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Dealing with a 4″ drip ledge on 4″ of rigid foam on basement wall.

Thomas Becker | Posted in General Questions on

I have a double 2×4 construction on my main floor with an almost foot thick wall. On my basement I decided to put 4″ of foam on the exterior and then I’m going to build an additional frost wall on the inside. My question is that with my 4″ of foam it creates a ledge that will require flashing and will stick out further from the main floor of the house and my wife is concerned about the appearance of this, I’m looking for ideas of how to remedy this.

So far we’ve tossed around the idea of putting foam upstairs to so they’re the same size, but I’m opposed to this as my wall is already a foot thick and the extra insulation will not pay off and likely only trap moisture. One idea I had has to put a thin stone veneer on the bottom and since it sticks out further will look like it’s thicker stone, then I’ll put a 5″-6″ capstone on the top, then I just have to deal with how to flash this and make it look nice. Any other ideas?

Information that may be helpful, the basement will be coated with parging, the main floor we were planning on putting hardi-board siding.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Thomas,
    In terms of water management, the top of the rigid foam should be beveled (cut at an angle) and should be protected by durable metal flashing that extends upward (so that it can be lapped by your housewrap) and downward, where it should terminate in a drip edge.

    Beyond that, it's all aesthetics. If you coat the rigid foam with parging, do a good job; a thin coat of parging usually looks terrible after a year or two. The best jobs include metal lath (secured with Tapcons and washers) and stucco over the foam.

  2. Michael Chandler | | #2

    I think the cap stone idea could look great. we did something similar in this project http://www.chandlerdesignbuild.com/schultz.php?photo=3 the flashing extends up behind the siding and brick ties anchor the cap stone on top of the stone veneer.

    We recently started using cast concrete detailing to make things beyond counter tops (especially as my concrete supplier now sells counter top mix by the yard out the back of a cement truck) take a few classes and invest in or rent a really good concrete vibrator (not an adapted sawzall or some junk from harbor freight) and you can form up a house worth of cap stones, stair treads, counter tops and fireplace surrounds in a few days of form building, a day of pouring, and a day of stripping forms and dressing the slabs. Martins advice is good as well. over three inches of foam you are stuck with Tapcons and washers. under three inches you can probably get away with nylon drive anchors from McMaster-Carr.

    Fiberglass reinforced surface bonding cement actually can work pretty well so long as you cover it with a solid top coat of Type S stucco and I'm a contrarian on this but I always use elastomeric paint on stucco so I can touch up scratches, stains and cracks.

  3. Thomas Becker | | #3

    Thanks Martin and Michael! Very helpful. Is there a detail I'm missing about securing stucco and metal lath to the wall using Tapcons? I went to the Tapcon website and didn't see anything long enough. I know that you can make it fairly tight to the foam, but I've read it's not a good idea to go to tight otherwise you can crack the foam? Are there longer Tapcon's, or is there a detail I'm missing?

  4. GBA Editor
    Martin Holladay | | #4

    Thomas,
    Tapcon screws are available in lengths up to 6 inches:
    http://www.concretescrews.com/tapcon-prices/blue-standard-tapcon.aspx

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