Direct Line magazine

Need help with structural troubles?

Updated on: 8 September 2020

A large crack in a house wall

Subsidence, damp, dry and wet rot, and woodworm can all affect a building's structure. Here's what to look out for:

Subsidence

What is subsidence?

Subsidence happens when unstable soil causes a building’s foundations to sink. Clay soil is particularly vulnerable and long periods of dry weather can also contribute. ‘Heave’, on the other hand, is when the ground swells because of increased moisture and the foundations rise.

How can I tell if I have subsidence?

Remember, cracks in walls don't necessarily indicate subsidence. All houses have them and many are due to settlement, which is caused by the weight of the building. Grouting or sealing is usually all that's needed to fill minor cracks.

Subsidence cracks are normally 1mm or more wide. They are often wider at the top than at the bottom. Watch out for a series of small, often diagonal cracks, suddenly appearing in plasterwork, around doors and windows or between different parts of the property, especially after long periods of dry weather.

How do I fix subsidence?

If you're worried, contact your insurer straight away. If you're buying a home and think there's a risk, commission a RICS or ISVA Home Buyer's Report. In a few extreme cases you may need to replace or deepen the foundations.

Damp

There are three main types of damp:

  1. Rising damp is the most common. It's caused by moisture from the ground rising through the walls. It can loosen plaster and cause stains on internal walls. Rising damp only reaches up to one metre above ground level.

  2. Penetrating damp is caused by moisture coming through the roof or walls and is usually easy to spot.

  3. Condensation is usually caused by a lack of ventilation.

Shouldn't I already be protected against damp?

Unless the property is very old, walls are normally protected against rising damp by a damp-proof course built into the wall.

How do I cure damp?

For rising damp, you inject a chemical damp-proof course and re-plaster the internal walls with a waterproof layer up to 1.2 metres high.

How do I know if I have damp?

You can commission a report from a specialist damp company. This is often provided for free as part of the quotation process.

Timber troubles

  1. Fungal decay, which is more commonly known as dry rot and wet rot:

    • Dry rot needs moisture content of over 20% for spores to develop and spread. In extreme cases the timber becomes so brittle it can be broken up by hand.

    • Wet rot needs higher moisture content (40-50%) and becomes dormant in drier conditions. It doesn't usually spread to other materials, but it stains wood and causes splits and cracks.

    To treat rot, you must first remove the sources of damp. You may need to repair or replace affected timber and you should treat all timber with fungicide.

  2. Woodworm are wood-boring insects that lay their eggs on, or in, timber. The hatching larvae then bore through the wood. Woodworm are treated with insecticides.

Do I have to replace my timber?

An attack has to be very severe to warrant replacing or repairing structural timbers. Usually treatment of the rot is enough. The same specialist companies that handle damp work often also cover timber problems and reports.

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