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I'm building a deck over a walkout basement. I want to put a concrete patio below. Can I dig the footers (3 total) to depth of 30" below the frost line and then do a monolithic pore of the concrete for footers and slab? I plan to use simpson post base over the footer location imbedded in the concrete. The other option is to use the concrete tubes and do the footers/concrete piers first and then poor the slab around, but trying to save time.

Thanks

  • Hello, and welcome to Home Improvement. Interesting question; let's see if you get a good answer. And, you should probably take our tour so you'll know how best to participate here. – Daniel Griscom Oct 9 '19 at 23:55
  • draw two pictures, plan and elevation (just draw by hand and take a picture). I am unclear on the walkout basement, is there a patio attached to the walkout door and a staircase the comes up to grade? How large is that patio? How high up would the deck over this space be, I picture more than 8' in elevation? The concrete slab would be the patio? and the footings are just for the 3 posts that will support the deck above? 3 because the walkout wall is serving as one of the supports? 30" below your new frost line which uses the surface of the patio? The slab will heave and pull footings. – Fresh Codemonger Oct 10 '19 at 2:06
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Since you’re not making your concrete patio as deep as the footers, your patio will be subject to frost heaving. This means that if you mechanically connect (e.g. build in a single pour) footers and patio, you’ll make your footers subject to frost heaving as well, even though they reach below the frost line.

I believe heaving of the patio might be mitigated if you pour it over a bed of crushed stone, like basement and garage slabs are done, but I don’t have experience with this.

Side note: you should use concrete tube forms regardless, as they will make your footers relatively smooth, making it much harder for anything subject to heaving to “catch” them and jack them up.

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  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how best to contribute here. – Daniel Griscom Oct 10 '19 at 2:52

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