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I am having an addition built on my home with ~600 square foot basement underneath. Because one of the basement foundation walls is very near (~1 foot) from the original home foundation, the concrete contractor is planning to leave the basement form on that outer wall (and cutting the top of the form off). I believe this is because it is too difficult to get into that small space to disconnect all of the links that hold the forms together. The original home's foundation is a slab and the forms are wood.

Is this acceptable/standard practice? What other possible solutions are there?

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  • How did they get it installed prior to the concrete being poured? It seems that if there was room to access before, it should still be accessible now.
    – jwh20
    Sep 30, 2020 at 16:41
  • @jwh20 They probably built it one row at a time, like a brick wall. They can't reverse the process because the concrete wall is in the way now.
    – Harper - Reinstate Ukraine
    Sep 30, 2020 at 17:06
  • It will be more difficult to check the quality of the pour / of the set concrete if you leave them on.That is of course a benefit for whomever is doing the pour. Not as much for you.
    – Stian Yttervik
    Oct 2, 2020 at 11:44
  • @jwh20 they probably set up the outside form basically right against the excavation, then set up the inside form, without figuring how they'd get the outside one off.
    – Huesmann
    Oct 5, 2020 at 16:20

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Sounds like a hack-job approach to me.

That wall could be built from concrete blocks (aka CMUs or concrete masonry units), with bond-block rows and reinforcing steel, and grouted full, making it effectively solid, without abandoning forms in place - or rather, the forms would be the block wall.

Of course, poured concrete contractors and masons are not usually the same people, so this would not be a solution a concrete contractor would be liable to think of.

Alternatively, a form never intended to be removed and not made of wood that will rot - the insulated concrete form or ICF. Two sheets of styrofoam tied together.

But your pictures imply that this is a done deal.

If termites are a problem in your area, they may find that form tasty.

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  • Whoever you call will give you their version of the fix. Their version may not be anywhere near the right fix. If you call a plumber for an electrical issue.... you may have a leak.
    – DMoore
    Sep 30, 2020 at 16:08
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    I upvoted this answer because you alerted the OP to a termite problem. If they leave wood in the ground, they’ll have a problem.
    – Lee Sam
    Sep 30, 2020 at 16:36
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    Yes, they would have been much better off using ICF for that section.
    – Harper - Reinstate Ukraine
    Sep 30, 2020 at 17:07
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    A termite problem would be short-term and certainly manageable. It's not a good reason to make a mountain out of this molehill.
    – isherwood
    Oct 1, 2020 at 12:47
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    @isherwood I can't tell if your comment is upvoted because it's good information or because of the pun. Thanks, Stack Exchange.
    – user253751
    Oct 2, 2020 at 10:15
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Check with a termite control company and/or the state agency that studies termite control. Also check with your homeowner's insurance company. Having all that buried wood would invite termites.

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    Also ask the contractor how they plan to dampproof that section.
    – CCTO
    Oct 1, 2020 at 16:27
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It is possible to remove those forms. We did plenty of that when I worked for my dad. Usually contractors want to keep and re-use the form panels because they are expensive. There are only two real drawbacks to leaving the panels on the foundation:

  1. You will not be able to coat the exterior of the foundation wall with any waterproofing. Usually something like an asphalt emulsion is used to prevent water ingress through the wall.
  2. You might have a slight smell of diesel around the base of the structure since that is what is commonly used to spray on the panels to prevent the concrete from sticking to it.
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What's not standard practice is for a wall to be poured so near another parallel foundation. That's a somewhat unique situation to begin with. Normally the floor system for an addition would rest on the original foundation unless there was a problem with the original. (I've since learned that the existing is a slab foundation. Obviously the new wall is necessary for the addition's basement.)

That said, this probably isn't a problem. The wood will eventually decay and cause some degree of soil settling, but you'd probably have than anyway. If you expect it and plan for it you should be fine.

One possible concern would be regarding waterproofing. If you're having the concreted sprayed, or if a membrane is being installed, you'll have to decide whether it'll be effective over the wood.

Otherwise it's really no different than tree roots or other organic material in the soil.

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  • ...you'll have to decide whether it'll be effective over the wood. It won't. Full stop.
    – J...
    Oct 1, 2020 at 17:39
  • Not true. Wooden foundations are a thing. They have waterproofing as well. Plus, we don't know what system is being used.
    – isherwood
    Oct 1, 2020 at 18:07
  • Well, those forms are stuck in the dirt now, so I'm not sure how you expect to waterproof it without digging down underneath the form's bottom edge. Wooden foundations have a process and rules about how they're made. Leaving a form on a concrete pour is not the same thing at all.
    – J...
    Oct 1, 2020 at 19:16
  • I assume that the forms rest on a footing just like any foundation wall would and could be waterproofed with a membrane just as well. I'm not interested in arguing further, though.
    – isherwood
    Oct 1, 2020 at 19:32
  • Fair, but it's pretty sketchy regardless, and it's exactly the kind of thing (a nonstandard hack) that I'm sure we'd all not hesitate to lambast if the post was OP unpacking this 20 years later and trying to recover from a mess that could have been prevented by just doing things the right way at the start.
    – J...
    Oct 1, 2020 at 19:36

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