Cracks have appeared on my gable wall. Should I be concerned?

I have a dormer bungalow (built in 1987) and this year some cracks have appeared on the south-facing gable cavity wall of the house – on the inside and outside. Should I be concerned, and if so what next steps should take?

It would be difficult to give an accurate assessment of the cracking without the benefit of a site inspection. Given the age of the property they are not likely to be settlement related and I would assume they relate to an external factor. There are a number of issues to consider mainly in identifying what, if anything, has changed in the recent past.

Did you carry out any alterations to the dwelling and in particular the rooms within the attic that may have caused a stress or outward pressure on the main load-bearing walls? This could result in cracking to the gable wall.

With a dormer structure the weight of the roof is mainly supported on the front and rear walls and if any roof members are cut to facilitate an internal alteration the triangulation of the structural roof member may be affected and exert an outward pressure on the walls at wall-plate level. This can lead to cracking to the gable wall close to eaves level.

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Is there any works on the adjoining site that may have caused vibration damage to your property? For example, is there a site being developed next door with heavy excavating which may send vibrations through the ground and affect your foundations temporarily, but enough to cause some vibrations that might lead to cracking to your external wall finish.

A common cause of movement in a house is shrinkage or swelling of the soil resulting from changes in the amount of moisture in the soil.

Seasonal movement

Similarly, are there any trees or vegetation growth growing close to the gable wall that might change the soil properties resulting in drying of the soil and induce some settlement under the foundations which would lead to seasonal movement and cracking to the wall. Was a large tree cut down recently close to the house? Finally, it might be worth having your drains checked for blockages.

Once the cause of the cracking is identified you then look at the best method of repair. Damage assessment tends to be subjective with words like “light”, “bad” and “severe” used to describe the crack.

The British Research Establishment issues guidelines and categorise cracking from 0 (for hairline cracks) to 5 (for large structural cracks) which may require partial rebuilding. Mostly cracking falls into categories 0-2 where the cracks can be repaired by filling and redecoration. I suspect your cracking is in this area.

However, moderate cracking now may indicate progressive movement that is going to get worse and cause further damage. You should contact your local building surveyor or engineer who will advise on any threat to stability and safety, the extent of repair required and if further monitoring is required. – Pat McGovern

Pat McGovern is a chartered building surveyor and member of the Society of Chartered Surveyors Ireland scsi.ie