I have a bump out in the works that grew from an inital 30″ x 10 ft cantilever to a 30″ x 30 ft bumpout that would have to included a ‘boxed’ section as the joists don’t run the same direction along the bump out. To complicate things, the cantilever-ed area would only have 6″ joists (true 6″….1930’s) and required running back 8′. We’ve decided to just put 44″ piers every 5′ and not bother with the cantilever…which I think I’m ok with. However the carpenter wants to run a 2′ trench conecting the piers and pour a quasi-foundation wall that the rim joist of the boxed extension would sit on, to enclose the bumpout (and keep criters from below….the bumpout is only a 6-8 inches above grade). I’m afraid those 2′ sections will give frost something to lift, and cause more harm that good. What do you think?
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quasi?
Can you define what you mean by "quasi-foundation wall"?
You may want your builder to keep in mind that, according to code, the bottom of untreated wood joist clearance to grade is 18" min. and untreated wood girders is 12".
may be reading to much into this but you call him carpenter, not the builder or contractor. as numbnuts pointed out, just for starters, the proximity of the joist to grade is to close. is he a licensed contractor? your addition going to be inspected?
why the 2x6? im guessing your trying to match up to an existing floor level. if your that close to grade why not a slab?
Bump out details
Thanks for all the requests for more info....sorry I was away from the world. I hope this fills in the details:
the bumpout project has a licensed general contractor. When we expanded the original plan to include the boxed sections, it was his carpenter who came up with the pier idea (and he and his brother got tasked with the job....brother to do the bulk of the digging). The gen's architect on call did the drawings for the permit office, who required the 18" clearance to grade, but allowed the bumpout if the space between joists and grade were 'enclosed.' Again the carpenter came up with what I call 'the quasi-foundation' to fill the permit office requirement and strengthen the rim joist. (The 6" joists are to match floor height). Permit office will inspect the dig to make sure we have the piers 42" required here in Nortehern IL (zone 5)...but even though they seem ok with the revised plan, I'm wondering about frost uplift on the 'quasi-foundation' section, which again is only 2'.
In theory, if you fill under the rim with pea gravel (maybe 8 inches) you can avoid uplift problems. You need some layer (plywood, plastic, whatever) between the concrete and the gravel to prevent the concrete from infiltrating.
Hope theory holds
Thanks. I appreciate your comment. I feel a little better....I think.
Jeff
really?
What theory is that?