We are working through the plans on our house/renovation and the topic of spray foaming the attic came up. I'm in favor of doing it mainly to keep the HVAC equipment inside the building envelope and save on some of the heating/cooling costs.

The wife isn't a fan and one of the main reasons she brought up is roof leaks. We actually had a hole shot in a roof (as far as we could tell) at a previous house and obviously developed a leak. She's concerned with the annual hail storms we get in DFW, we could get a leak in the roof but not know it because of the spray foam and it would be a much bigger issue because of mold/rot/etc.

Does anyone have any information spray foam and leaks? I can find a ton of data on all the great things about spray foam, but nothing about downsides to it.

The biggest problem I came across researching this is that you have to take fresh air exchange into account on these (requiring modification to the HVAC system), and the exhaust setup for any gas powered furnace or water heaters has to be done differently since there will be no air exchange with the outside. That extra trouble and expense made a conditioned attic not really worth it to me.

I would strongly consider it for a new build, but it seems like it would be a bunch of trouble to retrofit.

If you use closed cell foam on the roof, moisture that gets down to the decking isn't going to make it down to the attic. Replacing the decking would be a problem if you had to do it, because the foam is strongly adhered to the lumber/decking.

On a new build/new roof, you could put 2 layers of decking on the roof so that the top one could be replace if needed.

I think he's worried that a roof leak would not be discovered until a lot of damage has been done.

There's not a good way to identify leaks with a spray foam install. The number one thing with a sealed attic is making sure your roof is fully waterproof with a sheet good or roll on product (not just a tar paper underlayment). If your wife won't budge on the issue, you could look into using a mineral wood insulation instead. It won't have the same air sealing effect as the closed cell foam, and you may not be able to build up as much r-value, especially under the joists, but you would be able to identify any random holes in your roof more easily.

Dr. Venkman said:

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I think he's worried that a roof leak would not be discovered until a lot of damage has been done.

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I would say inspecting your roof would be the way to prevent this if you're worried about it. If you're waiting for a roof leak to stain your ceiling before you go looking for it you're gonna have a bad time.

Roofs have rotted forever because of leaks... spray foamed or not.

That said, I wouldn't do a conditioned attic with an existing roof. If you're replacing the roof and decking, you can create a vent space between the decking and the insulation that will make things dry and keep the structure of the roof safe. If you're spraying directly onto decking, if the roof waterproofing system fails, you have the opportunity for moisture to affect the structure.

I'd agree that it is hard to justify on an addition or retrofit. I would just ventilate the new roof really well and seal the drywall. If you add an area of the house that is very tight when the rest isn't, you could cause some ventilation or pressure differential problems. You could always hire an HVAC engineer to run some numbers. It would be money well spent that would pay a return in a couple of years.

Renovations are always a pain - and while i"m a huge fan of keeping the attic from getting hot in the first place, odds are on a renovation it's just not worth it, especially for the cost.

On a new build? All day and twice on Sundays I'd do it.

I did an extensive addon/remodel in Houston (went from 2200 sq ft to 4400 sq ft). I did spray foam insulation in my attic and have had no issues. In fact, my electric bill is about 1/3 of what it was previously in half the size house. I would do it and not look back. You will be glad you did.

The foam is very flammable. Another property of foam to consider

sangredevino said:

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The foam is very flammable. Another property of foam to consider

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https://preferredsolutions.net/products/

Quote:

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This product has Class A/Class 1 flame spread and smoke developed ratings and qualifies as an Alternative Thermal Barrier Assembly when installed exposed without thermal barriers, ignition barriers or other fire protective surfaces in accordance with QAI Evaluation Report No. B1020-1, Edition 6.

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Spray foam is great. If you are building new, it is very much worth it. As mentioned above, just make sure to account for fresh air turnover. I wouldn't worry about leaks. We diagnose leaks all the time with spray foam houses.

Open cell foam is not waterproof. This allows water to migrate thru it and leaks will show a stain on your ceiling.

Foam is NOT "very flammable".

In the building science classes I've attended, they teach that in the average home, 65 to 80% of the heating and cooling cost leave thru the attic. Saving a third or more on an electric bill is very reasonable.

The ventilation issues are solved with an "ERV".

A lot of the homes in my neighborhood have Ridge Vents. Our builder didn't design them in, but while my next door neighbor had his roof replaced, he had one installed. I asked the roofer if he could just put in a ridge vent without redoing the entire roof, as I have really good shingles. He said a better solution to get the heat out of the attic would be a solar attic fan. He said not to get one of the ones at the big box stores as they have a lot of plastic, but said i should look at Attic Breeze.

All Metal parts, made in the USA, designed for Huricane winds. Anyhow, I am probably going to get one in the next month or so.

http://www.atticbreeze.net/

http://www.atticbreeze.net/homeowners.html

Don't you also need to account for a way to get air in through the soffit so you're not just pulling all your conditioned air up through the ceiling into the attic and out the attic breeze thing?

