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Seismic retrofit for a Terra Cotta structural block foundation?

Wundershun | Posted in Expert Exchange Q&A on

I’m doing a large remodel this next year on a 1906 farmhouse in the pacific NW. The basement foundation is terra cotta structural block. Anyone have any ideas on how to do a seismic upgrade with this type of foundation?

Thanks in advance! 

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Replies

  1. Expert Member
    KYLE WINSTON BENTLEY | | #1

    Wundershun,

    A few pictures would help, but in short of the 120 year history, you may be better off doing nothing.

    There are solutions that involve composites bonded directly to the structure, but they're expensive, and in reality somewhat untested.

    Can you give us just a little more detail about the height of the walls, soil and drainage conditions, floor plan, etc?

    1. Wunderbar | | #2

      Hey Kyle,

      Thanks for your reply. For being 120 years old, its in great shape but we (Pacific NW) are supposedly overdue for an earthquake so I figured while the house is being renovated I should reinforce it the best I can. I attached an overview picture of the house plans.

      The basement walls are 7' tall terra cotta block with a concrete slab, soil drainage is good and roof has large overhangs that keep the foundation dry. Sump pump hasn't kicked in once in the last several years.

      I was thinking id build out a 2x4 wall against the block foundation up to the floor joists, closed cell spray foam to insulate and adhere wall to the block. Then interior sheath that wall up into the floor joists with blocking

      1. Expert Member
        MALCOLM TAYLOR | | #3

        Wunderbar,

        Unfortunately this isn't something you can design yourself. You need to consult a structural engineer.

        1. Expert Member
          KYLE WINSTON BENTLEY | | #4

          In some ways, this is akin to retrofitting a permanent wood foundation, right? The exception is that the tile essentially provides some protections to the insulation and structural support to the floor. In some other ways, it's the worlds oddest SIP, with a tile and wood frame skin?

          1. Expert Member
            MALCOLM TAYLOR | | #5

            Kyle,

            Yes, but the wildcard is the seismic part - and there, the devil is in the details. How the new wood foundation shear-walls are anchored to the footings below and framing above needs to be engineered. Then there is the problem of the load-paths which are now taken up by the existing foundation, and what effect the mass of that foundation will have on the new walls when it breaks apart in a seismic event.

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