How Thick to Pour a Garage Floor

Concrete Slab Types

• The amount of concrete you’ll need depends on the type of slab you’ll be pouring. In areas where the ground freezes in winter, the traditional T-shaped foundation places underground footings below the freeze zone. After the walls are built, you pour the floor. If your cold-country garage will be heated, you can build a frost-protected floor with just one concrete pour. A slab-on-grade foundation and floor is simpler still but feasible only where the ground won’t freeze. Slab edges are poured much thicker -- that is, deeper -- to establish the footing.

Concrete Considerations

• Never pour your garage floor on frozen ground or base materials, whether fine gravel or sand. An even, well-compacted base helps ensure that the floor has relatively even depth and strength. Make sure the base slopes correctly too, directing drainage away from your house and other buildings. You’ll need 2500-psi (pounds per square inch) concrete, at minimum, but a high-performance 4000-psi mix is recommended in cold climates where concrete is subjected to frequent freezing and thawing. Local concrete contractors can recommend other mix specifications, to handle conditions in your area.

Family Garage

• The minimum recommended depth or thickness for a concrete family garage floor is 4 inches. If you choose 2500-psi concrete, add fiber-mesh reinforcement to the mix, incorporate wire mesh or use rebar (reinforcing bar) to reinforce and strength the poured floor. You may want to use the same thickness of concrete used for your driveway, especially if your concrete driveway has held up well.

Heavy-Duty Garage

• Add at least an additional 2 inches of concrete for extra strength if you’ll be parking RVs, large pickups or a many vehicles in your garage. A heavy-duty concrete garage floor of 6 to 8 inches should hold up to almost any use. High-performance concrete of 3500 to 4000 psi is also recommended for heavier vehicle loads. Rebar or other structural reinforcements add still more strength.