Bug-proof foam coat?
My energy retrofit is in progress, and because of the peculiar way
the sill meets the foundation on the gable walls of the house, there’s
an inch-plus gap between the block wall and the metal flashing the
builders attached to the sheathing to serve as the bottom base for the
rigid foam on the exterior. We’re wondering how to fill this gap. I
looked at it and thought that a quick fillet of closed-cell sprayfoam
would be perfect, assuming it would stick permanently to both
the vertical concrete and up to the aluminum extending horizontally
out from it; the problem is that bugs will still tunnel through any
exposed foam. This is all *below* the bug-screen that’s being
wrapped under the lower edges of the polyiso on the walls, so
it can’t be incorporated into what’s already being done.
So the question: is there some sort of spray-on *coating* one could
apply to cured spray-foam to bug-proof it sufficiently for exterior
use? That would make for a really easy solution to this remaining
gap in my envelope. Some sort of fiberglass or other hard-setting
resin??
_H*
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Hobbit,
How about a piece of pressure-treated lumber ripped on the table saw -- a long 1x1?
Possibly. How would it best be attached, Tapcons into the block wall or
something? Above the metal is just foam edges so that's not very substantial.
I'd also like to make sure this whole mess gets a good air-seal, so it needs
something more than just a wood [or azek or whatever] blockoff
across the gap. We've decided that drying the sill toward the outside is
hopeless [see my earlier Q&A post] so it's going to dry upward into the
rest of the original assembly and toward the inside where I have better
humidity control anyways.
_H*
Can you get any plastic, like UHMWPE in there? Treated wood is not necessarily a deterrent to bugs. I just happened to read this from U Mass, Amherst: "While pressure treated wood can kill termites, it will not kill ants." I picked up several treated timbers at the dump a few years ago and they were riddled w/ ant channels. Maybe newer or different treated wood is unbearable to the little suckers; best to ask a bug pro about that.
Well, the solution is turning out to be a simple L-bend
of metal, pop-riveted up into the horizontal flashing
under the foam edge and with a nice thick bead of
Dynaflex 230 caulk into the gap and against the block.
We mocked it up on a section and it looks like it'll
work fine, just with slightly more work-factor to
get it done. Fortunately it's only two sides of the
house instead of all four.
_H*