Expert: Daniel Humphrey - 2/19/2009

Question
I am looking at a piece of land for a future home.  I was wondering how hard is it to put in a foundation when dealing with a steep grade.  I see the back of the house having no windows while the front would be a full walk out.  It looks like the grade would be 20-25 degrees.
Thanks

Answer
Paul,

To put in a typical foundation of footer and stemwall on a steep grade, it means you need to excavate the footprint about 6 feet larger all around than the finished building, for scaffolding and other safety and efficiency reasons. If the excavated cut is greater than 4 feet, you will need to terrace the bluff in steps. This extra excavated space is then optionally backfilled once construction is complete. Any backfill is structured and drained so that there is no water or earth pressure against the wall.

A slope of 20 to 25 degrees is fairly steep probably means the cut will be large and you will need to stockpile material to the sides if you plan to backfill. For this reason, you will need to access the house site from all directions with an excavator or loader. If this is not possible, the easiest and most pleasant solution is to construct the terraces so they are part of the landscaping and do not backfill. This is much better for the house as well, and allows light from all sides.

It is best not to build on backfilled areas, since that dirt is prone to slump; keep the house entirely on undisturbed or properly compacted soil. But if you cut and fill, this allows you to have a front yard or flat driveway.

The other approach is to put in pilings on a steep slope and approach the building from above.

Sorry this reply took so long. I answered it earlier in the week, but the answer didn't get sent for some reason. Good luck with your property search.

--Daniel