Gap in exterior ridged foam – looking for advise
Josh_Man
| Posted in General Questions on
Hey Everyone –
This is my first post on GBA so I am excited for the feedback!
I have been reading green building advisor for some time and I appreciate all of the thorough and complete answers to people’s questions, it’s really awesome to see how much knowledge the community is willing to share with others!
I have a quick question for the group if you don’t mind.
I have ridged 2 inch foam wrapped around my slab on grade foundation and I have treated plywood that runs down about 6 inches onto the ridged foam board so my siding runs flush all the way down to the grade. The foam doesn’t stick out proud.
However, I had a mini blowout when pouring the concrete and now I have a decent size gap between the ridged foam board and the sheathing. I have (attache) a picture.
I am wanting to create a tight air seal on the house, and this obviously looks to be an area of concern.
What would you suggest I fill that open gap with? Should I try to simply jam more ridged foam in there? If so, how do I attach it to the other foam so it doesn’t just fall out. It’s also not all the same width so it not as easy as that. so there will def be gaps.
What about spray foam? will that work in an exterior application that has heavy weathering here in MN?
Your thoughts is VERY much appreciated!!
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Replies
User...299,
What are you planning to do to cover the exterior foam, and how did you plan to air-seal the bottom of the walls where everything was aligned?
Malcom - thanks for the reply, much appreciated.
The foam will be covered by the grade, we haven't set the final grade as I want to get all the flashing work done before we bring dirt in to back it in.
For the air seal, I am planning on using a peel-and-stick 40 mil through-wall membrane as an both an air and vapor barrier on that vulnerable part of the wall like a perm-a-barrier, textroflash, CCW 705, or similar type product that will run down 2 or so inches onto to the foam board and 10 inches up the plywood. Additionally I used a sill gasket on the majority of the bottom plates.
Additionally, I have (attached) the finish details.
Easiest is to just replace the damaged strip on top. For the corner, I’d build a form with plywood parallel to the sheet TIGHLY Lined on the inside with a scrap piece of housewrap (staple it to the plywood on the inside). Get one of the little 12 board foot two part spray foam kits and fill the void between the damaged foam and the plywood form. That form needs to be solid like you were going to pour concrete into it since you don’t want it to bulge out as the foam expands.
When you’re done, remove the plywood form. The housewrap will let it release from the foam. You’ll be left with cast-in-place two part spray foam in the shape of the original sheet of rigid foam, just with some housewrap glued to it. Don’t try to remove the housewrap or you’ll damage the foam repair.
Once you have it repaired, think about your detailing plans as Malcolm mentioned.
Bill
Bill -
Really appreciate the advice, thank you!
Good news is where you see the bottom strip of treated plywood missing below the OSB, that's simply because I was unsure what to do in the area with the gap. I figured if I had to put more ridged foam in there it would be impossible to access, because I would have to go from underneath.
So on the bright so, it sounds like I can put my treated plywood skirt in the area where it is missing, which would create the "box" you are referring to, but in my case it will be permanent, so I can skip the house wrap.
That being said, is there any type of kits you would recommend or brand, and is this closed cell, open cell something different?
Thanks!
Josh
I’ve used the Dow kits before and have had good luck with them. For the relatively small repair you need to make, I’d look at their small 12 board foot kit. These really small kits work best if you keep them in a bucket of warm water while you’re spraying the foam.
Bill