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Adding a Basement: Is our contractor doing it right?

Posted by jenica (My Page) on
Mon, Nov 12, 07 at 14:35

We are having a walkout basement added to our almost 100 year old house and I wanted to make sure our contractor was doing this right as he is extremely cheap. We were just going to get the house level but he qouted us so cheap we asked him how much for a basement. He only wants $7500-8500 for the job, including materials and labor. The house is on a hill and the crawl space was already 6 feet deep on the down hill side but decreased to about 1 foot deep on the uphill side.

So far he opened up the cement block wall to accomodate a backhoe and has dug out the area to about 8 feet deep. The thing I was wondering about is except for opening the wall to accomodate the backhoe he is leaving the existing foundation walls alone. He plans on building new walls, about a foot in from the old walls, on top of the concrete floor he is pouring. On the walkout side of the basement the new wall will stop and be capped off when it is at the level of the old wall, leaving a shelf of sorts. On the other walls the new walls will run all the way to the joists. By doing this he is leaving the house supported by the existing walls and footers and the new walls will not be load bearing, although he will be installing new posts through the middle of the basement. He's doing it this way because he can't jack up our house due to an attached brick fireplace, concrete porch and wrap-aroung deck. Is this okay?

By the way, he isn't asking for money up front, we just pay for materials as he needs them and he gets the balance when he finishes the job. He is also: laying PEX tubing so we can have hydro-radiant heat floors, roughing in plumbing for a future bath and for washer/dryer hookups, water sealing, and adding a 36" x 54" window.

I'm just worried because this seems a little too good to be true, he can't take our money and run, so that leaves doing a crappy job. So is our house going to fall down or what?

Follow-Up Postings:

RE: Adding a Basement: Is our contractor doing it right?

Now that he's broken through one of your basement walls and removed two feet of soil, it's a little late to be having second thoughts!!

So it's labour only. Assuming this is a smallish house--say 2,000 sf or so, the price is low. But, for some parts of the country, I suppose, not absurd for a no-invoice deal.

But, as you have described it, there may be a lot wrong with the way he's doing it!

On a house I bought to renovate, I was presented with a similar situation. The previous owner had lowered the basement floor by about a foot by breaking the concrete floor up and and digging. Then he had laid a new wood floor directly on the soil! (The basement was totally finished when I bought the home, so I didn't realize what I was buying.)

In lowering the floor, he had dug lower than the footings--in this case, bricks laid perpendicular to the brick foundation wall. Essentially, he undermined the house. (And since it was a semi-attached, he had partially undermined the adjoining home too.)

A professional engineer designed the fix: a rebar reinforced retaining wall around the entire perimeter of the basement to provide lateral support to the footings. Since I was doing that, I also lowered the basement a bit further and put in new sewer lines.

My concern on your home is that the excavation has undermined your footings too. He left a foot of undisturbed soil between his excavation and the walls. That's not adequate. Putting up stud walls to secure wall finishings is fine.

None of this work was done with a building permit, I take it. Before you proceed any further, I strongly suggest you contact your local building officials or a qualified professional engineer to design this project properly. Don't be surprised if the municipal inspector puts a "stop work" order on it.

It's only a bargain if it's done right!!

RE: Adding a Basement: Is our contractor doing it right?

We apparently have a miniscule home at 1100 sq ft. We had our home raised on jacks, set on "cribs", eight to ten feet of dirt dug out, a block foundation installed and waterproofed, a new furnace and all downstairs plumbing, doors and windows, done for 30k.

Is there a partial basement or something now? Most 100 year old home aren't built on slabs.

RE: Adding a Basement: Is our contractor doing it right?

Digging below footers (or in the area below a 45 degree line from the footer downwards) is NOT a good idea.

At the very least you need a geotechnical engineer, and also possibly a structural experienced in house foundation design to tell you if the footers have been compromised.

Depending in the type of soil and how far below (and close) the support has been removed the edges can blow out allowing the base of the wall to shift into the new hole.
You can figure out what happens to the house above.

In many cases 'benches' are left along the footers inside to prevent shifting.
The bench is often as wide as it is tall.
If the footer is 3 feet off the new floor, a 3 foot wide by 3 foot tall bench is left.

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