ying new foundation to existing foundation

huangyhg

tying new foundation to existing foundation
what are your thoughts about tying a new building foundation wall to an existing foundation wall if the new building's superstructure is designed so it could stand alone if the existing building were to fall down?  do you recommend doweling or not?  does doweling help settlement issues?

if it is a small, light addition, i would definitely dowel it together with the existing and calculate the new footing working together with the existing.
if it is a larger, heavier addition with say column loads in excess of 75 to 100k, i would try to make it independent.
not knowing the specifics of your case, but in general, if i am adding an addition on to an existing building, i try and dowel the footings together to prevent differential settlement between the existing part and the new part.
( i am assuming spread or strip footings here, not a pile system)
most of the expected settlement for the existing part will have already occured if it has been there any significant period of time. the new section will still undergo its settlement. this could lead to differential movement between them with could throw off brick lines, precast revels, etc that could be considered objectionalbe from an appearance point of view.
usally, i use rebar drilled and epoxied into the old footings.
keep in mind that in ibc chapter 34, if you increase the load in any element more than 5% then you have to check that element and bring it up to the new code if it isn't adequate.