OSB Radiant sheathing & Tyvek housewrap exterior walls

I am looking at building a new house. I am going 2 x 6 exterior walls & blown cellous insulation. I am going to put the OSB radiant sheathing on the roof. My question is should I also put it on the exterior walls with the radiant side on the outside. I am also going to have the house wrapped with Tyvek. The house is going to be brick. I live in Dallas, TX where it gets hot.
Am I wasting my money on doing both and am I going to cause any moisture & vapor problems?

Asked by Anonymous
Posted Tue, 11/24/2009 - 01:03

Tags: GBA Pro help

1.

Debra,
The aluminum-foil side of radiant barrier sheathing must be facing an air space for there to be any benefit. If the foil faces out, and the house is wrapped with Tyvek, you would indeed be wasting your money on the radiant barrier sheathing.

OSB is a poor choice of sheathing behind brick because it does little to prevent inward solar vapor drive. I strongly urge you to consider using foam sheathing behind your brick veneer.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 11/24/2009 - 05:36

2.

I was going to wrap the house and than put the osb radiant sheathing over the wrap.

Answered by Debra Markwardt
Posted Tue, 11/24/2009 - 08:07

3.

Debra,
If you install Tyvek under your OSB, it can't act as a water-resistant membrane (WRB).
If you really want to use radiant barrier OSB, you'll have to figure out a way to detail the OSB as the WRB. That means taping all the seams carefully, and coming up with a plan on how you expect to flash your windows to the OSB. Really, the only way to do it is to depend on the long-term integrity of the glue in your flexible flashings or tape. If the adhesive ever fails, so does your WRB.

That's why most people prefer to depend on physics (lapped membranes like Tyvek or asphalt felt) for keeping their WRB watertight.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 11/24/2009 - 10:17