Basement excavation and drainage, Belmont

We’re going to be finishing this basement which will include creating a new bedroom, playroom and bathroom. We start by taking out the existing concrete floor in order to increase the floor to ceiling height to meet minimum code requirements. We’ll be finishing with an 84″ height.

We began excavation by removing the concrete floor which was only about 3″ thick. What we found under the concrete was 100% clay. That’s right, no dirt or stones, just clay. We have had a very difficult time getting rid of this material – none of the local dumps will accept it.

Come to find out there is not only no footing under the existing concrete foundation walls but the walls only go down 5″ below the original floor’s surface. Since our future floor is to be 5″ below the original, we have a problem! We also found that the five steel columns supporting the beams were set in only 4″ of concrete, over clay. So we brought in an engineer per building inspector direction who inspected and instructed us to replace the columns with new footings 10″ deep (below the future floor) and 24″ in diameter. He also instructed us to dig under the existing foundation walls and back the depth of the walls in order to pour a wall extender. We are doing this in 5′ increments and reinforcing with 1/2″ rebar every 2′ on the vertical and horizontal.

Since we’re installing an internal perimeter drain we need to extend the foundation walls by 14″ in height (12″ in depth – current foundation wall thickness).


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