Cracks in walls: which ones a surveyor worries about

Most cracks in walls are cosmetic, caused by plaster shrinking, minor thermal movement or the house settling over many years. Surveyors worry about cracks that are wide (generally 5mm or more), taper from one end to the other, run diagonally from the corners of windows and doors, appear on both sides of the same wall, or show signs of recent or ongoing movement. Those cracks may point to subsidence, failing lintels or other structural problems.

Key points

• Hairline and fine cracks up to about 1mm are usually cosmetic.
• The pattern, location and age of a crack matter as much as the width.
• Tapering diagonal cracks around openings are a classic sign of movement.
• Cracks that keep reopening after repair suggest ongoing movement.
• A structural engineer can investigate and monitor cracks your surveyor is concerned about.

How do surveyors assess cracks?

When a surveyor carries out a Level 2 Home Survey or Level 3 Building Survey, they look at:

• Width - how wide the crack is, often measured roughly with a crack gauge.
• Shape - whether it is straight, stepped through mortar joints, or tapering.
• Direction - horizontal, vertical or diagonal.
• Location - near windows, doors, corners, chimney breasts or extensions.
• Inside and out - whether the crack goes through the wall.
• Age - fresh, clean edges suggest recent movement. Dirt, paint or old filler suggests it is historic.
• Context - soil type, nearby trees, drains, alterations and the age of the house.

They then use their judgement to decide whether the crack is cosmetic, historic and stable, or a sign of possible ongoing movement.

Crack width categories

Surveyors and engineers often refer to a widely used classification of damage in BRE (Building Research Establishment) guidance, which groups visible cracking in walls broadly by width and ease of repair:

Width is not the whole story. A 3mm tapering crack in the wrong place can be more significant than a 5mm vertical crack that has been stable for decades.

Which cracks are usually harmless?

• Fine cracks in plaster caused by shrinkage, especially in new builds or after replastering.
• Cracks at the joint between walls and ceilings, often due to slight timber movement.
• Hairline cracks around door frames, caused by doors being slammed.
• Cracks in new builds as materials dry out, typically in the first year or two.
• Small vertical cracks in long walls caused by thermal expansion and contraction, particularly in walls without movement joints.

These are usually dealt with during redecoration.

Which cracks worry a surveyor?

Diagonal tapering cracks

Cracks that run diagonally from the corners of windows and doors and are wider at one end can indicate that part of the building is moving relative to the rest, such as with subsidence or heave. Our guide to subsidence and house surveys explains this in detail.

Stepped cracks in brickwork

Cracks that follow mortar joints in a staircase pattern are common in movement. They can be caused by foundation movement, but also by defective lintels or wall ties.

Horizontal cracks

Horizontal cracks in brickwork, particularly at regular intervals in cavity walls, can be a sign of wall tie corrosion in older cavity walls. Horizontal cracking in rendered walls may also indicate other issues.

Cracks above windows and doors

Cracks above openings, sometimes with sagging brickwork, can mean a failing or missing lintel. This is common in older homes and where windows have been replaced without adequate support.

Cracks at extensions and bays

Cracks where an extension or bay window meets the main house often indicate differential movement, because the extension has shallower foundations. Some movement is common. Wide or growing cracks need checking. See our guide to buying a house with an extension.

Cracks around chimney breasts

Cracks around chimney breasts, particularly where breasts have been removed below, may indicate that the remaining chimney is not properly supported.

When should you get a structural engineer?

If your surveyor recommends further investigation, follow it before exchange. A structural engineer can:

• Assess the cracking in detail and give a view on the cause.
• Recommend drain surveys, trial pits or soil tests.
• Set up crack monitoring over several months if needed.
• Recommend and specify repairs.

Monitoring takes time, which can be a challenge in a purchase. Talk to the seller about timescales, or consider whether a price reduction reflects the uncertainty. See our guide on renegotiating after a survey.

What questions should you ask the seller?

• Have the cracks been there long, and have they changed?
• Has there been any insurance claim for subsidence or structural movement?
• Have any repairs, underpinning or helical bar work been done?
• Are there guarantees or engineer's reports?

The TA6 property information form asks some of these questions. Your conveyancer can raise more.

Should you fill cracks before or after buying?

If you are the buyer, do not rely on freshly filled cracks as a sign that a problem has gone away. Recently filled and painted cracks can hide the history of movement, and surveyors look out for new filler and patch repairs. If you notice signs of recent decoration around cracking, ask the seller why.

Once you own the home, fill cosmetic cracks during normal redecoration. For anything wider or recurring, wait for advice from a surveyor or engineer, because filling a crack that is still moving simply means it will reopen.

Cracks in mining areas

In former mining areas, cracking can be linked to ground movement from old workings. See our guide to buying in a former coal mining area.

If you want a surveyor to assess cracking in a property you are buying, get a fixed-price survey booked with a local RICS or RPSA regulated surveyor. A Level 3 Building Survey gives the most detail where movement is a concern.

Related guides