A garage slab costs $6 to $12 per square foot installed by HomeGuide's concrete slab page, or $2,400 to $6,900 for a two-car garage floor. In North Jersey the footings under it must reach below the frost line, which the state code lists at 3 feet for the northern counties.
Every dollar figure on this page is a national figure published by HomeGuide (read October 2026), not a price from us. HomeGuide publishes no figure for New Jersey or Newark, so we do not claim one. On a real job, the price moves with access down a narrow driveway, any old garage to remove, footings deep enough for frost and the finish you pick.
How much does a garage slab cost?
A garage slab costs $6 to $12 per square foot installed by HomeGuide's national figures, with materials $3 to $7 and labor $3 to $5 per square foot. A two-car garage floor of 400 to 576 square feet runs $2,400 to $6,900, and a 20 x 20 slab $2,400 to $4,800. A gravel base adds $1 to $3 per square foot, and removing an old slab $3 to $8 per square foot. HomeGuide gives no price per cubic yard of concrete.
| Slab | HomeGuide national range |
|---|---|
| 20 x 20 | $2,400 to $4,800 |
| 20 x 30 | $3,600 to $7,200 |
| 30 x 30 | $5,400 to $10,800 |
| 4 inches thick | $6 to $8 per sq ft |
| 6 inches thick | $8 to $10 per sq ft |
How thick should a garage slab be?
A garage slab is commonly 4 to 6 inches thick. HomeGuide says most two-car garages are made with reinforced concrete 4 to 6 inches thick; that is common practice, not a code figure we quote. A thicker slab or thickened edges are used for heavy trucks, a car lift or a slab that carries the walls. The plans for your garage set the thickness, the reinforcement and the stone base.
Do garage footings need to go below the frost line in New Jersey?
Yes, in most cases garage footings must go below the frost line. The New Jersey edition of the residential code lists a frost line depth of 3 feet for northern New Jersey, defined as Mercer and Middlesex Counties and every county north, which includes Essex, Hudson and Union. The code allows an exception for some small free-standing buildings, and the building department decides if yours qualifies. Footings that are too shallow heave in winter and crack the slab.
Can you build a garage on a sloped lot?
Yes, a garage can be built on a sloped lot with stepped footings, a taller foundation wall on the low side or a retaining wall. West Orange and parts of Belleville have many sloped yards. The slab grade has to fall toward the door, not toward the back wall, and the driveway has to meet the door at a slope a car can climb in snow.
How do I keep water from running into my garage?
Keep water out of a garage by setting the slab a little higher than the driveway, sloping the ground away on every side, and carrying roof water away with gutters and downspouts. Where a driveway runs downhill toward the door, a trench drain across the entry catches runoff. Many old Newark garages sit lower than the yard around them, which is why they flood in heavy rain.
Does a detached garage need its own foundation?
Yes, a detached garage needs its own foundation, usually a footing below frost around the edge and a slab inside. It stands apart from the house, so it is not tied to the house foundation. A kit or metal garage also needs a proper footing or slab, built to the maker's anchor drawings.
How much does it cost to demolish an old garage?
Demolishing an old garage costs $1,000 to $5,000 on average by HomeGuide's national figures, or $3 to $10 per square foot. A wooden garage runs $1,000 to $3,500 and a detached brick garage $1,500 to $5,000. Cleanup can add $1,500 to $3,000, and a dumpster $300 to $700 per week. Demolition needs a permit, and the power to the garage has to be cut first.
Why do old garage slabs crack in North Jersey?
Old garage slabs crack mostly because of frost, poor base and water. HomeGuide notes that concrete tends to crack in colder climates where the ground freezes regularly. Many garages from the 1920s to the 1950s were poured thin, on soil with no stone base and no footing below frost, and decades of freeze and thaw broke them up.
How long does a garage slab cure before framing?
A slab needs time to cure before the walls go up, and the plans or the concrete supplier set how long. Light framing can often start within days, but concrete keeps gaining strength for weeks. In North Jersey winters, cold slows curing, so a winter pour needs insulated blankets and protection from freezing. A slab that freezes early can scale and crack.
Thinking about a garage on your lot? We come out, measure, check the driveway and whatever is standing there now, and send a written quote. Call or text (917) 909-5756.