My two story brick house (Toronto, Canada, circa 1920) is about 5 feet from my neighbor's similar house. Both houses have full basements; my house extends about ten feet farther to the rear than his does.
He want to add an extension on the back of his house, again with a full basement. He is proposing that his contractor dig down for the new basement, excavating all the soil right up to my foundation wall. He would then pour footings and build the foundation on his side of the property line according to code and by-laws, and backfill the space between my foundation and his new foundation. My foundation is solid brick, three layers thick up to the first floor joists.
There would be some sort of heavy equipment used to remove the soil from next to my wall, the wall would have the inward force of the soil removed for some time, and then the soil would be replaced and compacted.
My question is basically: What risks would I be exposing my house to with this process?
Best Answer
Two big risks.
One, they excavate properly but do not backfill properly. This will cause settling over time to your foundation. (Highly likely)
Two, they do not excavate properly and dirt falls from under your foundation during excavation causing immediate damage (unlikey, but possible)
Have them excavate the basement for shotcreting (excavation is held off your foundation at least a foot or so), and then shotcrete the foundation walls instead of a stand form and pour. This eliminates both problems.