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Foam sheathing

My whole house has been sheathed with OSB. My builder will be applying housewrap to this next week. I will have "innie" type windows installed as well. He will also be covering the housewrap and OSB with a layer of foam board. Since the housewrap is under the foam, is it necessary that he tape all foamboard seams? I would assume since the housewrap is under the foam, this would not be necessary?

Asked by Aron Robinson
Posted Sat, 01/26/2013 - 07:49
Edited Mon, 01/28/2013 - 08:28

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4 Answers

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Another question I have associated with this same process.....my garage is attached to the house. Should the outside perimeter of the garage walls be sheathed as well? If not, what is done concerning the inside wall of the garage that separates the inside of the house from the garage itself? I only have a large portion and smaller portion of wall that separate the garage from the inside of the house.

Answered by Aron Robinson
Posted Sat, 01/26/2013 - 08:08

2.
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Aaron,
Answers to many of your questions can be found here: How to Install Rigid Foam Sheathing.

First, I hope that your rigid foam will be thick enough to keep your OSB above the dew point in winter. For more information on this issue, see Calculating the Minimum Thickness of Rigid Foam Sheathing.

Second, the housewrap can be installed under the rigid foam or over the rigid foam -- it's your choice. For more information on this issue, see Where Does the Housewrap Go?

Third, you can't flash your windows properly unless you know where your WRB is. You can use the rigid foam as your WRB, or you can use the housewrap as your WRB -- but you have to choose one or the other before you start flashing. For more information on this issue, see All About Water-Resistive Barriers and Using Rigid Foam As a Water-Resistive Barrier.

Q. Since the housewrap is under the foam, is it necessary that he tape all foamboard seams?

A. Taping the foam seams is not necessary, but it is highly recommended. The tape will reduce air leakage and improve the thermal performance of the wall.

Q. "Should the outside perimeter of the garage walls be sheathed as well?"

A. All walls need some type of sheathing (for example, OSB). You don't need to install rigid foam on your garage unless you plan to heat it.

Q. "If not, what is done concerning the inside wall of the garage that separates the inside of the house from the garage itself?"

A. This wall is part of your home's thermal barrier. It needs to be insulated and carefully air sealed. You should also check with your local building inspector or fire marshall to be sure that the wall meets local requirements for fire safety.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 01/28/2013 - 08:40

3.
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Thanks martin. I am in kentucky so half inch foam should be fine. The house is currently sheathed in osb. After reading your reference related to osb I hve some concerns. Would you recommend I go forward with applying the hlf inch foam sheathing outside the housewrap? Btw...my siding will be cement board. My wall is 2x6 and will have propink dense loose fill fiberglass. So my wall would be drywall, 2x6 filled w/propink, osb, housewrap,half inch foam board, cement siding. We have not added foam board yet. Would you recommend adding it or passing on using the foamboard? Aron

Answered by Aron Robinson
Posted Mon, 01/28/2013 - 12:30

4.
Helpful? 0

Aron,
Installing 1/2-inch foam is good.

One inch or 2 inches would be even better.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 01/28/2013 - 12:50

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