Foundation Design is Critical

Carl,  I've picked a ranch house plan that I like. The plan calls for a slab foundation.

The lot I have is sloping. I had an excavator look at it and he said I will need a lot of fill to make it work. He said I might want to consider a basement.

The house is 2000 sq. ft. and I can count 18 corners on the foundation. Would a basement go under all of this or be combined with some slab. Is this too expensive to do?

Also, if $80 per sq. ft. is average to build a house, how much more is it to do one with multiple foundation offsets and multiple roof lines?

Hi M.C.,

Decision, decisions, decisions.

As I have said many, many times in many, many articles, building a new house, home addition, or doing a major remodeling job is all about “shopping”, and making decisions, no matter who the General Contractor is. You even have to shop for and make structural decisions. It can be exhausting. That’s one reason why I am here.

The two most expensive structural components of a house are the foundation and the roof.

While a slab foundation is normally the cheapest foundation, because of the many offsets (corners) on the plan you chose, and the slopping lot, you may have a very expensive foundation no matter what type of foundation you choose.

For a full slab foundation on a sloping lot, you would have to build a raised slab that not only has a lot of expensive fill dirt, but SOLID concrete walls to contain the fill dirt. The concrete walls may be as high as a basement wall on at least one side.

A partial basement that “steps up” to a slab or crawl space for the rest of the house, as you mentioned is a good alternative.

However, a walkout basement, either full or partial is probably your best bet.

Walkout basement

Whatever foundation you ultimately decide to use, you will need a foundation plan for that foundation. Many home plan services or home designers offer their home plans with various foundations alternatives. If not, the charge for doing so should be nominal

Will a full basement or a partial basement be too expensive?

Get some foundation bids from foundation contractors for any and all options, or if you are using a general contractor, have him (her) get them and then decide.

Don’t forget to factor in your decision the fact that you will be picking up expandable space in that walkout basement area.

A cheaper alternative I have used is to level the actual building site (dig into the slope), build a retaining wall (with a drainage system), and build the house on a slab foundation on the resulting flat area.

Photo courtesy of

Get some bids on this option too. The retaining wall could be made from wood, railroad ties, stone, block, brick, etc., or even an earth berm made from your own dirt.

The earth berm/slab is the cheapest alternative. However, it won’t work on all building lots. Your excavator seems pretty savvy, ask him.

Remember, you are still only in the planning stage and this is what the planning stage is all about.

If the house plan you chose doesn’t work you for any reason, you haven’t gone too far to decide on another plan without losing too much money.

As for $80 per. sq ft., besides the fact that a one level home is more expensive to build than a 2 story, add the fact that yours has 18 offsets, plus multiple roof lines, you will be way above $80 the Median average. (Median average = 1/2 of all the homes cost more to build and 1/2 cost less) and average cost per sq. ft.)

The following is from the very 1st step of estimating with the residential building cost calculator found on my “Getting Started” page. It is sound advice from experts in cost estimating:

“The shape of the outside perimeter of the foundation is an important consideration in estimating the total construction cost. Generally, the more complex the shape of the foundation, the more expensive the structure is per square foot of floor area.

The shape classification of multiple story or split-level homes is based on the outline formed by the outer most exterior walls, including the garage area, regardless of the varying level. Most structures have 4, 6, 8 or 10 corners, as illustrated in the example. Small insets not requiring a change in the roof shape can be ignored when determining the shape.”

How much over $80 per sq. ft. will you be? Run the calculator for your house plan or any proposed plan and find out.

That’s the beauty of the residential building cost calculator, it allows you get a good idea of the cost to build for any shape, size, or design house before you get too far along in your home building project.

Good luck,

Carl Heldmann