Insulation Exterior Retrofit
Livingkeith
| Posted in Energy Efficiency and Durability on
I’m in the planning stages of replacing all the windows (Acorn aluminum dual pane) and siding (vinyl). I’m in CZ 4 and my house was built with let in bracing and 1/2” Dow xps sheathing(not taped even around windows). I did however have wet blown cellulose insulation put in the walls when we built the home. My question is: I would like to add another 1” of xps to the exterior before the siding and since I currently have no wrb to speak of should I just off set the seems and tape the seams of the second layer of foam or Tyvec between layers. Any thoughts would be appreciated.
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Replies
Put your second layer of foam right over the first with the seams offset. You only really need to tape the outermost layer, so you don't have to do anything with the existing layer if it's intact. I would just check that there aren't any protrustions (nails proud of the original layer, for example) prior to putting up the new layer. I don't see any need for tyvek between the layers unless you want a slip surface, but I don't think you really need that here. If you want to use a WRB, it would normally go on the outermost surface before the siding goes up, which would be INSIDE the rainscreen if you're using a rainscreen (i.e. housewrap over the foam, then vertical furring strips, then finished siding materials).
If you had issues with the window flashing before, I'd double check that there are no hidden moisture problems under the original layer of foam in the immediate area of the window before putting up the second layer in those areas.
Note that if you have any wall-mounted electrical (outdoor receptacles or light fixtures) you'll want to put in mounting details for those prior to installing that outer layer of foam.
Bill
Thanks so much for the advice. I was hoping to avoid the furring strips and just go back with vinyl siding. My understanding is 1.5” of foam is kind of the sweet spot of that being possible. I have full basement and am trying to avoid being so proud of the edge of the foundation walls if possible. The idea of having a bit more to nail to is intriguing for sure. I was planning on using zip r3 where I have penetrations and maybe corners where some backing details are needed for the siding.
Also this is a photo taken from my uninsulated garage attic looking back towards the house. Any suggestions on what material I should use to air seal this wall.
I’m guessing there is a cathedral ceiling room on the other side.
Usually the bays get filled with fiberglass, covered by 2” polyiso rigid foam and can spray foam to air seal around the edges.
It’s actually where the garage gable hits the second floor wall. It appears that there was 1/2” xps there and the builder removed it. Possibly code reasons?? I was going to try to put xps on and try to foam around to air seal unfortunately it is tough access and part of the garage ceiling will have to be removed to gain access. Oh the 90’s and how little we new about building science. Here in St. Louis you still hear “a house needs to breathe”. Just last week I heard a lead framing carpenter talking about how ridiculous it was that a homeowner that had came in and caulked all the joints in the framing.