Insulating rooftop ducts with spray foam - retro - hot/dry climate

Here in Tucson, AZ we have a lot of ducts on the rooftop. This is because many older homes are flat roofs and only had swamp coolers when they were built. This leaves no other place but the roof to install ducts for AC. Many of these ducts were never insulated. Many homeowners do not want to replace whole duct systems just to insulate on the inside of the duct - for obvious cost reasons. They always call us as an insulator to take care of this and we have always passed on it.

Recently I suggested that we start using closed cell spray foam to insulate these ducts, but we must protect them from the searing desert sun. My plan is to find out the best roof coating that I can use to cover the spray foam and have a solution for all these homeowners.

1) Do you see any potential problems with this solution?

2) Any recommendations for roof coatings?

Craig

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Replies to This Discussion

Permalink Reply by Hal Skinner on May 15, 2012 at 12:09pm

Hi Craig,

I have been coating rooftop AC units and exposed metal ductwork since 1988. Our coating later became one of the first Energy Star 'Cool Roof' coatings. It is a roof coating and can also be used as an exterior or interior paint..

You are fighting radiant heat energy and foam does next to nothing to stop that. You need a radiant barrier on those metals.

I could drown you in statements and pictures from homeowners, church pastors and business owners where we have dropped the temperature of the air coming in and the building temp from 5 to 25 degrees, I coated the roof and AC unit duct on this home in Yuma in 2006. You can apply it with a brush, roller or strong gas spray rig.

The next year I went back to Yuma and coated the roof, AC unit / duct and painted the exterior of the identical house next door.

Go to my website at www.ct-coating.com and you will see many more pictures and statements.

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Permalink Reply by Craig Bird on May 15, 2012 at 12:23pm

Hal - Can this be applied directly to spray foam? Aside from the reflective properties, how does it compare to other roof coatings in terms of durability? Can I purchase the material only, for use in our installations? Please private message me pricing if so. Thanks,

Craig

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Permalink Reply by tedkidd on May 15, 2012 at 12:26pm

Around here spray foam is used for roofing.

WRT Hal's comment about foam doing nothing to stop radiant heat loss/gain, I'd have to disagree. Foam is an excellent 'Insulation' against conductive, convective, and radiant heat transfer. You'll want all three for ducts, particularly if they are outside.

Roof foam does need a UV coating after installation. I'm not sure if he's seeing this as either/or, but to me it's a both. I suspect Hal's coating might be perfect for that task, I know first hand that white reflective roofing has amazing benefits. I wouldn't apply it to ducts without insulating first, you really want to bring the ductwork "inside" the thermal envelope, and foam can create that envelope.

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Permalink Reply by Craig Bird on May 15, 2012 at 1:09pm

I agree, no coating is going to get the surface of those ducts below ambient temp. Our ambient temps get to around 110 in summer, so the foam is essential to maintain the interior duct temperature.

I think most roof coatings have UV blockage, so I will make sure the coating I use has good ratings for that.

Hal - I checked your coating against the Energy Star certified list and do not see it listed. I find different Reflectance ratings on different Cerama-tech websites so I don't know if it doesn't meet Energy Star (0.61 vs Estar 0.65 or above) or if your manufacturer didn't go through the expense of certifying.. I know testing has to be performed for maintenance of the reflectance rating to a 0.50 or better after 3 years. I do not see that testing on your spec sheets.

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Permalink Reply by Hal Skinner on May 15, 2012 at 2:16pm

You can find our certifications on this page of our site, both our Energy Star Certification and our Emissivity certification. We were one of the first few dozen to achieve it. Then they started allowing the manufacturers to 'Selfcertify their own produts/

http://www.ct-coating.com/MSDS___labs__calcs.php

Recently, the DOE started re certifying these products at the DOE's labs and at the DOE's expense. Some of them lost their Energy Star as their results were not even close to their results stated.

Can you give me the URL of the roof products list you are talking about? We have always been on the list. If it is a list put out by the CRRC, no, we wont be on that list and never want to be.

We used to apply Cour coating over foam but not any more. Too masny problems with the foam allowing moisture underneath and rotting the roof pan, off=gassing. Our coating is effective against all three modes of heat transfer. And, no, it is not a refrigerant. The surface temp will be within 5 degrees of the ambient air temperature at the time.

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Permalink Reply by Craig Bird on May 15, 2012 at 3:42pm

It is the Energy Star website. You are not on the list for certified coatings. (Roof product resources on right).

As a building science professional, I find it insulting to be told a coating can stop conductive heat on an industry forum from a peer. A coatings thermal resistance is negligible - period. In no way can solar reflectance be converted to an equivalent r-value.

Keeping a roofs surface temperature within 5 degrees of ambient can be said of almost any good reflective roof coating.

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Permalink Reply by Hal Skinner on May 15, 2012 at 4:09pm

Just called the corporate office and nobody knows why. EPA is already closed, will be calling them tomorrow.

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Permalink Reply by Hal Skinner on May 15, 2012 at 5:34pm

The last time anyone looked at the list / downloaded the list was on Feb 01 2012 at 13:30 hrs. They have updated it since then. Thank you for pointing that out. We are on page 17 of that list. They updated it since then. Dont check it very often, never really had a reason to until now.

A couple years after Cerama-Tech, 2 more showed up, 'Cera'-Tech and 'Ceram'-Tech. One of those is also gone.

It's an EPA glitch that will get fixxed.

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Permalink Reply by Craig Bird on May 16, 2012 at 10:34am

Looks like they updated it today May16 - no Cerama-Tech. Maybe they don't allow coatings that stop conductive heat...LOL

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Permalink Reply by Craig Bird on June 14, 2012 at 12:33pm

Still no Cerama-Tech on the June 6th list - they must not like you guys.

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Permalink Reply by Sean Lintow Sr on May 15, 2012 at 8:30pm

The only issue(s) I can possibly see that Tedd didn't mention is possibly expansion & contraction - also make sure you check the manufacturers directions as most require cleaning & priming for proper adhesion. As for the roof coating, I would check around with some local roofers & see what they have used & is still holding up. Along those lines I would cover not only the foam but the entire roof.

Have you checked into the SPFA for info on this?

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Permalink Reply by Jason Sherwood on June 14, 2012 at 8:59am

First, you need to make sure to use a catalyzed urethane primer before laying spray foam. This will make sure the spray foam adheres. Then, spray on a urethane elastomeric coating system, which protects it from the weather elements.

Hope that helps. You can read more about the process here: Spray foam roofing

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