||09-09-2009 10:40 AM
Piers under pad for outdoor fireplace?
A friend is preparing to pour a pad for an outdoor fireplace, with two flanking walls at right angles (forming an "L"). He plans to keep the pads under the two walls separate from the pad supporting the fireplace. The wall pads will "float", i.e. be set on 4" compacted crushed mixed stone, 4" concrete with mesh. They will adjoin, but not be connected to, the fireplace.
For the 50"x70" pad under the 3000lb fireplace + several ton built-up hearth, we were thinking 6" or 8" rebar-reinforced (1/2" on 18" o.c.). The frost depth is ~40" (N. Ohio). Given the high and heavy fireplace sitting on top, letting it "float" above the frost line seems like a bad idea.
One suggestion we heard was to dig piers underneath the pad to below the frost line. Reasonable? How many/what size? Can they be poured at the same time as the pad, or do they need to be poured separately? Would "open holes" suffice, or better to go with a back-filled pier form like the big-foot?