On a hot, sunny day, the temperature on the surface of a traditional black roof can be more than 150 degrees Fahrenheit (65 degrees Celsius). When you imagine that sweltering rooftop next to many others, it's no surprise that the air in a large city filled with dark, heat-absorbing rooftops can often be hotter than the air in surrounding areas.
Even in rural and suburban neighborhoods, the heat absorbed by a traditional roof on a sunny day raises temperatures inside the house, contributing to higher air conditioning requirements, steeper energy costs and discomfort for those without air conditioning. Fortunately, the remedy for all this extra heat — a cool roof — is relatively low-tech, low-cost and increasingly easy to find.
A cool roof is a roof designed to maintain a lower surface temperature in bright sunshine, more than 50 degrees F (28 degrees C) cooler than a traditional roof. The surface of a cool roof reflects more sunlight and releases more heat than a so-called hot or dark roof. While the term "cool roof" is sometimes used to describe any roofing surface that is cooler than a standard rooftop, green certification programs such as LEED, Energy Star and the Department of Energy Building Technology Program base their respective cool-roof credentials on a roofing material's ability to reflect the sun (solar reflectance) and release absorbed heat (emissivity). The higher the solar reflectance and emissivity (in decimals on a scale from 0 to 1), the cooler the roof. 0 would represent truest black and 1 would represent truest white.
Ready to save money, conserve energy and cool the planet by turning your old, hot roof into a cool roof? Read on to discover 10 ways to cool your roof!
- Roll Out the Modified Bitumen
- Go With a Single-ply Membrane
- Build It Up
- Add a Coat of Cool
- Select the Perfect Shingle
- Make It Metal
- Pick a Tile, (Almost) Any Tile
- Get a Little Misty-Eyed
- Go Green (Literally!)
- Rock On!
10. Roll Out the Modified Bitumen
Just about any kind of roof can be replaced with a cool roof. And some roofs can be converted to cool roofs by adding special coatings or surface materials. In some states and municipalities, cool roofs are required for all new commercial construction.
Cool roof requirements are based on the roof's slope, with more stringent requirements for low-sloped roofs — those that rise less than 2 feet (0.6 meters) in height for every 12 horizontal feet (3.7 meters) — than for steep-sloped roofs, which rise more than 2 feet (0.6 meters) in height every 12 horizontal feet (3.7 meters). To determine which roofing materials are best for your home or building, first determine the slope of your roof, then select the cool roof product that best suits your slope, budget and architectural style.
One of the most common cool roof options for a flat or low-sloped roof is a modified bitumen roof. Modified bitumen roofing is a membrane made up of sheets of plasticized or rubberized asphalt held together with rolled reinforcing fabric and fastened to the roof deck with hot asphalt or cool adhesive. Traditional modified bitumen roofs are black or gray with a low solar reflectance, meaning that they absorb, rather than reflect, most of the sun's light. But simply applying a white coating over the surface of the material at the factory can raise the solar reflectance to acceptable cool roof standards.
9. Go With a Single-ply Membrane
Another type of cool roofing material used for low-sloping roofs is a single-ply membrane. Single-ply membranes are prefabricated plastic or vinyl sheets containing solar reflective coatings or materials. The sheets are rolled onto the roof deck, then attached to the structure with some combination of chemical adhesives, mechanical fasteners or ballast, such as gravel or pavers. Single-ply membranes don't require any additional coatings or surfacing — the cool roof properties are integrated within the product itself.
There are several types of single-ply membrane, but the three most common are polyvinyl chloride (PVC), ethylene propylene diene monomer (EPDM) and thermoplastic polyolefin (TPO). Not all single-ply membranes are cool roof products.
8. Build It Up
Built-up roofing is the term for the standard tar-and-gravel roof. Because it's inexpensive, easy to apply and easy to repair, it's among the most commonly used roofing systems for flat and low-sloped roofs. Built-up roofing involves layering a base sheet of asphalt or bitumen with fabric, followed by a protective layer of gravel, mineral granules or some sort of aggregate rock.
