In addition to ASTM test protocols and coating manufacturers’ specifications, standards and guidelines are available from industry associations, government agencies, and various metal roofing manufacturers to inform decision-makers about their coating selections and how exterior coatings should be expected to perform when exposed to various climate conditions over time.
When testing how a coating’s color changes based on its exposure, samples are cast on a pre-coated primer. Color instrumentation is then used to measure the color of a batch of paint versus the standard, in three scales:
- light to dark (or white to black);
- red to green; and
- yellow to blue.
Any color coating can be scored by a number based on where it falls on each of these scales.
Many coating manufacturers’ warranties cite Delta E on their paint, which refers to the change in the color from when it dried to its current length of exposure. Delta E quantifies the difference between two colors, such as the unexposed reference and the color after exposure. A Delta E of 1.0 is typically the smallest color difference the human eye can see. The combination of sun, heat, and moisture affects the color shift in Delta E and damages the roof’s coating far more quickly than any one factor alone.
Environmental considerations
The primary environmental concern with liquid coil coatings is the solvents used. Some of these solvents are considered volatile organic compounds (VOCs), which have been associated with ozone depletion when released directly into the atmosphere. When coil coatings are applied by responsible finishing facilities, the VOCs are safely captured and incinerated before the painted material leaves the factory. In some cases, the heat from incineration is then re-used to heat different parts of the coating process.
The coating selection for metal roofs can also have positive environmental advantages. Until recently, the roof has been one of the least energy-efficient components of the building envelope. Seeing the opportunity for innovation, options such as ‘cool’ metal roofs have come to the forefront of commercial building design.
A cool roof is one reflecting the heat emitted by the sun back into the atmosphere, keeping the roof’s temperature lower, thereby reducing the amount of heat transferred into the building space below. Cool roof requirements appear in national and local energy codes, green building initiatives, and energy rebate programs because a cool roof reduces air-conditioning use and lowers utility bills. It also mitigates the urban heat island effect, where roof and pavement surfaces retain heat, which in turn, contributes to elevating temperatures, increased greenhouse gas (GHG) emissions, and local climate disruptions. Cool roofs minimize these adverse effects, while increasing occupant comfort and reducing the occurrence of health issues associated with poor air quality and smog.
There are two key properties important to the temperature a roof will reach in direct sunlight:
- solar reflectance (SR)—the amount of solar energy immediately reflected from a surface; and
- thermal emittance (TE)—the amount of heat energy a surface can re-emit in the form of infrared (IR) energy into the atmosphere.
A cool roof with a high SR and a high TE will have a lower surface temperature compared to that of a roof with a low SR and a low TE. A lower surface temperature translates into less heat gain into the structure below, resulting in a cooler building, which means less energy used and lower energy bills.
Research by the Oak Ridge National Laboratory’s (ORNL) Buildings Technology Center shows metal roofing retains SR better over time than any other roofing product. Enhancing this performance, coil coatings for SR metal roof are available with 70 percent PVDF resins and solar reflective pigments. Depending on color, many cool roof applications will specify a two-coat, factory-applied, oven-baked finish with a minimum SR value of 0.25 and TE value of 0.85 to 0.90 for typical coatings.
Energy not reflected away or re-emitted can heat a roof’s surface, whereby the flow of ambient air causes convection heating, potentially contributing to higher urban temperatures. A heat island describes built-up urban areas that are hotter than their surrounding rural areas. According to the U.S. Environmental Protection Agency (EPA), the annual mean air temperature of a city with one million people or more can be 1 to 3 C (1.8 to 5.4 F) warmer than its surroundings. In the evening, the difference can be as high as 12 C (22 F). The elevated temperatures can result in higher energy costs to cool buildings for the entire city.
Understanding how a roof is built is crucial to knowing how to work on it. There is more to a roof than just a bunch of boards nailed together with some type of covering on top of them. It takes a lot of skill to know how to roof and how to work on them.
I can’t agree with you more Jason. There really is a lot of skill and knowledge that goes into roofing. Knowing how to do exterior coatings for example is crucial because if they are not done properly there could be leaks in the roof.
Jeff, this was just the information I was looking for about coatings. My husband and I want to replace our roof with a metal one. We have heard good things about them. We are also trying to decide if we should get a coating. I will have to show this to my husband and see what he thinks.
