Finished Basement with ADU in Mercer Island

Our Solution

Repair Point identified and addressed the moisture source — a failed exterior drain tile section that was repaired from the interior using a channeled drainage system and new sump pump. Interior walls received a vapor barrier and dimple mat system. Two egress windows were cut into the concrete foundation wall (engineered for structural adequacy), each with properly sized window wells and drainage. A new exterior entrance was created at the south foundation wall, with a covered landing and exterior stair to grade. The ADU was fully permitted as an attached accessory dwelling unit through Mercer Island's permit office. The finished space includes a full kitchen, full bathroom, one bedroom with egress, and a combined living/dining area.