Traditionally, the asphalt and surface gravel in a built-up roof have been black or dark gray, trapping much more light and heat than they release, but there are several ways to make a built-up roof cooler. One is to replace the surface layer with white gravel or reflective marble chips to increase its solar reflectance. Another is to apply something called a mineral surfaced cap sheet, which incorporates reflective granules or a reflective coating into the roofing material itself. Finally, special coatings or pigments can sometimes be added to an existing asphalt surface to convert a standard roof to a cool roof. This typically requires one coat of a reflective material and another of an emissive material that releases heat.
Cool vs. Traditional Roof Costs
The average cost to install a cool built-up roofing system, or any cool roof system, is comparable to that of a traditional roof. While some cool roof products are slightly more expensive than traditional roofs, the extra cost is often recouped through energy savings.
7. Add a Coat of Cool
Cool roof coatings are best applied to low-sloped roofs in good condition. They are divided into two categories: cementitious coatings, which contain concrete or ceramic particles, and elastomeric coatings, which contain added polymers that make them less brittle and more adhesive to building surfaces.
Both cementitious and elastomeric coatings improve the solar reflectance of the roof surface. The primary difference is that elastomeric coatings act as a watertight membrane, while cementitious coatings must be applied over roofing materials that have already been thoroughly waterproofed.
Cool roof coatings are sprayed, rolled, or brushed onto an existing flat or low-sloping rooftop to create a bright white, paint-like reflective surface. These coatings are more commonly used in re-roofing projects than in new construction.
6. Select the Perfect Shingle
For the steep-sloped roofs found on most U.S. homes, standard asphalt shingles can be replaced with cool asphalt shingles containing specially coated reflective granules to help them better reflect sunlight. Shingles made from wood, polymer and metal can also be coated to improve their solar reflectance.
Shingles are generally not as reflective as any of the cool roof options available for low-sloping roofs, but their familiar appearance and traditional style make them a popular choice for residential construction. A cool shingle with white granules costs about the same as one with the old, standard dark asphalt granules, while a shingle with its specially coated granules colored to match the desired color of the roof can cost a little more.
5. Make It Metal
Unpainted metal roofs are naturally reflective (high solar reflectance), but they tend to hold heat in (low emissivity), so they are generally a better choice for steep roofs than for flat or low-sloping roofs, which receive more sunlight throughout the course of a day. A factory-applied cool roof coating can improve the heat releasing properties of a metal roof, enough so that some coated metal roofs are able to qualify as cool roofs.
A standard unpainted metal roof can be a cost-effective solution for some steep-sloped applications, since it is already reflective and requires no additional technologies or materials to achieve cool roof status.
4. Pick a Tile, (Almost) Any Tile
While they aren't as widely used as shingles, both traditional and "cool-colored" tiles can be good choices for cooling a steep-sloped roof. Some traditional tiles have naturally reflective properties, depending on their color and the type of the clay they contain. Cool-colored tiles are created with pigments that reflect solar energy in the infrared spectrum.
Cool-colored tiles are typically produced in earth tones such as brown, green and terracotta. Many qualify as Energy Star materials for steep-sloped roofs. The cost of these cool-colored tiles is comparable to the cost of traditional roofing tiles.
3. Get a Little Misty-Eyed
If you'd rather enjoy the benefits of a cool roof without the addition of new surface materials or coatings, consider a roof mist coolingsystem. Also called an evaporative cooling system, a roof misting system lowers surface temperatures by spraying an extremely small amount of water across the roof, allowing the water to cool the roof as it evaporates. Think of it as akin to the way sweating cools your body.
At its most basic, a roof misting system can be little more than a garden hose set to the mist setting and aimed across the roof. (The same method will also quickly and effectively cool your stone patio or wooden deck on a hot day.) More sophisticated roof mist cooling systems typically feature a misting pump with a built-in thermostat, timer and 360-degree misting nozzles that are strategically placed so the water hits every part of the roof. These systems are available for both industrial and residential use.
2. Go Green (Literally!)
While a rooftop garden isn't technically a cool roof, it achieves many of the same benefits as qualified cool roof products and reduces stormwater runoff to boot.