Emily Smith
It’s interesting to see that roofs can be made out of metal. I suppose I have seen some roofs made of metal on barns. When I lived in the Philippines, it seemed like everyone’s roof was made of metal. It was really loud when it rained.
I really liked your part about the exterior coating that can be added to add more aesthetic and performance characteristics. Metal roofs are really cool and they definitely have their pros and cons.
My wife and I were planning to replace our roof here soon, and we were thinking about getting a metal roof. We have heard some good things about metal roofs, but we just weren’t sure if that was the best option for us. I really appreciate you telling me that these roofs last longer then other ones. I think that is going to be super important to me, because we plan on living here for a long time. Thanks a ton for this information! It was a huge help.
One of the new trends I’ve noticed in my area is copper roofing. Whether or not it is used for the whole roof or just as an accent, I really like how it looks. My roof needs to be reshingled soon, but maybe I should upgrade to a metal material instead.
Thanks for sharing this advice on getting metal roofing and coatings for your home. I had no idea that steel and aluminum are some of the most recycled materials in the world– that is really awesome! Just the fact that I could recycle 100% of my roof after it has gotten too old makes me feel like I am helping the environment a lot.
This is some great information, and I appreciate your point that metal roofing lasts longer. My asphalt shingle roof is getting kind of old, and is in pretty bad shape. I want to have my roof replaced, and I was wondering if metal could be a longer lasting option. Is metal roofing available for residential property, as well as commercial? Thanks for the great post!
I love the copper roof on in the pictures of the hospital. I’ve noticed several houses and business in my town using metal for their roofs. This trend is really attractive and practical too! Matching it to the stone, like the way this building has, makes it stand out even more.
I have seen some roofs with metal on it, I didn’t know that some where made of recycled material. I think recycling is great, and it is cool to see all the different ways we have come up with to use those recycle materials. The fact that they last longer is nice too.
Thanks for your information. I have heard a lot about metal roofs helping keep a house cool, but I never really understood it. However, I also didn’t think about the reflective ability of the roof. It is like difference sun shades have on the temperature of parked cars. When it is time to replace my roof I will have to consider getting a metal one.
I need to replace the roof on my business, and I have been thinking about using metal material. That being said, you talk about how steel is the most common material used in the manufacture because it is the most economical metal roofing. I would definitely think that this would be the best option because, as you say, steel has such a high durability. So, the economical cost of this type of metal roofing is not just in the manufacture, but in the overall longevity of the roof. I will definitely look into this option for my own roof. Thank you for sharing!
I think it’s really great that metal roofs can be a more energy efficient. I think it would be great to see these more in residential areas to cut down on heating and cooling bills. Do you know if solar panels can still be installed on metal roofs?
I love the look of copper or any other metal material on a roof. I think it is much more attractive that shingles, so I am glad to hear that it also lasts longer. When we have our roof redone, I am planning on switching to metal. I’ll have to look into getting a coating to make it last longer.
There is so many types of roofing materials these days. I really like the look of the metal roof. I also like that it is light in weight. And I am glad there are ways to prevent corrosion in the metal roofing. Any roof can be a big investment for it to have to be replaced a few years down the road. Glad there are ways to protect my investment!
There are almost endless benefits for having a metal roof so this was really informative. The trick is to figure out exactly what would work best for your specific situation. Thanks for the advice!
With metal roofs, they offer many benefits over traditional roofing materials. One of them is that they are very durable. How often do you see metal roofs flying off during a wind storm? Also, you are thinking green when you go metal since aluminium and steel are some of the widely recycled metals out there. Just be sure that for whatever metal you choose, that it gets installed by a professional.
Metal roofing is the No1 solution when it comes to return on investment, resale value and low maintenance costs, not to mention it is the most stylish looking roof that you can install… With all that in mind it’s not hard to see why it is becoming the most popular roofing choice for new home owners.
I think it’s cool that there is a special protective coating that’s purpose is to take the corrosion, instead of the metal. I also think it’s great that metal roofs are 100% recyclable. I’m all about recycling because there’s no need to make something new when there are already materials ready to be used. Thanks for the info!
The benefits of metal roofing as mentioned in the article do sound interesting. Reading about it has me thinking of the aluminum sheet that my uncle fabricates at his shop. I’m having thoughts about maybe using the sheet as a roof to cover my shed.
