How Much Does a Garage Slab Cost? (Monolithic vs. Stem Wall Footings)

Quick answer: a 2-car garage slab (24x24 ft, 576 sq ft) at 5 inches costs about $4,250 to $7,540 as a plain floating slab, or roughly $7 to $14 per sq ft. With a monolithic thickened edge it runs about $4,830 to $9,240. In cold climates, a stem wall on frost-depth footings adds roughly $4,700 to $11,300, for a total near $9,000 to $18,800.

The floor itself is the easy part of a garage slab. The real cost question is what holds up the walls. In a warm climate, a slab with a thickened edge does the job in one pour. Where the ground freezes, the building department will usually want footings below the frost line, and that can roughly double the price or more. This guide prices both, with the math shown.

Garage Slab Cost by Size

These are slab-only prices: no footing upgrade, no excavation and no building above. The IRC minimum for a slab on ground is 3.5 inches and plenty of garages are poured at 4 inches (a 4-inch 24x24 runs about $3,950 to $7,170). We price at 5 inches because a garage floor carries point loads from tires, jacks and jack stands, and the extra inch costs little. Price your own footprint in the slab cost calculator or on the garage slab page.

Option 1: Monolithic Slab with a Thickened Edge

A monolithic (or turn-down) slab is poured in one piece. The floor is 4 to 5 inches thick, and around the outside the concrete turns down into a beam about 12 inches wide and 12 to 18 inches deep, with 2 continuous #4 bars in it. That beam is the footing. The walls sit on top, held by anchor bolts set in the wet concrete.

The edge is cheap because it is mostly concrete and a trench, poured by the same crew on the same day. Its limit is depth: even the 18-inch edge only reaches below the frost line where the frost line is shallow. Size other footprints with the concrete footing calculator.

Option 2: Stem Wall on Frost-Depth Footings

In the northern US, frost can reach 36 to 48 inches or more below grade. Footings above that depth can heave. The usual answer is a spread footing at frost depth, a short concrete stem wall (also called a frost wall) up to slab level, and a floor slab poured inside the walls. It takes two or three separate pours with inspections between them, so it costs much more than a turn-down edge.

No single price list covers stem walls, so here is the build-up for the same 24x24 garage (96 ft of perimeter), assuming a 16x8-inch footing and an 8-inch wall about as tall as the frost depth:

That works out to roughly $49 to $118 per linear foot of wall. Your local footing size, wall height and rebar schedule will come from the building department or an engineer, so treat this as a budgeting range, not a design. A concrete block stem wall on a poured footing is a common alternative; get prices for both if a mason works in your area.

Floor Details That Change the Price

• PSI: IRC Table R402.2 sets the minimum for garage floor slabs at 2,500 PSI in mild climates, 3,000 in moderate and 3,500 PSI air-entrained in severe-weathering areas, since cars bring in snow and salt. Moving a 2-car slab from 3,000 to 3,500 PSI adds only about $40 to $100.
• Vapor barrier: IRC R506.2.3 requires a 6-mil vapor retarder under floor slabs, but its exceptions include detached garages and other unheated accessory buildings. Put one in anyway if you might heat the garage, finish the floor with epoxy or store anything that hates moisture. On 576 sq ft it costs about $144 to $259.
• Base: a 4-inch compacted gravel base (IRC R506.2.2) plus excavation adds about $1.40 to $3.30 per sq ft, or $810 to $1,900 for a 2-car garage. Use the gravel base calculator.
• Slope: IRC R309.1 requires the parking area of a garage floor to slope toward the vehicle door or a drain. At 1/8 inch per foot, a 24 ft deep garage falls 3 inches front to back.
• Joints: a 5-inch slab should have joints no more than about 15 ft apart. Two joints, one each way, split a 24x24 into four 12x12 panels.
• Reinforcement: #4 rebar at 18 inches runs about $1.00 to $1.75 per sq ft and is in the high end of our ranges. See the rebar calculator.

Which Foundation Should You Choose?

If you are in a warm or mild climate, or building a small detached garage that qualifies for the frost exemption, a monolithic slab is the cheapest sound choice, with one pour and one footing inspection. If you are in a cold climate and the garage is attached or larger than 600 sq ft, plan on a stem wall or a frost-protected shallow foundation and budget accordingly. A stem wall also raises the wood framing well above grade, which helps with snow, splash and termites. Comparing a 24x24 slab on its own? See the 24x24 slab cost breakdown.

DIY or Hire a Pro?

A garage slab is a structural element that will be inspected, and it takes 9.78 cubic yards for a 2-car floor alone. Even experienced DIYers usually hire a crew for the pour and finish. You can save on demolition, clearing and the final cleanup. Before signing, check the bid with the concrete quote checker and make sure it states floor thickness, edge or footing size, PSI, base depth, vapor barrier and anchor bolts. Wait at least 7 days before parking on the new floor.

Sources and Method

Slab prices use the same line items as our calculator (see our methodology). The stem wall build-up uses our ready-mix, forming, trenching and rebar rates applied to the volumes shown. Code references: IRC R403 (footings, including R403.1.4.1 frost exemption and R403.3 frost-protected shallow foundations), IRC R506 (slabs on ground) and IRC Table R402.2 (concrete strength), with ACI 332 for residential concrete and ACI 302.1R for floor construction. Frost depth, footing size and permits are set locally; your building department and, where needed, an engineer have the final say.