Digging Out, or Excavating a Basement Under A House

From: Karen
"Hi Carl,
We have a small (around 1200 sq. ft.) A-frame one and a half story house on a sloped lot. We have a crawl space that is about 4ft or more and are wondering about the wisdom and cost of excavating to a full basement.

We would like to have walk-out access and would be willing to do some of the work ourselves. We have been getting a full range of responses from "yeah, that's easy" to "no, you don't want to do that."
Thanks for any help."

Hi Karen,
I would say that digging out, or excavating a basement under a house that sits on a crawl space could be one of life’s more challenging tasks.
As we can see, in a crawl space, there are piers to content with as well as the original footings. The soil under the original footings can NOT be disturbed or your house will be destroyed. It would be hard, if not impossible, not to disturb this soil if you try to excavate the crawl space.

I have read in some forums about “digging at an angle” so as to NOT disturb the soil under the footings, but I don’t have much faith in that solution, but even if that was a viable solution, you’d cut down the resulting sq footage considerably…and with more work to boot.

And then there are those pesky piers to contend with. Steel I beams would be required to replace them. And then…..oh hell!.....

The only way I would even think of attempting this project is to call a house mover and have he house jacked up, excavated, new footings, new foundation, laid, and the house “set” back down on the new foundation. Done!

Other than the cost of the house mover and demolishing the old foundation (and hauling the trash to the dump), the new foundation costs would not be significantly more than building any new foundation. I would guess 15 to 20k, depending on how much labor you contribute,

The house jacking rough estimate can be obtained by contacting a house mover…I would guess, 10-15K. (See list of House Movers for your state below)

If you finish the basement, you would be almost doubling the size of your house and increasing its value. You would also have the enjoyment of having additional well lighted living space at a moderate cost per sq. ft.

Have a floor plan drawn up by a local home designer so that you can plan your space.

Be sure that the elimination of piers is allowed for in the structural details.

If you, or the designer, are in doubt as to the structural requirements, have a structural engineer review the plan.

I have discussed the need for structural engineers many times. Their services are often “free” when you buy your steel beams from their employers.

Photo courtesy of: Deitz House Moving Engineers, Inc.
This 140 years old house was lifted from its' crumbling old foundation and supported while the earth was removed from under it.

After the excavation phase was complete, a new eight feet tall poured wall was installed under the house. In addition to creating a stable and level foundation, the customer gained 1,320 square feet of usable living space.
This is an end view of the house during the initial stage of the of the excavation phase. A front end loader was driven under the house and used to remove the dirt and existing rubble foundation.

For other Movers by state, here is the International Association of Structural Movers

Good luck,