Everything to Know About Cool Roofs: [The Definitive Guide]
The roof is one of the most important parts of any building because it protects everything inside. Not only that, but the roof can also be a major contributor to the heat gain/loss of a building.
According to the Department of Energy, a conventional roof can reach 150°F or higher on a summer day, while a reflective roof can stay more than 50°F (28 °C) cooler given the same conditions.
That is a huge difference and can save you money on your energy bill by reducing the amount of air conditioning needed.
Roof technologies have come a long way in the past decade. Developers and building owners are now able to choose from a wide variety of roof types and materials that can help them achieve their energy-saving goals.
But there are many rooftop solutions that can lead to energy savings. I am sure you have heard roofing terms like white roofs, cool roofs, and green roofs.
But what do these mean? Are they a part of one big family? Or are they completely different things with their own benefits and drawbacks?
These questions point to the need for this definitive guide. We are going to cover everything about cool roofs and how it differs from other types of roofs that seem similar on the surface.
What is a cool roof?
A cool roof is a type of roof that has been specifically designed to reduce the amount of heat gain in a building. This is done by using materials or coatings that reflect more sunlight and emit less heat than traditional roofs.
Cool roofs can be made from a variety of materials in different designs. The main goal is to reduce the heat that is transferred into the building. As long as implemented roofing technology cuts down solar heat gain and cools the building, it is considered a cool roof.
There are many different cool roof strategies that can be used to reduce energy demand for cooling. One of the most common methods is to use reflective roof coatings that are specially designed to reflect sunlight and heat away from the building.
That means simple improvements like roof coatings or better attic insulation can help reduce cooling energy consumption. A homeowner can easily implement these cool roof strategies without much difficulty or expense.
Another cool roof strategy is installing a white roof. You’ve probably heard of this one before, but what exactly is a white roof?
A white roof is a roof that is either white in color or has a very close tone to white. White roofs are achieved either by using materials that are white in color or by painting the roof with a white roof coating or by installing a white membrane on the roof.
All of these options act in the same way by reflecting sunlight away from the building to reduce heat gain.
I am sure you have heard about green roofs by now. Green roofs are vegetated roofs with living plants, which helps cool the building by shading it and emitting water vapor. They also have the added benefit of absorbing rainwater and reducing stormwater runoff.
As you can see, there is no single way to design a cool roof. Different techniques and materials offer different benefits. These strategies can be used together or separately to achieve the best results.
Now that we have a better understanding of what cool roofs are, let’s take a look at some of the benefits they offer.
What are the advantages of cool roofs?
The benefits are numerous, which is why so many people have been shifting towards cooler roofing options. Here are some of the main benefits you can expect.
Energy savings
Cool roofs are designed to reduce the heat gain of a building, which helps keep energy costs down. This is especially important in warmer climates where air conditioning is needed to keep the building cool.
According to the EPA, cool roofs can provide an average yearly net savings of almost 50 cents per square foot. It is an impressive reduction in energy consumption.
May qualify for rebates
There are many rebates and incentives available for installing a cool roof. Some utilities provide rebates or other incentives for the purchase of ENERGY STAR-qualified products.
You can check the ENERGY STAR Rebate Finder to find out whether your local utility offers these incentives.
Reduced greenhouse gas emissions
Cool roofs also help reduce greenhouse gas emissions by reducing the need for air conditioning. This has a positive impact on climate change and helps prevent global warming from getting worse.
Reduced peak demand
Cool roofs can also help reduce peak demand since it is typically the highest during the hottest part of the day. This can help reduce the need for new power plants, which leads to fewer emissions from those plants.
Also, reduced peak demand will likely lower the cost of electricity. Because you will less likely need energy during the hottest parts of the day, you can reduce demand charges and use more energy during off-peak hours.
Helps to downsize new or replacement air conditioning equipment
If you are in the market for a new or replacement air conditioning system, a cool roof can help downsize the equipment needed.
This is because of the reduced need for cooling due to decreased heat gain. Having a cool roof can help you save on the cost of your new air conditioning system.
Improved comfort
Another benefit of cool roofs is improved indoor air quality. A cooler roof means less energy needed for cooling which also keeps the temperature inside the building lower. This can increase the comfort of a home or business and make it better for living in general.
