Diagonal Cracks Above Windows in Toulon: Foundation Settlement

Are you noticing cracks running diagonally from the corners of your windows? In Toulon, on the Var’s clay soils, this symptom often points to differential settlement of the foundations. In practice, one part of your house is sinking more than another, and the walls are deforming. DTU 20.1 (masonry walls and partitions) tolerates hairline cracks, but beyond 2 mm of width, action is needed. Here’s how to analyse the situation and respond effectively.

Identifying the cause: moisture or clay shrink-swell?

In Toulon, the subsoil is often clay-based. During droughts, clay shrinks and the foundations lose their support. If your cracks appeared after a heatwave or a water leak, the diagnosis becomes clearer. Check whether any trees are too close to the house: their roots draw out moisture and worsen the phenomenon. Also check the doors and windows: if they start sticking, the deformation is active.

Measuring progression: active or dormant cracks?

Place a plaster crack monitor over each crack and note the date. If the monitor cracks within a few weeks, the movement is active. If nothing changes after three months, the crack has stabilised. Warning: an active crack wider than 5 mm is a red flag. In that case, don’t delay in calling in a professional. A building expert can take precise measurements and determine whether deep foundations are needed.

Addressing the surroundings: drainage and vegetation

Before considering major works, start by eliminating external causes. Move trees that are too close to your façade (at least a distance equal to their mature height). Check that your gutters direct water well away from the walls. Install perimeter drainage if the soil drains poorly. These simple measures can stop the cracks from progressing. In Toulon, where the mistral wind dries out the soil quickly, controlled watering in summer can help maintain stable moisture levels.

Reinforcing the foundations: suitable techniques

If settlement is confirmed, several solutions are available. Micropiles or underpinning are the most common. For a single-family home, cement grout can also be injected beneath the foundations to stabilise the soil. This work must be carried out by an experienced contractor, following a prior geotechnical survey (standard NF P 94-261). Costs vary, but it’s better to invest than to watch the structure deteriorate.

Recourse and guarantees

Your home insurance may cover this damage if the settlement is due to drought (natural disaster declaration). Article 1792 of the French Civil Code also protects homeowners for 10 years after construction. If you bought the property recently, check whether the seller had a disclosure obligation. For a dispute, a court-appointed expert can be assigned. In Toulon, the BRGM publishes clay shrink-swell risk maps: check them to assess the risk in your area.

Go further

• Ten-year structural warranty and completion guarantee insurance: how compensation works in the event of defective work
• Neighbour’s tree branches in Toulon: pruning, trimming, and the right to have them removed — Article 673 of the Civil Code
• Cracks in a wall: is it serious? When to call in an expert

Frequently Asked Questions

Are diagonal cracks above windows serious?

Yes, this can indicate foundation settlement. These stair-step cracks starting from the corners of openings are often caused by ground movement. It’s important to get a quick diagnosis from a professional to assess the severity and avoid structural damage.

How do you repair diagonal cracks above windows?

The repair depends on the cause. If it’s active settlement, the foundations must first be stabilised (micropiles, resin injection). The cracks can then be treated on the surface with a flexible coating or by epoxy resin injection. A structural engineer’s opinion is recommended.

When are cracks above windows dangerous?

They are dangerous if they widen, lengthen, or are accompanied by other signs such as sticking doors or sagging floors. If they are fine (less than 2 mm) and stable, they may just be cosmetic, but monitoring is still needed. If in doubt, consult an expert.

📅 Mis à jour le 25/09/2026 — Cassini Expertise, expert bâtiment indépendant (06·83·13·40).