Adding a Basement

[Chris Padilla]

Who here has experience with adding a basement to an existing house?

I'd sure appreciate leads to people experienced in this sort of thing. With the stock market crusing again, I am starting to see the funds for such a venture...again.

The way I see it, I'd need my house lifted, and I believe a good path under my house to dig would be through the garage floor/driveway. A couple of big problems I see is a pool that is located only 5' from the house in the back yard (might it need to be emptied?) and a large 200 year old oak tree located about 15' from the house (roots). I guess there are also issues with plaster cracking from the lift but I don't have any plaster in the house (all drywall).

I am in the Bay Area (San Francisco/San Jose) of California...Silly-con Valley if you like.


Thanks!

[Scott Greaves]

Hi Chris,

We just got through doing this with our cabin. A little background:

The cabin was not built on the best of foundations to begin with. Some serious settling was happening. Since this is where we want to live when we retire, we needed to take action to preserve the structure.

The original foundation was wooden piers, so moving the house as quite simple. We contacted a house mover, and he came in and moved the house off the foundation, then came back and put it on the new foundation. What we saved by having the house out of the way for the excavation and concrete work more than paid for having the mover come back a second time.

There were problems. The fireplace was old enough that they couldn't move it, and had to tear it out. That resulted in a big hole in one end of the house! But since we needed some stairs to the new basement, this hole came in hand for a stair well.

When we're done we'll have about $70,000 in to this project, but that also includes a new roof (trusses, etc), a new deck, new septic system and a new 2-car garage built on one end (to help cover up the hole left by the fireplace!). This will more than double our space, since we're adding the garage. And it will add more than double that amount to the value of the property, not that we plan on selling, but it's a way to tell if it's worth the effort.

I'm sure you have specific questions, so please ask!

Scott.

[Kevin Gerstenecker]

Chris, I know a Contractor in my area who does this quite often. He started doing this years ago, when they first introduced the small, Skid Steer Loaders.............Bobcats, if you will. He noticed right away he could fill a niche in a market that was not feasible before these little machines were available. He is pretty much known now as the authority on digging basements under existing structures. It has been years since I saw him do one, but if I remember right, they jacked the house up, installed temporary piering, and dug a ramp between the piers and drove the Bobcats under the house and went to town. The Piers had some sort of offset design to them, to allow room for the forms for the basement walls to be poured. I am sure the technology has improved since then, but it was cutting edge in the mid to late 70's when he started this. I guess it is still done........I would contact a House Mover or large, established Excavating Contractor and see it they have any suggestions for you. I know it was pretty neat to see them do it, and the homeowners just had to love having a basement "all of the sudden".

[Lee Schierer]

No matter how you go about it, it will be a lot of work. Your first stop since you live in an area known to shake a bit from time to time is to see what the building codes will allow for a basement and what the response of houses has been when the earth shakes that were built on basements.

When I was in High school, I helped hand dig a new basement under part of a house. It was dirty, hot, tiring work. We would first dig out an area so we could support the house, work in timbers to support the house and raise the house slightly. Dig out the remaining dirt, build the footer and walls, then lower the house back down, then remove the dirt supporting the house jacks. When I was 30 I did a similar job on my present house where I had to replace the existing basement walls due to some improper drainage issues that created structural problems. Again much manual labor is involved, so if you are paying for labor the costs will be high. It also takes some hefty jacks to lift a house. I was able to borrow some heavy blocking materials and some old railroad screw jacks.