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Separating house from rubble (fieldstone) wall: can I use Azek?

Rich Cowen | Posted in Energy Efficiency and Durability on

The house I bought last year has a fieldstone wall and I am undertaking another round of repairs this fall. I have read that it is possible to jack up the sill of the house all around in order to put a capillary break between the fieldstone wall and the wood framing members of the house. See:

http://www.buildingscience.com/documents/insights/bsi-041-rubble-foundations

This seems like a good idea in our case; the building science document describes putting a form of plastic as a membrane to protect the framing of the house from the stone below.

It would be even better for us if we can use a thicker product so that the house would be permanently lifted by 1/2 inch to 1 inch when we are done. This would make it easier to fit floor joists under the first floor, right now there is only a 6 3/4 inch gap between the basement roof and the foundation, not quite enough to fit 2″ x 8″ (or 4″ by 8″) lumber.

Has anyone used asek for this?
Or high density xps?
Other products?

Any advice on this would be appreciated.

-rich

p.s. I read elsewhere that the compressive strength of wood is above 2000 psi while the compressive strength of Azek is 1000psi. Of course, wood with lots of insect holes is probably a lot weaker than Azek and that is what we are dealing with in a few places.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Rich,
    I would be inclined to use a robust rubber or butyl membrane as a capillary break, as the BSC website advises -- something like EPDM roofing or butyl. If you want to shim up your house, it's easy enough to add a new 1x8 or 2x8 pressure-treated sill on top of the rubber membrane.

  2. Jill Neubauer Architects | | #2

    Hi
    I was just at a Building Science seminar last week and Joe described jacking up his antique house one inch to slide a piece of ice and water membrane in b/w the top of the rubble wall and the sill around the perimeter of the house. He did this may years ago and has had no issues. His only mistake he said was not turning up the outside edge of the membrane onto the sheathing and then counterflashing with the building wrap.

  3. Bob Coleman | | #3

    "His only mistake he said was not turning up the outside edge of the membrane onto the sheathing and then counterflashing with the building wrap."

    could you explain further?

    does the ice and water shield membrane wrapped around the wood sill?
    i guess this would help shed water if the outside lip turned up over the sill and you could put building wrap and flashing over it.

  4. Bob Coleman | | #4

    i would use the tired an true pressure treated wood in this case. no need to be the experimental lamb on this, and Azek is not cheap especially in a size to cover a foundation wall width.

    you would still want and ice and water shield like membrane that can wrap and adhere.
    in my plans to do this i have the water shield wrap the wood sill, and a sill membrane underneath to help fill in some of the gaps as the fieldstone is not perfectly smooth (you could try to patch and smooth it out but the 1inch gap doesn't leave much to go with. i also plan on using a metal termite shield and lots of appropriate caulk as air penetration and water penetration is important too.

    the epdm gaskets look ideal too

    a better idea for experimenting if you want to be risky and green would be installing something more thermally broken like a high psi 1" foam plank or similar.

  5. Rich Cowen | | #5

    Thanks to all... Ice and water shield sounds good.

    Bob, what climate zone are you in? I am wondering how much I have to worry about termites here just south of Nashua nh. The bigger issue for us is mice and files -- they love the gaps under the sill, and also under the vinyl siding.

    Termites can be controlled by a pest control service.

    Carpenter ants are perhaps the biggest concern because the chemical that stops the termites only is effective against ants for a year or so. So does your metal barrier do anything to stop ants? And would termites be more likely to enter a house by burrowing under the foundation, where it is dark? Or do you have foam on the outside of the building which could provide termites a place to make a dark tunnel?

  6. Bob Coleman | | #6

    i'm in roughly the same zone as you iLL

    building codes may dictate if you have to worry about termites
    the metal strip also provides a drip edge, and possible decoration; there are a number of products like this and also building codes vary on what they will allow

    i'm no expert but generally the edge discourages the termites/ants from 'crawling' around it. foam is not a food source but can provide shelter to either pests, although why they would hang out there when no food is around is a good question. foam products are made that have borates in them that will make both pests unhappy.

    and part of the point of green building would be to eliminate pest services if possible....

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