Insulation retrofit of brick veneer homes
My house was built in 1984 and has a classic southern Ontario style from the 80’s – brick veneer, 2×6 framed walls, OSB sheathing, and felt paper for the WRB with fiberglass on the inside and poly vapor barrier. As part of a basement finishing project, we upgraded the foundation walls to about R-20 and the rim joist to R-40 (Closed cell spray foam + rockwool).
I would now like to start planning retrofits for the rest of the house.
What are my options to try to get to R-40 walls while avoiding moisture problems? I would ideally like to do exterior foam but the brick is in good shape and I imagine it would be expensive to remove it. Does anyone have experience with that and insight on cost?
Adding foam to the outside of the brick seems like it might not work because of convection in the ventilation gap between the brick and the OSB (about 1″ but with quite a bit of mortar squeeze out). The mortar droppings and squeeze out could also exacerbate vapor drive so filling the cavities with closed-cell spray foam seems like it could be risky by preventing the OSB from drying to the interior and you would still have thermal bridging at the studs.
I live in Ottawa, Canada so the climate ranges from hot and humid in the summer to downright frigid at times in the winter.
Grateful for any ideas the community might have.
-Patrick
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Replies
Is the goal R40 center cavity, or R40 "whole assembly", factoring in all of the thermal bridging and R-values of structural and cladding layers?
>"I would ideally like to do exterior foam but the brick is in good shape and I imagine it would be expensive to remove it."
The demolition cost of brick veneer for siding is "within the statistical noise" of the costs relative to installing continuous exterior insulation and NEW siding.
>"Adding foam to the outside of the brick seems like it might not work because of convection in the ventilation gap between the brick and the OSB (about 1″ but with quite a bit of mortar squeeze out)."
Filling the gap with injection foam or slow-rise polyurethane (open cell or closed cell) works. It's not sufficient on it's own to provide dew point control at the OSB layer without interior side vapor retarders, but if adding sufficient insulation on the exterior side of the brick it's fine. For a 2x6 wall the IRC calls out R11.25 minimum on the exterior of the sheathing for dew point control.
An inch of slow rise closed cell polyurethane in the cavity would be about R6, and with R23 rock wool in the cavities it would take another R10 or so exterior to the brick to hit R40 center cavity.
But replacing the 1" gap + brick layer with ~4" -4.5" of rigid polyiso would deliver R20+ on the exterior for R40+ at center cavity, without substantially increasing the wall thickness, and probably for less money than a slow rise foam pour + R10 exterior to the brick.
Thanks for the quick reply Dana. Not sure about whether to target the whole wall or center of cavity. I got the R-40 from Building Science Corporation's 5-10-20-40-60 rule. Seems like that is typically a center of cavity target. But the idea of filling the gap left by the brick and cavity seems like a good one. This would make the foam flush with the concrete brick ledge on the foundation, which seems like a tidy way of finishing things off. I imagine also that attaching foam to studs and sheathing would be easier than to brick.
>" I got the R-40 from Building Science Corporation's 5-10-20-40-60 rule."
The BSC is referencing only "whole-assembly R", not center-cavity. At 16" o.c. a 2x6/R20 wall comes in at about R15. The interior and exterior cladding adds another R1-R2, so for R40 whole-wall you'd be looking at adding R23-R25 of continuous insulation, something like 4" of foil faced polyiso.
Pattrick,
The R40 target is good for a new build where you can get there for "reasonable" cost. In a retrofit situation, going much above R25 even in the colder Ottawa area makes little financial sense.
If you don't like your brick, the best way to increase the insulation R value with EIFS over 1.5" to 2" of foam. That would get you up to an R25 assembly with the existing batts or R27 with mineral wool. Trying to do something about the air gap behind the brick is pointless. The best is to seal up the vents on the top and bottom and take the extra R1 insulation value the air gap gives. The cost of getting foam in there would probably take many many decades in energy savings to recover.
If you don't want to touch the outside, the simplest is a layer of rigid insulation under your drywall. Getting 1.5" of polyiso under the drywall and with mineral wool batts would get you up to R30. Hanging drywall over 1.5" of insulation is not too hard, you just need longer screws and mount the electrical boxes further forward (some you can mount directly over the stud to offset them) .
I second Akos on the financial implications. I live across the river in Gatineau in a similar brick veneer home built in 1989. I had the same kind of thought process last year. After going through different scenarios, I couldn't find one which made sense for the façades that have brick cladding. I heat with natural gas and the cost per ton of CO2 saved was in the 4 digits if I remember correctly. The cost was before counting the footprint of the material that would be sent to the landfill and the footprint of new material.
I'm thinking of taking a route similar to the one Akos proposes for a significant portion of the home.
It would be great to know what you decide to do. I hope you will keep us informed.
I'll piggyback on the thread and a question:
If insulation is added on the exterior walls and the inner walls are kept intact with the interior poly, how low can the permeance of the added insulation be without creating significant risk for the wall assembly?
Your thoughts are much appreciated.
Edit: I reduced the number of questions to one hoping it would be more likely to be answered.
Chess