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Community and Q&A

Wall construction for 5,000 sq. ft. full masonry home in Chicago

aladd1n | Posted in Green Building Techniques on

Hello there,

I am a homebuilder and I am about to start framing next week on a 5000 SF home. I am looking to build the home as efficiently as possible while staying within my clients budget.

This is what I am planning so far:

Exterior Walls: 2×6 Exterior Walls with 1/2″ OSB exterior Sheathing and 2″ Ridgid Foam Exterior Sheathing

Question: How does the 2″ rigid foam work with a full masonry exterior? Would I hold my 2×6 walls 2″ in from the rim board to have the foam sitting on top of the floor and flush with the rim board?

Insulation: Blown-in Cellulose insulation in stud cavaties

Question: Should I consider 1″ of spray-foam for air sealing and then cellulose on top of it?

Foundation Insulation: 2″ rigid foam under basement slab floor, 2″ rigid foam on interior of 9′ basement walls.

This home has a 18′ deep wall under the basement for a basketball court. The wall is 16″ thick poured concrete.

Question: would 2″ rigid foam insulation on the exterior of the foundation be advisable here?

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  1. GBA Editor
    Martin Holladay | | #1

    You are in Climate Zone 5.

    Q. "Would I hold my 2x6 walls 2" in from the rim board to have the foam sitting on top of the floor and flush with the rim board?"

    A. No. The rigid foam should cover the rim joist area as well as the wall area, so the framing should be in the same plane.

    Q. "Should I consider 1" of spray-foam for air sealing and then cellulose on top of it?"

    A. My usual advice on foam insulation: You can put foam insulation outside the sheathing if you want, or inside the sheathing, but don't do both. If you want to put rigid foam outside the sheathing -- and I think that's a good idea -- don't install any spray foam between the studs. That way, your sheathing can dry to the interior if it needs to.

    Q. "I will install 2 inches of rigid foam on the interior of the 9' basement walls."

    A. That's less than the minimum insulation requirements of the 2012 IRC. The code calls for a minimum of R-15 in that location. Your local code may differ, but I recommend that you install at least R-15 -- in other words, 3 inches of XPS or polyiso, or 4 inches of EPS.

  2. wjrobinson | | #2

    Refer to your plans.

    Martin's advice is good so what now, cut and paste his post, take it to whomever stamped the plans, staple, stamp, resubmit to building department, have sets made for all subs and crew, sign change orders, get deposits on the change orders, get the homeowners approval, study the new techniques quick via some YouTube videos, order the new materials and get instant delivery,

    Building for the lowest cost is only done by starting with assembling a complete plan, right down to paint colors, and Flooring choices PRIOR to all on-site work.

    Deciding on how to frame a week before start is....

  3. aladd1n | | #3

    Thank you for your feedback.

    My question on the exterior foam insulation is that on a full masonry home, I have a 5" Brick Ledge after the rim joist. If I added 2" thick foam, the brick ledge would be reduced to 5" which is not enough for my air gap and masonry.

    All of the wall sections I have seen with exterior wall sheathing seem to be using hardiboard or other siding.

    Please let me know if there is a wall section that shows how exterior foam works with a brick or stone veneer. If it is not a good fit to use exterior foam along with masonry veneer, I will probably switch thinking to have foam insulation on the interior side of the walls.

    Thanks again for your help.

  4. GBA Editor
    Martin Holladay | | #4

    You need to design your house before beginning work on your foundation. Your foundation can have any size brick ledge you want, as long as you design the foundation to suit your needs. See the detail below for one way to do it.


  5. user-4310370 | | #5

    I did see these thermally smart brick ties made for use over rigid foam, these or something similar would be helpful. YMMV since I have not used them, I just took note from an earlier post.

  6. wjrobinson | | #6

    3 business days left to change plans, get approvals... demo existing foundation, build the new internet found one...

    this is exciting... stand by... can it be done.

  7. rocket190 | | #7

    Poor planning yes, but saying that building a thicker foundation wall is the solution doesn't seem like a good solution. If you have a 12" thick wall and 2x6 framing, by the time you add sheathing, a 3.5" thick brick, and an air gap, you only have room for 1-1/2" of foam which won't meet code in northern climates. Is the solution a 14" thick concrete wall. Sounds awfully expensive and wasteful to me.

    Myself, I wouldn't want my house to overhang the foundation wall like on a Larsen truss.

  8. user-659915 | | #8

    You can always increase the width of the brick ledge by bolting on a steel angle. Commonly done when adding a brick veneer as a retrofit.

  9. Expert Member

    I think you are including some elements that don't sit on the foundation in your equation. You have the brick, which is usually set so that it overhangs the foundation by 1/2". The airspace, sheathing and a 2"x4" sill plate. Brick veneer can be set on an 8" wall. Adding 2" of foam only brings it to 10".

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