Adding external rigid foam: What to do about existing brick cladding?
I have an existing house in a mixed-humid climate (Delaware). The house has 2×4 batt insulated walls with exterior 1 inch EPS.
I want to add about 4 inches of exterior rigid foam all around and re-side. I have read about REMOTE and PERSIST and the 1/3 rule.
I see no problems with the retrofit until I get to the entire north wall that is brick-clad (with the 1 inch foam and 2×4 wall behind). I’m not much interested in tearing down the brick. Is there a way I can add 4 inches of rigid foam (or other insulation) to the inside of the north walls and avoid problems with moisture or condensation due to temperature gradients?
The existing walls have no moisture problems and no specific, discrete membrane layer or WRB–just sheetrock, studs with fiberglass, foil-faced EPS, and siding (from inside to outside).
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Replies
Dan,
Adding 4 inches of rigid foam on the interior of your north wall will greatly reduce the wall's ability to dry to the interior. That raises the bar significantly on the integrity of your moisture-management details.
A wall that can dry in one or two directions is very forgiving. A wall with a limited ability to dry out can work -- but it isn't forgiving of moisture problems.
Whether your proposed retrofit works well for 100 years or is a disastrous mold factory depends on the integrity of your wall's WRB. Although you claim that your existing north wall has no WRB, it does: it's the foil facing on your exterior foam.
If that foil facing is well detailed, and if all of the seams between these foam panels are sealed with long-lasting tape or Z-flashing -- and if the foil facing is perfectly integrated with your window flashing, door flashing, and all of your wall penetrations -- and if you have good flashing at your weep holes, and if your weep holes are unobstructed by mulch and properly located above grade -- and if your mason understood the proper method of flashing a brick wall above bay windows and other bump-outs -- and if your mason did a good job keeping mortar out of the air space behind the brick veneer -- then your wall will work well.
If you have any questions concerning these details, your plan is risky.
Dan,
You might be better off with a more vapor-open insulation interior to the brick-clad wall, but as long as you avoid an interior vapor barrier (such as foil-faced foam or sprayed closed-cell foam), I don't think you'll have a problem since you have an exterior WRB/vapor barrier and (I assume) an air space behind the brick which will prevent solar-driven moisture diffusion.
Martin
How well will the wall perform insulation wise with the air gap behind the brick if you have 2-4 inches of rigid on the outside.
If a guy was in the panning stages with an older house without an interior vapor barrier how would you handle it.
MY thinking would be to blow cellulose or open cell foam into the cavities. Then find a way to will the air gap with open cell. Depending on the climate then put at least the minimum amount of rigid to keep the brick above the condensation point. This would also keep water off the brick and the heat too. There would not be vapor drive through the brick because bulk water and heat will be kept away.. The irregularity of the brick would proably provide enough of an air gap to allow the brick to pass any vapor to the outside. Anything on the back side of the brick and wall cavity could dry to the interior.
Robert,
It's certainly possible to attach rigid foam to the exterior of your brick veneer. If you do a meticulous job sealing the weep holes the sealing the top of the air gap between the brick and the wall sheathing, there should be no need to fill the entire air gap with insulation. Because mortar droppings are a common phenomenon, I imagine it would be very hard to fill the air gap with insulation.
You can add as much foam insulation to the exterior as you want, and then install conventional stucco or synthetic stucco (EIFS) over the foam. You might want to contact an EIFS rep with experience installing EIFS over brick veneer.
Needless to say, all of your windows and doors will need to be detailed very carefully.
Robert;
We would love to speak with you in greater detail about your project and some of the specific construction details to help ensure a successful application. We are one of Dryvit's (EIFS) oldest distributors in the US, and you are actually in our territory. Call us 800-445-1719. Look forward to hearing from you.
Correction: that was directed toward Dan. Sorry.