I have, it feels soft. The guys putting up 20 decks a year, almost exclusively with composite decking, getting the home owner calls, won't go past 12" o.c. joist spacing. They do NOT use conventional lumber for decking any more, it rots and cracks and no home owner stains their deck every 3 years.
It was first relayed to me by a contractor who builds mostly decks. Roof top and regular. I have 2 investment properties with trex decking, one was built at 24 oc, 1 at 16. Forget about 24, you can see the banana, the 16 feels very soft. Not like a conventionally framed deck with 1x planks, much...
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Fixed, or not fixed, on wood joists though, you'll get a...
12" o.c. is a must when using trex decking. It's on every single job I do and 16" o.c. is a diving board after 2 years.
Bounce, L/18 (or less) on the joists and oversize the beams.
I would think the building department would make the owner(s) backfill the pit. They don't like open pits next to sidewalks for extended periods of time.
This looks like Philadelphia. The rubble wall is clearly at the same bottom of elevation as it's no longer neighbors. Do you mean the front porch area?
You can undermine walls within reason, similar to an underpinning operation. You can even underpin the location of house that is about to fall...
I'm assuming those are helical piles. It is not uncommon for them to be 4" or so off centerline. I've come to the conclusion you need a portion of the slab to resist the torsion from this eccentricity. Forget about the grade, many times the foundation is basement, well below grade.
I'd thicken...
Should be fine. What do they have specified, 2 grade beams going into the assumed over excavated garage/basement location (18' wide)? I put a 2x4 key and thickened slab in anticipation of the builder not compacting the soil properly.
My guess is the elevation is facing South and in an area of freeze/thaw commonly occurring during the winter (i.e. 20^ at night, 40^ day) during winter months. Water is collecting directly under the lintel and it is popping out the concrete to the rebar.