Subsidence Cracks vs Hairline Cracks
Updated: Apr 2
In this post we will look at the different types of cracks in walls ranging from subsidence cracks to a common hairline crack that you may see on a ceiling or plastered wall.
We discuss which cracks you should be mindful about when buying a property (or ones that exist in your own home), the different type of cracks and what implications they may have when buying or selling a house. Generally, there are two main types of ground movements that can lead to structural cracks appearing in buildings. The below two diagrams are from The Arboricultural Association:
1. Ground Heave Cracks
2. Subsidence Cracks (when the ground beneath structural walls / foundations is no longer able to support structural load from above)
Which type of wall is cracking?
In order to understand how serious a crack in the wall may be, it is important to consider establish if the wall is actually a structural wall or not? In older properties like Victorian & Edwardian period houses, generally as a rule of thumb, be weary of cracks in outside walls as usually all external walls are structural loadbearing walls. Cracks in internal non-loadbearing walls may not always be related to an underlying structural problem.
Hairline cracks can present them in different forms, patterns and lengths. In most cases, hairline cracks are not a sign of structural failure. Often, a wall or ceiling could have been freshly plastered and the hairline cracks appear due to shrinkage in the plaster. In older properties, hairline cracks in plastered ceilings can occur due to minor deflection / movement of timber joists which support the floor above.
There are times where you may need further technical advise and guidance on the cause of a crack, like the one pictured above. The wall that was photographed by our surveyor was in fact an outside load bearing structural wall, but the crack was due to an underlying water penetration issue that was adversely affecting both the external and internal wall.
Ground Heave - Diagonal upwards stepped cracking, like the image above of a client's home, normally tells us that the ground may be heaving. In other words, the earth is swelling and and pushing up against the foundations / structural elements of the property causing the brick wall to crack.
Subsidence Cracking - This type of cracking is normally vertical or diagonal, stepped downwards from high to low. This can happen when there has been a lengthy dry and hot summer which causes the earth to become dry, loose moisture and contract. As the earth begins to recede, the foundations of a house can begin to subside (sink) into the ground. There can also be other reasons for subsidence such as a failure of below ground drainage that begins to wash away the earth beneath the foundations of a house and nearby trees extracting moisture from the ground.
The image above was taken whilst surveying a client's house in London where a vertical crack through both the brickwork and mortar can be seen.
Boundary walls can also become affected by ground heave and subsidence. The boundary wall pictured above was taken from a client's building survey. The good thing here (to a certain degree) is that boundary walls can easily be demolished and rebuilt without having too much structural implications i.e. underpinning of the foundations. Settlement Cracks
In older houses, settlement cracks may appear in internal and outside walls of a house. Settlement cracks simply reflect historic movement and as the name suggests, the cracks should have settled. Settlement cracks normally concern home owners and home buyers as they can sometimes give a false impression that the building suffers from structural problems. Settlement cracks are usually harmless as long as the cracks are not getting bigger, longer and wider with time. A competent surveyor will be able to advise and differentiate for you if the cracks within your house are in fact settlement cracks.
I Have Cracks In My Walls, What Can I Do?
1) Monitor your cracks over a period of time! This may mean taking a photograph of the crack with your mobile phone, standing in the same place and taking a picture again in another two weeks time. Once you get 12 weeks worth of photos; compare them! Browse through them like a timeline and pay special attention to the crack to see if it getting bigger, longer and wider.
If you notice that the cracks are not progressive and have stopped moving; then the property may have undergone natural settlement which is not a great cause of concern.
2) If the cracks are getting bigger, it may be time to call in the experts. A building surveyor may be a good starting place as they maybe able to give you an idea of the suspected cause of the issue and what additional investigations may need to be undertaken to fully address the problem i.e. a CCTV drain survey to ensure they is now below ground drainage failure.
ZFN Chartered Surveyors can undertake full structural surveys, visit our quote page now to get a fee estimate for your structural survey!