Lowering Basement Floor Disaster 3

A big backhoe should level it quite easily.

just wow. astounding.

I think that first you have to figure out what final depth of basement you're shooting for. I presume you're working for or with the new owner and you may need to develop a few options to determine a price range. On one end of the price range is filling the basement back in with crushed stone and a new slab back to the 6' ceiling height just to undo this abomination. The other end of the range is doing whatever it takes to result in a legit living space. That would be a pretty involved shoring and underpinning operation. Not easy, but nonetheless possible, I'd expect.

For that option:
1) shore the framing. basement to first, first to second, etc. leave space to work on the interior around the edges;
2) pick a spot and begin with underpinned foundations, excavating from the outside, too. If this goes well, you get to a point where the whole foundation wall has the support of, say, 3x3 footings spaced at 9' around the perimeter, each with a wall segment under the existing.
3) continue underpinning to develop continuous support under the wall;
4) new slab.
5) new owner sues the zero asset LLC that the flipper used to buy this property.

It would be easy to imagine that the new owner would never be able to claw back the money to do this right and could decide to fill the basement and lose the 'habitable' space.

I think the homeowner wants to keep the 7' basement height, but I will tell her she can get a price to fill it in too.

Do you think underpinning is worth the risk though? 100+ year old brick wall with no footing, can't excavate from the outside since this is a city with row homes. There's not much to rely on if you dig under the wall.

I think the easiest and cheapest way to keep this current height would be to build a new bench footing on the inside. Then wouldn't have to dig under those old walls. Just trying to figure out what shape/size. Also, might want to do that in stages like a traditional underpinning job just so that the wall isn't compromised further.

How close is the wall next door?

Anything you do could create issues there?

Short props every foot would be a good start.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Bench footing...interesting. I've designed them before, but didn't know they had a name.

Perhaps 3 options:

Best/Most Expensive: Underpin the existing walls and maintain full living space. It's certainly possible. If you can get the attention of PEinc, he'll be able to help you out. Check out their website...if anyone here has the credibility to talk about underpinning, it's him. But yes, underpinning of historic structures with rubble stone walls and unreinforced brick masonry can be done. They're not exactly easy, but they are possible.

Medium Option: Bench footing. Lose some interior space, but less invasive as full underpinning and less expensive.

Worst/Cheapest option: back fill the basement to the original depth.

Just a few feet on each side. Check out the street view from June 2022. Red sticker on the door. Was sold a month later, last July.

All of these houses are probably built around the same time with crappy brick basement walls. Too close to do anything from the outside.

pham, those 3 in that order were exactly what I was thinking. And funny you said that about bench footing, I had the same thoughts originally when someone told me those have a name; never knew until recently.

But a lot better than literally the wall next door.

Should mean you can underpin from the inside though. Assuming the property line is mid way between the houses. A cross section sketch of your thoughts would be useful to avoid misunderstandings.

What about the floor?

Water table high enough not to need some sort of water sealing?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

So this was noticed because the new homeowner was getting a lot of water in her basement every time it rained. She called a waterproofing company and as soon as they cut a couple of holes in the sheetrock they said WTF we can't do anything you need to get someone out here.

I don't think water table is an issue here, but water intrusion definitely is. Obviously the wall just stops right now and the water probably pours down under the wall into the basement. Hopefully the new footing will help seal some of that up and she can figure out what the best waterproofing approach is once we have a structural design.

I'll send what I have sketched so far in a minute.

This is what I had sketched up so far after discussing with the contractor. The homeowner is okay with losing some space for a less expensive repair. Of course they would like to keep that 7' clear height so that's why a bench footing seems like the best option here.

But I do feel like this needs to be performed in a stage-like procedure, just because of current condition. Those studs are retaining soil so I don't think I'd want them to remove the whole thing at once. Maybe 8-10ft lengths.

Thoughts?

Where are those 2 x 3 studs in this?

If this was being done before the floor had been lowered then I can see it, but now you need to do something about the missing foundation under the wall surely. The existing foundation, such as it is, under the bricks has been severely compromised and now needs reinforcement.

Can't see why you can't underpin in sections at a time, say 3 ft with some sacrificial support legs

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

You have to tie that little triangular 'blob' into the wall to restrain it at the top. The bottom of the wall may move. IMHO, not a good fix. You should be looking at 'real' underpinning, else re-do the wall. It's an expensive fix.

In my experience, bench footings generally go underneath the existing wall, and are part of underpinning. You really need a geotekkie for this type of problem.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

If the bench and the slab are going in as separate pours, I'd give the bench a bit of a toe, and provide a construction joint detail showing crossing bars if you're going to do it in segments.

I wonder if it would be better, since it looks to be a small house and basement, to do a system of excavation shores a foot up from the existing footing and at or just below grade level to brace the walls against each other, strip everything out, and then pour the whole bench and slab together. Not easy to maneuver around, but most good contractors with experience in this kind of work are able to work around that kind of thing.

Sorry, that detail was pulled from an old job, that I just modified briefly this morning. The 2x's are just right up against the wall currently. You're right that this detail was used in the correct procedure.

Maybe I do a combo of both. Underpinning with a bench-like notch in front to secure the base of those old bricks.

Shore existing walls. Excavate dirt & remove bits of old slab. Pour down about 1'-4" of concrete for underpinning with a notch in front. Do this in a 3-stage approach x 3 ft long sections. Pour floor slab when finished.

What about shoring to prevent against sliding until the new slab is in? Horizontal across the basement short way (16 ft) from wall to wall? Right now they are lucky the soil is pretty stiff, but as all of this is removed in sections I don't want a sliding failure.

dik - that depends. In a small enough basement, the bench can act as a beam, resisting the thrust of the wall and delivering it to the perpendicular benches at each end, which in turn react against the bench on the far side. You can also tie it into the slab and dump the moment there, though the slab gets a lot more expensive.

For the record, I dislike bench footings, probably only did it once before. Underpinning is always my first choice where possible. This is just a tricky one because it's already dug out, it's a 100+ yr old brick wall, & there's no footing to underpin against.

FYI this house is a 35' x 16' rectangle.

Well if you can get them to do underpinning, great. Your detail looks good, but I'd take the underpinning down far enough that it doesn't need the slab to resist any loads. Can you tell where the original basement floor was? Putting the 'mini-bench' up to that level would be a good idea to keep the stresses from retaining in their historic range.

3ft should work. If the wall's in good shape you could probably go to 4ft, but this isn't the place to get greedy.

Those fixes don't address the water permeation issue. If you are going to the trouble of pouring a slab, probably should include some drainage features and a sump and pump?

pham

I've used benching as well as flush with the wall underpinning for numerous foundations... depends on the loading... only once for brick, mostly for field stone foundation walls. The benching is part of the underpinning.

16' span with maximum soil pressure... I wouldn't hang my hat on it.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik