A Practical Guide To Cool Roofs And Cool Pavements Primer
January 2012A Practical Guideto Cool Roofs andCool PavementsPrimer
Readyto LearnPrimerCool Roofs andPavementsCool roofs have the abilityto reflect and reject heatbecause the roofs areprepared with materialswhich have properties ofhigh solar reflectance. New Delhi Chief Minister, Sheila Dikshit,India-Express.com, January 20, 201167
IntroductionWorld temperatures are rising at anunprecedented rate.According to the Intergovernmental Panel onClimate Change, the Earth’s average temperature is on track to increase by between 2 and7 degrees Celsius (4 to 13 degrees Fahrenheit)this century. This dramatic change in temperature will produce a climate never beforeexperienced by human civilization. Cities areoften significantly warmer than the surrounding landscapes because urban surfaces absorbmore sunlight than natural landscapes, citieslack vegetation, which cools landscapes byevaporating water, and urban areas releasemore heat from human activity includingair conditioning, vehicles, and industry. Thedifference between outside air temperaturesin a city and its surrounding rural areas canbe 5 to 9 degrees Celsius (9 to 16 degreesAdapted from LBNL Heat Island Group.Coverage percentages shown represent the mostcommon ranges of urban land area by type but thereis some variability by city. Some studies indicate thatpavements can comprise up to approximately70 percent of urban land area.85 Frural farmland8Higher temperatures adversely affect ourhealth, our energy consumption, and ourenvironment.Rapidly increasing temperatures stress ecosystems, increase the frequency and durationof heat waves and exacerbate air pollution.Together, these factors are creating serioushealth risks to people around the world. Inaddition, increasing wealth in the developingworld is spurring the rapid deployment of airconditioners that are taxing electrical gridswith their energy demands.Roofs and pavements cover about 60percent of urban surfaces, and absorbmore than 80 percent of the sunlight thatcontacts them. This energy is convertedto heat, which results in hotter, morepolluted cities, and higher energy costs.4The Summer Urban Heat Island Effect29 CFahrenheit) or more in summer months.1 Thisphenomenon is called the summer “urban heatisland effect.” Addressing this heating effectwill only become more important becausethe world is rapidly urbanizing—within 50years an estimated 80 percent of the world’spopulation will live in an urban area.231–32 C 88–89 F33 Ccommercialdowntown urban92 F30–31 CCool roofs and pavements can help cooldown buildings and cities.Studies of a city’s “urban fabric” indicate thatabout 60 percent of urban surfaces are coveredby roofs or pavements. About 20 to 25 percentare roofs and 30 to 45 percent are pavements.3Because these surfaces are dark and typicallyabsorb over 80 percent of sunlight that contacts them and convert that solar energy intoheat, our built environment exacerbates thewarming effects of climate change. Replacingand upgrading roofs and pavements with morereflective materials could reverse this warming,turning urban surfaces into assets instead ofburdens. Vegetated roofs, permeable pavements, and shade trees are other coolingstrategies that are complementary with coolroofs. Cool roofs paired with appropriate levelsof roof insulation help keep buildings morethermally comfortable. Cool, reflective roofsand pavements should be a priority strategybecause they are cost-effective, typically payback within one year, and help cities bothmitigate and adapt to climate change whilemaking them more desirable and comfortableplaces to live.86–88 Fsuburban residential30 C 86 Fparks9
How it WorksIt’s simple.Cool surfaces are measured by how much lightthey reflect (solar reflectance or SR) and howefficiently they radiate heat (thermal emittanceor TE). Solar reflectance is the most importantfactor in determining whether a surface is cool.A cool roofing surface is both highly reflectiveand highly emissive to minimize the amountof light converted into heat and to maximizethe amount of heat that is radiated away.Every opaque surface reflects some incomingsunlight and absorbs the rest, turning it intoheat. The fraction of sunlight that a surfacereflects is called solar reflectance or albedo.White roofs reflect more sunlight than darkroofs, turning less of the sun’s energy intoheat. Increasing the reflectance of our buildings and paved surfaces—whether throughwhite surfaces or reflective colored surfaces—can reduce the temperature of buildings, cities,and even the entire planet. Most roofs are dark and reflect no more than20 percent of incoming sunlight (i.e., thesesurfaces have a reflectance of 0.2 or less);while a new white roof reflects about 70 to80 percent of sunlight (i.e., these surfaceshave a reflectance of 0.7 to 0.8). New white roofs are typically 28 to36 degrees Celsius (50 to 65 degreesFahrenheit) cooler than dark roofs inafternoon sunshine while aged white roofsare typically 20 to 28 degrees Celsius (35to 50 degrees Fahrenheit) cooler.5The Albedo EffectComparison of a black and a white flat roof on a summer afternoon with an air temperature of 37 degrees Celsius(98 degrees Fahrenheit).Source: Adapted from data from LBNL Heat Island Group. Numbers do not sum to 100 percent due to rounding.1011
The BenefitsKey Cool Roofs TerminologySolar Reflectance (SR or albedo)The fraction of sunlight (0 to 1, or 0 percent to100 percent) that is reflected from a surface. SRtypically ranges from about 0.04 (or 4 percent)for charcoal to 0.9 (or 90 percent) for fresh snow.High solar reflectance is the most importantproperty of a cool surface.SRSA1.00coolestSolar Absorptance (SA)The fraction of sunlight (0 to 1, or 0 percentto 100 percent) that is absorbed by a surface.Surfaces with high solar absorptance tend to gethot in the sun. If the surface is opaque, solarabsorptance equals 1 minus solar reflectance.0white roofblack roofcoolest1.0Solar reflectance (SR) and absorptance (SA) havean inverse relationship. The more heat a surfacereflects, the less heat it absorbs.Thermal Emittance (TE)The efficiency (0 to 1) with which a surface emitsthermal radiation. High thermal emittance helpsa surface cool by radiating heat to its surroundings. Nearly all nonmetallic surfaces have highthermal emittance, usually between 0.80 and0.95. Uncoated metal has low thermal emittance,which means it will stay warm. An uncoatedmetal surface that reflects as much sunlight as awhite surface will stay warmer in the sun becauseit emits less thermal radiation. TE is the secondmost important property of a cool surface.Solar Reflective Index (SRI)A coolness indicator that compares the surfacetemperature of a roof on a sunny summer afternoon to those of a clean black roof (SRI 0) anda clean white roof (SRI 100). SRI is computedfrom solar reflectance and thermal emittance,and can be less than 0 for an exceptionally hotsurface (e.g., a solar collector) or greater than100 for an exceptionally cool material (e.g., a verybright white roof ). (See the graph on page 23for a visual explanation.) An SRI calculator canbe found at ator/SRI-calc10.xls.Uncoated metalsri 68Coated metalsri 92sr 0.75te 0.08r lowsr 0.75te 0.83r lowMetal that is painted and coated has a considerably higher thermal emittance than uncoated metal.This raises its SRI to 92, which is much cooler thanuncoated metal, whose SRI is 68.The values in the above examples are estimates.6 Actualproduct values may vary. Please consult the Cool RoofRating Council or a manufacturer for actual values.Benefits to individual buildingsEnergy savings potential Increasing thereflectance of a roof from 0.1-0.2 to 0.6 cancut net annual cooling energy use by 10 to 20percent on the floor of the building immediately beneath the roof by reducing the needfor air conditioning. 7Cost savings potential Retrofitting 80 percentof the 2.6 billion square meters of commercialbuilding roof area in the U.S. would yield netannual energy cost savings (cooling energysavings minus heating energy penalty) of 735million, and offer an annual CO2e reductionof 6.2 million tonnes. Expanded to a globalmarket, cool roofs could be an investmentthat saves billions of dollars.8 In addition, coolcoatings are treated as a maintenance productfor tax purposes and are allowed to be writtenoff in the year they are installed, rather thancapitalized over 39 years like traditional roofmaterials.Improved roof and equipment life Extremechanges in surface temperature can damageroofs and the expensive equipment on them.Cool roofs reduce temperature fluctuations andwill likely lengthen the life of roof equipmentand material. Extending roof life also helpsreduce waste going to landfills. A cooler roofUnless otherwise noted, all dollar values are USD.is also likely to improve the efficiency of solarPV panels.Short payback period Cool roofs are typicallylow cost investments. If the roof needs to bereplaced anyway, choosing a white coloredmaterial often costs the same as a dark colored alternative. (Please see page 36 for a fulllist of cost differentials by materials). Further,installing a cool roof is a retrofit that does notinconvenience the building occupants. Theaverage annual energy cost