Dry basement feasible in Berkeley, CA?

[Wayne Whitney]

Hello all,

I'm in the process of buying a 1910 fixer here in Berkeley, and the biggest repair it needs is a new foundation. I'd like to add a partial basement while I'm at it, if it can be kept dry. So I'm wondering if that is possible given the local conditions:

The house is in the Berkeley "flats", but Berkeley gently slopes from the hills in the east down to the bay in the west. I understand that the soil here is typically clay and thus not very permeable. Therefore most of the rain that falls over Berkeley travels several feet below ground down to the bay. There's about 20 inches of precipitation during the rainy season from November to March.

The basement I'm planning has a floor slab that is 5 feet below grade on the upslope side (4 feet on the downslope side). My contractor proposes to seal the retaining walls and slab with a "paraseal membrane", and to use a gravel drain field under the slab and at the upslope wall. For the other walls he has proposed using miradrain drainage board. Perimeter drainage pipes and a sump pump are also in the works.

So, will these measures, if properly executed, keep my basement dry in my conditions? If not, are there additional measures that would work? Obviously I am talking about this with my contractor, but I thought I'd ask the net opinion.

Thanks, Wayne

[Jimmy]

Probably. If you can do the perimeter drain and make it work by gravity that's better. That only works when you have a low place to drain to (lower than your footing.) If it is really wet there (sounds like it) I'd do a drain inside and outside the foundation. Gutters piped into the drain system are also a good idea as your roof will dump a significant amount of water right where you don't want it.

Here's a site with some information that will educate you a bit: