Spray Foam On The Back Side Of Tounge & Groove Ceiling? - Construction - Contractor Talk

Spray Foam On The Back Side Of Tounge & Groove Ceiling?

 
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Old 06-03-2010, 12:40 AM   #1
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Spray Foam On The Back Side Of Tounge & Groove Ceiling?


I have a client who would like to have her roof replaced and help solve the huge ice damming she has.

The interior is catheterized T&G ceilings. The insulation is then fiberglass R38.

I think a BIG part of the problem, is there is nothing but that paper vapor barrier behind the ceiling.

Foam would seal it up 100% applying just 1" and then going over that with the rolled fiberglass.

I'm confined that would work, but am open to suggestions?

A concern is the foam could come through the T&G ceiling. I've heard different from 2 different foam contractors. One says it will, the other says no way.
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Old 06-03-2010, 01:14 AM   #2
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Re: Spray Foam On The Back Side Of Tounge & Groove Ceiling?


This is a difficult question to answer. No doubt, the foam will find its way into the joints and any knots to some degree. The question is, will the foam work its way deep enough into the joints for it to be visible from the interior of the home?

I wouldn't take the risk. If I were asked to bid this job, I would factor in laying poly in all the rafter bays to prevent the foam from physically contacting the T&G.

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Old 06-03-2010, 06:21 AM   #3
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Re: Spray Foam On The Back Side Of Tounge & Groove Ceiling?


Open cell foam would be good choice....or, if you have rafter bays, simply use EPS board, which can be found in about any needed thickness, and cut to fit. Foam could be sprayed directly over the EPS board to seal it. I would not install fiberglass, which does nothing.
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Old 06-03-2010, 07:04 AM   #4
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Re: Spray Foam On The Back Side Of Tounge & Groove Ceiling?




First; Poly in the rafter bays will prevent the foam from adhering to the substrate - which can and will lead to air leaks as it is not fully in contact & can become decoupled (you could apply a thin strip of tape to the offending areas)

Second; Open Cell requires a vapor barrier to be applied - if you are worrying about ice dams that means that your codes should be requiring it to be installed from the inside which would be impossible with the T&G there (Closed Cell already is tested & approved - i.e. no Vapor Barrier req)

Third; Open Cell will push through any gaps in the T&G due to its expansion characteristics - Closed Cell will also fill any gaps and can push through if there are any open seams or holes, but it will not be as much

J-Peffer - where are you located at?

Based on your location will determine how many lifts (1.5" to 2.5") you should apply for Closed Cell only install - in most locations - 2 lifts is fine, whereas some really cold climates need 3 lifts.

Next - Joasis idea on the rigid foam has some merit, but the foam can still push through if the rigid foam is not installed tightly & you spray in Open Cell... One way around all this & to keep costs down is to spray 1 lift of Closed Cell & then follow it up with Open Cell - we both agree also that Fiberglass is worthless

Thermal Transfer - depending on your area - you might want to put a layer of Rigid foam down over the sheathing to block that means of heat transfer
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Old 06-03-2010, 07:42 AM   #5
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Re: Spray Foam On The Back Side Of Tounge & Groove Ceiling?


T&G needs to be able to move - expand and contract.

I would be worried that this foam might stop this and cause cracking in the boards. Perhaps you could bang on some building paper as separation point between the two products...
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Old 06-03-2010, 11:38 AM   #6
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Re: Spray Foam On The Back Side Of Tounge & Groove Ceiling?


John - same problem as mentioned above with the plastic

If you have sealed the house & roof up properly, have proper ventilation & moisture control,etc... expansion & contraction is not an issue as the temperatures & humidity will mostly remain constant inside the structure
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Old 06-03-2010, 11:41 AM   #7
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Re: Spray Foam On The Back Side Of Tounge & Groove Ceiling?


Wow, great info guys!

I'm located in Western Michigan, the house is a lake front home that's exposed to the high wind speeds off the lake.

The family has had some real issues with the house, but I'm in experienced with the foam. In my area, there are very few foam contractors, and I've gotten different options and opinions from both. Obviously, research is required then!