A green roof, or rooftop garden, is a vegetative layer grown on a rooftop, with varying levels of materials in between. For example, they may or may not contain an irrigation systems. Green roofs shade the buildings below from direct sunlight, and reduce both surface temperatures and surrounding air temperatures through evaporation and transpiration, the processes by which plants remove moisture from the soil and emit it through their leaves. Rooftop gardens are so effective, they can lower a city's ambient temperatures by up to 5 degrees Fahrenheit (minus 15 degrees Celsius), according to the U.S. Environmental Protection Agency (EPA).
With costs ranging from $10 to $24 per square foot for materials and installation, green roofs are more expensive than other cool roof options. But it's hard to put a price on the innumerable benefits they provide in addition to roof-cooling, such as beautification, improved air quality and noise reduction.
1. Rock On!
Ballasted roofing systems are roofs in which a membrane is laid on the roof deck, then held in place by the weight of concrete pavers or natural stones. These stones also provide an insulating barrier against solar heat, much like an adobe building in the desert or an old stone farmhouse that stays cool inside, thanks to its thick stone walls. Ballasted roofing systems are relatively inexpensive, and ballasted areas may be combined with rooftop gardens to reduce the overall cost per square foot of a landscaped roof.
While ballasted roofing systems don't meet current Energy Star guidelines for cool roofing options, the EPA recognizes their effectiveness in energy savings. They also do meet the cool roof standards in Chicago, which has been one of the earliest adopters of rooftop gardens and other green roofing technologies.
Originally Published: Feb 14, 2011
Lots More Information
- 10 Best Roofing Materials for Warmer Climates
- What can I do to my roof to save on energy costs?
- What Is a Green Roof?
- Top 10 Green Roofing Options
- Asphalt Roofing Manufacturers Association. "Steep Slope Cool Roofing Systems Increase Energy Efficiency." (May 9, 2022)
- Cool Roof Rating Council. "General Cool Roof and Wall FAQs." (May 9, 2022)
- Cool Roof Rating Council. "General Cool Roof and Wall FAQs." (May 9, 2022) https://coolroofs.org/resources/end-user-faqs
- Energy Star. "Other Types of Roofing That Can Save Energy." (May 9, 2022)
- Energy Star. "Other Types of Roofing That Can Save Energy." (May 9, 2022) https://www.energystar.gov/products/building_products/roof_products/other_types_roofing_that_can_save_energy
- EPDM Roofing Association. "City of Chicago Recognizes Ballasted EPDM as 'Cool Roof" Alternative." May 29, 2009. (May 9, 2022)
- EPDM Roofing Association. "City of Chicago Recognizes Ballasted EPDM as 'Cool Roof" Alternative." May 29, 2009. (May 9, 2022) https://epdmroofs.org/wp-content/uploads/2018/03/2009_05_29_cityofchicagorecognizesballastedepdmascoolroofalternative.pdf
- First American Roofing & Siding, Inc. "How Much Does It Cost to Replace A Rubber Roof in 2022?" June 15, 2021. (May 9, 2022)
- First American Roofing & Siding, Inc. "How Much Does It Cost to Replace A Rubber Roof in 2022?" June 15, 2021. (May 9, 2022) https://firstamericanroofing.com/rubber-roof-cost/
- Heat Island Group. "Cool Roofs." (May 9, 2022)
- Heat Island Group. "Cool Roofs." (May 9, 2022) https://heatisland.lbl.gov/coolscience/cool-roofs
- Hoff, Jim. "Is Ballast Green?" Professional Roofing Magazine. October 2008. (Feb. 4, 2011) http://www.professionalroofing.net/article.aspx?id=1368
- Hydrobreeze Misting Systems. "Roof Cool Misting." (May 9, 2022)
- Hydrobreeze Misting Systems. "Roof Cool Misting." (May 9, 2022) https://hydrobreeze.com/roof-cooling-misting-system/
- National Park Service. "What is a Green Roof?" (May 9, 2022)
- National Park Service. "What is a Green Roof?" (May 9, 2022) https://www.nps.gov/tps/sustainability/new-technology/green-roofs/define.htm
- Pacific Gas and Electric Company. "Cool Roof Design Brief." March 2012. (May 9, 2022)
- Pacific Gas and Electric Company. "Cool Roof Design Brief." March 2012. (May 9, 2022) https://www.esci-ksp.org/wp/wp-content/uploads/2012/03/Cool-Roof-Design-Brief.pdf
