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Understanding Subsidence

Released On 8th Oct 2018

One of the most serious issues a building surveyor may come across when inspecting a property is subsidence. If left untreated, it can affect not only the structural safety of your home, but its resale value, too.

Subsidence is definitely a red flag if you’re buying or selling a property, but there are ways to deal with the problem. If spotted early, positive action can prevent the damage from getting worse, and steps can be taken to rectify it with the proper structural support.

If you suspect that a property you’re thinking of buying might have subsidence, our overview of this topic will help understand more about it, but there’s no substitute for having a proper survey carried out by a qualified building surveyor.

Contact us for jargon-free advice and to arrange an inspection.

What is subsidence?

Subsidence occurs when the ground beneath your home sinks, causing your foundations to collapse and sink, too. You can easily understand that this can cause significant weakness to the building’s structure and stability as one side sinks, causing cracks to appear.

What causes subsidence?

The causes of subsidence can be complex, involving more than one factor, but there are some common reasons for it to occur.

Clay soil

Clay soil is made up of about 30% to 35% water and it expands or shrinks very easily during dry or wet weather, or when nearby vegetation saps the moisture in the soil. For this reason homes built on clay soil can be more prone to subsidence.

Leaking drains and pipes

Burst pipes or long-term leaking drains can wash away the fine particles in the soil under your home, reducing support and causing the foundations to subside. Alternatively, the ground can become so wet that its softened state can’t support the weight of the building, and this can also cause subsidence.

Roots from trees and shrubs

Roots from trees and shrubs can also cause subsidence as they grow under your home to seek out moisture. Although roots can directly cause foundation damage, the changes they cause to the soil condition as the roots expand and contract with moisture are also significant factors. Willows, silver maples and elm trees are thought to have particularly aggressive rooting habits.

Poor ground

It isn’t only older building at risk of subsidence. Even newer houses can have subsidence problems in some circumstances.

Although all new houses “settle” to some extent as the ground beneath the foundations compacts under the weight of the building, this should be minimal and damage is usually limited to cosmetic, rather than structural repairs.

Excessive soil compaction can lead to considerable downward movement of newer properties, which can cause subsidence. This can occur if builders have used inappropriate material when making up ground or haven’t compacted ground material sufficiently before construction begins.

Signs of subsidence

Cracks are the most visible sign of subsidence, but don’t be alarmed by every crack you see – in most cases they are likely to be caused by natural shrinkage and swelling due to temperature and humidity conditions. It’s also common to see small cracks in fresh plaster.

Warning signs of potential subsidence can be:

  • cracks wider than 3mm on interior and exterior brick walls
  • cracks that are wider at the top than at the bottom
  • diagonal cracks spreading across the wall
  • crack around windows or doors
  • cracks where an extension joins the house
  • cracks that appear after prolonged dry weather
  • cracks that get bigger quickly
  • cracks extending below the damp-proof level
  • sinking floors – look at gaps and cracks in skirting
  • windows and doors sticking
  • noticeable leaning of the building

Should you buy a house with subsidence?

The very word strikes fear into a buyer’s heart, but although subsidence is certainly not a problem to be taken lightly, modern remedies such as underpinning mean that most subsidence cases are perfectly manageable.

The important thing is to be completely informed as to the extent of the problem. A full independent building survey is essential; following this you will be able to assess the likely costs to fix the subsidence and negotiate a purchase price with the vendor.

Before you go ahead and buy any property with a history of subsidence, even if it’s been treated, it’s a good idea to look into the potential cost of future buildings insurance, as well as any exclusions or excesses that might apply.

Some mortgage lenders are risk averse when it comes to properties with a history of subsidence, so they’re more likely to be sold to cash buyers, but subsidence certainly isn’t the kiss of death that it once was.

Reporting subsidence in your survey

Your survey report is a detailed document that will evaluate any subsidence issues found in the property.

During the survey, we’ll inspect the property to see if it’s suffering from subsidence, looking at walls (internal and external) floors and ceilings. We’ll identify possible causes, indicate if the subsidence is likely to deteriorate and inform you of any corrective work that’s required.

You might need the opinion of other professionals, depending on what’s causing the subsidence. For example a tree surgeon or drains expert can offer advice on defects caused by overgrown vegetation or leaking drains.

If in doubt, get a survey

If a visual inspection of a property gives you any cause for concern you should err on the side of caution and instruct a full building survey before taking your purchase further.

Contact us on 07711 491000 or email for a no obligation quote.

Tags: Root growth, Structural support, Subsidence, Underpinning, Foundations, Clay soil, Cracks, Leaning