How can I minimize concrete usage when lowering a basement floor?
I’m considering underpinning my 1912 poured concrete foundation in order to get more ceiling height. At the slab’s highest point, it’s 6’10” from slab to joist. I’d like to get 8′ between finished floor and finished ceiling. Our neighbor’s house was built at the same time by the same builder and doesn’t have a footing, so ours probably doesn’t either.
I’d like to add as little new concrete as possible in order to avoid the embodied carbon. I can think of a number of ways to go about doing that, but I need a gut check on whether they’re feasible.
Option #1: Underpin with concrete and build a non-concrete “slab”
This seems like the most conventional option. It looks like the easiest way to do a non-concrete slab is by building a floating floor. Do underpinned foundations need some kind of structure to resist horizontal forces? If so, could that structure be provided by lumber at the walls or concrete beams poured between the footings?
Option #2: Lift the house and replace the concrete foundation with a permanent wood foundation
This seems like it might be cost-prohibitive. Is it possible to build a permanent wood foundation in place without digging a trench around the exterior? Since we’d be digging down after lifting the house, we’d have to put the jack posts in at or below the desired depth. Would we have to pour footings for the posts?
Option #3: Underpin with a permanent wood foundation
This seems the least possible. We’d need to install PWF in phases without an exterior trench and we’d be using lumber to support the weight of concrete. Is this even remotely feasible?
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