Cracks in walls – what’s normal and when should you worry?

This article is for general information only and is not intended as advice. Each property has its own set of unique circumstances, and all potential issues with regard to cracking should be investigated by a surveyor on a case-by-case basis before making any decision.

Whether you are buying your next home or a buy-to-let investment, knowing that the building is in good condition is key. If there are walls that have cracks in them, would you know if this is a minor nuisance that’s easily fixable, or a major structural problem that could impact the property’s value?

At Cosey Homes, our RICS Building Survey (Level 3) and Specific Structural Inspections are designed to check all visible building elements and deliver comprehensive professional advice, so that homebuyers can make informed purchase decisions based on fact. Minor surface cracks are usually nothing to worry about. However, wall cracks that are the result of structural movement are a whole different story.

Why are there cracks in the wall?

We should start by pointing out that finding cracks in the wall is not at all unusual. In fact, most properties have them at some point. Cracking can occur naturally as a result of the settlement, for example in the following scenarios:

• In new-build properties and building extensions, the foundations will settle under their own weight over time, and this can lead to the appearance of hairline cracks.
• Hairline cracks can also appear on interior walls that have been freshly plastered and are drying out over time.
• In older houses, temperature and humidity changes can cause the structure to slightly expand and contract naturally over time, leading to cracks in the wall.
• Furthermore, if timber window frames are replaced with uPVC double glazing and there is no supporting lintel, cracks can appear around the window.
• If the property is located on a busy road, cracks in walls can occur as a result of road traffic vibration over the years

When do wall cracks suggest subsidence?

Superficial cracks and hairline cracks, such as the ones mentioned above, can generally be remedied with straightforward painting and decorating. Larger cracks, however, could be a sign of subsidence or heave, which are major structural movements that can do real damage to the property’s foundations. This could be due to a number of factors:

• Tree roots: If tree roots have found their way underneath the foundations, they may take up moisture from the soil under your property. Large trees that grow within 5-10 metres of the house should be investigated, with willows, oaks, poplars and ash trees posing the biggest risk.
• Heavy rainfall: Wet winters and dry summers can spell trouble for houses built on clay soil. Subsidence in clay soil tends to be cyclical, with shrinkage in the summer when the soil is bone dry, and expansion during the wetter winter months when flooding may occur.
• Long, dry summers: Clay soil in particular is porous, meaning it shrinks when dry, pulling away from the foundations. After the record-breaking temperatures in the summer of 2022, there was a surge in subsidence insurance claims – the highest in 16 years.
• Underground leaks: Burst pipes or long-term leaks from damaged drains can wash away the subsoil unnoticed for long periods of time, eventually causing foundations to subside. Or the ground can become overly saturated to the point of no longer being able to support the weight of the building.

How wide are the cracks in the wall?

If you are concerned that there are serious cracks in your property, a good place to start is by getting the tape measure out. Generally speaking, cracks that are wider than 15mm, or that appear suddenly, should be investigated without delay by a surveyor or structural engineer who will categorise them as follows:

Negligible: Hairline cracks under 1mm wide can be easily dealt with by redecorating
Slight: 1-5mm wide cracks can be rectified with interior filler or external repointing
Moderate: 5-15mm wide cracks may need professional building work
Severe: Large cracks up to 25mm may indicate structural damage and should be inspected by a professional urgently
Very Severe: Cracks wider than 25mm are typically a sign of major structural damage and may need underpinning and rebuilding. Seek professional help at once.

Another telltale sign of subsidence cracks is that they tend to run diagonally across a wall and are typically wider at the top and taper in at the bottom. Take a careful look, particularly around doors and windows. Large vertical cracks are another obvious sign that may indicate structural movement.

If you have identified cracks in the wall of the property you are looking to buy, and you’re not sure how serious they are, it is good common sense to seek professional help. Contact Cosey Homes for an instant online survey quote or call our friendly, knowledgeable team on 0330 053 5823.