Plywood window boxes
Hello.
I am currently building my first passive house in Nova Scotia Canada.
(Trying at least)
The wall construction, is a larsen truss system (2×6 structure, 1/2″ OSB taped seams on exterior, 11-7/8″ TJIs, plywood sheathing, typar, wood siding).
For my window rough openings, I have created 1/2″ plywood 4-ply window boxes. I taped/sealed the interfacing joint with the OSB sheathing around the perimeter, and all exterior window box corner edges.
Now that I have installed the TJIs and sheathed the outside with plywood, I am questioning whether or not I should have taped the exterior front-face edges of the window boxes.
I have read (specifically through the 475 website that I should have done this, because plywood edges leak, and can have a significant impact on the air barrier performance).
Should this be of great concern? Is there something I should do now (before window installation) to minimize the potential impact? Maybe they just want me to use their tapes?
Please provide your comments.
I am open to any advice.
Thank you.
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Replies
Phil,
Your question is a little confusing. It sounds like you are using your OSB layer as the air barrier. Assuming that seams and cracks in the OSB sheathing were sealed -- ideally, this sealing was verified (or will be verified) with a blower door -- your air barrier should be OK. (Of course, you'll still need to seal the gap between the window frame and your window buck.)
When it comes to sealing the cracks at the exterior side of your window buck, the most important aspect of this work is water management. Presumably, the Typar is your WRB, so you want to make sure that the WRB is integrated with the water management details that you have used to flash your window buck.
Hi Martin,
Thank you for your reply. I will clarify my situation.
From inside to outside, my exterior walls assembly is as follows:
- Drywall (currently not installed)
- 2x6 stud wall 24" O.C.
- 1/2" OSB sheathing / AIR BARRIER (all seams taped with 3M 8067 on outer surface)
- 11-7/8" TJIs 24" O.C.
- Plywood sheathing
- TYPAR / WATER BARRIER
- Battens/Siding (currently not installed)
The interior of my window boxes are flush with the inside face of the 2x6 stud wall.
And the exterior of my window boxes are flush with the inside face of the plywood sheathing.
All window boxes are made from 1/2" 4-ply plywood.
I have taped all seams where the exterior face of the OSB interfaces with the exterior surface of the window boxes. And I have also taped all outer corner edges of the window boxes.
I also plan to tape from the inside of the window boxes to the outer layer of the Typar (WRB) before installing my windows.
My concern is on the exterior side of the window boxes, specifically the front-face plywood edges.
Should I have taped those edges to avoid air leakage?
Here is the link to the 475 blog that talks about preparing for high-performance windows.
https://foursevenfive.com/how-to-prepare-for-high-performance-windows/
The section entitled >> Get Faster and Better: Think Before You Start << shows a pictures of the taped plywood edges.
Although, they are referring to the interior side of the plywood window boxes, they are nonetheless expressing concern about plywood edges leaking.
What is your opinion?
Phil,
Your re-statement of the situation doesn't change my response. If I understand correctly, you have two layers of sheathing: an OSB layer (which is the air barrier) and a plywood layer (which is adjacent to the WRB).
The plywood layer is on the exterior side of your air barrier. However, that doesn't mean that airtightness doesn't matter. Many people install two air barriers. Taping can't hurt. But remember: at this layer (where the window boxes meet the plywood), water management and flashing details matter most. So you'll probably be using a peel-and-stick flashing at these seams -- depending, of course, on how you plan to flash your window rough openings.
Phil,
I can tell you from experience, window boxes, doors, etc. will leak around the edges. I glued and screwed 3/4" plywood boxes for my home and even with a continuous bead of glue, I could still feel some air. I used spray foam and Siga to seal from the outside and caulk on the inside.