saving (coolingenergy saving minus heating energy penalty)for a white roof on a commercial building is 0.36 per square meter ( 0.033 per squarefoot).9Improved thermal comfort In a building thatis not air conditioned, replacing a dark roofwith a white roof can cool the top floor ofthe building by 1 to 2 degrees Celsius (2 to 3degrees Fahrenheit),10 enough to make theseliving spaces noticeably more comfortable andeven save lives in extreme heat waves. Coolerroofs are more comfortable and functional forresidents of regions where the roof is usedas living space. Appropriate levels of insulation are also an important part of improvingthermal comfort.When it comes to energy savings,the power of one can become thepower of many.Thermal Resistance (R-value)A measure of a material or system’s ability toprevent heat from flowing through it. The thermalresistance of a roof can be improved by addinginsulation, a radiant barrier, or both.12One cool roof saves its owner 10 to 20 percent on energyspent on air conditioning on the top floor of the building.If building owners installed cool roofs on 80 percent ofU.S. commercial buildings, they’d save 735 million everyyear. Photo: Arlen13
Benefits to pavementsCity-wide benefitsConventional paving materials can reach peaksummertime temperatures of 50 to 65 degreesCelsius (120 to 150 degrees Fahrenheit),heating the air above them.11 There are manykinds of paving options that are lighter in colorand create more reflective paved surfaces.Additionally, many kinds of permeable pavements, including reinforced grass pavements,can also cool a pavement surface through theevaporation of moisture stored in the pavement. If pavements are too bright, they cancause undesirable glare, but there are manyshades of gray that are reflective that do notcause too much glare.There are a number of additional benefits tolight colored pavements beyond cooling.Improved durability Testing and researchare underway to evaluate the durability andlongevity of cool pavement materials in avariety of usage conditions. Asphaltic pavements that stay at lower temperatures may beless likely to rut.About 20 to 25 percent of urban surfaces are roofs and30 to 45 percent are pavements. Photo: Eric KononNighttime illumination Parking lots andstreets that use light colored pavements willallow for better visibility and safer streets atnight and may also reduce the need for streetlighting.Improved water quality Higher pavement temperatures can heat stormwater runoff which, inturn, can affect metabolism and reproductionof aquatic species. The U.S. EnvironmentalProtection Agency classified elevated watertemperature as a “pollutant of concern” in theClean Water Act.New Orleans Hot Weather Energy DemandDemand for electricity can increase steadily once temperatures begin to exceedabout 20 to 25 degrees Celsius (68 to 77 degrees Fahrenheit).Source: Adapted from Sailor,D. J. 2002. Urban HeatIslands, Opportunities andChallenges for Mitigationand Adaptation. SampleElectric Load Data for NewOrleans, LA (NOPSI, 1995).North American Urban HeatIsland Summit. Toronto,Canada. 1–4 May 2002. Datacourtesy Energy Corporation.average electric load (mwh)120010008006004002000-100102030maximum daily temperature ( c)4050Reduced summer heat island effectSimulations run for several cities in the U.S.have shown that city-wide installations ofhighly reflective roofs and pavements, alongwith planting shade trees will, on average,reduce a city’s ambient air temperature by 2 to4 degrees Celsius (4 to 9 degrees Fahrenheit)in summer months.12 Reducing urban temperatures makes cities more comfortable andenjoyable to live in and promotes healthierpopulations.More resistant to heat related deaths Coolroofs can cool the areas in a building wherethe risk of death during heat waves is high.For example, there were 739 deaths in theChicago heat wave of 1995. Virtually all of thedeaths occurred in the top floors of buildingswith dark roofs.13 Subsequent heat waves haveclaimed thousands of lives in the U.S., France,Russia, and elsewhere.forego the need for additional investments inpeaking generation capacity. Approximately 5to 10 percent of U.S. peak electricity demandfor air conditioning is a result of the urbanheat island effect.14 Research indicates thatpeak electricity demand increases by 2 to4 percent for every 0.5 degrees Celsius (1.8degrees Fahrenheit) increase in temperatureabove a threshold of about 15 to 20 degreesCelsius.15 Rosenfeld et al. (1996) estimatedthat eliminating the urban heat island effect inLos Angeles—a reduction of 3 degrees Celsius(5.4 degrees Fahrenheit)—could reduce peakpower demand by 1.6 gigawatts resulting in asavings of about 175 million per year (at 1996electricity prices).16 Approximately 15 millionReduced peak electricity demand In climatezones where summer brings peak electricitydemand from air conditioning, cool roofs areof great value to utilities and grid operators.They can improve utility capacity utilizationand therefore profitability, reduce transmissionline congestion, avoid congestion pricing, andTen Most Deadly Heat EventsEvents are listed by country and year with the number of deaths shown in thousands.Source: EM-DAT: The OFDA/CRED International Disaster Database. 