Did you know roofs can help the environment and fight global warming? Today, many cool roof varieties exist to reflect the sun’s rays, keeping the building below much cooler. The special properties in these roofs help reduce air pollution, greenhouse gas emissions, and urban heat island effects. We looked into the pros and cons of cool roofs to help you understand what makes the materials so special and whether it is right for your next roof replacement.
What Is a Cool Roof?
A cool roof is not technically a type of roof, but rather part of a collection of roofing materials that all share the same properties.
- It absorbs less heat.
- It reflects more sunlight.
- It reduces energy consumption.
Cool roofs no longer need to be white to efficiently reflect the sun’s rays. These roofing materials and coatings lower a roof’s surface temperature and decrease heat transfer.
Cool roofs strongly reflect sunlight, or solar energy, through solar reflectance (SR), and efficiently emit absorbed heat, or infrared radiation, through thermal emittance (TE). The Cool Roof Rating Council (CRRC) classifies cool roofing materials as those that possess both high solar reflectance and high thermal emittance over a three-year testing period.
Solar Reflectance Index (SRI)
The U.S. Green Building Council evaluates all cool roofing materials using the solar reflectance Index (SRI). SRI combines solar reflectance and thermal emittance into one standardized measure.
SRI uses a scale of 0 to 100 and is determined through a complex equation. Black roofs with no reflective properties start at zero, while reflective white roofs have a value of 100. Common asphalt shingles with reflective granules sit at a value between 21 to 30 on the SRI scale.
The higher your SRI value, the more sunlight your roof reflects, lowering the surface temperature of your roof and reducing the heat transfer into your home.
Pros of a Cool Roof
The name couldn’t be more obvious. Cool roofs literally keep your home cooler and stabilize room temperatures. They are energy efficient, durable, improve air quality, and decrease the rate of smog formation.
Reduced Energy Costs
According to the CRRC, cool roofs can save you between 7% to 15% on your annual energy costs. The specialized materials reflect sunlight, reducing the amount of heat absorbed by your home. The less heat your roof absorbs, the more stable your indoor air temperatures.
On average, cool roofs are 50 degrees cooler than traditional roofing materials, and according to one California study, they can save you up to 50 cents per square foot annually on your heating and cooling costs.
Temperature Stability
Cool roofs do not need to be coupled with an air conditioning unit to stabilize indoor temperatures. In fact, floors directly below a cool roof see a five- to six-degree reduction in air temperature without one.
These roofing systems reduce temperature fluctuations, making your home more comfortable.
Longer Lifespans
Air conditioners and roof replacements both make the list of the top 10 most expensive home improvement projects, and extreme heat and ultraviolet rays degrade these systems.
Traditional asphalt shingles break down with sun exposure. Luckily, cool roofing materials are less likely to crack and fade, even in tropical climates like Florida and Texas.
The reflective surfaces of cool roofs reduce heat transfer into your home and overall air conditioner load. A cool roof reduces the demands on your air conditioner by 10% to 40% and extends the lifespan of your unit.
Improved Air Quality
The urban heat island effect occurs in densely populated cities. Pavement, buildings, and other non-natural surfaces absorb and retain heat, increasing energy costs, air pollution, and ground-level temperatures.
Cool roofs decrease this effect by reducing heat transfer into the outside air and lowering urban air temperatures. When air temperatures are lower, emissions and smog are reduced, increasing overall air quality.
Cons of a Cool Roof
Cool roofs are popular for many reasons. While the specialized reflective materials don’t cost more than traditional roofing systems, there are some disadvantages of cool roofs.
Dirty Appearance
The notion that lighter colors reflect sunlight while darker colors absorb it is not new. About 90% of U.S. buildings have dark-colored roofs. However, with the rise of global warming and more conscientious consumption, lighter-colored cool roofs are gaining popularity.
Light-colored roofs are more energy efficient and a great option for hot climates, but they also have a major drawback. They show dirt and dark streaks of sun-thriving algae more easily.
