Garage Floor and Slab Cracks:
Which Ones Are Normal and Which Ones Mean Something
Concrete cracks. That’s expected. What tells you more is which way the crack runs, whether one side has dropped, and what’s happening at the edges of the slab.
Concrete garage floors crack. In Russ’s recent reports, some kind of garage slab crack shows up in 89 out of 269 houses, about a third. Most of those were noted as typical and left at that.
A few weren’t. A patched crack that had split open again, with the slab uneven on either side. A floor with pronounced settlement and one section sitting lower than the next. Cracks in the floor that lined up with stair-step cracks in the brick over the garage door, on a house where the driveway sloped toward the building and water pooled at the door.
The difference between those and the ordinary kind isn’t the crack. It’s what’s around it.
Why concrete slabs crack in the first place
Concrete shrinks as it dries. A slab the size of a two-car garage can’t shrink without pulling itself apart somewhere, so builders cut or tool straight grooves called control joints into the surface. The idea is to make the slab crack inside the groove, in a straight line, where it doesn’t show. Plenty of slabs crack beside the joints anyway, or run a crack corner to corner.
Temperature swings do the same thing on a smaller scale. A garage isn’t heated like the house, and the slab near the door sees more of the weather.
In most houses, the garage floor is a slab poured inside or against the foundation walls. It isn’t the footing that holds the house up. That’s why a crack in the garage floor usually stays a crack in the garage floor.
Cracks that are usually just concrete
These show up in Russ’s reports over and over, and the usual recommendation is to monitor them or seal them:
- Hairline cracks with no height difference across them
- Cracks that run along or out from a control joint
- Cracks that start at an inside corner, a floor drain, or a post
- Craze cracking, a web of fine, shallow surface cracks from the concrete drying too fast or being overworked during finishing
- Chipped edges along a control joint, where tires have broken off the shoulder
- Saw-cut overcuts, where the blade cutting the control joint ran past the end of the line
None of these mean the ground under the slab is moving. Sealing open cracks and joints keeps water and debris out, and that’s about it.
Cracks that get a closer look
The pattern changes when the soil under the slab is the cause. That usually means settling fill, water washing soil out from under the edge, or a slab that was poured over ground that wasn’t compacted well. Here’s how Russ sorts what he sees:
- Hairline cracks, flat across, no staining. Documented as typical.
- A crack that was patched and has cracked again in the same spot. Something is still moving.
- One side of the crack sits higher than the other. Russ’s reports flag walking-surface offsets over about 1/4 inch as a trip hazard.
- The slab slopes toward the house, or water stands on it after rain.
- The slab has dropped noticeably near a wall, or cabinets and framing along that wall have shifted with it.
- Cracks in the floor line up with cracks in the stem wall, the brick, or the drywall above. That’s when a structural engineer referral comes up.
Drainage is often part of it. A driveway that slopes toward the garage, short downspouts, or a slab edge that sits below the soil outside can all put water under the concrete. The posts on grading and drainage and differential settlement in post-war houses cover how that plays out on the rest of the foundation.
The driveway, walks and patio outside get their own post: cracked, sunken and heaved concrete.
Real Inspection Photos
Garage Slabs From Russ's Inspections
Garage floor cracks from Russ's recent reports, from typical to settled.
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Cracking and settlement in a garage slab. Russ recommended a concrete contractor or structural engineer find the cause. -
A slab crack at the garage door. On this house it lined up with cracking in the brick above and a driveway that sloped toward the garage. -
Moderate settlement across a garage floor. The report recommended checking whether the movement was still active. -
Craze cracking: fine surface cracks from the way the concrete was finished. It doesn't mean the slab is moving. -
Chipped edges along a control joint. A concrete contractor can patch and seal the joint.
New construction slabs
Buyers of new houses are often surprised to see cracks in a slab that’s only months old. Shrinkage cracks in the first year or two are common, because the concrete is still drying out. A new slab with a couple of hairline cracks along the control joints is the normal case.
What’s worth putting in writing to the builder is the same list as an older house: a crack that keeps widening, one side higher than the other, water coming up through it, or cracks that connect to the walls. Many builder warranties spell out what slab cracking they cover, often by width or by displacement. Read that section of your warranty before the one-year walkthrough.
The new construction inspection guide covers what a final inspection on a new house includes. Trusted Home Inspections does not offer pre-drywall or phase inspections.
What the inspection can and can’t see
A home inspection is visual. If the garage is full of boxes, two cars, a workbench, and rubber mats, most of the floor can’t be seen, and the report will say so. Epoxy coatings, paint, and snap-together floor tiles can hide cracks and patches too. Russ notes worn or damaged epoxy when he sees it, but he can’t see through it.
For a crack he can see, the report documents where it is, what pattern it follows, whether there’s displacement, and whether there’s staining or water. When the slab looks like it’s settling, the recommendation goes to a concrete contractor, a foundation specialist, or a structural engineer, depending on what else is moving. The post on structural engineer vs. home inspector explains that handoff.
- Ask the sellers to move cars, boxes, and mats off as much of the garage floor as they can
- Note any crack that has been patched, and ask whether the sellers know when
- Look at the brick or siding over the garage door for cracks that match the floor
- Check where the downspouts near the garage drain
Most garage floor cracks are shrinkage, and the report will call them typical. Displacement, re-cracking after a patch, settling at the walls, and cracks that connect to the structure above are the patterns that get a closer look.
If you’re still at the showing stage, the garage checklist for showings covers the door, the fire separation, and the rest of the space. To set up the inspection, you can book online.
Garage Floor Cracks FAQ