2007. Available at em-dat.net, UniversitéCatholique de Louvain, Brussels, Belgium. Data downloaded on 20 September 2007.56,000Russia (2010)19,490France (2003)15,090Spain (2003)Extreme heat is not isolated to the tropics.In the U.S., an average of 400 deaths each17year are directly related to heat, andmany more—an estimated 1,800—perishfrom a range of illnesses that are exacer18bated by heat stress. The average annualdeath toll from heat far exceeds that ofany other natural disaster in the U.S.9,355Germany (2003)2,695Portugal (2003)France (2006)1,388Andhra Pradesh, India (2003)1,210Belgium (2003)1,175Switzerland (2003)1,039Madya Pradesh, India (2002)1,030014A hot summer day in Chicago. Photo: Zane Edwards10203040506015
Respiratory illness resulting from air pollution is a majorglobal health problem. Photo: Kathmandu, Nepal byMichael Rennerof that amount was due to more reflectivepavements. A 2004 analysis of New York Citywhen electricity averaged 16.5 cents per kWhfound that a one degree reduction in temperature would cut energy costs by 82 millionper year. Electricity prices have subsequentlyincreased by over 20 percent.19Air quality benefits City-wide temperaturereduction not only makes cities more comfortable, but also improves air quality becausesmog (ozone) forms more readily on hotdays. Ozone pollution is a major contributingfactor to respiratory illness, which the WorldHealth Organization predicts will be the thirdleading cause of death by 2030.20 Simulationsof Los Angeles indicate that lighter surfacesand shade trees could cool temperatures andthus reduce smog in excess of EPA-definedsafe concentrations by 10 percent.21 Acrossthe U.S., the potential energy and air qualitysavings resulting from increasing the solarreflectance of urban surfaces is estimated tobe as high as 10 billion per year.22The role of shade trees Planting and maintaining an urban tree canopy is another way tocool cities while adding beauty and characterto neighborhoods. Trees cool cities by shadingthe ground and structures around them butalso through evapotranspiration—a process bywhich trees release water into the atmospherethrough their leaves. These cooling effectscan be significant. Studies indicate that treegroves can be 5 degrees Celsius (9 degreesFahrenheit) cooler than open ground aroundthem. In addition to saving energy, the use oftrees and vegetation as a mitigation strategycan provide air quality and greenhouse gasbenefits. 23 For more information on the costsand benefits of tree programs see ReducingUrban Heat Islands: Compendium of Strategies:Trees and Vegetation by the U.S. EnvironmentalProtection Agency.Air-conditioned vs. non air-conditionedbuildings Cool roofs are valuable in bothair-conditioned and non air-conditioned buildings. In air-conditioned buildings, the indoorair temperature is controlled, so installing acool roof does not change the comfort of thebuilding. However, a cool roof can reduce airconditioning costs by as much as 20 percent ina single story building.24In non-air-conditioned buildings, particularlythose that are poorly insulated, cool roofs cannoticeably improve the comfort of the buildingby lowering the indoor air temperature of thetop floor of the building by 1 to 2 degreesEasy to monitor Compared to many climatechange mitigation strategies, the area of coolroofs and pavements installed is relativelyeasy to measure and monitor with aerial andsatellite imagery.Unless otherwise noted, all dollar values are USD.16Celsius (2 to 3 degrees Fahrenheit).25 This temperature reduction is enough to save lives inextreme heat waves and make non-conditionedwork environments like barns and warehousesmore usable and comfortable for employees.Air sealing and insulation are important investments for improving the comfort of poorlyinsulated, non-air conditioned buildings butrequire access to walls and attic spaces. Coolroofs can be deployed on almost any structureand, because they do not require wall or atticaccess, they typically have a lower