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King Mondo 10-16-2012 10:02 AM

Attic insulation.
 
Can attic insulation touch the underside of the roofing? My roof is barn shaped and has no soffit vents, just two gable vents and a ridge vent. I want to add more insulation but don't know if I can place tight up against the corners where the roof meets the attic decking. I don't have to worry about covering soffit vents because there are none.

Thanks

Windows on Wash 10-16-2012 10:59 AM

Yes and No.

If you had soffits, no.

If the space is conditioned, you should seal all the top plates. The moisture that moves on bulk air movement does need a space to vent out through to get to the gables.

Squished 10-16-2012 01:33 PM

Where are you located? (what climate zone?) I'm in MA and by code insulation can only touch the underside of the roof it's spray foam (open or closed) when a ridge and soffit vent isn't present. Fiberglass insulation requires both a ridge and soffit vent here if it's in the rafters due to condensation.

Gary in WA 10-16-2012 10:14 PM

Vented or not, it should never touch. Fig. 5 is bad enough having the two surfaces radiation-coupled; http://www.buildingscience.com/docum...bout-diffusion How do you stop it? Just "flip it over" fig.7.

The solution (only flipped) fig. 7; http://www.buildingscience.com/docum...n-crawlspaces/

Condensation and wetting of the fiberglass gives a big R-value reduction, 60-70%; http://archive.nrc-cnrc.gc.ca/eng/ib...ling-heat.html

Best to use foil-faced rigid foam board or SPF (check locally for fire-codes) where the roof gets close to the ceiling below (over the exterior top plates). This helps prevent wind-washing or at least air movement from the gaps in the framing as well: http://www.conservationtechnology.co...eakagePathways

Drywall leaks air at the top plates of all walls, exterior/interior leak warm air (that you paid for!) in a heating climate, 24/7; http://www.buildingscience.com/docum...ation-packages

Gary
P.S. Welcome to the forums!

Windows on Wash 10-17-2012 08:33 AM

Quote:

Originally Posted by GBR in WA (Post 1032369)
Vented or not, it should never touch. Fig. 5 is bad enough having the two surfaces radiation-coupled; http://www.buildingscience.com/docum...bout-diffusion How do you stop it? Just "flip it over" fig.7.

The yes and no was referring to spray foam Gary as Squished pointed out.

King Mondo 10-18-2012 06:17 AM

Attic Insulation
 
1 Attachment(s)
Thank you all for the replies. One of the main reason I wanted to know if I could shove insulation all the way in to the corners was that I second floor windows that the top of the windows are exactly level with the attic floor and I have had ice dams over the windows before that have leaked into the house even with the ice barrier under the shingles. I was thinking that too much warm air was moving up over the windows into the attic where there is virtually no insulation at those points. I thought by packing insulation over the top of where the windows are that that may prevent ice dams. You can see by the photo that the attic space is very low.Attachment 59026

Windows on Wash 10-18-2012 06:20 AM

Spray foam that location and closed cell will be a better choice given the higher R-Value and vapor impermeability.

Squished 10-18-2012 06:33 AM

Nearly the same situation as me. Spray foam is the only way to go. Depending on budget, closed cell is best but open cell will work too. Here's how they did mine right to the edge of the roof:

http://i222.photobucket.com/albums/d...001_121835.jpg

The pink insulation you see is in my ceiling only purely for noise barrier from the AC unit in the attic, which you really can't hear anyway.
http://s222.photobucket.com/albums/d...001_121835.jpg

King Mondo 10-18-2012 09:09 AM

Attic Insulation
 
Thanks again for the pray foam suggestion. Unfortunately I think the spray foam is out of my budget. Even getting back in the corners will be a challenge even If I lay down insulation. The roof height in the attic at the center is 4' and with the pitch as it is you have to lay down on your stomach just to try as get a good look. Needless to say I've hit a few roof nail with my head.

Squished 10-18-2012 09:21 AM

Quote:

Originally Posted by King Mondo (Post 1033230)
Thanks again for the pray foam suggestion. Unfortunately I think the spray foam is out of my budget. Even getting back in the corners will be a challenge even If I lay down insulation. The roof height in the attic at the center is 4' and with the pitch as it is you have to lay down on your stomach just to try as get a good look. Needless to say I've hit a few roof nail with my head.


Get a quote for open cell foam if you're on a budget. I was the same way. Get LOTS of quotes, prices vary drastically. I had a difference of 50%+ in my quotes, all for the same job.

Also, check with your state and local utilities, sometimes they offer rebates on it. In my case, my local electric company paid for half of my entire attic.

Windows on Wash 10-18-2012 09:58 AM

For your purpose, I would just get a 600 board foot kit of closed cell. You can get some pretty good distance with it as well and seal up that outside top plate and up the insulation there.

That mansard is probably not vented.


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