Modifying Brick ledge for 2″ of foam.
pt1
| Posted in General Questions on
We are building a house with 2×6 walls with 2″ of rigid foam over OSB. The house will be all brick. There is only enough room between the brick ledge and the wall for 1″ OF foam. What are my options? Simply make the bridge ledge wider,, move the 2×6 walls in an inch. Increase the thickness of the basement wall from 10″ to 12″ . I am concerned that I will not have enough space to accommodate the floor joist. Thanks, Phil
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Replies
Philip,
Are you talking about a concrete brick ledge (part of your foundation wall) or a ledge made of steel angle?
I am talking about a concrete brick ledge that is part of the foundation wall. Thanks.
Phil,
What stage are you at? Has the foundation been poured yet?
No, but they will break ground this week, maybe as soon as tomorrow. My builder has been discouraging me from doing the 2" foam. I live in rural east central Illinoi (intersection of 57 and 70), and I have received resistance to my plans. I original wanted to do 2X6 waLLS 24 O.C., and the framer declined the job, when we were less than a week out.. I have now agreed to 2X6 16 0.c. with blown fiberglass or cellulose in the cavity. They wanted only 3/4 " foam on the outside, but I am pushing 2" to make sure there is no condensation on the interior wall. The average winter temp is 29 degrees.
I plan to spray the attic floor with closed cell foam, then blow in 18" to 24" of insulation on top of it. The attic will be ventilated. I also plan to to insulate the band sill with spray foam. The basement walls will be insulated with 2" of foam on the ouside, and I will have 1" of foam under the basement floor. The house will 3400 square feet and will utilize geothermal. The HVAC people are pushing a 7 ton unit, which I think is oversized, especially considering my effort to insulate. I am now working with my 4th HVAC guy. I have been insisting on Manual J heatload and rigid metal unlined ductwork, and no ductwork in the attic.
Who would have thought that this part of the process would be so frustrating.
Phil,
Who's designing your home?
I's not sure how wide your brick ledge is; there are several ways to detail a brick ledge, mudsill, joists, and the 2x6 bottom plate.
Suffice it to say that if you want 2 inches of foam, and an airspace, and then brick veneer, it's possible. You just need to design your foundation and ledge details to accommodate all of the elements. If you're not sure how to do it, you should probably consult with a designer or an experienced builder.
Then hire a foundation sub who follows the plans.
Plans should detail specs desired. Then hire subs that build to plans. Then with building permit posted, break ground.
Stick to your desired plans and get new subs.
In your climate, one inch of exterior foam should be sufficient to minimize condensation potential. But you would improve your thermal envelope and save forest resources (and costs) by using 24" oc framing. There is no good argument for 16" oc framing. You should find another framer.
If I could get by with 1" that would be great, then I would not have to modify the brick ledge. I originally wanted to use 1" of tongue and groove PIR, but others have been urging me to use 2" to reduce any chance of condensation, and I was told that 2 " exterior rigid foam was standard building practice for a cold climate.
Thanks,
Anything is possible: check out this passive all brick house: http://www.cropthornehouse.co.uk/
Philip,
If you haven't poured the foundation yet, what's the problem? Two inches of rigid foam is clearly much better than one inch. You're only doing this once -- so for goodness sake do it right.
What about Brick Straps?
Is "OK" to fasten brick straps "thru" 2 inches of foam?
I'm with Martin. Modify the brick ledge depth...it's just form work at this point. Maybe a little more concrete depending on all the details.
I would definitely insist on a manual J, or get one from a 3rd party to verify. 7 tons sounds like a lot for your tight details and is suspiciously close to the old rules-of-thumb.
I spoke with the concrete contractor about modifying the brick ledge. He think I will need to go from from a 10" wall to a 12". I have to be careful about moving the 2X6 wall towards the interior because I may not have enough space for the floor joists. If I use the Bibb insulation system I can get a r-23 interior cavity , and with 1" Pir board (R-6.5), I get a Dew Point of 38.4 using Joseph
Lstiburek formula Interface temp. = Indoor temp. – [(Indoor temp. – Outdoor temp.) X (Cavity R / Total R)], so it seems like I must go to 2" of foam board to get above the 40 degree dew point.
Still haven't figured out the quote thingy here...
could you split the difference and corbel the brick some for the first 4 or 5 rows or so? I've also seen a detail with a kind of ledge formed into the wall on a deep foundation. how deep does yours go? did you sub give you an upcharge for the added concrete? there's got to be a creative way to ultimately accomplish your goals!
I would explore going with an 8" or 10" wall and using a galvanized angle studded to it, or with nelson stud embedments.
Regarding brick straps:
In commercial construction, 2" foam may be common behind brick veneer, but the inner walls are commonly concrete block. Masons embed brick straps in the concrete block (either one piece or two piece design). Insulators then use 16" x 96" foam boards - squeezing them between the straps sticking out of the block.
For steel or wood construction the options are more limited. Here is a product that fits the bill:
http://www.heckmannbuildingprods.com/indexprd.htm#positie
Their longest brick tie will work with up to 3 1/2" - 4" of foam. Of course, these things aren't cheap like the typical corrugated brick ties used in residential construction (you're going from pennies each to dollars each).
The Positie product would pose the same problem as the "structural screws" used for applying furring strips through several inches of foam - namely, the requirement of hitting the stud.