- Remodeling Expense. "Cost of Modified Bitumen Roof." (May 9, 2022)
- Remodeling Expense. "Cost of Modified Bitumen Roof." (May 9, 2022) https://www.remodelingexpense.com/costs/cost-of-modified-bitumen-roof/
- Sentry Roofing, Inc. "Benefits of Single-Ply Roofing Membranes." Jan. 16, 2020. (May 9, 2022)
- Sentry Roofing, Inc. "Benefits of Single-Ply Roofing Membranes." Jan. 16, 2020. (May 9, 2022) https://www.sentryroofing.com/blog/single-ply-roofing-membranes/
- U.S. Department of Energy. "Cool Roofs." (May 9, 2022)
- U.S. Department of Energy. "Cool Roofs." (May 9, 2022) https://www.energy.gov/energysaver/cool-roofs
- U.S. Environmental Protection Agency. "Reducing Urban Heat islands: Compendium of Strategies." June 2014. (May 9, 2022)
- U.S. Environmental Protection Agency. "Reducing Urban Heat islands: Compendium of Strategies." June 2014. (May 9, 2022) https://www.epa.gov/sites/default/files/2014-06/documents/coolroofscompendium.pdf
- U.S. Environmental Protection Agency. "Using Green Roofs to Reduce Heat Islands." (May 9, 2022)
- U.S. Environmental Protection Agency. "Using Green Roofs to Reduce Heat Islands." (May 9, 2022) https://www.epa.gov/heatislands/using-green-roofs-reduce-heat-islands
Please copy/paste the following text to properly cite this HowStuffWorks.com article:
Here are ways to cope with the high summer temperatures that heat the roof and the top floors of residential buildings
- Grow a roof garden. ...
- Paint the terrace white. ...
- Add shade. ...
- Go for heat-resistant flooring. ...
- Install solar panels.
Place incoming vents low in the roof, ideally in a cool place. Under the eave is a good spot because the air there doesn't receive direct sunlight, so it's cooler. Air entering from a cool area will keep the temperature in the roof cavity low.How cool roofs can help fight climate change? ›
Cool roofs can: Lower local outside air temperatures, thereby lessening the urban heat island effect. Slow the formation of smog from air pollutants, which are temperature-dependent, by cooling the outside air. Reduce peak electricity demand, which can help prevent power outages.What is a cool roof system? ›
A cool roof is a roofing system that delivers higher solar reflectance (the ability to reflect the visible, infrared and ultraviolet wavelengths of the sun, reducing heat transfer to the building) and higher thermal emittance (the ability to radiate absorbed, or non-reflected solar energy) than standard designed ...What is the coolest roof material? ›
#1 Metal Roofs
Metal roofs are perfect for hot climates because they excel under extreme temperatures. Metal is reflective and considered a “cool roofing” material. Highly reflective paints and coatings can even further improve your roof's energy efficiency. Metal roofs have continued to increase in popularity.
To make your concrete roof into a cool roof, install a modified bitumen roof. Modified bitumen roofing is a membrane made up of sheets of plasticized or rubberized asphalt held together with rolled reinforcing fabric. The heat from the rays of the sun will get absorbed.Why are cool roofs better? ›
One of the more direct benefits of cool roofing materials is the reduced amount of heat that gets trapped inside of your home. This will increase your home's comfort levels and allow you to sleep better and overall just be more comfortable during the summer and spring months.Does putting ice in front of a fan work? ›
According to the GHI, placing a bucket of ice in front of a fan as a homemade AC unit is just as effective. 'As the air passes over the ice it will be chilled and will circulate refreshingly cold air around the room,' they explain.How do I keep my roof cool in the summer naturally? ›
Another way of reducing roof temperature is stacking bundles of damp straw (a natural insulator) on a plastic sheet on the roof. However, the best way to keep a roof cool is a terrace garden (the mud used to grow plants acts as an insulator) though it may be time-consuming.What are three ways to cool buildings naturally? ›
- Windows and shading. Opening windows is a common way people try to cool buildings – but air inside will be just as hot as outside. ...
- Paints and glazes. ...
- Building materials. ...
