Should I be worried about condensation in the wall?
DenmarkDave
| Posted in General Questions on
Hi GBA
in process of building a house in Denmark ME. The house has ZipR (1″ foam attached) sheathing and 1.5″ closed cell spray foam in the stud bays. Several large windows next to each other are framed by LVLs, and there is no room for additional interior insulation. This wall will have exterior cladding + 1/2″ of OSB Sheathing + 1″ of foam + 5.5″ of wood LVL and windows grouped in one section. Is there a potential for interior warm moist air getting to the back side of the sheathing and depositing condensation inside the wall?
thanks in advance for your comments
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Replies
Denmark Dave,
Your description of the wall assembly is unclear.
1. In the area of the wall that you are concerned about, do you have 1-inch Zip R sheathing or 1/2 inch OSB sheathing?
2. In the area of the wall that you are concerned about, does the wall assembly have 1 inch of closed-cell spray foam against the interior side of the sheathing, or 1.5 inch of closed-cell spray foam against the interior side of the sheathing?
3. Assuming that the wall that you are concerned about has 1/2-inch OSB sheathing and 1 inch of closed-cell spray foam on the interior side of the sheathing, is there any additional insulation between the studs?
Hi Martin,
some clarification
1. yes. there is 1" Zip R sheathing on the entire exterior wall including this area
2. no, the LVL takes up the entire space from the sheathing to the interior wall board. Along this wall there is window - LVL - another window. On the interior there will be wall board attached to the LVL.
3. yes there is additional insulation in the wall cavity away from this window area: spray foam + dense pack.
Denmark Dave,
No, you don't have to worry about condensation, as long as you pay attention to air sealing. This type of window wall needs careful air sealing on the interior side of the wall.
Hi Martin
thanks for the answer. for Internal air sealing, the current plan would be to tape and seal the wall board, and use vapor retarding paint. Should liquid wrb or other sealant be used around the window openings or on the LVL in addition to flashing membranes and sealing around the windows?
thanks
Dave
Denmark Dave,
Vapor retarder paint does not contribute to air sealing in any way. Its purpose is to reduce outward vapor diffusion, not to reduce air leaks.
In a wall with taped drywall, the air leakage paths include the crack between the bottom of the drywall and the subfloor (which usually connects to the crack under the bottom plate), at the crack between the top of the drywall and the top plate (which can allow air in the stud bays to reach the attic), around electrical outlets (an argument in favor of airtight electrical boxes), at penetrations like electrical and plumbing penetrations, and at window rough openings and door rough openings.
The best way to seal at window and door rough openings is to use a high quality tape on the interior side to bridge the crack between the window frame (or door frame) and the rough opening lumber.
For more information on air sealing at windows, see this article: Windows in Double-Stud Walls.