Basement Underpinning Problem

[Jeff]

Hi,

Half of our basement was dug down about 6 inches more than 30 years ago. I just pulled down some wall panelling in the dug-out section, and

discovered that there is about a 4 inch gap between the bottom of the foundation wall and the basement floor. I can clearly see earth fills this gap.

Here are a couple of photos of the gap:

The house was built in the 1920s, and the foundation is poured concrete. The basement floor is poured concrete. The earth is very sandy, and we do not have a problem with water via the gap. There are no cracks in the foundation wall, nor are there cracks in the exterior brick of the house to suggest bad settling. I have only uncovered a small section of the walls so far.

I've had a couple of contractors in who suggest an expensive "proper" addition of footings. Another contractor suggested the earth be dug out

several inches past the exterior of the foundation wall, and back-filled with concrete to make a sort of 1/2 footing. Or I was considering just filling in a few inches of concrete on the inside to prevent the earth from spilling inwards. But I don't believe that will add any structural support.

Do I really need expensive several-feet deep footings with weeping tile, etc., to replace the earth that hasn't moved much in all this time?

Any opinions are appreciated.

Thanks, Jeff

[chuckster]

You can hire a contractor to jack up the slab, (Google, concrete jacking.) If you let it go as is and build the wall again use treated lumber on the bottom plate. This floor job was done wrong from the beggining, because the slab was never pinned to the footing, wall or laid on a ledge. This will be a costly project no matter which way you go.

Jeff wrote:

[mwlogs]

It's not all that uncommon in older houses to have had someone dig the basement deeper. Often these had dirt floors anyway, or at least a very thin (1-2 inch) concrete floor. I've seen where they've taken the floor below the top of the footer, leaving a 3-4 inch 'step' at the wall. Since your wall does not appear to have a footer, they've dug below the bottom of the wall.

Bringing this job to code will be an expensive undertaking since it would require excavating, and probably building entirely new footers and foundations. If as you state, the work to lower the basement floor was done

30 years ago, and you haven't had any problems with water leaking in , or settling you could just close it ack up and hope for another 30 years.

A general contractor is going to have to do it to code - pulling permits, etc. Something less than code, such as what you've describe is probably not going to be all that much less expensive, so think long and hard before taking the short-cut. Particularly if you ever plan to sell the house. There may be disclosure issues with knowingly having 'fixed' something and not brought it up to code. Leaving it as is would be less of an issue since it isn't uncommon to have things in older houses that aren't up to current code - and know they exist (such as plumping of electric issues).

[BobK207]

Jeff-

How much perimeter wall are we talking about? One or two story house?

Maybe you can find an engineer & a contractor with a little imagination?

Perhaps the existing condtion could be improved piecemeal by digging away a small section, backfilling with reinforced slightly expansive concrete....you'd have to have the solution engineered & ok'd by your local building dept. The work could be done one section at a time. That wall is probably pretty stout...it's just missing a proper foundation.

here is a link to the screw type underpining referred to by another poster

depending on local conditons you might get away with a reasonable number

cheers Bob

[Pat]

There are two ways of looking at this. First and properly, you're pretty well screwed. It should be immediately fixed and fixed properly

-- and it's be unbelievably expensive.

The second way of looking at is is that it hasn't moved in the last 80 years so it ain't going anywhere .. esp. since you don't have water or frost at that level.

Personally, I thing the biggest problem you would have is something undercutting the wall and having it look support. I am not an engineer, so please disregard my advice and I do not intend to tell you what to do, merely what I would do if I owned the house.

I would put a 2x12 about a foot out from the wall. I would then drill holes 6" out from the wall and drive rebar a foot two down, say every 2 feet. Then put a couple of piece of rebar running parallel to the wall, connecting the pieces I drove into the ground. Then I would fill the area between the wall and the 2X12 with concrete. That (and the rebar) might keep the concrete wall from being undercut.

wall | | |~~~~~ | top of new concrete | | | | new wall | | dirt } | | } | | floor ------|------ | rebar | |

But consult someone smarter than me before you do anything like this. I don't want to be responsible for your house falling down.

[kevin]

Hi Jeff,

I think the stuff about bringing it "up to code" is nonsense, in this case. This isn't a new house, this isn't new construction, addition, etc.. I'd be surprised if there even was a "code" to speak of in this case, which means that whatever your building inspector says is okay, is okay, and anything else isn't. If you involve your building inspector, that is.

If this has been 30+ years, with little to no movement in that earth, I think starting in on a massive excavation and foundation job would not be called for.

First, do you know how thick the wall is at that point? It could be a simple 8" thick wall that ends abruptly. Or it could have a thickened half-footer edge (i.e., a footer but only on the outside of the wall, so not visible from inside).

Your idea of just adding some concrete at the corner of the wall and floor is done pretty often around here, as far as I can tell. We had an offer to do our garage basement this way (but we didn't end up doing that). It would be much cheaper than any alternative, and likely work just fine -- get some more opinions from foundation and concrete workers. It involves first drilling into the floor and bottom of the wall, and inserting rebar pegs. Then you build a small set of forms, and pour a beam (maybe 1 foot high by 1 foot thick) around the edge. The rebar pegs help bond it to the wall and floor. The purpose is to take some load off the soil under the wall (via the rebar pegs, transfering load to the 1 foot wide new concrete base), and to keep that soil from moving. With a concrete pump, a team of workers could have this done in a few days.

-Kevin

[marson]

The building has been this way for 50 years. what problem are you trying to fix? is it settling? why would it start in the next 50 years? you can't bring the building up to code (lack of footings is just one item in a long list). besides, even if you did, your return at resale time would be pennies on the dollar.

if it was mine, i'd stand up a form board and cover the exposed sand with some concrete. provided the foundation is relatively plumb, level, and square and not moving, spend your money on windows, insulation, siding, kitchens, baths. might as well flush some money down the toilet as retrofitting footings on a perfectly good foundation.

[Goedjn]

If it hasn't moved in 30 years, the chances are it's not going to, at least until the next earthquake, flood, If you WANT to fix it, there is a range of choices, trading off how much space in the basement you're willing to give up, how much money you're willing to spend, how much time and effort you're willing to put in, and whether you want to involve your local authorities and/or contracters.

If you trench just a few inches into the slab, and pour a knee-wall up against the base of the existing wall, you only have to make the knee-wall in a way that will keep it from rolling. THat will be structurally sufficient until and unless the soil outside the wall actually liquifies, which is unlikely. It won't be waterproof, though.

Failing that you could use timber jacks to take the weight off the house, drive pilings sideways into the dirt under the existing wall, and excavate 2' to 4' sections and pour footings under them. (In that scenario, you'd use expanding concrete) How big a chunk you do at once in that case depends on how big a hole you think the wall will span without support while you're working. I don't think I'd be willing to try that with a rubble wall, but from the picture, you've got monolithic concrete, right?

This latter is essentially the same thing you'd do if you were trying to put a window in, but you're putting them is really low, and filling them with concrete afterwards.

--Goedjn

[Jeff]

Thank you for all your opinions. They really helped me make up my mind.

I'm going to call in an engineer to make sure it doesn't look too dangerous, and if it still looks stable after all this time (which I hope it will) I'll do as little as possible to stop the sandy earth from spilling out.

Thanks again. Jeff

it's not going to,