Brick veneer wall assembly and basement insulation techniques?
I am currently in the process of having a home constructed in Western KY zone 4. The basement floor and walls have been completed.
Background:
-walk out basement
-poured walls
-capillary break was NOT installed between footing and wall structure
-minimal external insulation on poured walls (5/16″ foam board to protect waterproofing)
-vapor barrier was installed above gravel bed before floor was poured.
-no insulation below slab
?1. how will the lack of a cap. break affect my options for basement insulation (basement will be finished)?
?2. At this point, what are my options for an insulation system for the basement? I spent hours scouring through BSC documents and am more confused now than ever.
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Other issue: I am also at a loss on the proper procedure for insulating the above grade portion (main level).
Background:
-will have brick veneer
-4″ brick ledge has been installed in the concrete wall assembly above grade
-will be using traditional 2×4 framing
?3. Should my wall assembly in this climate zone be designed to dry both inward and outward?
?4. Am I in the “transition zone” – climatically speaking – where I should avoid using insulated sheathing between the brick and osb?
I have once again poured through numerous documents primarily by BSC and am at a loss on the best design in my scenario… exterior sheathing? Interior insulation only? Exterior + interior insulation type?
At this point, I am almost to the point of letting the main builder just make all of the decisions and probably result in a home that has been “typical” for the last 40 years.
Any thoughts or advice will be welcomed!
Regards,
JM
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Replies
Jeremy,
Before I answer your questions, I'm going to provide some advice to GBA readers: remember to nail down your insulation plan before construction begins, so you aren't scrambling the way Jeremy is.
Jeremy, don't worry. Everything is going to be OK.
Q. "How will the lack of a capillary break affect my options for basement insulation?"
A. Many homes lack a capillary break between the footing and the basement wall. While this approach isn't ideal, your home will be OK.
First of all, make sure that you have a capillary break between the top of your concrete wall and your mudsill. The usual product to use for this purpose is closed-cell sill seal.
Second, you will be insulating your basement walls on the interior, using either rigid foam or closed-cell spray foam. This insulation layer will limit vapor diffusion from the damp concrete to the interior of your home. As long as you adopt good insulation details, you'll be fine. Follow the advice in this article: How to Insulate a Basement Wall.
Q. "I am also at a loss on the proper procedure for insulating the above-grade portion."
A. In your climate, you have to think about inward solar vapor drive, especially because you are installing a so-called "reservoir cladding" (brick veneer). (For more information in inward solar vapor drive, see When Sunshine Drives Moisture Into Walls.)
That's why it would be a good idea to install a layer of foil-faced polyisocyanurate (rigid foam) insulation on the exterior side of your wall sheathing. (From the inside out: gypsum wall board, 2x4 studs filled with insulation, OSB or plywood sheathing, a layer of polyisocyanurate, an air gap, and brick veneer.) In Climate Zone 4, your climate is warm enough that you don't have to worry about wintertime condensation or moisture accumulation at the sheathing layer, so you can install any thickness of polyiso that you want. Of course, thicker insulation is better, because it insulates better.
You can install almost any type of insulation you want between your studs (although I would advise you to avoid closed-cell spray foam). Good choices would be dense-packed cellulose or mineral wool batts -- either of which would perform better than fiberglass batts.
Q. "Should my wall assembly in this climate zone be designed to dry both inward and outward?"
A. If you follow my advice, and install rigid insulation on the exterior side of your wall sheathing, your wall will be designed to dry inward.
Q. "Am I in the transition zone - climatically speaking - where I should avoid using insulated sheathing between the brick and OSB?"
A. No. Rigid foam insulation can be installed on the exterior side of wall sheathing in every climate on the planet. For more information on this topic, see Calculating the Minimum Thickness of Rigid Foam Sheathing.
Martin,
Thank you so much for the clarification!
Would the use of housewrap be advisable as below?
OUTSIDE > IN
-Brick
-Airgap
-foil faced .5" polyiso (reflective foil out and taped seams)
-??house wrap (Tyvek equiv.)
-OSB sheathing
-2x4 studwall
-mineral wool batts
-gypsum wall board
-latex paint
Thank you!
Jeremy,
Q. "Would the use of housewrap be advisable as below?"
A. Yes. I'm sorry that my description of the assembly forgot to include housewrap.
If you have at least 12-18" of above grade exterior exposure on the poured concrete foundation it has quite a bit of capacity to dry toward the exterior, limiting the risk to the foundation sill.
Surface grading & or surface drains at the drip line of the roof overhangs. can keep the soil nearest the foundation comparatively dry too, further enhancing the drying capacity of the foundation.
Roof overhangs of 12" per story of building height can also do wonders for limiting the direct rain-wetting of both the brick and the exposed foundation.
The polyiso is a bit on the thin side for your stackup. While the labeled R value beats the IRC prescriptive of R2.5 for 2x4 assemblies in climate zone by R0.5, it's actual wintertime performance (when wintertime moisture drives are at their worst) it will be substantially underperforming it's value. Having R15 in the 2x4 cavities rather than R13 also pushes it closer to the margin. The solution would be to bump the 1/2" polyiso to 3/4" (or even 1"), which would give the OSB sheathing plenty of dew-point margin.
Fattening out the polyiso to 1"/ R6 would also bring the wall's R value up to IRC 2012 code minimum levels (even with derating for temperature):
http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_11_sec002.htm
IRC 2012 code-min is R13+ 5c.i, which is slightly higher performance than your proposed R15 + 3 c.i. (even without derating), since that "extra" R2 in the wall cavities is cut down to only an extra R1.5 due to the thermal bridging of the framing. If you went with R15 + 6c.i., even derating the R6 to R5.5 for temperature, you'll be ahead of a code minimum thermal performance.
Give it another half-inch- it's worth it on both moisture resilience and thermal performance grounds.
Dana - Thank you for the extra insight on the R-value combination with c.i.. My only concern with increasing the thickness of the polyiso is the depth of my 4" brick ledge... any thicker and I will be running out of space for air gap (if this hasn't already happened). Also, I had planned on using windows with jambs designed for 2x4 walls... yet another result of improper prior planning.
If the dimensions can tolerate another 1/4", even going with 3/4" polyiso would be worth it for the extra margin, even if it meant narrowing the vent cavity behind the veneer to 1/2-3/4". As long as the mortar slop has air between it and the next layer, the capillary path is broken, which is the primary reason for the gap. Mortar extending all the way from the exterior that is in direct contact with a foil facer will likely corrode a hole through the facer at that point over time, but if it's just a pin-hole that's not a problem.
With a 1" gap it's pretty easy for the brick masons to keep up with it as they go- it's tougher at 1/2", but not impossible.
Thank you all for the replies. I have reached a small dilemma in my process:
It appears that the mason will be able to spare the 0.5" for the polyiso.... But that is all. However to add another 0.5" to my window jambs will cost another $1000. Total project cost for adding 0.5" polyiso and window jamb extensions = approx $2800. Is this worth the cost to add this small amount of c.i.?
Thanks again
(Yes - the lesson that I have learned thus far ---- proper prior planning prevents pitiful poor performance)
How many square feet of wall area are we talking here?
Approx 3500 total structure wall area.
1100 surface area would be unconditioned attached garage