0 Helpful?

Closed-cell spray foam and Roxul insulation

Good Day,

I am building a new house in zone 6A and would like to know the pros and cons of using 2" of closed-cell spray foam along with 3" of Roxul inside the wall cavity as well as 1.5" of EPS on the exterior with a building wrap on top (furring with steel siding on top of the EPS and housewrap).

This is the method my building inspector has recommended and I want to know what everyone thinks. Thanks in advance.

Asked by user-1145621
Posted Jun 18, 2012 1:13 PM ET
Edited Jun 19, 2012 3:21 AM ET

Tags:

4 Answers

Select your preferred way to display the comments and click "Save settings" to activate your changes.
1.

The closed cell foam can shrink over time leaving air gaps. Is there a reason you can't put thicker foam board on the exterior?

Answered by user-901114
Posted Jun 18, 2012 8:21 PM ET

2.

Wilf,
Assuming that you are planning to install OSB or plywood sheathing, I don't recommend that you sandwich your OSB between two layers of foam. If you want to include foam in your wall, you should choose to put that foam either on the exterior of the OSB (as you propose doing with 1.5 inch of EPS) or on the interior of the OSB (as you propose doing with the spray foam) -- but not both.

It's best if the OSB can dry in at least one direction.

Answered by user-756436
Posted Jun 19, 2012 3:19 AM ET

3.

My building inspector won't agree to having more foam board on the outside of the building and not having a vapour barrier on the inside. Originally I wanted to go with (from outside in) 1" ISO followed by 2"XPS and cellulose in the wall cavity without a vapour barrier on the warm side. I wanted the wall to breath to the inside. He wants me to put EPS on the outside with either a spray foam cavity or cellulose cavity. He has agreed with EPS and spray foam saying it would breath out through the EPS. Now I am really confused.

Answered by user-1145621
Posted Jun 20, 2012 6:55 AM ET

4.

Wilf,
Probably the easiest way to satisfy your building inspector is to install vapor-barrier paint or a smart vapor retarder (like MemBrain) on the interior of your wall.

Answered by user-756436
Posted Jun 20, 2012 7:15 AM ET

Other Questions in Energy efficiency and durability

How to insulate a cathedral ceiling from within the rafter bays

In Energy efficiency and durability | Asked by Terry Sharpe | Feb 24, 17

Follow up question re: basement subfloor (climate zone 7a)

In Energy efficiency and durability | Asked by N/A N/A | Feb 24, 17

Installing LP Smartside over foam and 24 inch centers

In Green building techniques | Asked by William Costello | Feb 17, 17

How to insulate a shipping container home?

In Energy efficiency and durability | Asked by N/A N/A | Feb 24, 17

How to get notifications from comments

In General questions | Asked by Gerald Pehl | Feb 19, 17
Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!