- Hybrid and phase change materials. ...
- Water evaporation.
The average energy savings for a cool roof range between 7% to 15% of total cooling costs. A cool roof can also help prolong the life of an air conditioning system by reducing the strain on the system during hotter times of the day and year.
Energy Savings: Typical roofs can be 50°-90°F hotter than the surrounding air and transfer that solar energy down into the building. By reflecting the sun's energy back into the sky, cool roofs become only 10°F hotter than the ambient air and keep buildings far cooler than either black painted roofs or steel roofs.How much is a cool roof? ›
Although costs will vary greatly depending on location and local circumstances, cool roof coatings on a low-slope roof might cost $0.75–$1.50 per square foot, while single-ply cool roof membrane costs vary from $1.50–$3.00 per square foot.What color is a cool roof? ›
COOL Roof Shingle Colors
Typically, COOL asphalt roofing shingles run toward the lighter hues: White. Light gray. Light tan.
The most durable types of roofing are slate and clay tiles but they're more expensive than materials like metal or wood. Functional roofing alternatives like green roofs and solar shingles are among the most expensive types. Replacing an old roof is one of the best and most profitable ways to invest in a home.What is the best roof style? ›
A hipped roof is the most stable roof style because weight is evenly distributed around its base. Additionally, its shape is more resilient against high winds and heavy rains, making it a great option for people that live in areas where severe storms are common.Do solar panels cool your roof? ›
According to a study conducted by researchers at UC San Diego Jacobs School of Engineering, solar panels reduced the amount of heat reaching the roof by an incredible 38%, keeping a building's roof 5 degrees cooler than portions of a roof exposed to sunlight directly.How can I keep my roof water cool in summer? ›
- Construct a shaded cover for your tank.
- Roof garden with creepers is a simple and relatively inexpensive way to do it.
- Encase the tank in some kind of insulating material.
- Colour your tank with white paint so light is reflected.
A body of water in a courtyard – a pond, fountain or runnels of water flowing throughout the space – all do the same job. And inside, placing an earthenware pot of water near a window or draughty spot can help to cool the place down.Does spraying the roof cool house? ›
Yes, water on the roof will help cool it. Cooling with liquid water running off from a sprinkler is not efficient, but evaporative cooling from a small amount of water (like a periodic sprinkle) is very efficient.
However, green roofs offer added benefits such as reducing and filtering stormwater runoff; absorbing pollutants and carbon dioxide; providing natural habitat; and in the case of intensive green roofs, serving as recreational green space.Who uses cool roofs? ›
Cool Roofs allow building owners, architects, civil engineers, energy consultants and policy makers to optimise the energy and environmental performance of a single building or an urban environment, depending on the use, design, environment and the surrounding climate.Do cool roofs work in the winter? ›
Spoiler alert: Yes. For a number of reasons, cool roofs still have energy-saving benefits in cool climates.What does putting a bowl of water in front of a fan do? ›
Stick a bowl of ice water in front of your fan to help circulate the cooler air. This DIY hack works surprisingly well and takes less than 10 minutes to make.Does putting a wet towel over a fan make it cooler? ›
Wring the cloth out so that it's damp, not dripping wet. Lay the cloth over the fan. As it blows the air out, it'll circulate through the cloth and the air will feel cooler.What material stays cool in the sun? ›
A fabric made of engineered silk keeps skin about 12.5°C cooler than cotton clothing and provides relief from hot weather. Approximately 15 per cent of global electricity goes towards keeping us cool.What can absorb heat? ›
Known (sensibly enough) “sensible heat materials,” substances like stone, cast iron, and aluminum get noticeably hotter as they absorb heat. With a quick touch, our senses tell us so.How can I cool my house without electricity? ›
- Close windows and blinds during the day. ...
- Only open the windows when it's colder outside. ...
- Dampen the curtains at night. ...
- Identify the coolest room in your home. ...
- Close the doors of rooms that aren't being used. ...
- Avoid cooking indoors. ...
- Wait until nighttime to turn on appliances.
- Ice-water bath and frequently stirring the food. ...
- Ice paddles (plastic container filled with water and frozen) used to stir food in an ice-water bath.
- Adding ice as an ingredient (if water is an ingredient).
