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mystic_cobra 01-28-2013 11:39 PM

Unique attic situation and need assistance
I am a DIYer and I have a colonial style house built in 1965 in Northern VA. The center portion of the house is two stories and then it has a one-story "wing" on either end with separate attics. Three total attics that are not connected. One wing is a garage and the other is a living room/dining room and part of my kitchen. Based on the layout of the house, I think it was built this way and that it is not an addition.
This is what it looks like. The area in question is the wall to the right of the moss covered roof (save that for another day). The portion of the wall separating the attic space from the living space. To the right of that wall is a stair well in the middle and two bed rooms.

The insulation in the attic floor was recently redone by me during the kitchen renovation. The wall in question is poorly insulated. The wall temperature (measured via non-contact infrared thermometer) is 68 on the lower portion of the wall that has more living space behind it, 61 on the upper part of the wall with poorly insulated attic on the other side, and 58 on the 3/16" uninsulated plywood access door into the attic. Outside temp is 44 currently. Coolest temp I measured in the attic tonight is 45. This wall is cold to the touch in winter and hot in the summer. I wish I had taken these measurements three days ago when the temp was 10. Both of the rooms upstairs that are against that wall are guest rooms that we keep closed off most of the time so it has not been a major issue.

This wall in question is made up of the following from the inside out and is shown below from the attic opening:
1. (painted) drywall - unknown thickness
2. traditional 2x4 studs with NO insulation-I can see into the wall at the attic access door
3. roughly 1/2" gap that's not sealed on the ends as seen in the pic
4. 2x4 studs with old batt insulation that has shrunk and appears to be about 2" thick
5. some kind of press board or fiber board that is about 3/4" thick (says Armstrong TEM... on it). Some of it is not attached very well and it will move back and forth about a quarter inch between the roof truss and the 2x4 studs. There are roofing nails holding it in some areas.
6. 2x4 roof truss

I would like to insulate this wall as much as is practical without tearing down the interior drywall. I was considering sealing up the ends around the opening and adding a layer of 2" rigid foam insulation on top of the press board from the attic side. These would have to be cut into large triangular sections and slid in between the 2x4 chords of the roof rafter. With this large gap and possibly other unknown issues inside the wall, would this be a wasted effort? Obviously, some foam on the door would help.

Any advice? Looks like the 4x8 sheets of 2" rigid foam are only $31 and provide an R-13. I'm guessing I'd need 2 or 3 to cover that wall.


Gary in WA 01-29-2013 11:18 PM

If the foam is fastened and canned foam air sealed to the cold in winter side of the wall. After installation, add some f.b. rips to cover the truss cord/struts over-lapping the in-between f.b. pieces some for a thermal break from the cold attic. Add ignition barrier if required on f.b. per local AHJ.


mystic_cobra 01-29-2013 11:49 PM

Thanks for the reply. So, I like the rigid foam combined with canned spray foam idea for the gaps.
The second suggestion, I'm not sure I understood. Are you saying to cut long strips of the rigid foam board (say 5-6" wide) and lay them as another layer over top of the truss chords to cover the rigid foam edges where they meet the chords?
Do I need to use some kind of special tape to cover the seams or will the overlap be sufficient to seal out the air?

Gary in WA 01-30-2013 07:26 PM

Check w. AHJ on covering the f.b. with ignition barrier or not, may let you get by with foil-faced rigid board or none at all, depends on local Ins. and conditions in attic;


Then caulk perimeter under the over-pieces and foil tape the exposed edges to protect from flames. Need it as air-tight as possible.


mystic_cobra 01-30-2013 08:39 PM

Is AHJ a person?
Looks like the Dow link is bad.
I'm pretty sure the rigid foam board at my local home depot has foil on both sides but I guess all the edges and seams would need foil tape, right?

Gary in WA 01-30-2013 11:03 PM

Always good to check with Authority Having Jurisdiction. I changed the links, thanks.


mystic_cobra 02-06-2013 01:41 PM

I spoke with a code official at my county office and he said that fire proofing is not required on the attic side of that wall.

I'm going to take Gary's advice and use the foil covered foam board, seal all the gaps with spray foam, and the edges of the foam board with metal tape.


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