install costthan air sealing and insulation.There is a growing global market for airconditioning as a first response to hot indoortemperatures, particularly in rapidly developing countries like India and China. Electricair conditioning is an expensive and energyintensive first choice for cooling. It furthertaxes electric grids that are already straining tomeet new demand. Cool roofs and pavementsare a cheaper alternative that could forestallthe purchase of AC units, especially on the topfloors of buildings.Benefits to the planetGlobal cooling potential Replacing the world’sroofs and pavements with highly reflectivematerials could have a one-time cooling effectequivalent to removing 44 billion tonnes ofCO2 from the atmosphere, an amount roughlyequal to one year of global man-made emissions.26 Every 10 square meters (100 squarefeet) of white roofing will offset the climatewarming effect of one tonne of CO2. Assuminga 0.15 increase in reflectance is realized byswitching to a lighter pavement option, coolpavements would “offset” approximately0.5 tonnes of CO2 per 10 square meters (100square feet), or 300 tonnes of CO2 per lanemile (1.6 kilometers) of highway. Assuming theaverage car emits 4 tonnes of CO2 per year,the combined “offset” potential of replacingthe world’s roofs and pavements with highlyreflective materials is equivalent to taking allof the world’s approximately 600 million carsoff the road for 20 years.Case StudyThe Greenhouses of Almería, SpainThe semi-arid Almería region of southernSpain has the most dense concentration ofgreenhouses in the world. In preparation forthe hot summer months, farmers whitewashthe roofs of the greenhouses to help lowerinside temperatures. Researchers studyingweather station data and satellite imageryhave found that the cumulative effect of theincreased reflectivity has also cooled outsidetemperatures. Over the last 20 years, temperatures in the Almería region have fallenby 0.3 degrees Celsius, in contrast to a 0.5degree Celsius increase in temperatures insurrounding regions that do not have highlyreflective greenhouses.27Google satellite view of the whitewashed greenhouseroofs in Almería, Spain. The greenhouses cover approximately 350 square kilometers (135 square miles) of thisregion. Credit: GoogleAir conditioners in Hong Kong. Photo: Niall Kennedy17
Readyto LearnPrimerChoosing CoolSurfacesWhite is the coolest, butnot the only, color to choose.Building owners can choosealmost any color they like.1819
Choosing a Cool RoofThe cool roof options available to a buildingowner depend in large part on the buildingand roof type they are working with. Thatsaid, there is a cool option for nearly everytype of roof. Cool roofs are relatively easy toimplement for commercial buildings. The roofsof most commercial and high-rise residentialbuildings are low-sloped (i.e., almost flat ),28and are generally not visible from the street. Asa consequence, there is little resistance or costto changing the color of these roofs duringroutine retrofits or when waterproofing.In contrast, residential buildings often havesteep-sloped roofs that can be seen from theground. In many parts of the world, white isnot currently a popular color for residentialroofs, and as a result there can be aestheticconcerns about using white materials. ToCommon Building Types and Roofing MaterialsCool roofing options are available for all standard roofing materials. (See table on page 24).address this, roofing manufacturers havedeveloped “cool” materials in popular roofcolors (e.g., red and gray) that strongly reflectthe invisible heat component of sunlightand much of the sun’s energy away from thebuilding.29The desirability of cool roofs depends onlatitude, altitude, annual heating load, annualcooling load, peak energy demands, and sunblockage by trees, buildings, and hills for theparticular building. Cool roofs on buildingsin some far northern communities such asAnchorage, Alaska or in forested mountainousareas such as at Lake Tahoe, Nevada, may notbe appropriate. That said, whether or not acool roof is appropriate in any climate dependson the building, its energy usage pattern,existing needs, and costs.A flat-roofed commercial building in Shenzhen.Photo: dcmasterRed tile roofs in Dubrovnik. Photo: Marcel OosterwijkA steep-sloped single family home with asphalt roofshingles in the U.S. Photo: Eric Allix RogersMulti-story buildings with concrete or cement roofs arecommon in India. Photo: John RobertsCorrugated metal roofs in Rio de Janeiro.Photo: whl.travelUrban rooftops in Mexico City. Photo: StorkholmPhotographyCaution: Mind your surroundingsCool roofs must be considered in the context oftheir surroundings. It is relatively easy to specifya cool roof and predict energy savings, but somethinking ahead can prevent other headaches.Ask this question before installing a cool roof:Where will the reflected sunlight go? A bright roofcould reflect into the higher windows of tallerneighboring buildings. In sunny conditions, thiscould cause uncomfortable glare and unwantedheat for you or your neighbors. In these cases,building owners can opt for a cool colored roof toprovide some improvement in reflectance withoutsignificantly affecting neighboring buildings.2021
