Home>Discussions>INSULATION & HVAC>Spray Insulation and preservation of my ridge vent
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Mastercarpentry
Re: Spray Insulation and preservation of my ridge vent
Mastercarpentry

This is done on the ceiling joists, not the rafters, and I'm speaking of standard insulation, not foam.

The best place to insulate is at the end of the conditioned space, ie the ceiling, not the roof. Foam can be direct-applied to the underside of the roof but it offers few benefits compared to it's cost in this application. And if you foam, you'll have to close off soffit and ridge venting which might exacerbate humidity issues in the attic space. Unless your future plans include making the attic into a room just go with the standard insulating practices and use the money you'll save for other stuff.

Phil

keith3267
Re: Spray Insulation and preservation of my ridge vent
keith3267

Are you trying to make the attic a habitable (living) space?

hvacjesse
Re: Spray Insulation and preservation of my ridge vent
hvacjesse
keith3267 wrote:

Are you trying to make the attic a habitable (living) space?

I am. I want to increase my living area in the house and also save money on heating costs. With the venting set up my house has the freezing cold air in my attic causes drafts downstairs and I always feel like I am playing catch up to make my house warm.

I have already started the project and am moving right along but I got so many different views and thoughts about this.

The most intriguing of which came from a registered PE, Professional Engineer.

Skip the batts, and just spray foam everything because the soffit vents are not necessary with this kind of insulation.

I told him that I have a ridge vent system and I wanted to preserve it and he told me I can spray right over the underside of it, no problem.

I have already installed almost all the baffles to preserve the soffit venting and the ridge vent and i am actually very satisfied with how its working out.

Thanks for all the comments.

Mastercarpentry
Re: Spray Insulation and preservation of my ridge vent
Mastercarpentry

Either venting or foam will work, but with you planning on finishing the space the foam will make that part go easier. If I did the foam, I would eliminate the vented ridge-cap and replace it with shingles because it would no longer be needed and it serves as a potential point for water ingression. Offset the cost somewhat by selling the used (carefully removed) ridge vents on Craigslist or to the roofer who removes them.

I'm a fan of 'attic rooms' as a great use of space but in some climates they're are best used as a 3 season space- they can present cooling problems here in the sunny south even with great insulation.

Phil

rhd1953
Re: Spray Insulation and preservation of my ridge vent
rhd1953

My 1924 house in the Quad-Cities had no venting at all. At some time the roof was chopped off, leaving no overhang or venting.

I had the attic rafters/underside of the roof sheathing spray-foamed (after replacing the roof). It is now part of the building thermal envelope (unvented attic). The reasons are:
-no venting required
-air tight at all the roof locations (at the foot of the roof in particular)
-strengthens the roof considerably
-6" of spray foam eliminates heat loss/gain
-while they did install a ridge vent, it was sealed by the spray foam (except under a finished room in the attic).
Note: spray foam is not cheap, but it really does seal and insulate. It's critical that it be applied correctly, improper mixing/application of the spray which results in incomplete curing, requires removal of the the spray foam.

Code Citation:
2009 IRC, Section R806.4; 2012 IRC, Section R806.5, Unvented attic assemblies
Unvented attic assemblies (spaces between the ceiling joists of the top story of the roof rafters)
shall be permitted if all of the following conditions are met:
1. the unvented attic space is completely contained within the building thermal envelope
2. no interior vapor retarders are installed on the ceiling side (attic floor) of the unvented attic
assembly [2009 IRC]; no interior Class I vapor retarders are installed on the ceiling side (attic
floor) of the unvented attic assembly [2012 IRC]
3. where wood shingles or shakes are used, a minimum ¼ inch vented air space separates the
shingles or shakes and the roofing underlayment above the structural sheathing
4. in Climate Zones 5, 6, 7 and 8, any air-impermeable insulation shall be a vapor retarder, or shall
have a vapor retarder coating or covering in direct contact with the underside of the insulation
[2009 IRC]; in Climate Zones 5, 6, 7 and 8, any air-impermeable insulation shall be a Class II
vapor retarder, or shall have a Class III vapor retarder coating or covering in direct contact with
the underside of the insulation [2012 IRC]
5. either Items 5.1, 5.2 or 5.3 shall be met, depending on the air permeability of the insulation
directly under the structural roof sheathing

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