When building a house, the roof is an integral part that you can’t live without.
However, many traditional styles of roofs are actually doing more damage than good, especially when it comes to the amount of heat they attract inside the house.
Having a home with excess temperatures means you rely more heavily on your HVAC systems, and this ends up costing you more money while putting a greater strain on the environment.
After some research, it was discovered that with the right choice in roof materials, designs, and colors, a home could drastically reduce its internal temperature, and so the concept of the cool roof was born.
So, what is a cool roof, and can it reduce utility bills?
A cool roof is a broad term used to describe a roof with a special coating or tile used that reflects sunlight and absorbs less heat. Its main goal is to reduce energy usage inside the home by maintaining reduce temperatures which means less of a reliance on cooling systems, and less money spent by the homeowners.
Building or adapting cool roofs for residential homes is a green initiative that hopes to reduce our energy usage and lessen our impact on the planet.
If you want to learn about how to make your roof greener and reap these benefits for yourself, check out this comprehensive guide that can teach you everything you need to know.
Contents
What Are Cool Roofs?
A cool roof is a specific type of roofing system that works more effectively at keeping the heat of the sun away which means a cooler house.
These roofs are built to have a higher rate of solar reflectance than a standard roof, and it can reflect various wavelengths of the sun and reduce the amount of heat that it delivers to the building beneath it.
A cool roof also produces a higher thermal emittance than regular roofs, which means they’re able to radiate absorbed solar energy back into the atmosphere.
They’re built to be more durable and at a higher strength than others, and although typically used to be light in color, these days they can be a lot more flexible in their design.
The History of Cool Roofs
In recent years, it’s become clear that roofs play a major role in the temperature of the house they’re protecting.
Rooftops are known as one of the biggest contributors to heating issues inside of a house, even when there are other cooling systems at play like good insulation and air conditioning.
Before this was widely known, it was commonplace for a roof to be made with dark and non-reflective materials, mainly because they were cheaper and thought to be more durable and protective. Unsurprisingly, these materials were also adept at seeking and absorbing heat which then transferred down to the house and occupants below, creating more of an issue.
Because of these roofs being built predominantly in densely populated cities, they were found to create “heat islands” which occurs when all of them work together to increase the temperature.
Some studies found that the city temperatures during the day where these heat islands were found could be up to 5.4 degrees F warmer than their surroundings, and up to 22 degrees at night.
In the 1980s, the Departments of Energy in California and Tennessee conducted research into new solar radiation control coatings of rooftops and how they might use this to combat the excessive heat issue, not just at home but in the entire neighborhood.
They found that a household’s energy usage decreased with these specialized coatings, as well as other methods like lighter roof colors and solar reflective coatings, which means the area did as well.
It wasn’t until around 2001, when there was a huge demand for energy in California and continual blackouts, that people started thinking about ways they could permanently reduce their need for energy.
Cool roofs were one of the standout solutions and have been developed further to be a mainstream option today for people building or renovating their homes.
How Do Cool Roofs Work?
Although seemingly simple on the surface, the science behind a cool roof and how it actively lowers temperatures can be quite complex.
Two main factors are working together to deliver this temperature drop: solar reflectance and thermal emittance, and without the other, they wouldn’t be as effective.
A roof’s solar reflectivity is a measurement of how well it can reflect sunlight away, which means reflecting the heat as well. This can be measured on a scale of 0% to 100%, and the higher the percentage the more reflective and cooler the roof. A standard cool roof today is capable of achieving around 65% which means just a small percent of this makes its way into the house.
Secondly, the thermal emittance of a roof is how well it’s able to release the heat it’s absorbed. Depending on where you live and the usual climate, you may want a roof that absorbs heat, especially during winter, but for warmer areas, it’s not advisable. This is also determined on a scale from 0% to 100%.
To determine a roof’s properties, it can be given a value on the Solar Reflectance Index (SRI) which looks at both of these figures and comes up with an average score. A roof with a higher SRI is a cooler roof, with numbers ranging from 0% to 100%.
When you compare these figures with a standard roof that contains no cooling properties, these materials only offer between 5% to 15% solar reflectivity. Dark roofs are even more troubling, with a higher thermal emittance due to their shade, so you can see why standard roofs have been a huge issue when it comes to keeping a house cool.
Types of Cool Roofs
There is no single right answer when it comes to choosing a roof, as you need to look at the local climate, positioning, and structural design of a building to determine what is best.
However, there are two main categories that cool roofs fall under with the low sloped roof and steep sloped roof, and within each of them are preferred techniques used to make them cool.
Low Sloped Roof
A low sloped roof is one with only a minimal incline, which may even appear completely flat from the street.
These are more commonly found in commercial and industrial buildings, but not as common in residential homes, simply because they cover a larger space.
Having a cool roof in this design is essential as the roof is the main place where heat transfers inside the building, and thankfully, there’s a huge number of techniques possible for achieving this coolness.
Foam roofs
A lightweight and flexible foam-like material has been placed on top to offer insulation, and it requires minimal ongoing maintenance at a low cost.
Coated roofs
A paint-like finish is applied to the roof’s surface and can be used with all roofs including asphalt, metal, and gravel. There is a range of ENERGY STAR rated cooling techniques to choose from with these coats so it depends on what you’re looking for specifically.
BUR systems
A Built Up Roofing System or BUR puts to use various materials and techniques. With these different plies used together, it provides a thick and protective layer that keeps the sun’s light and heat away.
Modified bitumen
Sometimes referred to as “mod-bit” this roofing system uses an asphalt base on the surface of the roof so that it works with both hot and cold days to keep the temperature maintained.
