Step one is shooting the grade across the pad
Before anyone argues about foundation types, somebody has to put an instrument on the pad and take a shot at every corner and a few points in between. What comes back is a number: how many inches the ground drops from the high corner to the low one. That single number does more of the deciding than anybody's preference does.
Ground that is near enough to level can take a monolithic pour, because the thickened edge can run around the perimeter at one elevation without burying itself at one end and standing in the air at the other. Ground that drops hard cannot. Keeping a floor level over ground that falls away means one of two things: bringing the low side up with imported fill, or stepping a footing down the slope and building a wall up off it to make up the height. On a hillside lot the second one usually costs less and puts the bearing on dirt that has been sitting there a long time, instead of on fill that was pushed in last month.
A monolithic foundation is one truck day for the whole thing
On a monolithic build the perimeter and the floor are formed as a single piece of work. The perimeter is a turndown edge, meaning the concrete runs deeper around the outside than it does anywhere across the middle. A trench gets cut around that outside line, the outer face gets formed, stone goes in across the field, steel goes into the edge and mesh or bar goes into the floor, and the whole thing gets poured in one visit. The edge and the floor come out as one piece of concrete with no joint between them, which is exactly why it is called that.
The single visit is the appeal and it is also the catch. Everything that has to be under or inside that concrete has to be settled first: plumbing coming up through the floor, sleeves for anything else that passes through, the vapor barrier, and the sill hardware pushed into the wet edge on your framer's layout. After the finishers walk off, nothing gets added without cutting concrete.
Footing day, wall day, then floor day
The other way is a sequence rather than an event. The footing is poured first, flat and wide in the bottom of the trench, with its steel tied in and with dowels standing out of the top or a keyway pressed into it. Those are what the wall grabs later. After it sets, we set forms on that pad, lap the wall steel into the dowels, and pour the wall as a second event. Then the forms come off, the tie holes get patched, and the wall stands there waiting on the framer.
The floor is its own pour after that and it does not have to happen the same week. On a crawl space build there is no floor slab at all, because the floor is framed across the top of the wall. On a garage or a shop with a stem wall, the inside gets filled, stoned and poured once the shell is up and the finishers can work under a roof.
Both of those pours usually come off hose rather than a chute. A footing trench and the top of a wall form are two of the places a loaded ready mix truck cannot safely reach, which is why our own trailer mounted line pump goes on nearly every foundation we pour.
What each one does to your framer's start date
This is the part that moves more jobs than the engineering does. Nothing gets framed on a monolithic foundation until the concrete is in, because the concrete is the thing the first plate bolts to. That puts your framing crew behind our pour date and behind whatever the weather does that week. A wet stretch in March pushes everybody who was waiting on us.
Footing and stem wall breaks that dependency apart. The framer can be up and roofing while the inside of the building is still dirt, and the floor goes in later, under cover, on a day that suits everyone's calendar. If you were lucky to book the framing crew you booked, that flexibility is worth real money even when the concrete side costs a little more.
The questions we ask on the phone before we come out
None of these are trick questions and you can answer most of them standing in the yard. Fill is the one people forget to mention. A pad that got flat because somebody bladed dirt into the low side still needs a footing that reaches ground capable of holding a building, which means either a deeper trench or getting that fill back out. Either way the footing bears below the frost line that applies at your address, that depth comes from local code and from your elevation, and we confirm it and put it on the written estimate before anybody digs.
Both builds sit in the same 8 inch foundation band on our estimator, $14 to $22 per square foot installed, with any floor slab priced on its own line. Which one your lot takes moves you around inside that range rather than into a different kind of work.
- How far the pad drops from the high corner to the low corner
- Whether it is stick framing that needs a perimeter to bolt to, or post frame that carries itself
- Whether the shell has to go up before the floor goes in
- How tall the crawl space or the stem wall has to be at the low end
- Whether the pad is undisturbed ground or fill brought in to level it