Spray foam (closed cell) directly to roof sheathing?
B3llo38
| Posted in General Questions on
Hey guys, so I have a back indoor/outdoor sunroom on the back of the house. It used to be essentially all screened windows when we purchased the home. The framing was rotted out so I tore it all out and added new framing and windows. After the fact my wife wants to eventually make it more living space of course… anyway.
I was going to insulate it myself but due to time and work etc I figure ill get a few companies out here and get pricing. The only company I had out so far was highly recommended from a lot of the builders in the area. However I wasnt really comfortable with what he suggested.
The exterior walls are 2×4. On the exterior I have tyvek and plan on adding 1/2″ to 1″ foam board then siding over that. Interior I planned on doing Rockwool comfortbatt unfaced. I just like it better then faced fiberglass. For the ceiling I am torn… they are 2x8s and im in the northeast in South Jersey.
I was thinking to have the styrofoam vent baffles installed from the soffits to the attic opening to keep airflow moving. Id then most likely add another power roof vent or something in that attic opening on the roof to help remove additional heat. (Cant do gable vent, to many wires and I dont feel like moving them).
The insulator came by and said no, he will do 6″ of spray foam directly to the roof sheathing and r15 faced on all the exterior walls (paper pointing interior) for a vapor barrier. Im not a huge fan of that spray foam idea due to roof rot and no where for moisture to go etc.
I plan on adding a mini split and a return in this room for hvac its about 400 sq ft.
Also I will be raising the floors up 8 inches in here and insulation the floors and adding vapor barrier on the concrete.
Hit me with all of your insulation ideas please.
Also the rear of the home (where this is) gets direct sun pretty much all day.
I couldnt add the pictures so heres a google drive with them
https://drive.google.com/drive/folders/1nLPZ896os2o0x99bOUxUekaVDp5m6tz4
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Replies
When you write: "roof rot and no where for moisture to go etc."
What specifically is your concern?
Bulk moisture (water) from the outside & the "foam" will cover it up so you don't know it is there?
Moisture in the form of vapor, condensing on a cold surface (changing from vapor to water)?
Honestly im not completely sure. Ive just been reading stories of "hot roof" etc. I have a vented attic as of now. He said he wants to completely seal up the soffits and the wall that connects the room to the current vented attic.
The spray foam idea is still new to me. I just picture the sheathing getting moldy for some reason. Also ive been hearing about shingle companies shying away from warranties.
B3llo38,
There are all sorts of vented assemblies you can use that don't require spray foam.
I would also suggest using a different material for the baffles than foam to allow better drying into the vent space. Plywood, OSB, fiberboard, or house-wrap are all permeable and work well.
Two suggested options:
- Furr down the rafters to create a deeper cavity and fill with batts.
- Fill the existing cavities with batts, and add a layer of foam board underneath them.
Be careful adding any powered exhaust to the attic. It can create negative pressure and draw air from the house below.
Thank you Malcolm. Would adding just a regular roof vent be fine? There is a ridge vent but its not the biggest
B3llo38,
You want at least 50% of the area of the roof vent openings to be at the soffits. If you can keep that ratio and add more near the peak, then yes.
Ideally id like an 1.5" gap between the sheathing and the spray foam for venting from the sofits to the ridge vents. Then 4.5" of spray foam before drywall.
Like i stated before the idea of removing the venting and completely sealing up and spray foaming against the sheathing just doesnt sit right with me
B3o38,
If you are intending to use spray foam in the roof cavities rather than permeable insulation, then foam baffles are fine. My suggestions were alternatives to using spray foam altogether.
If you want a 1.5” gap - this is what we would do all the time
Buy a 1.5” foil faced polyiso board, score on one side the diameter of the joist bay
Fold over one side (w/foil intact) so it creates 1.5” air space
Spray 3” of foam on surface & edges to seal in place
Lots of successful closed cell foam “hot roofs” assembly applications …
You’re right, you may void the shingle warranty
When I did my hot roof application for my own home, I didn’t really pay much attention to a roof shingle warranty
- formerly worked for a spray/injection foam (closed & open) contractor