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Here's what I would like to do. I want to install roofing felt, then 2" pink foam board and cover it all with house wrap. Then install vinyl siding. Can I do this?

Asked by dale nettleton
Posted Nov 19, 2012 8:33 AM ET


8 Answers

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The answer depends on your climate. If you live in a very cold climate, 2 inches of XPS may not be thick enough to keep your wall assembly above the dew point. More information here: Calculating the Minimum Thickness of Rigid Foam Sheathing.

Answered by Martin Holladay
Posted Nov 19, 2012 8:40 AM ET


I live in zone 4. Thanks for your reply.

Answered by dale nettleton
Posted Nov 19, 2012 9:12 AM ET


I don't see the benefit of the foam if it's covered with XPS (pink foam).

Answered by David Meiland
Posted Nov 19, 2012 9:35 AM ET


No currently it is osb. I want to cover the osb with roofing felt then add pink foam then go with a house wrap.

Answered by dale nettleton
Posted Nov 19, 2012 12:02 PM ET



I don't see the point of the house wrap or the roofing felt if you have a layer of XPS. Regarding the XPS, it should have its joints sealed against vapor passage. Neither the house wrap nor the felt will accomplish that function.

Answered by Ron Keagle
Posted Nov 19, 2012 12:46 PM ET


Two inches of foam will work in your climate.

There are several issues you need to resolve. One issue is: if you decide to install both asphalt felt and housewrap, which of these will be your WRB? You need to choose, because only one of these will be integrated with your window flashing and penetration flashing.

The second issue is: will you install vertical furring strips over the rigid foam, or will you try to fasten your vinyl siding through the foam with very long fasteners?

More information on these issues:

All About Water-Resistive Barriers

Where Does the Housewrap Go?

How to Install Rigid Foam Sheathing

Fastening Furring Strips to a Foam-Sheathed Wall

Can Vinyl Siding be Applied Over Furring Strips?

Answered by Martin Holladay
Posted Nov 19, 2012 1:01 PM ET


Don't forget that building codes require a WRB. Using rigid foam as a WRB is tricky; not all foams are approved for use as a WRB, and it's hard to get the flashing details right.

Answered by Martin Holladay
Posted Nov 19, 2012 1:05 PM ET


Thanks Martin. I see your point and had not considered that.

Answered by Ron Keagle
Posted Nov 19, 2012 4:01 PM ET

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