If you choose a lighter-colored cool roof option, you may find yourself cleaning it more regularly to maintain your curb appeal.
Increased Heating Requirements
A lot of factors affect cooling and heating costs, including your window-to-wall ratio, insulation quality, and floor plan. While cool roofing systems save homeowners on their electricity bills on hot days, they can actually cause a heating penalty of 5% to 10% in the winter months.
In many regions, the cost of electricity is higher, offsetting the penalty costs in the winter. However, if you live in a colder region where you regularly use your heating system, invest in good-quality insulation.
Susceptible to Moisture Accumulation
The surface temperature of a cool roof is approximately 50 degrees cooler than a standard roof. This drastic decrease in temperature is good for your utility bills, but it also can lead to damaging moisture accumulation.
Cool roofs accumulate moisture through condensation. Because cool roofing systems remain cooler for longer, they fall below the dew point, allowing condensation to form. Condensation can lead to rust and corrosion on metal roofing systems, speed up the deterioration of flashing, lead to mold and mildew growth, form ice dams, and warp insulation.
Many cool roofing options offer mold- and algae-resistant varieties but nothing will be a 100% fix. Vapor barriers slow down the accumulation of moisture, however, they add to the overall cost of your new roof.
Types of Cool Roofs
Cool roofs work on all roof types, including flat and low-sloped roofs. The reflective materials are a great option for both residential and commercial buildings.
Roof options and cool-colored products include:
- Membranes: built-up roofing, single-ply membranes, PVC, TPO, EDPM
- Shingles: asphalt shingles
- Slate
- Composite: shingle, shake
- Metal: standing seam, stamped tile metal roofing, stone-coated steel
- Tile: clay, concrete
- Wood: cedar shingle
- Foam: foam core tile
- Reflective coatings: paint, asphalt shingle granules, silicone, acrylic, polyurethane, aluminum, SEBS, Urethane, Latex
- Green Roofs
Is a Cool Roof Right For Your Home?
Your roof protects your family from the elements. You don’t have to sacrifice energy efficiency, comfort, curb appeal, or durability to benefit from the cost-saving advantage of a cool roof.
Your roof is the most expensive replaceable component of your home, and roof replacement provides the greatest return on investment of any home improvement project, according to the NAR.
You can recover 100% of your investment while increasing your home’s value, boosting your curb appeal, and lowering your monthly energy bills.
Best of all, a new cool roof does not cost more than its “non-cool” counterparts. If you need a roof replacement, a cool roof is a great option to help you save on your annual energy costs, and if it isn’t quite time to replace your roof, you have the option of adding a cool roof coating to your existing roof, depending on its material.
Consider the following factors when deciding if a cool roofing option is right for you:
- Budget: Cool roofing materials are not more expensive than other options. However, there is a wide range of price points for roofing materials that qualify as cool roofing options.
- Location: Cool roofs provide the most benefits to warmer climates.
- Projected energy savings: A professional roofing contractor can help you determine your annual energy savings when installing a cool roof.
FAQ About Cool Roofs
Yes. A cool roof relies on thermal emittance and solar reflectance to keep heat out of your home, resulting in less heat during the colder months when you need it. However, factors like insulation, roof orientation, pitch, and window-to-wall ratios all contribute to the thermal efficiency of your home.
The Department of Energy and the Environmental Protection Agency have teamed up to promote energy efficiency, offering location-based rebates and loans to homeowners and businesses for cool roofing materials. Some locations also require cool roofs in new construction.
Cool roofs stabilize indoor air temperature in your house. They can help reduce temperatures between 3.5 to 9 degrees Fahrenheit compared to traditional roofing materials.
Cool Roof Installation Next Steps
Climate change continues to affect our surrounding temperatures, and experts are continually looking for ways to fight back. As more regions join California’s minimum SRI requirements, considering your own cool roof options is not a bad idea.
If you are in the market for a new roof and want to reduce your energy costs, contact a local roofing pro to learn about cool roofing materials and the benefits they can bring to your home.
Main Image Credit: LancerE / Flickr / CC BY 2.0
