Here's my answer to a readers question in The Irish times on May 7th 2015
Cracks in walls
Q. In 2006, I built a four-bedroom house and was informed by the builders that as the property settles some cracking would occur. Cracking did start to appear over some windows, doors and ceilings. Over the years I have filled in these cracks, but they always reappear. The house is on an incline and I recently noticed a small hole under the property. Is the problem subsidence? If so, what steps should I take to resolve this?
All buildings will settle under their own weight and this typically results in cracking. Settlement cracking happens at weak points in the structure such as at the openings formed by windows and doors. Generally this settlement or “bedding down” of the property should be completed within the first ten years following construction. Your house is approaching its tenth anniversary. At this stage initial settlement should have ceased.
Expansion and contraction of building materials as they age will continue beyond this general timeframe. Movement can also happen as buildings expand when heated by the Sun and then contract when temperatures fall. This is known as thermal movement. It is common for houses to be constructed without joints that make provision for thermal movement. In the absence of these joints, settlement cracks can accommodate this normal thermal movement. This explains why filled cracks typically reappear. The building is simply expanding and contracting along the line of the settlement crack.
The sloping site you mention can leave properties prone to “differential settlement” meaning that some parts of the structure settle to a greater extent than others. This should not be significant in normal circumstances.
Subsidence on the other hand is different. In cases of subsidence cracking occurs when the ground that supports the structure moves away or is eroded and support is lost. This can happy for example if a water main or drain leaks and erodes the earth below the structure.
You mention that you have recently noticed a hole below the property. I assume that this is of recent origin or you would have noticed it before now. On the basis that there appears to be some erosion of the ground beneath your house, I would suggest that you engage a Chartered Building Surveyor or other suitably qualified professional to inspect and monitor the situation. The Surveyor will either give you piece of mind or will advise if you have an issue that needs attention.
Careful monitoring is necessary to allow correct diagnosis. Monitoring may involve the placement of simple measuring devices called tell-tales on the house. These record the amount and direction of movement taking place.
It would be very important to differentiate between settlement and subsidence as repair methods would be different. Repairs to subsidence may be covered by your home insurance if the house is not covered by a builders ten year warranty.
All buildings settle and crack and therefore I would not be unduly worried about cracks in buildings. However as there appears to be some movement of the ground in this case the matter should be investigated and the cause of movement established.