Do we need to tie the new footings into the old ones if we aren't doing a basement in the new addition space and only doing 4 ft? The architect is saying no, but I'm not too sure about that.
The architect is rite if your only doing a 4' wall it would be impossible to reach footing. The plans should show the tie in which will be epoxy rebar from pony wall into existing foundation wall. And pony wall will be sitting on piles in place of footing.
The new footings and foundation wall will need to be tied into the existing foundation wall and should be constructed of the same style of foundation. This will stop the addition moving independently and causing structural/stress issues in the framework and finishing where the they meet. By using the same style of foundation the whole property will move more uniformed as apposed to foundation and piles which have different loadings/pressures.
The building code (Part 9) requires that footings be on undisturbed soil. The architect can use Part 4 rules instead and disregard Part 9.
I added a sunroom to my home similar to what you're describing. I excavated a little deeper than required then added some clay and compacted it with a jumping jack before placing the footing and tying it and the concrete wall into the house foundation with 10m rebar. That was 17 years ago and there's been no detectable movement.
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