Steep Sloped Roof
These types of roofs are commonly found in residential buildings and have an obvious incline to them.
A steep sloped roof can either be made from specific materials like asphalt shingles or have a coating or treatment applies to its existing shingles that can affect its coolness.
Because these roofs are easier to see and require something aesthetically pleasing, common roofing techniques like tiling and shingling are the best approach.
Materials
There are a number of materials certified by ENERGY STAR as cool roofing materials and depending on your house, some may be more suitable than others.
- Metal roofs
A standard metal roof installed today will have a solar reflectance of around 70% which is high compared to previous designs. Another bonus of using metal is that it’s recyclable, lightweight but extremely durable in all kinds of weather and conditions.
- Asphalt shingles
These are asphalt mats made from things like fiberglass or organic felts. As one of the lower cost options, they’re a popular choice, and a standard white shingle has an SRI of around 30%, with colored tiles being even less.
- Tiles
These have a high solar reflectivity, with clay tiles being one of the better options for cool roofs. Their SRI sits at over 50% and is capable of around 86% thermal emittance. They’re also aesthetically pleasing, durable, recyclable, and come in a range of colors to suit your home.
- Reflective coatings
A reflective coating can be placed over an existing roof covering, giving them a better SRI and helping to cool the building below.
- Pigmented and white roof coating
A white roof coating is made with polymeric materials, and because of their white color can reflect up to 80% of the sun’s rays. Pigmented coatings aren’t as effective, reflecting around 20% or less, but both can be made stronger with additional coats.
- Aluminum roof coating
This resin coating is mixed with flakes of aluminum leafing which makes it look just like an aluminum sheet and is more visually pleasing. They offer around 50% solar reflectance in general, and when applied correctly, might reduce indoor temperatures by up to 20 degrees Fahrenheit.
- Roofing membranes
Various materials like fiberglass and polyester are mixed with polymeric materials like asphalt which turn them into the durable and flexible coating.
A single-ply membrane is popular among a majority of low sloped commercial roofs, but only come in either black or white colors, and they are now becoming commonplace with steep sloped as well.
- Thermoplastic membranes
The single-ply thermoplastic membranes are made with plastic polymers instead and molded together with heat.
These roofing systems are affordable and durable, and do a good job of keeping cool. They come in a white pigment mainly but can be tinted as required, so they’re a smart choice visually.
The Energy and Cost Savings of a Cool Roof
The main reason for people to have a cool roof installed is to save money and decrease their energy usage, and this is done by reducing your reliance on electronic cooling systems like fans and air conditioners.
According to the Green Building Alliance, a cool roof can use up to 40% less energy to keep your home cooler than the average building.
The costs you can save will depend on a few things, like the size of the roof, its condition, accessibility, and which coating or technique you decide on. Choosing one that’s easy to install and will last a long time is key to maximizing these savings, but eventually, they will pay for themselves with the saved costs of utility bills.
Other Benefits These Roofs Offer
It’s not just your wallet and the planet that can save a lot with cool roofing systems, but there are other benefits as well. Consider these while you’re weighing up whether a cool roof is the way to go for your house.
- More comfortable living
Having cool and regulated temperatures inside your house without relying on air-conditioning makes for a more comfortable living experience.
- Low maintenance
A cool roof system requires minimal maintenance once it’s installed and as a more durable option, has been built to stay with your home for many years.
- Heat Island Index
With everyone committing to cool roofs, the heat island index will drop, which means the entire neighborhood and community can benefit from lower temperatures day and night.
- Lower air pollution
With a decrease in the number of air conditioners being used, you’ll notice an obvious decrease in air pollution and harmful emissions. The air quality will also improve which means a healthier way of life.
California’s Roof Regulations
California continues to lead the way with its regulation of energy-efficient programs and construction in the state.
By setting regulations that ensure new buildings and those receiving upgrades or being retrofitted meet certain energy efficiency and environmentally friendly standards, they are doing their part for the planet, and it now includes roofs.
The Californian Building Energy Efficiency Standards for Residential and Nonresidential Buildings state that the reflectance, thermal emittance, and SRI of roofing materials and construction must meet a certain standard to be used.
These guidelines apply to new buildings as well as renovations where you’ll be replacing or recoating at least 1,000 ft2 of space in a residential home, or half of it, whichever comes first.
The standards also make clear what materials are to be used, ensuring in the future that all homes have some form of the cool roofing system in place so that the entire state can work together to reduce the heat island index and their reliance on electricity.
Related Questions
With a cool roof, you can do amazing things for your energy usage and cut your utility bills by quite a lot.
If you’re interested in learning other ways to reduce your impact on the planet with simple improvements and adjustments you can do at home, check out these commonly asked questions for more information.
Are Fans Eco Friendly?
If your home uses a ceiling fan to do the majority of its cooling, you’ll be pleased to know it’s one of the more eco-friendly options.
Modern ceiling fans are quiet and efficient, with up to five speeds to select from so you can ensure you’re only needing as much air and ventilation as you need.
How to Naturally Cool Your Home?
To keep your home cool without relying on power-draining air conditioning systems, there are some energy-efficient options.
Ceiling fans, heat blocking curtains and blinds, green insulation materials, and making use of the coolest part of the house during different times of the day can reduce your reliance on air conditioning and other energy-demanding methods.
What is the Most Efficient Cooling System?
Installing a geothermal heat pump can help naturally heat and cool your house using the earth’s natural resources, otherwise using a solar-powered electric cooling system can help.
There are loads of ways you can keep your home cool without traditional HVAC units, saving money from your utility bills, and reducing your impact on the planet.
