Spray foam roof vent closed???

[Overhaulin63]

Okay so I am investigating spray foam insulation for my garage. The most recent company I spoke with gave me a quote but also asked if I had a ridge vent. I said yes. They said they would also spray the vent closed because spray foam creates another atmosphere and we would not need it. Another atmosphere??

I don't understand why you would want to get rid of the ridge vent. Can someone shed some light on this topic, I am in the dark.

 

[The Cobbler]

if they are spraying the roof deck then I suppose, but I think you still need air space/ventilation under the shingles. if they are spraying the ceiling then the space above definitely needs ventilation.

 

[csp]

Why didn't you ask them what they meant by another atmosphere?

 

[Dave-H]

I went through this when we spray foamed our attic, converted to a bedroom. In our situation, we drywalled in the attic with a cathedral ceiling. This was a vented roof, so if we were blowing some insulation into the rafters we would need to install baffles or vents to make sure it remains vented. Then the envelope would be where the insulation is and the small area of the underside of the roof, where the baffles are, would not be conditioned.

When we decided to use closed spray foam, we were told that because it seals very nicely for air and vapor, it was possible to simply spray the foam into the entire cavity which provides fantastic sealing and insulation but renders the vents useless. In that case, they take a little extra foam and completely close off the vents. Then you've converted a vented roof to an unvented roof, which is OK as long as it's done properly and it's sealed well.

The spray foam performs fantastically. Probably by atmosphere he meant 'the conditioned area' or the envelope. It's common practice to spray right under the roof decking, at least here in Denver, which makes that layer of closed cell foam the border of the envelope/conditioned area.

 

[Randy in Maine]

I went through this when we spray foamed our attic, converted to a bedroom. In our situation, we drywalled in the attic with a cathedral ceiling. This was a vented roof, so if we were blowing some insulation into the rafters we would need to install baffles or vents to make sure it remains vented. Then the envelope would be where the insulation is and the small area of the underside of the roof, where the baffles are, would not be conditioned.

When we decided to use closed spray foam, we were told that because it seals very nicely for air and vapor, it was possible to simply spray the foam into the entire cavity which provides fantastic sealing and insulation but renders the vents useless. In that case, they take a little extra foam and completely close off the vents. Then you've converted a vented roof to an unvented roof, which is OK as long as it's done properly and it's sealed well.

The spray foam performs fantastically. Probably by atmosphere he meant 'the conditioned area' or the envelope. It's common practice to spray right under the roof decking, at least here in Denver, which makes that layer of closed cell foam the border of the envelope/conditioned area.

I did the same thing. It is the correct call.

 

[DC73]

. . . . but I think you still need air space/ventilation under the shingles. . . .

They've backed off this requirement. The thinking used to be that no air flow under the roof deck would shorten shingle life considerably but it turns out shingle color and climate has more to do with life span than does whether an attic is vented or not. Manufacturers still honor the shingle warranty.

DC

 

[Elginz]

If you foam directly to the roof deck you do not need an air space. There will be no heat or moisture build up as no moist air is getting to the deck. Moist air is not rising to the roof deck and being trapped there. Everything inside the roof deck would be conditioned space. There could be an issue if there are knee walls with unconditioned space behind them. Usually the roof deck behind the knee walls is foamed as well making the whole area under the roof as conditioned space. Then knee walls need not be insulated if the roof deck is foamed.

 

[Overhaulin63]

Great comments!

I have 3 doors on my garage (2- 16x10 and 1-10x10) when I have these doors open won't I have heat and moisture in the building with no where to go?

I have also been on roofs where they have cooked the sheeting, minimal ventilation, so bad it felt like you were walking on a waterbed. I don't want to cook my roof.

 

[Falcon67]

Okay so I am investigating spray foam insulation for my garage. The most recent company I spoke with gave me a quote but also asked if I had a ridge vent. I said yes. They said they would also spray the vent closed because spray foam creates another atmosphere and we would not need it. Another atmosphere??

I don't understand why you would want to get rid of the ridge vent. Can someone shed some light on this topic, I am in the dark.

Because when you spray foam the entire building envelope, the entire building becomes the "conditioned space". My boss's new house is like this - weird to look across an attic and not see anything but joints, wires and AC ducts. The downside for a living space - maybe not a shop space - is that you then need to engineer an air exchange system to get fresh air in to the sealed envelope.

 

[MadMechMaster]

Just now after reading this, I am very interested in the new ventilation requirements. My garage has a hip roof and what would be a low ceiling if I were to put in a traditional ceiling.

So closing the vents and spray foaming the whole thing is now acceptable?

As far as heat and moisture build up, a powered vent that you can close and open at will might help. Unconditioned space right now, but having HVAC in the future would require the space to be closed.

Interesting..