- Blast or tumble chiller.
- Central Air Conditioners and Heat Pumps. Central air conditioners and heat pumps are designed to cool the entire house. ...
- Room Air Conditioners. ...
- Evaporative Coolers. ...
- Ductless Mini-Split Air Conditioners. ...
- State of the Art Cooling.
Natural cooling - Natural cooling refers to the use of ventilation or natural heat sinks for heat dissipation from indoor spaces. Natural cooling can be separated into five different categories: ventilation, night flushing, radiative cooling, evaporative cooling, and earth coupling.What type of roof absorbs the most heat? ›
Black and dark-colored roofs.
In general, dark-colored roofing materials will absorb the heat and cause your attic and/or the top of your house to be warmer than a lighter colored material.
Acrylic waterproof paint: The distinct character of this waterproof roof paint makes it an excellent choice. It is amongst the most durable and effective paints for terraces and roofs, offering protection against the water of all pH levels. Its elasticity allows contraction, thereby expelling water from its surface.What is cool roof paint? ›
COOLROOF® is a Heat Reflective Paint or Sun Reflective Paint with an SRI value of 122, tested as per ASTM/LEEDS standards for green buildings. COOLROOF® is a high SRI and high Albedo coating which can be applied on all types of roofs. It is a sun reflective paint and aims to reduce the roof temperature.What is cooling paint? ›
Passive radiative cooling paint
PARC has developed a “self-cooling” paint that cools down any surface up to 10 ºC (18 ºF) below ambient air temperature. This is accomplished by engineering a paint combining a high solar reflectance with a high emittance in the sky transparency window.
In general, lighter-colored roofs reflect away heat rays from the sun, but dark-colored roofs absorb much of that heat and transfer it into the rooms below. So, yes, black roofs do attract more heat. Or course, color isn't the only aspect of your roof that affects home temperature.What color roof is best for hot weather? ›
Best of all, green roofs are considered energy-efficient and naturally reduce the heat island effect. They also add oxygen back into the air, making them particularly important for large urban sprawls and areas that experience high traffic congestion.Are cool roofs good for the environment? ›
Lower outdoor temperatures mean air-conditioning will run more efficiently. Along with lower energy consumption, energy grids will experience reduced demand at peak times during the summer months, thereby lowering emissions. Cool roofs can reduce heat-related mortality by up to 25-30 per cent.How are cool roofs sustainable? ›
Cool roofs have the ability to reflect sunlight and repel heat because the roofs are prepared, covered or coated with materials that have special characteristics. These are typically white roofs and they reduce the heat island phenomenon, minimizing thermal impact on the microclimate and on the local environment.How do green roofs help climate change? ›
Green roofs provide shade, remove heat from the air, and reduce temperatures of the roof surface and surrounding air. Using green roofs in cities or other built environments with limited vegetation can moderate the heat island effect, particularly during the day.
A cool roof reduces energy usage, saving you money, and will also stabilize the temperatures in your unconditioned spaces, like the garage or the bonus room. Installing a cool roof is most beneficial in a warm climate, where the winters are not cold enough to require the inherent heat gain of a traditional roof.What is the coolest roof Colour? ›
Well, generally speaking lighter colours are better at reflecting the sun's radiation away from the surface, with white being the colour that absorbs the least heat.What are 5 benefits of a green roof? ›
Environmental and human health benefits of green roofs include air purification, urban heat island amelioration, lower building energy costs, increased urban biodiversity, reduced stormwater runoff and improved stream water quality. And the roofs last longer and are aesthetically pleasing too!Do green roofs clean the air? ›
By lowering temperatures and reducing energy use, green roofs can help reduce concentrations of several pollutants that affect air quality, climate, and health.Which city has the most green roofs? ›
These roofs provide a host of benefits, including eliminating the need to develop new ways of containing storm water runoff. Chicago has more green roofs than any other U.S. city — including one atop City Hall.What are the three types of green roofs? ›
Three types of green roofs exist: extensive, semi-intensive, and intensive green roofs. An extensive green roof is characterised by its low weight, a thin layer of growing medium (green substrate), a mix of plants adapted to conditions on the roof, minimum maintenance and low installation costs.