Reduced urban heat island effect
Heat islands are areas that tend to be much hotter than the surrounding area. This is due to things like asphalt parking lots, dense tree canopies, and black roofs which absorb heat instead of reflecting it away from the building.
Because cool roofs reflect more sunlight, they help reduce this localized phenomenon called a heat island in cities.
Slowed the formation of smog
In hot weather, smog is more likely to form. A lot of times smog carries harmful contaminants that are bad for your health.
Cool roofs can help to slow the formation of smog by reducing the amount of heat that is trapped in an area. This reduces the amount of smog in the area, making it healthier for people to breathe.
Helps plants and animals
If you choose green roofs as a part of your cool roof strategy, you will also be helping plants and animals.
Green roofs can provide a habitat for insects, birds, and other wildlife. This can be a big benefit if you are trying to create an environment that is more sustainable and eco-friendly.
In addition, green roofs help reduce the amount of rainwater runoff. This is important because stormwater runoff can cause a lot of damage to the property if it is not managed properly.
Durability
Cool Roofs can be more durable than traditional roofs as long as they are properly maintained and installed.
This is because cool roofs reflect sunlight, which can cause traditional roofing materials to fade over time when exposed to intense sunlight. Cool roofs are more resistant to the sun’s ultraviolet rays and can last much longer without needing replacement.
What are the disadvantages of cool roofs?
They are not perfect! While the benefits list for cool roofs is very long, there are some disadvantages that may be important to you. Here’s a look at some of these drawbacks.
Initial cost
One of the biggest disadvantages is that cool roofs are more expensive than traditional roofing solutions. For homeowners on a budget, this can be an obstacle to overcome. However, the long-term savings from reduced energy costs can often offset this initial cost.
Maintenance
Another disadvantage is that cool roofs require more maintenance than traditional roofs. This is because the white or light-colored surfaces can become dirty faster and need to be cleaned more often.
All roofs require at least some maintenance to keep them in good condition, but cool roofs tend to need more attention than traditional options.
Increased energy consumption in the winter months
Cool roofs are not suitable for all locations. They work best in warm climates where the sun is intense and air conditioning is needed to keep buildings cool. If you live in a colder climate with milder summers, cool roofs may not be right for you.
In fact, if you live somewhere with cold winters, your building will require more heating without much sunlight coming in. This makes a cool roof more expensive to maintain in the winter months because you will need to use more energy to heat the building.
Mold and algae growth
While a cool roof may help reduce moisture build-up inside the home, it can also cause problems in some situations.
Cool roofs may actually contribute to mold and algae growth if they prevent the roof from properly drying out. This can be a particular problem in areas with high humidity levels.
Glare from the sun
A final disadvantage is that cool roofs can reflect intense sunlight, which can be a problem for people who are sensitive to glare. If you are planning to install a cool roof, be sure to test it out in different areas of your property to see if there is any glare that may be a problem.
Common roof materials and their cool options
Now that you know the basics of cool roofs, let’s take a look at some of the most common roofing materials and their cool options.
Asphalt Shingle Roofs
Asphalt shingle roofs are the most common type of roofing in North America. They typically last 15 -30 years and have a low upfront cost.
Asphalt shingles come in different colors and textures, so homeowners can choose the one that fits their needs best. These traditional materials can be painted white or coated with a reflective material to create a cool roof.
Typical black or dark brown asphalt shingle with conventional pigments has a Solar Reflectance of 0.05 – 0.15. However, their white or light gray alternatives can have a Solar Reflectance of 0.25 which is a considerable improvement. Homeowners can have a cooler roof using asphalt roofs only by using lighter colors.
Built-Up Roofs
Built-up roofs are a common choice for flat rooftops and other areas where an asphalt shingle roof would not be appropriate.
They consist of multiple layers, usually made from gravel or tar topped with more durable materials such as rubber or built-up fiberglass mats. They usually last 10 – 30 years depending on the materials used, manufacturing quality, and climate.
Built-up roofs made from dark gravel will typically have a Solar Reflectance of 0.10 – 0.15. However, if the dark gravel in the roof is replaced with lighter gravel or white mats, the Solar Reflectance can be improved to 0.30 – 0.50 which makes it a cool option as well.
Similarly, aluminum coating over built-up roofs will offer a Solar Reflectance of around 0.25 – 0.60. However, if a white smooth coating is used, the Solar Reflectance can be increased to an impressive 0.75 – 0.85 which makes it a cool choice as well.
