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SeattleDIY 11-27-2008 01:11 PM

Can I double vapor barrier??
I am getting to the step of insulating my office area. I have R11 with paper barrier. I want to make it as air tight as possible. Can I put plastic also over the insulation?? what are the ramifications if I did??

Thanks and happy thanks giving

glennjanie 11-27-2008 05:28 PM

Welcome SeattleDIY:
There should be no problem with the two vapor barriers going in the same place. I would rather have the plastic anyway. The problem would come when the vapor barriers are on opposite sides of the insulation because it would trap the vapor in the insulation making it of little or no effect.

TaskBoy 11-28-2008 01:54 AM

May I tag on here? It's kind of related...Is it ok to put Tyvek over existing 35 yr. old building paper or should the old paper be removed?

glennjanie 11-28-2008 11:06 AM

Hello TaskBoy:
Its still in the same layer just as Seattle's vapor barrier will be. There should be no problem.

travelover 11-28-2008 02:58 PM

Isn't Tyvek permeable to vapor but water proof? It is typically just under the siding , but away from the warm side of the insulation where the true vapor barrier resides. So doubling up here shouldn't be an issue.

Square Eye 11-30-2008 05:52 AM

Well, actually... You should never double a vapor barrier. When a wall does get wet, you could end up with moisture between the vapor barriers and it will mold before it dries. This has been an issue for homes with insulated foam board on the exterior and a vapor barrier inside. This is also the reason we don't use plastic on the exterior side of the walls. Just a few cuts in the paper from top to bottom will break the vapor barrier OR remove the paper completely.
If you want to use the paper and skip the plastic all together, tape the insulation at cuts and joints. Make sure the drywall will seal the paper to the studs and plates and caulk the bottom plate to the floor. Use tape around windows and gaskets on electrical cover plates. Make sure your weather strips on your exterior doors are sealing properly and caulk the brick moulding to the siding or use a flashing tape around windows and doors before siding.

SPISurfer 12-01-2008 08:54 AM

Hey Square:
I have a couple of caulking issues.

1. What type of caulk do you use between brick and siding? I read somewhere to use polyurethane. Is this correct?

2. We need to recaulk on the outside of the aluminum windows to brick- acrylic caulk?

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