‘Subsidence’ is a word that you don’t want to hear as a homeowner. It affects thousands of homes every year, and is one of the most challenging and expensive problems to fix.
The quicker subsidence is diagnosed, the easier it is to fix. Unfortunately, many homeowners ignore the signs, which can result in it becoming very expensive to fix and even potentially hazardous. This post helps explain exactly what subsidence is, how to spot it, how to fix it and how to prevent it.
What is subsidence?
Subsidence is when the soil below a property starts to compact and collapse, causing the foundations to sink. This can cause the entire property to become unstable.
The biggest cause of subsidence is dry soil. Too much heat and a lack of water can cause shrinkage to certain types of soil (particularly clay). If there are too many trees planted near a property, this too can result in soil becoming dry and compacted due to the roots sucking up all the moisture.
The opposite problem – too much water in soil – can also cause subsidence. Flooding, burst underground pipes and inefficient drainage due to blocked guttering can all cause soil to get too wet, which can also cause a property to sink as soil is washed away and replaced with water.
What are the signs of subsidence?
There are a few telltale signs that a property is experiencing subsidence. These include:
- Cracks in walls: Shifting foundations can cause movement throughout a property, which can lead to cracks forming in walls and ceilings. Unlike non-serious hairline cracks, subsidence cracks are typically thicker and may follow the brickwork in a diagonal ‘stepped’ pattern.
- Sloping floors: If floors are sloping, this can be a sign of subsidence. Try rolling a ball across the floor in each room – if it rolls towards a certain corner each time, this could be a bad sign.
- Sticking/unclosable doors: Subsidence can affect the shape of door frames and cause doors to start sticking or not latch. There are other things that can cause doors to stick or not stay closed, and these could be worth ruling out first if you haven’t noticed any other signs of subsidence.
- Loose skirting boards: In some cases, subsidence can cause skirting boards to come away from the wall. Gaps may also form between walls and shelving units or walls and countertops.
- A leaning property: If a home is noticeably crooked, this is a sign of serious subsidence, and could require emergency repairs. Properties in this state that are ignored can be at risk of collapsing, which is something no homeowner wants to experience.
How can you prevent subsidence?
Regular inspections of your property, including soil checks using geotechnical instruments, can help you determine whether subsidence is likely to occur in the future. If the soil is too dry or too wet, you can then explore ways to introduce or extract water.
Trees and large plants around a property are often worth removing if soil is starting to get dry. This could prevent soil further compacting. In areas that get little rainfall, it may even be advantageous to add gravel or soil directly around properties to encourage water to get into the soil.
To prevent flooding around a property, there are many measures you can take. Firstly, make sure to clean out your guttering annually to avoid blockages that could result in water not draining and pooling around your foundations. Placing french drains a couple metres away from your property could be useful if your home is at the bottom of a slope. Other anti-flood measures can be looked into if you live near water.
How can you repair subsidence?
The most traditional way to fix subsidence is underpinning. This is an expensive and laboursome job that involves excavating earth beneath property and then adding a foundation material such as concrete to provide a stable base.
Newer methods are also possible – which can cost less and require less work. Resin injections are one example of this. This is typically recommended on properties experiencing lighter subsidence.
Certain home insurance policies may cover subsidence. This could save you the cost of having to pay for underpinning or resin injections wholly out of your own pocket.
Whatever solution you choose, make sure that you’re tackling the source of subsidence and not just repairing the after-effects – there’s no use in filling cracks or straightening out flooring if you have not fixed the foundations, as your home will only continue to sink.