Clay Tile
Clay is a natural material that is used to make roofing tiles in many different shapes and sizes.
Clay tiles are known for their durability and resistance to harsh weather conditions. It is a popular choice for homes in hot, dry climates because it is very durable and can last for 50 – 100 years.
A dark-colored clay tile with conventional pigments will have an SR of 0.20. However, this value can be improved to 0.40 by using Terracotta (unglazed red tile), color with cool pigments (SR of 0.40 – 0.60), or white clay tiles(SR of 0.70).
Concrete Tile
Concrete tiles are made from Portland cement, aggregate, and water. They come in a variety of shapes, sizes, and colors. They are often used on homes in colder climates because they have good insulation values and can last up to 50 years.
Conventional concrete tile with dark-colored pigments typically has an SR of 0.05 – 0.35. However, if a cool-colored pigment is used, the SR can be improved to 0.30 – 0.50. Instead, a white concrete tile can have a Solar Reflectance of up to 0.70.
Liquid Roof Membranes
Liquid roof membranes are made up of a single or two-component resin that is applied over reinforcing material (typically polyester or fiberglass felt).
This technology is applicable to a wide range of substrates (modified bitumen, certain single-ply membranes, B.U.R., concrete, or metal).
It can be squeegeed, rolled, or sprayed. It cures to become seamless, UV-resistant, water-resistant, chemical-resistant, and movement-friendly. Liquid membranes are also visually appealing because they can be found in a range of colors. They last around 5 – 20 years.
While the typical smooth black liquid applied coating has an SR of 0.05 to 0.35 and the smooth white version typically has an SR of 0.70 to 0.85 which makes it a great choice for cool roofs.
Metal Roofs
Metal roofs are produced from various materials such as aluminum, galvanized steel, and zinc. They are well-known for their sturdiness and tolerance to harsh weather.
Corrugated metal that has not been coated is often less durable than coated metal. Most metal roofs have a lifespan of 20 to 50 years or more, depending on the type of metal, surface treatment, and weather exposure.
While unpainted corrugated metal typically has an SR of 0.30 – 0.50, the white-painted option will have a solar reflectance of 0.55 – 0.70 making it a better option.
Similarly, dark-painted corrugated metal has an SR of 0.05 – 0.10 while the color with added cool pigments improves SR to 0.40 – 0.70.
Modified Bitumen
Modified bitumen is a versatile roofing material that can be easily applied to different substrates. It comes in rolls or shingles and has good resistance to moisture, heat, cold, wear, impacts, wind uplift forces. They tend to last 10 -30 years.
Typically modified bitumen with a mineral surface cap sheet (SBS, APP) will have an SR OF 0.10 -0.20. However, a white coating applied over the mineral surface (SBS, APP) will improve SR to the range of 0.60 – 0.75.
Single-Ply Membrane
Single-ply membrane roofing is a flat, synthetic polymer-based roofing material that provides a waterproofing barrier in a single sheet, as the name implies.
The material, which is often supplied in rolls, is either fully homogeneous or incorporates a reinforcing layer. Single-ply membrane roofs are lightweight, flexible, cost-effective, quick to install, and have a relatively long life expectancy which is 10 – 20 years.
The SR value of a black single-ply membrane (polyvinylchloride (PVC) or ethylene propylene diene monomer rubber [EPDM]) is in the neighborhood of 0.05.
While cool pigments can raise the SR value to 0.40 – 0.60, white pigmented membranes have an SR of 0.70 – 0.80, making them an excellent choice for cool roofs.
Wood Shake
Wood shake is a type of wood roofing material made by splitting a log into thin rectangles. They are usually light-colored, can be found with either smooth or grooved surfaces, and have an acceptable resistance to weather and insects. Wood shakes typically have a lifespan of 15 to 30 years.
The SR value for a dark color wood shake roof is around 0.35 – 0.50, while the bare wood shake can have an SR value of 0.40- 0.55.
Does aging affect the cool roofing properties of a roof?
As the roof ages, its cool roofing properties may diminish. The cooling effect of a roof may decrease as dirt and debris accumulate on the surface, or if the roof coating is scratched or worn.
Conversely, a well-maintained and regularly cleaned roof will likely retain its cool roofing benefits for a longer period of time.
