Protection of existing foundations

[aayvat]

My question is regarding the application of Frost Protected Shallow Foundations (FPSF) on existing basement foundations. I would like to excavate and pour a concrete stairway from the exterior of the house to the basement. An opening will be cut in the existing foundations for a doorway. The frost level is at 4'-6".

My concern is, with the excavation and the new stairway, the existing footing will be above the frost line. I would like to protect the existing footings using 2" rigid insulation horizontally above the footings (extending +/- 2ft beyond the foundation walls) as well as vertical on the foundation walls up to the level of the new door. A 4" slab landing with a drain will be poured 1"-2" below the level of the door with the drain going to the french drain along the footing.

Going down the new stairway, the left wall will be existing wall of the stairway going up to the main door of the house (first floor level) and a retaining wall will be poured on the right side with footings at same level as the footings on the house. These foundations as well as the existing stairway foundations will be protected in the same manner (2" styrofoam vertical and horizontal.

Does the application I've explained apply to basement foundations? Are there any better suggestions for accomplishing this design?

 

[shobroco]

I do it all the time. Look at the path for frost, & if you don't have the required earth cover (4' where I am) replace it with rigid EPS. 2" (R10) will replace 4' of earth fill, but look at the path around the insulation & make sure that the distance through the soil is 4' in whatever direction. That means 2' horizontally may not be enough.

 

[ACtrafficengr]

Are you concerned about heat loss or frost heave?

Does your site have the other requirements for frost heave? If you have sandy or gravelly soils and/or a low water table, it's probably more of a code thing than a practical thing.

I have a bulkhead door on an old house, with no insulation, but I'm also on a hill of class A soil, 10-15 ft above the water table. There are no signs of movement.