The level requirement
The footprint needs to be level within about three inches corner to corner. More slope than that and the crew either cannot set the frame square or has to shim legs, which weakens the anchor connection.
Check it with a string line and a line level before order day. If you are off by more than three inches, a few hours with a box blade fixes it and costs a fraction of a return trip.
Foundation options compared
| Foundation | Typical cost | Anchor type | Best for |
|---|---|---|---|
| Bare ground | 0 | Mobile home auger anchors | Open carports, barns, rural sites |
| Compacted gravel | 600 to 2,000 | Auger anchors through gravel | RV covers, equipment storage |
| Asphalt | 1,500 to 4,000 | Asphalt anchors | Existing driveways |
| Concrete slab | 4 to 8 per sq ft | Wedge anchors into concrete | Garages, workshops, anything enclosed |
When you actually need concrete
- Any fully enclosed building you will work inside
- Any building with a roll-up garage door, so the door seals against a flat surface
- Two-post lifts, which require a minimum slab thickness your installer will specify
- High wind coastal sites where wedge anchors are the only acceptable connection
Slab sizing
Pour the slab to the exact building dimensions, not larger. A slab that extends past the frame collects water at the base of the legs.
Four inches thick with fiber mesh handles most residential buildings. Go to six inches with rebar for commercial or anything with heavy equipment.
Access for the delivery truck
The crew arrives with a trailer roughly 40 feet long. They need to get within about 50 feet of the footprint and they need room to turn around.
Low branches, soft ground after rain, and narrow gates are the three things that turn a one day install into a rescheduled install. Walk the approach before delivery day.