Basement Addition Next to Slab-on-grade house
Basement Addition Next to Slab-on-grade house
(OP)
Hi, all. I’ve got to put a 2-story addition with a basement onto an existing slab-on-grade, 2 story home. The existing foundation is poured concrete, with a continuous footer, about 4 feet below grade. The house is 40 feet wide. The concern is stability of the existing structure during excavation and pour of the addition. I was wondering what the options are for shoring/underpinning, etc.
While I ‘d like to pour the new foundation essentially next to the existing one, I’d consider stepping out a bit if it would help lower the overall cost of the shoring requirements (e.g. if a sheet piling were driven next to the existing foundation, the new wall poured, and the sheet piling removed). The downside is the loss of basement volume as the location of the other wall is set. I’d be looking for the top of the new footer to be 6 feet below the top of the existing footer.
I don’t have any soil data at this point, I’d guess it’s a silty sand.
While I ‘d like to pour the new foundation essentially next to the existing one, I’d consider stepping out a bit if it would help lower the overall cost of the shoring requirements (e.g. if a sheet piling were driven next to the existing foundation, the new wall poured, and the sheet piling removed). The downside is the loss of basement volume as the location of the other wall is set. I’d be looking for the top of the new footer to be 6 feet below the top of the existing footer.
I don’t have any soil data at this point, I’d guess it’s a silty sand.





RE: Basement Addition Next to Slab-on-grade house
Underpinning is time consuming, manual labor intensive, and somewhat risky. It should be done by experienced contractors. The loads are light for residential construction, but the existing foundations are usually "lightly" reinforced or not reinforced.
RE: Basement Addition Next to Slab-on-grade house
DaveAtkins
RE: Basement Addition Next to Slab-on-grade house
RE: Basement Addition Next to Slab-on-grade house