Cool colorsSolar Reflectance of Common Roofing MaterialsSurfaces that are more reflective tend to remain cooler than those that are less reflective. Both solar reflectanceand (surface) temperature rise should be considered when assessing a cool surface material. The graph shows solarreflectance and temperature rise of common steep-sloped roofing materials (Air temperature is 37 degrees Celsius/ 13 degrees Fahrenheit). Source: Adapted from data from LBNL.100Cool colored metal roofs. Photo: Custom Bilt MetalsCool roofs come in many colors.Many roof materials in any color can be treated with a reflective coating, giving them ahigher solar reflectance than the standard version of that material.Standard ConcreteTiles (SR)0.040.180.240.330.170.12With Cool CoatingApplied (SR)0.410.440.440.480.460.41surface temperature change ( c)White is the “coolest” color, but there are coolversions of a wide variety of popular colors.Building owners have more choice than theyrealize. Highly reflective roofs can come inpopular colors such as red, green, and gray.Cool colored materials are available for alltypes of steep-sloped (pitched) and low-sloped(nearly horizontal) roofs. These materialsinclude asphalt shingles, metal, clay tiles,and concrete tiles. Highly reflective coloredroofs typically have an initial solar reflectance0.30 to 0.55, compared with around 0.10 forconventional dark steep-sloped roofs.80standard-colored metalstandard-colored tile or shinglecool-colored shingle60cool-colored metalcool-colored tile40white shinglewhite tilewhite metal2000.20.40.60.81.0solar reflectance (sr)Source: Adapted from data from American Rooftile Coatings.standardcool-coloredwhiteUncoated metalCool-colored metal (coated)White metal (coated)Ceramic tilesCool-colored clay tilesWhite coatingPhotos: CreativeCommons and LBNLBeware of “paint”Although many cool roof advocates call for building owners to “paint” their roofs white, usingwhite house paint to coat any kind of roof isinappropriate and ill-advised. Some roof coatingsare installed by using rollers like the ones usedfor indoor house paint, thus it may look likeroofs are being “painted.” In fact they are being“coated” with products made specifically forroofs. The major difference between paint andcoatings are that paints are typically cosmeticin nature and significantly thinner applicationsthan coatings. Also, coatings are more reliablyweather resistant.22Some shingle manufacturers will not honor thewarranty of their products if the roof has beenpainted or coated in any way. Be sure to checkwith your roof manufacturer before installing acool roof on top of your existing roof.In some countries, notably India and Greece,whitewashing homes to keep them cooler insummer months is a long-standing tradition. Thisis an advisable and appropriate practice for somebuilding materials, depending on availability andcost of more permanent alternatives.23
Common Roofing Materials and Cool Options *Roof TypeLife Expectancy(years)Roof SlopeNon-Cool Roof Options Non-Cool Roof SolarReflectanceCool Roof OptionsCool Roof SolarReflectanceAsphalt Shingle15 to 30steep-slopedblack or dark brownwith y light gray)or cool color shingle0.25Built-Up Roof10 to 30low-slopedwith dark gravel0.10–0.15with white gravel0.30–0.50with aluminumcoating**0.25–0.60white smooth coating0.75–0.85dark colorwith conventionalpigments0.20terracotta(unglazed red tile)0.40color withcool pigments0.40–0.60white0.70color withcool pigments0.30–0.50white0.70Clay TileConcrete Tile50 30 to 50 steep-slopedsteep-sloped0.05–0.35Liquid Applied Coating5 to 20low- or steep-slopedsmooth black0.05smooth white0.70–0.85Metal RoofUncoated corrugated metalis typically less durable thancoated metal20 to 50 low- or steep-slopedunpainted,corrugated**0.30–0.50white 0color withcool pigments0.40–0.70Modified Bitumen10 to 30low-slopedwith mineral surfacecapsheet (SBS, APP)0.10–0.20white coating overa mineral surface(SBS, APP)0.60–0.75Single-Ply Membrane10 to 20low-slopedblack (polyvinylchloride (PVC) orethylene propylenediene monomerrubber [EPDM])0.05white (PVC or EPDM)0.70–0.80color withcool pigments0.40–0.60painted dark colorwith conventionalpigments0.35–0.50bare0.40–0.55Wood Shake15 to 30steep-slopedSource: Adapted from coolcalifornia.org roofing options table. Photos: Creative Commons and LBNL24dark colorwith conventionalpigments* Spray polyurethane foam is not included in this chart because it is typically coated by a reflective liquid appliedcoating to minimize ultraviolet damage to the foam. ** Aluminum and metal have high solar reflectance but theirlow thermal emittances reduces their ability to stay cool.25
