Q&A – Which coating is more effective controlling the house temperature?

Q&A – Preparing for the hot summer months
May 16, 2024 at 12:00 p.m.

When prepping their home for the hot months to come, this homeowner wanted some help figuring out which roof coating would set their roof up for better temperature management.

A homeowner from California, Juliette, reached out to the AskARoofer experts about a quote they recieved for a coating on her modified bitumen roof. This is what they asked:

I have a modified bitumen roof. In 2011 Karnak #97 AF Fibered aluminum roof coating was applied. It is no longer effective in controlling the temperature in the house. We just received a quote to use Tropical 921 refex white elastomeric coating. My question is . . .will the Tropical 921 be as effective in controlling the temperature as the Karnak was? Or, would you recommend something else.

This is what roofing expert Bill Baley from C.I. Services had to say in response:

Hi Juliette, I do not know what part of California you live in – but choosing the right coating does require a consideration of the weather that is typical for where you live as well as a consideration on which coating might provide the best reflectivity and help keep the roof system cooler. I say this because if you are in an area of California where temperatures changes between cold in the winter and warm in the summer, the roof is being “temperature cycled” all the time and that is stressful on a roof system – as well as the coating system over it. Your current coating (Karnak #97 AF fibred aluminum roof coating) appears to have held up for 13 years so far and that speaks well of the coating’s performance in your climate zone. Most coatings like aluminum and acrylic begin to degrade by about 10 years of life and start to show signs of their aging – many times in a decrease of reflectivity ability. While both of the coatings you mentioned are generally good coatings, the actual reflectivity of each coating is different – at least when first applie

Here is a quick comparison taken from the Cool Roof Rating Council web site that describes the coating reflectivity ability:

So, in summary – based on these two ratings, the Tropical product has much higher reflectivity and Emissivity ratings and the SRI is double that of the Karnak product. This means that the Tropical 921 will be much more reflective, absorb much less heat and be more energy efficient. Now this doesn’t say one product is better than the other – only that the reflectivity is higher in the Acrylic product than in the Aluminum product. If that is your biggest concern, then the acrylic product would be the best way to go – but be sure the existing system is well washed and primed prior to the new coating application.

Hope that helps!

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