), roofing, foundation, and any other components that separate inside from outside. Because it is the first ‘line of defense’ against the elements, it is a vital area of thermal management innovation. Today there is much research focused on creating façades that adapt to changing environmental conditions and occupant needs. Click to download INNOVATING FOR BETTER BUILDINGS AS THE INNOVATION OPPORTUNITY WITHIN GREEN BUILDINGS (PDF 8.54MB) Mind Your Surroundings
Cool roofs must be considered in the context of your surroundings. It is relatively easy to specify a cool roof and predict energy savings, but some thinking ahead can prevent other headaches. Ask this question before installing a cool roof: Where will the reflected sunlight go? A bright, reflective roof could reflect light and heat into the higher windows of taller neighboring buildings. In sunny conditions, this could cause uncomfortable glare and unwanted heat for you or your neighbors. Excess heat caused by reflections increases air conditioning energy use, negating some of the energy saving benefits of the cool roof. (PDF 1.27MB) Highly Energy Efficient Buildings and Rooftop Solar Equipment Cool roofs may add only marginal energy savings to buildings that are already highly energy efficient. Highly efficient buildings are often well insulated to minimize the flow of heat through the walls and roof. This helps the occupied space stay cool in summer and warm in winter, regardless of the roof’s surface temperature. (PDF 576Kb)
However, dark roofs on well-insulated buildings can become very hot, so cool roofs help achieve the environmental benefits associated with lower roof temperatures. Keeping a roof cool may also extend its lifetime. Solar energy systems, such as photovoltaic (PV) panels and solar thermal collectors, absorb solar energy and can become hot in the sun. Solar equipment mounted flush with the roof's surface can act like a dark roof, transmitting heat to the building and increasing air conditioning demand. Physical gaps between the solar equipment and roof can reduce this effect, since airflow through the gap can remove some of the heat that would otherwise flow into the roof. On permanently shaded portions of the roof, the roof’s solar reflectance does not affect air conditioning demand. This includes regions of the roof that are completely shaded by solar panel. Some newer thin-film PV modules can be integrated directly with roofing materials. They may meet current cool roof requirements for steep sloped roofs but do not satisfy the more stringent standards for low sloped roofs. This publication contains guidance for builders engaged in or interested in green building products and practices for residential design, development and construction. Thoughtful orientation of a home can maximize solar heating potential in the heating season and minimize solar gains in the cooling season. Orienting a home to optimize its solar resource reduces energy use and, therefore, reduces the pollution caused by a home during its life. A builder should consider such issues such as slope, storm water management, local solar angles, and high-priority vegetation when determining the optimum site for each home. (PDF 3.31MB) Google SketchUp Intuitive and fun to use
Learn more and use Google SketchUp to built your Relevant Articles GREEN BUILDING & SUSTAINABILITY RESOURCES WHAT IS A GREEN BUILDING?
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Pathways to Green Building and Sustainable Design: A Policy Primer for Funders At Green-Buildings.com you can get free expert advice about LEED Certification, Training, Green Building Products and any topic related to commercial green buildings. You'll also find the best LEED Exam Prep products, and local LEED Classes. LEED Certified Building Guidelines - This guideline provides a summary of the USGBC’s new LEED 2009 green building rating program. A roofing system is only one component of an integrated building design program. LEED takes into account the building envelope and interior design technologies that affect the energy usage, environmental impact, and social quality of the design, construction and operation of a building. This guideline describes potential points in the LEED 2009 Green Building Design and Construction credit qualifications for cool metal roofing products manufactured by Petersen Aluminum Corporation. (PDF 721Kb) Measuring Building Performance - Energy Efficiency Software Tools |
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Green Building DesignEnergy Efficiency In Buildings |