What happens as the surface ages?Rating productsOver time, white roofs get dirty; they collectsoot, dust, salt, and, in some climates,biological growth. As a result, their reflectancedecreases. The aged solar reflectance of awhite roof is typically 0.55 to 0.65. Replacing adark roof with an aged white roof still reducesthe amount of sunlight absorbed by around 40to 50 percent. Codes and standards typicallyuse the aged SR value of white roofs.Most countries have enacted some voluntaryor mandatory codes and standards for buildings and energy use. Some of these includelanguage covering cool roofs and pavements.In order for codes to be effective, there mustbe a broadly accepted rating and labelingsystem for materials.The reflectivity of pavements also changesas they age. Concrete pavement tends to beinitially more reflective and get darker withage and use. Dark asphalt pavement tends tolighten to a gray color over time. Despite thisconvergence in reflectivity, concrete typicallyremains more reflective than asphaltpavements.Determining both the initial and aged solarreflectance of a given material or roofing product requires testing. In the U.S., the Cool RoofRating Council (CRRC) has been established asan independent, non-profit organization thatmaintains a third-party rating program, whichrates and publishes a roof product’s solarreflectance and thermal emittance. The CRRCallows standardized t
36 degrees Celsius (50 to 65 degrees Fahrenheit) cooler than dark roofs in afternoon sunshine while aged white roofs are typically 20 to 28 degrees Celsius (35 to 50 degrees Fahrenheit) cooler.5 The Albedo Effect Comparison of a black and a white flat roof on a summer afternoon with an air temperature of 37 degrees Celsius (98 degrees Fahrenheit).
work/products (Beading, Candles, Carving, Food Products, Soap, Weaving, etc.) ⃝I understand that if my work contains Indigenous visual representation that it is a reflection of the Indigenous culture of my native region. ⃝To the best of my knowledge, my work/products fall within Craft Council standards and expectations with respect to
akuntansi musyarakah (sak no 106) Ayat tentang Musyarakah (Q.S. 39; 29) لًََّز ãَ åِاَ óِ îَخظَْ ó Þَْ ë Þٍجُزَِ ß ا äًَّ àَط لًَّجُرَ íَ åَ îظُِ Ûاَش
Collectively make tawbah to Allāh S so that you may acquire falāḥ [of this world and the Hereafter]. (24:31) The one who repents also becomes the beloved of Allāh S, Âَْ Èِﺑاﻮَّﺘﻟاَّﺐُّ ßُِ çﻪَّٰﻠﻟانَّاِ Verily, Allāh S loves those who are most repenting. (2:22
1. P274-0100-C — 1-stage cool, 1-stage heat for air- conditioning systems only. 2. P274-0200-C — 1-stage cool, 2-stage heat for a single speed heat pump, or an air conditioner with 2-stage heat. 3. P274-0300-C — 2-stage cool, 2-stage heat for 2-speed air-conditioning systems, or 2-stage cool, 3-stage heat for 2-speed heat pump systems.
If you’re unsure if you have records outstanding, please contact the office. Cool cards This term our cool card focus is 'I can do it'. Staff will be rewarding students who display an 'I can do it' mindset with a cool card. Students write their names on the cool card and place t
Play games, paint, cool off, and have fun! Dress to get messy. Ages 8-12. (90 min.) Preregister. Thu, Aug 15, 3:00 pm Be Cool at School Rock with “Pete the Cat” in his cool school shoes, and beat those “First Day Jitters” with other cool stories and games. Ages 5-7. (60 min.) Preregist
conducted between cool running water-treated burns and those that received either no first aid or an alternative to cool running water, and the 6 durational categories of first aid outlined previously. The relationship between adequate cool running water and the studied clinical outco
011 primary blue 030 cool grey 01 012 cyan 031 cool grey 02 013 turquoise 032 cool grey 03 015 dark green 033 cool grey 04 016 yellow green 035 warm grey 019 brown 037 warm grey 02 022 deep black 039 warm grey 04 AQUA COLOR SYSTEM. 8 9 REFILL. Wasser-basierende MOLOTOW Marker . Refill-Flasche · refi
