We are in the early stages of planning an addition and wondering if a basement is a stupid idea. We can't build to over 17 feet at the top of the roof ridge but would certainly like to have double the space on the same footprint.

Are there reasons (other than expense which is probably pretty darn large in this seismically active area) not to put a basement in an addition? There must be a reason people don't do it here where people want bigger homes but don't want to move. Surely it's not because they didn't think of it! I must be missing something.

I'm going to assume dirt removal would be done by the builder. (Or excavator?) I'd probably rather not take on that job myself. :)

But no, the lot isn't big enough to spread it around. (If it were, I wouldn't want to stack my rooms!)

In California (at least the Bay Area) one has to be concerned about expansive clay soils and thus, all below grade construction needs to be based on your specific soils conditions. In addition, proper waterproofing and drainage (sub-surface and surface) should be used.

That said, with the height and buildable area restrictions common in many areas in California, building a basement is an alternative to price out and consider. Good luck!

And yet, I'm glad we can't build up. I've seen enough midcentury neighborhoods ruined by bedrooms tossed over garages and backyards shaded by neighboring additions. This neighborhood has larger lots than many of the time and area, but the houses are situated to run pretty much the width of the lot. So it does make a difference when someone goes UP.