Digging out a Basement

Topic: 
Basements and Crawl Spaces
Question: 

I am currently considering rehabilitating my basement in a home built in the 1920's. The basement floor appears to be a thin layer of concrete over dirt. The foundation walls are constructed of concrete blocks. My problem is that the building code requires a ceiling height minimum of 90". The ceiling height is currently 81" in the front two rooms of the walkout basement. The two rooms underground have a clearance of 85" from concrete floor to floor joists above. I think one option would be to replace the concrete floor and dig out the foundation another 6" before pouring the new floor. Do you have any other ideas or suggestions? The four rooms in the basement equal close to 1000 sq. ft of potential living space in this house.

Answer: 

Let me start with a few "rules of thumb":

Of the 3 ways to add space to a house: building out is the least expensive, building up is more expensive and building down is usually the most expensive. And, a basement remodel has the lowest pay-back when the house is sold.

The biggest problem with the "digging out" part of a basement remodel has to do with the foundation. Most crawl space and basement foundations "stop" a few inches below the level of the existing soil level or floor. In other words, a new or revised foundation has to be built which extends down and below the level of the proposed new floor grade.

The construction of a foundation is not a difficult task in new construction. After all, you can bring in the best equipment to move the dirt, etc. Building a foundation with a 'house on top of you', is possible, but much more complicated.

This is not a job for the amateur builder. It requires very good plans and expert planning. George

Here is a follow up, and some information about digging out a basement from Liftco, Inc.

George,

I would like to input info on the digging out the basement question!

I was reading your response to this question and actually it is the least expensive of the three options. The trick is you just have to purchase more of it to benefit at a lessor cost. Example room additions in which you said "where the least expensive" are really the most expensive per sqaure foot. Figureing in sqaure foot a good contractor is anywhere $75.00 $125.00 per sq.ft. for room addition, in the midwest region.

A basement addition/replacement is approx. $ 25.00 per sq.ft. non finished. It is also a tax benefit in most states.

We are on the internet at http://www.houselifting.com/ check out our webpage.

Liftco, Inc.

And my reaction...

I looked at your web page and you seem to have some very nice systems for lifting houses. A system which makes a lot of sense in certain circumstances and conditions.

However, you have not convinced me about the relative cost of additions vs. lifting a house. For one thing, you are presenting cost per sq. ft. numbers which are not comparable. The $75-125/sq. ft. numbers are in the ballpark for finished additions. The $25/sq. ft. numbers are for a non finished basement. Depending on size, design and local conditions, plus many others details, your own numbers may prove my point.

I can think of several designs for an addition in which the structure and shell would cost less that $25/sq. ft., i.e. less than your ballpark estimates for lifting a house and adding a "shell" under the house. I can also think of lots of complicating factors which might make lifting a house much more expensive: fireplace foundations, heating systems, plumbing, high water tables, etc. As is so often the case, the devil is in the details.

I also don't understand how a basement addition has better tax benefits (if any) than other types of additions. As for the argument that "you just have to purchase more of it to benefit at a lessor cost", that holds true for almost any type of construction.

George