 

[CNGsaves]

^ ^ ^ This. Also spray company is not going to mess with blocking off that small crack all across roof peak for ridge vent . . . NOT going to happen.

Tell us OP are you getting Closed-cell or Open-cell ??

How much is the quote and how thick is the insulation ?? Building size ??

 

[DC73]

So closing the vents and spray foaming the whole thing is now acceptable?

Yes. Research unvented attics on BuildingScience.com and GreenBuildingAdvisor.com.

Open cell foam is less costly and can be used in some climates but closed cell foam may be required in colder climates.

DC

 

[Overhaulin63]

I actually priced the closed cell, R-value is higher, with the contractor and it looks like I'll be doing it myself. The contractor wanted $8500 and I could do it for less than 1/2 with the same material and I am sure it will take me more time and it may not look as good but I am okay with that. The garage is 32x60 with 12' ceilings. Everything I have researched says that its a waste to go more than 2" because the payback is diminishes quite a bit vs. the cost. Many have recommended doing the 2" plus bat insulation as the most economical route to go, but I can't speak from any personal experience but it does make sense to keep the cost down vs. 4" of spray foam.
I am considering putting up a ceiling and blowing in insulation above the ceiling, leaving the ridge vent, and spray foam from the ceiling down. Maybe?

 

[Falcon67]

That works also IMHO, provided you seal up the ceiling to reduce air movement to a minimum.

 

[dshop]

I had my 40x60 stick built shop spray foamed open cell. floor to ceiling, all the way around, no roof vent, 1 continuous surface. This was 9 years ago in Raleigh NC area, very humid and hot in July, Aug. The highest temp recorded inside the shop has been 84 with 102 outside temp...no AC, just insulation.
The winter low inside was 58 with 40 outside, again, no HVAC, just insulation.
My walls are 2x4 sprayed to the max 4" and paneled with OSB.

 

[ishiboo]

There's nothing wrong with a hot roof, and like many have mentioned it does not significantly affect roofing life. Yes, the ridge vent would just allow hot air to leave defeating the purpose of insulating if done between the rafters.

However. If there is no reason to (i.e., cathedral ceiling in a finished space), why do it? That creates an attic space which will have absolutely no ventilation.

If this is an empty attic, use the spray foam on the ceiling joists (it's cheaper anyway - there is less surface area to insulate). Otherwise, plan on some sort of way to cycle conditioned air through the attic space.

 

[Falcon67]

>There's nothing wrong with a hot roof, and like many have mentioned it does not
>significantly affect roofing life.

I've read that, and take exception to it based on personal experience. At least here in Texas where deck temps can get to 160F or better.

 

[75gmck25]

Assuming you use use spray foam to seal and cover the entire roof area in a garage, do you have to use an ignition barrier material over the foam?

The reason I ask is that when I finished my basement I put foam panels on the wall, and the inspector required them to be covered with drywall or other barrier material. I think the reason was that when the foam is exposed to fire it will give off hazardous fumes.

Bruce

 

[csp]

Assuming you use use spray foam to seal and cover the entire roof area in a garage, do you have to use an ignition barrier material over the foam?

Not by code you don't because a garage isn't a habitable space. It would be a good idea though.

 

[Overhaulin63]

I have been on roof that appeared to be in good condition but was like walking on waterbed and felt like you were going to fall through. We had a contractor come out and evaluate. He said because the soffit were closed off with insulation the roof cooked itself. When the roof came off you could see the OSB and become delaminated.

So if my garage has a vented soffits along with the ridge vent would they all have to spray foamed shut if we opted to go to the peak?

 

[DC73]

I have been on roof that appeared to be in good condition but was like walking on waterbed and felt like you were going to fall through. We had a contractor come out and evaluate. He said because the soffit were closed off with insulation the roof cooked itself. When the roof came off you could see the OSB and become delaminated.

So if my garage has a vented soffits along with the ridge vent would they all have to spray foamed shut if we opted to go to the peak?

You won't have this problem with closed cell spray foam because it blocks moisture from getting to the underside of the roof deck.

Fiberglass, cellulose, mineral wool, etc allow moisture to migrate to the underside of the deck. Building scientists are now recommending a ridge vent with a vapor membrane installed under it to allow water vapor to escape when using one of these insulations under the roof deck. They currently only recommend this for climate zones 1, 2, and 3 and are evaluating other climate zones like yours. But, closed cell foam already blocks moisture and so does not have this issue.

Go to GreenBuildingAdvisor.com and BuildingScience.com and research unvented attics. Pay particular attention to the more recent articles as the thinking has changed somewhat in the past 5 years or so. The GBA site also has a good Q&A forum that is frequented by building science gurus who can give you better advice than you'll find here. In your climate, it's very important to get the details right.

DC

 

[Overhaulin63]

Thanks everyone!!