7 Signs Your Driveway or Garage Floor Needs Levelling

Concrete slabs don't fail on their own. They're ground-supported structures that rely on continuous contact with the substrate beneath them. When that ground moves, whether through clay shrinkage, water erosion, or gradual compaction, the slab loses its bearing and follows. Voids form. Settlement begins.

The signs below are symptoms of that process at different stages. Some warrant early investigation. Others need attention now.

1. Standing water after rain

A properly laid slab is laid to falls: a gradient of around 1 in 80 away from buildings and toward drainage. When one section settles by even 5–10mm, that gradient reverses or neutralises, and water moves to the lowest point instead of away from it.

In the UK, with 1,200mm of annual rainfall in lowland England and considerably more further north and west, this shows up early and reliably. A puddle that sits for more than 30 minutes after rain stops on a dry day is not poor drainage. The slope has changed.

Why it matters beyond the obvious: water pooling adjacent to a slab edge is draining into the sub-base. Over time it washes out fine particles, enlarges the void, and accelerates the settlement that caused the pooling in the first place. It's a self-reinforcing cycle.

Urgency: Moderate. Worth monitoring and assessing before the next dry period.

2. A visible lip or edge between slabs

Run your foot slowly across every joint on the driveway or garage apron. A height difference of 10mm at a joint is enough to catch a shoe. At 20mm, you have a trip hazard that courts have upheld as actionable under the Occupiers' Liability Act 1957 for commercial premises, and a genuine risk for elderly visitors and children on residential driveways.

These edges often appear suddenly after a frost. One heave and settle cycle can open a joint by 8–10mm in a single winter, particularly on clay soils where sub-base movement is seasonal.

Urgency: High. Trip edges are the most likely cause of immediate harm.

3. Cracks running across the face of the slab

Knowing which cracks matter is the first skill.

Shrinkage cracks appear within the first year of laying and run in a roughly random pattern across the slab face. They're typically hairline (under 0.5mm), have no vertical displacement between the two sides, and don't progress significantly over time. These are cosmetic and normal.

Settlement cracks are different. They tend to run toward joints or at consistent angles, often reflect the shape of the void beneath, and show measurable vertical displacement between the two sides. To check: drag a fingernail slowly across the crack. If it catches on one side, one panel has dropped relative to the other.

Wide settlement cracks (3mm or more) that have developed progressively over 12–24 months indicate active ground movement beneath the slab, not a one-off event.

Urgency: Moderate to high, depending on the degree of differential displacement.

4. A hollow sound when tapped

Solid, well-supported concrete produces a firm, clean ring when tapped. A slab over a void sounds noticeably different: flatter, duller, sometimes almost reverberant.

To do this properly: use the handle of a hammer or a heavy screwdriver. Work in a grid pattern across the slab, tapping every 400–500mm. Mark the hollow areas with chalk as you go. The result is a rough map of void extent that a contractor can correlate with their own assessment.

Most homeowners are surprised by how large the hollow area is relative to the visible settlement. A slab that looks like it's dropped 15mm at one corner might have a void spanning several square metres beneath it.

Urgency: Dependent on size and location.

5. Doors or gates catching at the floor

A garage door that used to clear the floor and now catches, or a gate that scrapes where it didn't before, is recording a change in level. The door and its fixings haven't moved. The reference point has.

This sign is useful for two reasons. First, it's measurable: mark the current clearance between door bottom and floor with a pencil on the door jamb, and check again after six months. A reducing clearance is telling you the slab is still moving. Second, it indicates the direction of movement relative to fixed structures, which helps a contractor identify the source.

Urgency: Moderate. The rate of change matters more than the current clearance.

6. Gaps opening at edges and thresholds

Where a concrete slab meets a house wall, a garage threshold, or a step, the joint should be tight or filled with a flexible sealant. A gap that has opened over time means the slab has dropped relative to the fixed structure.

Beyond the cosmetic problem, this gap allows water to bypass the damp proof course at the threshold. Water in this location can cause dampness in the garage or hall floor, raise the moisture level in the sub-base (worsening future settlement), and in winter allow ice formation that forces the gap wider still.

Urgency: Moderate to high if the gap is at a house wall or threshold with a damp proof course.

7. Drainage running toward the house

After 10mm or more of rainfall, check where surface water flows. On a driveway, it should run toward the road or toward a linear drain at the front. In a rear yard, toward a gully. If it's flowing toward the house wall, pooling at the garage entrance, or sitting against a step, the slope has changed.

This is worth checking twice: once during and once after rainfall, as standing water can mask flow patterns.

Urgency: High if water is pooling against a house wall or entering a garage. The consequences extend beyond the concrete.

Acting on what you find

One sign in isolation, particularly standing water or a small lip, may not need immediate work. Several signs together, or any single sign involving water entering a building or a clear trip edge, should be assessed by a resin injection specialist.

The economics of early treatment are straightforward. A void beneath a 15m² driveway section treated at first signs costs considerably less than the same void treated after it has doubled in size, the slab has cracked through, and water has been entering the sub-base for two winters. See our cost comparison for the numbers, or request a free survey for your property.