I have an old home where the cement basement floor is far from smooth and level. In anticipation that we will someday need a new washer and dryer, and noting that some of them rotate at high speeds and need a solid base, I am thinking of having a plumber put in a new access to the sewer line (the pvc pipe the washer drains into; we now have just a basin), and a cement pad big enough for the new washer and dryer. Since the floor is thin, I anticipate the pad will be thicker and may extend above the floor, as those I have seen do. I don't know yet if there is sufficient clearance over the existing sewer to make the pad thicker, but even with the old floor. I think it may be traditional around here to elevate it, as our basements do sometimes have minor flooding.
I haven't selected the models yet, but the ones I have looked at seem to have different footprints. I want the pad to be big enough to accommodate whatever models we buy, but not so big that it is a tripping hazard.
So what would be a good size to make this?