Replies

1. GBA Editor
   Martin Holladay | Nov 19, 2012 08:40am | #1

   Dale,
   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.

2. 
   lonewolf20 | Nov 19, 2012 09:12am | #2

   I live in zone 4. Thanks for your reply.

3. 
   davidmeiland | Nov 19, 2012 09:35am | #3

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

4. 
   lonewolf20 | Nov 19, 2012 12:02pm | #4

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

5. 
   user-1140531 | Nov 19, 2012 12:46pm | #5

   Dale,

   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.

6. GBA Editor
   Martin Holladay | Nov 19, 2012 01:01pm | #6

   Dale,
   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?

7. GBA Editor
   Martin Holladay | Nov 19, 2012 01:05pm | #7

   Ron,
   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.

8. 
   user-1140531 | Nov 19, 2012 04:01pm | #8

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