Where is the supply air coming from? Also, your main heat problems in the attic are radiative and conductive, not convection. Keep that in mind when deciding your vent strategy.

Mr. AGSPRT04 said:

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Where is the supply air coming from? Also, your main heat problems in the attic are radiative and conductive, not convection. Keep that in mind when deciding your vent strategy.

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So, should I go with spray on radiant instead? I do have soffit vents, but the existing roof vents don't have fans and the heat just builds up.

Shalackin:

When you say you "diagnose leaks" all the time...can you provide some more info. on this? We're building new and had some leaking issues just before sheetrock (spray foam already in). It was great timing that sheetrock not done yet as it was much easier to diagnose and fix (hopefully). The issues are supposedly fixed but I'm considering having some independent inspections done after good rains to make sure no more leaking.

Soffit vents will help some since airflow will in theory be flowing along the underside of the roof decking. Assuming it's adequate, then it won't be pulling the air from inside the building envelope, at least not as much.

Usually your most bang for your buck on reducing reducing bills/increasing comfort is sealing penetrations and adding insulation. I don't know if I'd bother with a retrofit radiant barrier.

Mr. AGSPRT04 said:

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Soffit vents will help some since airflow will in theory flowing along the underside of the roof decking. Assuming it's adequate, then it won't be pulling the air from inside the building envelope.

Usually your most bang for your buck on reducing reducing bills/increasing comfort is sealing penetrations and adding insulation. I don't know if I'd bother with a retrofit radiant barrier.

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I'd agree with this. People disregard the importance of airflow between each rafter. The whole idea is that with the proper design, the convective current should immediately move the heat up and out of the ridge vent along all of the underside of the roof structure.

I think a big problem is that so many houses barely have a ridge beam by the time the roof is framed. I once built a house that had a 12" ridge beam. No room for a ridge vent there.

I remember studying retrofit radiant barriers in school and the result we came to was that it was not worth it. I am always curious abut how people claim to see such fantastic results from them.

BTW, folks, read Green Building Advisor. It gets pretty far into the weeds on the technical side but you can find some articles on venting attics in the south. Most of the info is for northern climates.

Ferg said:

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Mr. AGSPRT04 said:

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Where is the supply air coming from? Also, your main heat problems in the attic are radiative and conductive, not convection. Keep that in mind when deciding your vent strategy.

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So, should I go with spray on radiant instead? I do have soffit vents, but the existing roof vents don't have fans and the heat just builds up.

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Definitely don't do spray on radiant. That's pretty much a waste of money. Radiant barrier stops (reflects) the heat that radiates off the roof deck into the attic. You need an air gap for it to be effective. If you spray the underside of your roof decking with silver paint, you'll actually create the opposite effect and radiate whatever heat is in your attic back in.

Any pointers on blow-in insulation? I believe I have original blow-in insulation (1985) up in my attic. Instead of taking the old stuff out, could I just blow in some on top of it?

There are ways to bring the ducts into the building envelope while leaving the envelope at the ceiling.

https://www.greenbuildingadvisor.com/article/keeping-ducts-indoors

This was your initial point. I am staying out of the foam no foam part of the discussion. I just wanted to point out that you can keep mechanical in the envelope either way.

I've been thinking about this for our home for a while, and seeing a vendor for spray foam roof insulation at the home and garden show earlier got me to investigate this further. I got a quote from them the other day, but it seemed a bit expensive to me. He looked up our home info online without actually coming by, so don't know if that could be a factor. He quoted $6000 for our roughly 2000 sqft home with attached garage.

Anyone have any recommendations for a contractor? I have another guy coming by tomorrow to take a look. I definitely want to get a good mix of quotes for this. I am also considering the solar powered attic fan and weighing the pros and cons to each.

Re: attic fan
https://www.energyvanguard.com/blog/75600/The-1-Reason-Power-Attic-Ventilators-Don-t-Help

Mr. AGSPRT04 said:

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Re: attic fan
https://www.energyvanguard.com/blog/75600/The-1-Reason-Power-Attic-Ventilators-Don-t-Help

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Thanks for that. I haven't researched the attic fan as much as the foam insulation, and have wondered just how effective they could really be. That makes a lot of sense.

labmansid said:

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I've been thinking about this for our home for a while, and seeing a vendor for spray foam roof insulation at the home and garden show earlier got me to investigate this further. I got a quote from them the other day, but it seemed a bit expensive to me. He looked up our home info online without actually coming by, so don't know if that could be a factor. He quoted $6000 for our roughly 2000 sqft home with attached garage.

Anyone have any recommendations for a contractor? I have another guy coming by tomorrow to take a look. I definitely want to get a good mix of quotes for this. I am also considering the solar powered attic fan and weighing the pros and cons to each.

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After Harvey we put closed cell foam in the walls at my mom's house as we were rebuilding it.

We used Energy Assault Solutions. They're in Dallas and Houston.