There are few things that are more guaranteed to send a cold shiver of reluctance down a potential house buyer’s neck than the mention of ‘subsidence’. However, all is not lost if you have your heart set on a property that has suffered, or is suffering, from ground movement.
In this feature, we take a look at what causes subsidence and ground heave and how to spot the signs. We also cover what you need to consider if you are thinking of buying a property with risk of subsidence.
What is Subsidence?
Subsidence is the term given for the downward movement of the land beneath a property which causes the foundations to shift. When this happens, some structural damage can occur which is commonly seen with the presence of cracks in either/or internal and external walls.
Why Does Subsidence Occur?
There are a lot of reasons why subsidence can happen to a property, some of these are man-made whilst others are a result of natural risk factors.
The most common reason for subsidence in the South of England is due to clay rich soil. This type of ground can absorb a lot more water making it more susceptible to swelling (see ‘What is Ground Heave?’, below) and shrinkage.
Trees and mature shrubs can also contribute to movement in the surrounding earth as they can be responsible for taking too much water out, causing the soil to dry out.
Leaking water mains (and/or drains) beneath a property can also cause subsidence by softening the soil causing it to compact under the weight of the foundations.
In other parts of the UK, mining and quarrying activity close to your home can also have an impact on the ground’s stability.
Is Subsidence the Same as Settlement?
These two terms are often confused with one another but they are very different.
Settlement is common in new properties as the materials and foundations are slowly compressed under their own weight. There is a normal degree of downward movement in the earth upon which a property has been built. This is quite normal during the first ten years of a new build.
This is why most new builds are available to purchase with a 10-year warranty which includes structural insurance.
What is Ground Heave?
Ground heave is often overlooked when people consider the potential problems of buying a house but can cause just as many structural issues as subsidence can.
Where subsidence is caused by downward movement in the ground, heave is caused by the earth underneath (or around) a property moving upwards. It is typically caused when there is excess moisture in the surrounding ground. This can occur when trees are removed and is common in clay type soil.
Trees absorb a lot of water from their root structure and when a mature tree is removed, the excess water that is no longer being used to support the plant will, instead, cause the soil to expand. This expansion can cause some structural damage to a building which includes cracking, door and window frames becoming out of place and rising damp.
In the same way that unstable downward movement in the ground can present barriers to accessing home insurance, ground heave can also limit the number of insurers willing to provide you with cover.
Spotting Signs of Subsidence and Heave
Homes offered for sale where there has been a history of subsidence or heave must state this in the sale particulars. However, some property owners may not be aware of the issues and it may be left to the buyer to find this out during the survey process.
When viewing a home for the first time, there may be some tell-tall signs that could cause alarm bells to ring.
The most common indications of subsidence and heave in a property are
- Doors and windows sticking in their frames
- Cracks in walls, particularly near windows and doors
- External cracks in brickwork, particularly where this marries up with cracks in cavity walls
- Rising damp in walls that have damp-proof courses.
Cracks may not be obvious in rooms that have wallpaper but you can sometimes see visible evidence of crumpling where cracks may be occurring. This can be more noticeable where the wall meets the ceiling.
Before you abort your viewing, whilst cracks in walls can be an unsettling site, they may not be the cause for alarm that you might think. Movement in the property is just one cause for this kind of defect in walls but may be a result of building alterations, repairs, natural decay or even moisture/thermal changes.
The Building Research Establishment (BRE) has issued guidance on how to assess cracks in the home which can help the layman to identify problems with subsidence and heave.
Damage categories are broadly defined as follows:
- 0 – Hairline cracks: Under 0.1mm. No action required.
- 1 – Fine cracks: Up to 1mm. Can be decorated.
- 2 – Cracks easily filled: Up to 5mm. May be recurrent cracks but can easily filled and may require external repointing. Doors and windows may need some adjusting.
- 3 – Cracks that require some opening up and can be patched by a mason: Between 5mm and 15mm
- 4 – Extensive damage: Between 15mm and 25mm and may result in distortion of doors and frames, loss of bearing in beams, sloping floors or disruption to service pipes.
- 5 – Structural damage: Over 25mm, these kinds of cracks require major repairs.
In general, cracks that are under 5mm in width are not considered structurally problematic whereas anything over 15mm wide will require inspection by an engineer or surveyor.
Lastly, changes in the home such as alterations or extensions can start a new process of settlement long after the original property was built. New cracks can begin to appear during this time which may be perfectly normal.
Buying a Property at Risk of Subsidence or Heave
If you are thinking of buying a home that you suspect has suffered (or is suffering) from land shrinkage or swelling then there are some things to consider.
Firstly, you will need to find out from the estate agents whether any remedial works have been undertaken on a property due to subsidence or heave. This should already have been fully disclosed in the sale particulars but obtaining more detailed information is essential in order to proceed with making an offer.
You should find out if any underpinning has been carried out and get the full details of when this was completed. There should also be accompanying paperwork from the local authority to prove that the work was completed with full building regulations approval.
You will then need to contact your mortgage provider to ascertain if they will still lend against a property that has suffered from ground movement. They will want to have the details of any remedial actions before they can make a decision.
Most mortgage lenders will insist on the completion of a structural home survey carried out by an engineer. These types of report are costlier but will give both you and the lender an assurance that the property is a sound investment.
In addition, you will also be required to commission a full drain survey which will include the use of cameras to assess the state of the pipework beneath the property.
The two reports combined should allow your mortgage lender adequate information to assess whether the property is at further risk of movement, and thus structural damage.
If your mortgage lender is happy to lend against the property then the next stage is to obtain home insurance.
Many insurance companies will not provide cover on properties that have suffered from subsidence but there are some who specialise in this kind of policy. Though more expensive than standard insurance cover, they typically require higher excess fees.
If you are able to secure a mortgage and insurance on a property then this should give you some assurance as to the potential risk of purchasing it. The decision to proceed with an offer should reflect any repairs that are needed along with redecoration costs.
How to Prevent Future Subsidence and Heave
When buying a property with evidence of subsidence or that has previously been at risk from ground movement, it is important to take some preventative measures to protect your investment.
- Always plant trees and large shrubs some distance away from your home. Get advice from an arborist or tree surgeon on the types of trees you plant and how thirsty they are when it comes to soaking up moisture.
- Prune trees regularly to maintain their growth and to restrict their water needs.
- Always maintain your drains, downpipes and gutters
- Inspect your home regularly for signs of cracking
Lastly, if you have any alterations planned for your home (including extensions) always seek the advice of a structural engineer before you begin.
If you are looking to sell a home that has a history of subsidence or are looking for a new property then we can help you navigate the process.
To find out more about our services, contact us today on 0118 912 2370.