Any wall building consultants out there??
green654
| Posted in General Questions on
Not sure if we are allowed to post this or not…. I’m trying to find someone who is a consultant who can step in and help us design a wall system to keep moisture out of the walls. We’ve already started framing and I realize we are late in the game. Desperate for help. Thx!
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Many. Describe your assembly here - and include your location/climate zone - and you'll get many answers here. And I'd recommend reading this: https://www.buildingscience.com/documents/insights/bsi-001-the-perfect-wall
Right now we have wood framing up. Advantech Zip Sheathing. Tyvec Drain wrap. We have not yet put on Hardie Board. And we haven’t planned out the attic insulation completely yet.
The builder wants to do spray foam flash and batt on interior walls. I’ve read mixed things about this method.
I want to add exterior foam insulation but according to my builder, it’s too late to add this. So I need another plan to keep walls dry. And that’s why I need a building science consultant. Please send any names!
Flash and batt isn't really needed in the walls. You can do a good job of air sealing the old fashioned way (caulk and canned foam), and then use either batts or something like dense pack cellulose. I wouldn't bother with the spray foam in a wall.
I'm not sure why your builder thinks it's too late to put up exterior rigid foam. You can put rigid foam over drain wrap, that's not a problem. The usual order is studs / structural sheathing / housewrap / rigid foam / furring for rainscreen / siding. If you only have the house wrap up, you should still be able to add rigid foam. My guess is your builder just doesn't want to deal with the little bit of additional complexity detailing trim with the exterior rigid foam.
Bill
Figure 9: "The Residential Wall"—The best residential wall we know how to construct. Not cheap. Works almost everywhere – except in extreme cold climates where we would not insulate within the wood structural frame.
I like this one as it doesn't require an interior vapor retarder membrane and all the associated sealing issues. Seems like the 2021 IBC/IRC always shows an interior vapor retarder required even when the climate zone is only 6. I'd like it especially if the interior insulation could be dense pack cellulose.
Make sure that the wall complies with the recommendations in Table 2 A or B here. Even better, take an hour and read the whole thing. It includes air barrier recommendations, rainscreen (drainage space), etc.
Flash and batt is a code compliant way to build a moisture safe wall while avoiding a problematic Class I on the interior (which low exterior perm Zip often necessitates - see Table 2A).
Cellulose provides some moisture benefits over batt insulation.
Figure 3. "Continuous Only (No interior VR)" looks like a winner. Leave all the control layers and insulation outside the structural wall. Almost $3/sf for insulating with mineral wool to get an R30+ wall, though.