Air Barrier with Unsealed Top Plate
Hi there,
We’re doing a partial remodel on a 1910/1995 climate zone 4 marine home. We’ll be replacing siding and are currently contemplating to replace the crappy wrb with an air barrier/wrb product like WrapShield. We’ve got a straightforward path to sealing penetrations, the sill plate, the attic floor and most of the top plate.
However, some of the top plate is inaccessible (part of a vaulted scissor truss), and we aren’t likely to be able to seal it. How big of an issue is this likely to be? Is it large enough to make the external air barrier approach unworkable (and we should instead focus on internal air barrier)? Any thoughts on approaches to mitigate the unsealed top plate?
Thanks in advance!
Dave
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Wood is airtight so it can be part of your air and vapor control system; you just need to seal the other components to it using tapes, sealants or a combination.
However, our issue is that we don't have ready access to the top plate due to the scissor trusses so it likely goes unsealed unless we can find some clever solution to seal it.
So, the bigger question is does the lack of a seal on part of our top plate make the external air barrier unhelpful/unnecessary?
There are a lot of variables so it's hard to say how much impact not sealing those sections would have, but it's probably not enough to justify cutting out drywall. To find out, you could use a blower door to test the airtightness, and ideally while you're doing the work--it's easier to find gaps when air is rushing through them.