insulation and vapor barrier PolyISO


Old 06-04-12, 04:13 PM
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insulation and vapor barrier PolyISO

I new here , this my first post.

Climate is Zone 2 Albuquerque, NM . Home build in 1947 .

I'm an licenced electrician and I just replaced all the electrical in the home. I removed all the sheet rock and plaster on the walls and ceilings. The entire home is down to the studs and the electrical work is done except the final. I insulated the ceiling already to a value of R-50 that was achieved by the roofers whom added roofing insulation. So I'm need too do my walls next.

The studs in this home are not the standard industry size upstairs they are 2 x 3 7/8 actual dimensions, and 2 x10 downstairs industry standard. Refrigerated air has also been installed with the metal ducts and returns in every room.

The home exterior is stucco. The original stucco, not including the fiber board is about 1 thick . There is 30# felt paper over a inch fiberboard that meets the wall studs.

Since the upstairs studs are not industry standard and much larger than normal would R-15 work providing I can find it ? Is R-15 still made ? Since this home has A/C I take it would need to remove the face of the kraft paper to provide better drying of the wall cavity. I was thinking of R-30 in the 2x10 for the downstairs. R-25 for the ceiling downstairs\ upstairs floor.

Another contractor has offered me some thick polyisocyanurate made by Celotex, foiled on both sides. I'm NOT going to remove the exterior of the home to install this. Could this be used between the studs? I know this stuff is a true barrier, but could this cause me some problems with A/C . I don't think I can use fiberglass over the polyisocyanurate board or can you? If I could use this how should it be installed ? In any case I would still like to increase the R-value to the upstairs walls if I can.

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Old 06-05-12, 03:20 AM
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Welcome to the forums! If you can find R15, you can use it in the cavities. The one thing you don't want to do is compress the insulation. You also need to leave the vapor barrier on the insulation and install it toward the warm side of the house. This will technically keep warm and cool from touching and causing condensation. I am not sure how the polyisocyanurate will work in your area, but generally it can be used as a thermal break on the outside wall, then insulation added. You will need to seal the edges of the board in each cavity, which may prove to be a pita, since you have to cut it and seal each one. Others will chime in with good information from your area, so hang in there.
Old 06-05-12, 05:18 PM
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I did a test today with the Poly ISO. seems like very good stuff foiled on both sides also. I cut, taped and foild the seems on the polyiso (pic) on 10 foot by 9.5 foot wall. I placed the poly iso right up against the Fiberboard. I cut the sheet fitting tight between the studs then taped any seems with heavy duty foil tape. I also taped the edges that were fitted tight against the edges of the studs. I then installed R-14 insulation in the studs keeping the kraft paper on . Took me about 1.5 hours to do this. The hottest part of the day is about 5pm in June.

Here is my test with the polyiso (pic) . I used my hvac equipment temp meters. I used to do hvac way back when.

So I chose my Testo 925 digital temp meter for this test. Temps are rounded up above .5

Outside Temp- 87 Deg,

Surface temp on stucco, 120 deg, direct sunlight

Surface temp front side on the fiber board inside wall cavity ( this would be the front of the PIC) 110 deg,

Surface temp back side of the PIC in wall cavity, 102, deg,

Temp mid way inside the R-14 ( The Middle of the fiber insulation ) 94 deg,

Surface temp on the kraft paper, 87 deg,

Room Temp from center of room; with out any sheet rock on the wall with the A/C on 76 deg,


Test with out the poly ISO (pic) in the wall cavity, and only R 14 installed. (AKA as a 2- way drying wall )

This room also faces direct sunlight on the same side of the house.

outside temp 87 deg,

Surface temp on stucco. 120 deg,

Surface temp on front on Fiber board inside wall cavity. 112 deg,

Temp on R14 middle of fiber insulation. 105, deg,

Surface temp on craft paper, 98 deg,

Room Temp- from middle of room with out any sheet rock on the wall. A\ C is on. 89 deg

The difference this make is significant. 13 degrees difference in temp, wow !

I'm going to take that contractor up on his offer for all the foiled (PiC) for free.
Old 06-06-12, 03:19 AM
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I noted you had "pic" several times and must be having a problem posting them. Here's a way:

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