Do I need to ADD a deeper footing...

[vhm1958]

I will be adding a rectangular addition to the back of my house, where the grade slopes away fairly rapidly. I already have a walk out basement section (10 feet wide) with sliding glass door and patio, with 6 foot high retaining walls on either side to hold back the grade. I am thinking about WIDENING this walk out by removing dirt from one side (over to my new addition) down to the current walk out grade, thereby exposing my block wall foundation. My question is, wouldn't the footer in this newly exposed area now be "above" the frost line? How would I deal with that? Is there a deeper footer right where my current walk out is (underneath the sliding door)?

[Rich]

Typically the drop footing will occur at the walk out area (below frostline). Unless you excavate everything you may never know how far the footing goes down in the other areas. If you think it is above frostline you may be able to get insulation and do a shallow foundation as approved by NAHB guidelines. They've put a book out on it and it has been tested in areas such as Minnesota and done very well. It involves rigid insulation up the stemwalls and out from there so the frost will be pushed away from the footing instead of underneath it. Interesting concepts. I can give you some more insight into that if you're interested I bought the guidelines. :lol:
Not sure if that helps you any.

[dacosa]

We are planning to add a slab patio to the back of our house, which will eventually have a deck above and be enclosed (the patio area). The slab will be as close to the basement level as is possible. The HAHB shallow footer idea may be what we need. We will have to excavate near the footer level for the slab gravel and it's own footing (to allow for the bearing weight of the deck above).

The question: how close can the patio slab come to the footer level?

Code in our area is footer 36" below grade.

Thanks!

[Rich]

It would be best to get your ideas on paper and take it to the building inspector. A response you may receive is that your footer needs to have 36" of coverage. See if you can get ahold of the shallow foundation design requirements from www.toolbase.org or www.nahb.com and take them into the inspector and see if they'll buy off on it.
With protection above the footer by the patio slab and using the shallow foundation insulation requirements I would think you could get it accepted. Many inspectors don't want to step out of their little box though - so it might be a chore also.