The aged samples of most new roof materials have been tested to document their aged solar reflectance. Because cool roofs can only serve their intended purpose if they retain their original properties.
If you plan to invest in a cool roof, it is important to find out the aged SR value of the roofing material in addition to the initial SR value.
For most roof materials, the loss of cool roofing effects may be offset by using a higher albedo pigmented coating or paint provided the selected application is compatible with the roof material and is applied in accordance with the manufacturer’s instructions and industry best practices.
How could you compare different cool roof products?
When considering the purchase of a cool roof product, it is important to consider all aspects of the product and not just the solar reflectance. Because there is much more to a cool roof than just the SR value.
Some factors that also affect the overall performance of a cool roof are thermal resistance, thermal expansion, and contraction, wind uplift resistance, and installation/maintenance requirements.
Knowing there are many factors to consider, it may seem difficult to compare different cool roof products. However, most countries have developed voluntary and mandatory regulations and standards that can be used as a guideline for product comparisons.
In the United States, the Cool Roof Rating Council (CRRC) has developed a rating system that allows for the comparison of different roof products, using the solar reflectance and thermal emittance values.
The program ranks and publishes the results of roof products that have been tested and certified according to the standardized test techniques established by the American Society for Testing and Materials (ASTM).
Once a roof product is tested and certified by the CRRC, the results are then published on the CRRC’s online Rated Products Directory. Product manufacturers are then welcome to use this information when marketing their products.
Because all roofing products can be assessed by CRRC, customers and builders should look for the CRRC label when selecting a cool roof product.
There are similar initiatives in Europe, such as European Cool Roofs Council that has a certification program with similar requirements to the CRRC. Efforts of similar nature are underway in most other developing countries.
Is using solar panels a cool roof strategy?
Solar panels can be a great cool roof strategy much beyond their PV function of generating renewable energy. When installed on a roof, solar panels will use solar energy leading to a cooler roof surface and reduced cooling loads.
In fact, the cool roof effect of solar panels can be far more than most other cool roofing products provided they completely cover the roof. Since solar panels block sun rays even before they reach the roof, they will not allow solar light to heat up the roofing materials.
Why green roofs are considered cool roofs?
Green roofs, also known as vegetated roof systems are considered cool roofs. Because the plants and the substrate on which plants grow can absorb and transpire large amounts of heat.
The evaporation of water from the substrate and plant leaves also helps to cool the surrounding air. When designed and installed correctly, green roofs can significantly reduce the temperature of a building, thus reducing energy use.
What is a cool roof made of?
The term “cool roof” is used to describe a wide variety of roofing products. Cool roofs can be made of a variety of materials, including metal, asphalt, concrete, tiles, or even green roofs.
What makes a roof “cool” is its ability to reflect solar radiation, thus minimizing the heat gains through the roof.
How long does a cool roof last?
Cool roofs are made of various materials using various manufacturing techniques. While a white-colored clay tile can last more than 50 years, a bare wood shake can only last 15 years.
Therefore, there is no single best answer to the question of “how long does a cool roof last?”
However, all engineered cool roofing products are manufactured to withstand the demands of the specific application. Therefore, it is important to thoroughly understand the product specifications before making a purchase.
What other cool roof strategies are available?
We have so far mentioned three cool roof strategies: using a reflective coating, using light-colored materials, and installing solar panels, and green roofs.
However, there are other cool roof strategies available that can be used in combination with these strategies mentioned above to achieve an even greater cooling effect.
One such strategy is to install an insulating reflective barrier on the underside of a roof.
This can be done by using radiant barriers, which are typically aluminum foil-faced polyisocyanurate board or other lightweight insulating materials that reflect heat back into the attic and away from the ceiling plane below.
Another strategy is to have an air gap between the insulation and the roof deck to allow for air circulation. This can be done by using blown-in insulation or cellulose insulation that is installed in a way that creates an air space between the insulation and the roof deck.
Conclusion
There are a number of cool roof strategies that can be used to reduce the amount of heat gain through a roof, and thereby reducing energy use. The best strategy for any given situation will depend on the specific building and climate conditions.
It is important to select a product that has been certified by an independent organization such as CRRC so that a homeowner can be sure that a cool roof will perform as expected.
Finally, always know the details of the installation specifications and required maintenance procedures together with your local building codes. This will ensure that your cool roof will provide the desired energy savings for many years to come while maintaining its appearance for years to come.
