Foundation above Frost line
Foundation above Frost line
(OP)
The house I am investigating its foundation to see if it can take the load of a second floor addition is about 2 feet above the frost line. By code, the bottom of the footing has to be at least 3' down. I am thinking of using helical piers but the owner is concerned with the cost. The house is near a bulkhead and the material is (SM) with about N=3 down to 7 feet blow grade. Ground water is tidal. At low tide, water level is about 4.5' below grade.
Also, they are adding a one car garage attached to the side of this house. I am thinking of recommending a 6" concrete slab w/ wire mesh and the wall footing designed as grade beam 3' down supported by helical piers.
Any help or suggestion is appreciated.
Also, they are adding a one car garage attached to the side of this house. I am thinking of recommending a 6" concrete slab w/ wire mesh and the wall footing designed as grade beam 3' down supported by helical piers.
Any help or suggestion is appreciated.





RE: Foundation above Frost line
If you underpin, then underpin old and new.
RE: Foundation above Frost line
RE: Foundation above Frost line
Next about the "code". In my general area they talk about "frost depth" to 4 feet, but no one actually does any scientific determination, usually. However, in your case, for 3 ft. frost depth,why not approach the building inspector with this idea.
Dig down one foot around the outside, place a 2" thick sheet of the pink, closed cell insulation, running it up the wall to ground surface also. In this case, extend it out three feet and use one foot up the wall (from a 4 ft. wide sheet). We do that a lot here and have no problems with shallow footings or slabs on grade.
RE: Foundation above Frost line
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But the helical pier is a good idea, just don't mix a shallow footing foundation with a deep foundation system, they won't wove the same.
Jim Houlette PE
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