What makes extensions and conservatories more susceptible to ground movement?

Typically, differential settlement, shallower foundations and load bearing differences make extensions and conservatories more prone to ground movement.

Differential settlement

Different parts of a property’s foundations settle at different times. The natural settlement of the main house typically occurs over many years, whereas the new extension or conservatory is still settling. This typically causes stress and cracking at the junction where the old and new structures meet.

Shallower foundations

Extensions, especially conservatories, are usually built on shallower foundations than the main house, often because they’re considered lightweight structures. However, shallow foundations are more susceptible to changes in weather and soil moisture content.

Load differences

The difference in loads between the extension or conservatory and the main house reflects how these structures respond to ground movement. For example, conservatories are typically made up of large, expansive glass panels rather than solid masonry, and can have shallow perimeter footings or slab foundations. This exerts less downward pressure on the ground beneath, meaning it tends to move more when the ground shrinks or swells.

The main house is heavier and exerts greater pressure on the soil below, keeping the foundations firmer and more compact. This makes it less responsive to small changes in the soil conditions.

The challenges of UK soil

A mix of prolonged dry spells and heavy rainfall has a significant effect on soil conditions in the UK, especially in regions dominated by clay soils, which expand during wet weather and shrink during dry periods. This can cause vertical movement beneath foundations.

Extensions and conservatories are affected first because shallow foundations sit within the zone most affected by changes in moisture. The main house often has deeper, more stable foundations and is therefore less susceptible.

What are the common warning signs homeowners notice?

Understanding the warning signs can help address the issue early and avoid expensive repair work. Here are some of the common indicators in extensions or conservatories to look for:

• Unexplained cracks in glass walls or roofs

• Sloping or uneven floors

• Sticking doors or windows

• Gaps or separations between the extension or conservatory and the main house

When is a professional assessment needed?

If you notice the above signs and they appear to be an ongoing issue, rather than a historic one, then it’s best to seek professional help. Similarly, if the cracks grow rapidly or become wider, typically between 3-5mm, then a professional assessment is needed. Early intervention will help reduce disruption and costs.

Ground movement specialists can conduct a geotechnical survey of the ground conditions and assess the risks. Once monitoring and data collection are complete, they will provide recommendations on the best solutions to remedy the problem.

What repair options are available?

Traditional underpinning, which involves excavating small pits beneath existing foundations and filling them with concrete, is a common solution for addressing ground movement. This method, however, can be disruptive, costly, and take weeks to complete.

Alternatively, modern ground solutions use non-invasive techniques that stabilise the ground and re-level structures. These solutions mean minimal excavation, faster installation and a reduced impact on occupants.

It’s important to note that there is no ‘one-size-fits-all’ solution. That’s why it’s crucial to complete a full assessment of the soil conditions, structure type and the extent of the movement. This is where Mainmark can help.

Mainmark’s approach

We provide fast, effective subsidence treatments for all kinds of homes. Our extension and conservatory subsidence remediation treatments can take around a day to complete, saving time and money – as well as minimising disruption.

Our specialist methods include Teretek® ground injection and JOG computer-controlled grouting solutions, which are non-invasive treatments that do not require extensive excavation.

Mainmark used these methods to lift and re-level a three-storey semi-detached house extension in Camden, London, which was suffering from subsidence. The techniques strengthened the foundations and achieved a significant lift of 21mm along the side wall, fully closing the gaps at the front and centre of the property with minimal disruption. Residents were also allowed to stay at home during the remediation works.

In short, while extensions and conservatories are more susceptible to ground movement, this does not necessarily mean the entire house is affected. It’s important to seek expert advice early on if any of the warning signs appear to avoid any further structural damage, and to avoid significant disruption and costs. With our wide range of subsidence treatments, you can rest assured that we have the expertise to remedy the issue.

If you have any concerns about an extension or conservatory, we’re here to help. Contact us today.