Thanks for sharing this info, Jeff! Considering the possible benefits that can come with a metal roof, I don’t see why more people are springing to have one. Being able to have my roof reduce my energy costs with special coating sounds like a deal to me.
I’ve heard that a lot of people are using metal roofs lately, and I’ve been considering doing the same. However, I had no idea that an exterior coating was an option. Reading your section about the metal coating, it sounds like a really good option. Perhaps I could look into the latter option, thanks for this help!
There seem to be some really good things about metal roofs. I didn’t know that the material could be one-eighth the weight of other roofing products. I feel like each of the advantages of using metal each has its own sets of benefits.
Does anyone know if metal roofing panels can be recycled if their coated with paint, silicone, or some other finish layer?
I like your advice on how metal roofing is 100% recyclable at the end of its useful life. I would imagine that being able to recycle your roofing material once it is no longer useful would be really beneficial. My husband and I are looking to install a new roof for our home so maybe we should consider installing a metal roof.
Thanks, but nothing about metal roof paint.
In your article, you stated that metal roofs can be designed to withstand extreme weather conditions and are more fire-resistant than other roofing materials such as wood or asphalt. My neighbor came over last night because he noticed that some or our shingles on our roof were damaged. Can a metal roof be installed on any type of roof or any kind of house? Hiring a roofing contractor might be our best option.
I think metal roofing is a great decision. Like you said, they are made from recyclable materials, and can be recycled later! Plus, they are super energy efficient, which is a killer at my house. I would love to have a metal roof to help cut down some of my bills.
I learned a lot about roof coatings by reading this article. It was cool to learn that roof coatings can help to reduce a building’s carbon foot print within the community. I hope this article can help us to know what is best for our roof if we ever need to work on it.
It’s interesting that you pointed out that metal roofs last longer than most other roofing types. My roof is getting pretty old, and the shingles are starting to crack, so I want to have it replaced before I start having trouble with leaking. It would be nice to not have to worry about replacing it again for a long time, so maybe I could have metal roofing installed.
Thanks for bringing to my attention that metal can be much lighter than other roofing materials. My wife and I need to replace our roof, and we’ve been talking about potential materials, but we thought metal roofing would be too heavy for our house to support. The durability of metal is enticing, so now that we know that it’s actually lighter, we’ll look more into that option.
I thought it was really interesting how the article mentions that metal roofing can last much longer than other materials. I have also heard that they provide excellent insulation qualities as well. Despite a higher initial cost, these benefits seem to make a metal roof pay for itself in the long run!
I appreciate that you went into detail of what metal coatings contain. I was unaware that exterior coatings contained elements that make the application very easy. Honestly, it’s surprising how we can use science to help develop things like coatings for metal. It’s exciting!
Great information about benefits of metal roofs and coatings! It is the No. 1 solution & 100% recyclable. Thanks for sharing this advice on getting metal roofing and coatings for home.
I never knew that metal roofs last longer than non-metal roofs. I also like how you mention that metal roofs are 100% recyclable at the end of their life. I’m looking for a greener option for my roofing material, so maybe I should consider a steel roof.
Thanks for explaining the benefits. My husband told me to call some roofers and install a metal roof for our house. I am now looking up some roofers to install it.
The roof that we’ve been using was broken after the last hurricane, and now, my dad was planning to get it replaced with a possibly sturdier one. I was researching for options when I came across your article. I honestly thought it was great how you said that metal roofing is a lot sturdier than its non-metal counterparts. Aside from that, metal roofing is also 100% recyclable making it useful in more ways than one. Thanks for sharing this. I’ll make sure to let my parents know.
I’m grateful for your advice about the benefits of metal roofing because they can last longer than most non-metal roofing products, and their materials contain recycled content and are 100 percent recyclable at the end of their useful life. Our roof is a bit worn out, and we’re considering on replacing it. Thanks for mentioning that metal roofing is can be designed to withstand extreme weather conditions and are more fire-resistant than other roofing materials. Thanks for the tips! http://www.earhartroofing.com/past-projects
I have never heard about metal roofs lasting than non-metal roofs. I want to mention that metal roofs are recyclable at the end of their life.
Great, thanks for sharing this blog. Much thanks again.