Spray Foam insulation soffit questions

[jabingham81]

Ok, have a 24x32x12 going up. The trusses are 4' on center and its just metal on perlins for the roof. I want to spray foam the whole building so we do not have to put a ceiling in it. Question is should I be using vented or non vented soffit? and should the soffit be getting spray foamed?

 

[Bobthetractor]

So if you're going to climate control the building then you want to seal it completely. If not, then I'm not sure. I actually asked the same question on here a few days ago and haven't gotten a response yet. My gut says leave it open so the hot air can escape. Are you going to seal the ridge as well?

Also, you didn't ask but I'd suggest closed cell over open cell and I'm unaware of any SPF option that can be left open without a thermal barrier drywall/intumescent paint to meet fire code. I don't care personally but if you're getting it inspected they probably will.

 

[rok_hunter]

I just went through this on my 30x40x12. The builder didn't add any soffits because the roof overhang on my design didn't allow the space (it's something like 3"-5"). They offered and extended eve/overhang that would have allowed a soffit but it was more expensive, and I planned to seal it for spray foam anyway so it would have been a waste. My design did include a Ridgeline vent at the top of the roof but it was sealed by the foam, too. I went with closed cell for many of the reasons already listed, in addition to the general stiffening of the walls that came with it. The foam installer offered a hybrid (1" closed cell followed by 3" open cell) that offered a slightly higher R value and lower cost, but had less stiffening and would have required the thermal barrier already mentioned. I'm sheeting my interior with plywood anyway, but wanted the stiffness from going completely with closed cell.

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[MrSurly]

What *I* did: I built my building with overhangs and soffits strictly for appearance. I then had the building spray foamed to seal it as tightly as possible. When the spray foam guys arrived they used a stapler and some super-thin sheet polyethylene (like the produce bags at the grocery) to seal the area above the plate, to prevent the foam they sprayed from getting over into the soffit area as it would be purely a waste of foam. I have a pic of that viewed from the outside, somewhere, I'll post up later. The soffit panel itself was the same price either perforated or not. Mine is perforated because at ordering time, I hadn't decided which way to go. I am VERY glad I went this way. the perf or not perf soffit panel makes no difference for my build as there is NO air movement there, but I like the look of the perf.

 

[yeldogt]

On stick built you fill/ coat everthing no venting -- nothing to vent.

Is the roof aproved to be direct insultaed that way?

 

[MrSurly]

Is the roof aproved to be direct insultaed that way?

If you are asking me(?)
Yes. Despite the many claims from people who claim this will “void your warranty”
I have been unable in four years to find any back up for the claim.
The metal manufacturer did NOT void my warranty afaik.
I can find no prohibition on the practice.


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[yeldogt]

If you are asking me(?)
Yes. Despite the many claims from people who claim this will “void your warranty”
I have been unable in four years to find any back up for the claim.
The metal manufacturer did NOT void my warranty afaik.
I can find no prohibition on the practice.


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You or the OP ....

I have no experience with pole buildings -- or direct insulation to the underside of a roof.

I do foam all my projects ... but -- they always have plywood walls and roof deck

 

[MrSurly]

Here’s what my soffit looks like without the perf panel in place. The poly that the guy stapled in was left loose in some spots and tight in others. Foam didn’t care. The foam just “poofed” it out to fill. At first I worried that the poly he was using would be too weak and the foam would rupture it, but my concern was unfounded. These guys knew just what they were doing.
Sorry for the bad lighting.