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Community and Q&A

Porch off a floating slab

joe_eugene | Posted in General Questions on


My house is built on an insulated floating slab in southwest Wisconsin. I’m planning to build a roofed porch off the west side of the house, and am wondering the best approach. The porch will be a gable roof coming off the gable side of the house. It will span about 30 feet across the house, and go 15 feet out from the house. My plan for the porch is to set posts on concrete piers, like a pole building.

A friend suggested burying the posts 4 feet, not connecting the porch to the house, then floating the flashing from the house over the roof. For various reasons, I don’t like this option.

Another option I’m considering is not burying the piers beyond the frost line. I’m thinking of 12-inch diameter piers, putting them in the ground 2 feet deep on a 2-foot footer.

Does anyone have experience or advice on this? Would 2 feet be the right depth, or should I go a little deeper?


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  1. user-2310254 | | #1


    I'll give your post a bump.

  2. this_page_left_blank | | #2

    I'm not an expert, but it seems to me that your options for footings are floating, insulated, or below frost depth. Having footings partially buried in the frost zone is exactly the worst condition for frost heave.

    I would build the porch so that it matches the house foundation; same insulation and floor. NOT connected to the house. The roof I could see attaching to the house; the base shouldn't be moving much laterally, and it should be moving up and down with the house. I could also imagine attaching the porch roof to the house via flexible interface, like solid rubber which would absorb any unexpected movement. The flashing would be fixed to the house, and not to the porch roof.

  3. walta100 | | #3

    I was frankly shocked by the foundation that went under my porch. It is massive it is the full depth of the basement and filled with trucks loads of clean rock. If you want the porch roof to flow out of the main roof they will need to be well connected below ground. If you are unwilling or unable to make the porch firmly part of the house I say do not connect it to the house at all.


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