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
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.