Garage slab slopes to drain — level it with SLU, sleepers, or dimpled panels before flooring
A garage slab is pitched ~⅛″ per foot toward the door to drain (IRC R309.1), so you can’t floor over it flat — the low end leaves a wedge gap. Level the plane first: self-leveling underlayment for small slope + tile/LVP, PT sleepers + plywood for hardwood or cold climates (cavity takes R-10 foam), or dimpled floating panels for floating floors in mild climates.
What this diagram shows
A cross-section showing why a garage floor needs a subfloor system before finished flooring. A garage slab is poured to pitch about one-eighth inch per foot toward the garage door so it drains, per IRC R309.1, so a level floor laid on it would leave a growing wedge gap at the low end. The calculator picks one of three fixes from the slope, the finish, and the climate. Self-leveling underlayment is a poured cement layer that floods the low end to a flat plane — the thinnest fix, for tile or luxury vinyl on a small slope, and it adds no insulation. Pressure-treated sleepers topped with plywood are shimmed level and create a cavity that can hold R-10 rigid foam — used for nail-down hardwood, a large slope, or a cold climate, and it raises the floor the most. Dimpled floating panels sit on an air gap that lifts the finish off the cold, damp concrete — the fast option for floating vinyl plank, laminate, or carpet in a mild climate, but it needs a fairly flat slab to start.
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