I did consider EPS board at one point, and then going foam over that.

The customer brought up plastic, I liked the direction of her thoughts, but not the non permiable substrate.

I was thinking simple resin paper. It comes in a 3' wide roll.

I'll cut it down to 21" on the miter saw, and roll it down each cavity.

Applying the foam on that, it should bond very well to the paper, and the rafters on each side and still give you a 100% seal which is really what I'm going for here.

Fiberglass batts for R-Factor sake?
And Still use air baffles, soffit intake and ridge vent?

All great info guys, appreciate it!
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Old 06-18-2010, 08:19 PM   #8
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Re: Spray Foam On The Back Side Of Tounge & Groove Ceiling?


Quote:
Originally Posted by J-Peffer View Post
Applying the foam on that, it should bond very well to the paper, and the rafters on each side and still give you a 100% seal which is really what I'm going for here.
I'm not sure that it would seal correctly, which is what SLStech was pointing out. Generally it's sprayed directly to the underside of the roof sheathing, which is what has been approved for non vented attics/ceilings. If you stray from that you're just guessing about long term performance IMHO.


Quote:
Fiberglass batts for R-Factor sake?
And Still use air baffles, soffit intake and ridge vent?
Well, if you're going to vent it I guess you don't have to worry if it's completely air-tight. What you'd be doing is called flash and batt, but I'm not familiar with it being used in attics.

Whatever you do I'd take off the gutters and run Grace down the eave and onto the gutter board. That along with continuous soffit vent, continuous baffles in every rafter bay, and ridge vent would probably take care of the ice dams using just fiberglass batts (depending on the roof design).
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Old 06-20-2010, 09:15 PM   #9
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Re: Spray Foam On The Back Side Of Tounge & Groove Ceiling?


Man, there is more than one way to do this. I think I would put XPS or EPS in between the rafter bays. I would then foam the edges of the rigid with a foam gun and cans. then I would spray in closed cell foam and fill the rest of the the rafter bay. You could do a non vented roof at this point but you would want to make sure that the foam entirely filled the rafter bay before you reapplied the sheathing. you would also want to make sure there were no other air leaks or spaces between the exterior sheathing and foam. If you wanted to keep it vented, I would nail strips to the side of the rafters and spray the rafter bays to top of the strips. You would have to do some trimming of the spray foam to keep a decent air space. the strips would guide your air space size. Or you could position the strips so you could staple or nail more rigid foam to the top of them and still maintain a decent air space. Again I would use a foam gun to seal the rigid foam to the rafters. unfortunately you can't put foam on the underside of the rafters which would be ideal. If that was an option then forget everything I just typed.
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Old 06-20-2010, 09:27 PM   #10
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Re: Spray Foam On The Back Side Of Tounge & Groove Ceiling?


I fix the same problem for a customer last year only had t&g on ceiling and r 38 unfaced and the ice would hang off 8 feet from eves home only 7 years new so we put four layers blue 2 in foam and one layer 2 in foil face in side with taped seems will saved on heat bill that for sure, would have sprayed but cost was to much and theres only mabee two people up here that spray polyurea
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Old 06-22-2010, 08:35 PM   #11
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Re: Spray Foam On The Back Side Of Tounge & Groove Ceiling?


Quote:
Originally Posted by J-Peffer View Post
I have a client who would like to have her roof replaced and help solve the huge ice damming she has.

The interior is catheterized T&G ceilings. The insulation is then fiberglass R38.

I think a BIG part of the problem, is there is nothing but that paper vapor barrier behind the ceiling.

Foam would seal it up 100% applying just 1" and then going over that with the rolled fiberglass.

I'm confined that would work, but am open to suggestions?

A concern is the foam could come through the T&G ceiling. I've heard different from 2 different foam contractors. One says it will, the other says no way.
give or take - I would do a sample on an outside exterior my self -- and youll get a positive ANSWER...... grab a test peice ----- foam works i mean really it does... just put a barrier under the wood ... incase ....

in most case

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