Lowering the Floor

For a house built in 1925, having 7'4" high ceilings in the basement was very generous, and if it were as simple as that we probably would have left them at 7'4". There were a number of issues though.

The first was that while the height at the center of the room was 7'4", at the walls the height was 7'1", with a gentle slope towards the center of the room. This was presumably done so that any water that wept from the concrete block walls would drain away. We needed the floors to be level for the room to be used, so to level the whole thing without removing concrete we at best probably would have ended up with a 7'0" ceiling height.
Another problem was that in some areas the concrete floor was pretty badly cracked.
In order to install the drain tile, the slab all the way around the basement within 2' of the wall needed to be removed.
We needed to install new drains to allow for the new shower, bath, toilet, and laundry areas, which required busting the concrete and laying new drain lines.

Once we looked at all these issues, it made sense to remove the slab. And once we removed the slab, it made sense to lower the floor height, which required underpinning the foundation.

Underpinning

Everyone we talked to kind of hemmed and hawed about lowering the floor. "Underpinning, huh?" they would say. Is it really that bad? "Well, no..." In the end we obviously found a contractor who was willing to do it, but one of the bidders backed out because his concrete guy said it wasn't possible. Our house is still standing, so it obviously was possible.

So how is it done? Inside our basement our contractor measured out 3 foot wide sections around the entire perimter of our basement. Then, after the slab was removed they would dig out under the foundation from inside the house to a depth of 2 feet or so, by hand. So now you could look at the wall of the basement from inside and see a 3 foot wide, 2 foot deep hole under the foundation, with nothing supporting the foundation where the hole was. After the hole was dug out, they would put a form in place and pour concrete into the hole to completely fill it up to the base of the existing foundation. They would do a section on each wall They did this work in January and February, and there was nothing to see from outside as all the work was done from inside the basement by hand.

Everybody always wants to know cost, and it's really hard to say because for home remodeling projects, the contractors really bid on the whole thing, and they're pretty much guessing. Their estimates go something like "The Smith house took 3 months, and this new project looks about the same as the Smith house, so it should take about 3 months." To dig out and underpin our 625 square foot basement probably cost between $15k to $20k, but you have to keep in mind this was balanced by all the other things that needed to be done. We got a signicant discount from the waterproofing contractor because they didn't need to cut and remove the slab to install the drain tile. Likewise the plumber just laid out the floor drains on the ground after the slab was removed without having to first cut concrete and dig. So all the costs kind of get mixed together into the final cost.

Steel I Beam

So there was another issue we looked at. Right in the middle of what was to be our new home theater space was a support post. That post was under the beam that was the center support for the house. Obviously we needed to move the post, and in order to do that we needed to use a steel beam to span the larger distance.

One we started talking about using a steel I-Beam, our architect had another clever suggestion. Everybody always seems to lose me the first time I try to explain this, so pay attention.

Most people are familiar with the following: Looking up at your exposed basement ceiling you have the 2x8 floor joists which support the first floor. Somewhere in the middle of the room, running perpendicular to the floor joists is a wood or steel beam which sits below the floor joists and holds them up. So you have a beam running across your ceiling which helps to hold up your house.

With me so far?

So here's the clever suggestion: Take a steel I-Beam and weld a steel plate to the bottom, so that you have something like an inverted T. Now carefully prop up the first floor with temporary braces and remove the existing support beam. Now, cut out the floor joists right down the center of the room wide enough that you can push the new steel beam up into the joists. The ends of the floor joists will now rest on the plate that you welded to the I-Beam, and the I-Beam itself won't be below the joists, it will be up in the joists. Or another way to say it, the ends of the joists will be resting on the lip of the inverted T.

After all the effort and money spent lowering the floor, gaining another 6 inches in ceiling height without having a beam hanging down below the ceiling was a great thing. The disadvantages? Well, cost really wasn't one, as the steel beam was relatively inexpensive. It does take a bit of faith to cut your floor joists, but if it's done properly it works great. You will get some cracking of the plaster on the upper floors as the house settles onto the new beam. The only other issue is that any mechanical stuff that ran above the beam between the joists now cannot since the beam now blocks them. So for instance your ductwork can't run there anywmore.