Shop slab thickness is one of the most-asked, most-overcomplicated questions in residential concrete. The honest answer comes down to the load.
The decision matrix
Sized to typical residential and light-commercial loads:
- Four inches, fiber mesh: storage shed, garden shed, light foot traffic only
- Five inches, wire mesh: residential garage, ATV storage, light hobby work
- Six inches, #4 rebar 12-inch grid: home shop, truck and trailer parking, woodworking shop, welding bench
- Six inches, #4 rebar 12-inch grid, thickened edge: pole barn slab, equipment storage, hay storage
- Eight inches, #5 rebar 12-inch grid: shop with a two-post or four-post vehicle lift, tractor work, heavy equipment
Base prep matters as much as thickness
An eight-inch slab on poor base will fail before a six-inch slab on proper base. We never quote thickness without quoting the base prep underneath it. Both numbers matter, and skimping on either one wastes the other.
Common mistakes
Two we see often in rural Douglas County:
- Over-spec: an eight-inch slab for a residential storage barn is overkill and a waste of $1,500 to $3,000
- Under-spec: a four-inch slab for a shop with a lift will crack at the lift posts within a year or two