Originally Posted by
Rick Hurst
Years ago when my family built homes it was nothing to have a poured slab set for months before framing ever begin.
That's not a problem for slab-on-grade slabs. The earth is the support, it can only help to allow the slab to sit there.
However, as soon as you design the loading around piers/pilings, all kinds of different things can happen.
Lets say you have on pier which is 1 foot square (1 sf) and the load on it is designed to be X pounds, and another pier which is 2 feet square (4 sf) and the load on it is designed to be 4X pounds. When the house is constructed, both piers have the same soil loading ... X pounds per square foot.
BUT, when the house is nothing by a slab, the loading on the 2 foot square pier is now only X/4 pound per square foot (it has 4 sf soil contact area as compared to the 1 sf soil contact area of the other pier, both only have the slab weight on them). Speaking basically of course, the limited weight of the slab throws off this calculation some, but that's the general idea. The pier with X pounds per square foot will settle more than the pier with X/4 pounds per square foot.