This is what a cavity wall actually is, how you identify one, and whether you can alter one during a renovation, according to the experts

If your home improvement plans involve making changes to existing walls, you'll need to understand what kind of walls you are dealing with, especially as homes are built with multiple different types. Depending on the age and construction of your home, you may be dealing with a cavity wall. But how can you know for sure?

The exact process of removing or altering a wall varies based on the type of wall you have and whether it is a load-bearing wall or not. And so it's crucial that you correctly identify the type of wall you have so that work can be carried out safely.

In the case of cavity walls, I asked the pros your burning questions, including how you can identify one, whether they are load-bearing and if they can be altered or removed.

What is a cavity wall?

'A cavity wall is a wall that is made up from one outer brick wall, an inner brick or concrete block, with a cavity (space) in between them,' explains Mark Irving, building expert at Build & Plumb. 'The idea of a cavity wall is to provide a barrier between the interior and exterior of a property, to prevent dampness and provide insulation.'

Given their purpose, your cavity walls will be your home's exterior walls, rather than a partition wall between rooms.

Architect Níall Hedderman from Capital A Architecture adds: 'The whole point of building a cavity is that the outer part of the wall can get soaked in the rain while the inner part remains dry. Water can't get across the cavity and eventually drains out through the weep holes.

'Modern homes regularly have insulation fitted in the cavity during construction but it usually doesn't fill the entire cavity. An air gap is left to make sure water can escape out through the weep holes.'

How do you identify a cavity wall?

Not all external walls will be cavity walls, and the best way to check is to ask a trusted builder who will be able to confirm what kind of wall you are dealing with.

But for your own curiosity, there are some clues that you can look out for to try and identify a cavity wall yourself.

'A cavity wall can be built using any type of masonry; brick, block or stone and the outer surface can be coated in render, harling or pebbledash,' explains Níall. 'So it isn't possible to tell at a glance whether a wall is solid or has a cavity, but there are some tell tale signs.

'First off the age of the building, if a home was built after the 1920s it is far more likely to have a cavity wall.

'Second, look for weep holes. These are gaps at regular intervals between the bricks, usually at the bottom of the wall and sometimes also above windows or doors. The gap is about the same size as the short edge of your mobile phone and in modern homes they are made from plastic. Weep holes exist to allow moisture to escape from the cavity.'

The thickness of the wall can also be a useful indicator, but it's not an exact science, says Mark: 'An often obvious clue is the wall thickness, as cavity walls are generally thicker than other wall types. However, this really depends on the age of the house. Older, solid walls can be thicker than cavity walls.'

Can you knock down or alter a cavity wall?

It is possible to alter or knock down a cavity wall, but you'll need to make sure you employ a professional to do it for you.

Whether you are adding in a new external doorway, or knocking through while building an extension, professional input is required to ensure the changes are made safely.

Tackling this job on a DIY basis to save money will be a false economy, and the risk of causing serious damage to your home is too high to chance it.

FAQs

Are cavity walls load-bearing?

While the outer skin of the cavity wall is largely decorative, the inner skin is load-bearing and, as with any load-bearing wall, you will need an experience builder and a structural engineer, who will determine what size and type of beam you need to support the weight of the structure above.

This will need to adhere to the building regulations too, which means you will need to apply and have the work inspected at various points. If altering the wall is the only work you're doing, then a submitting a Building Notice should be fine, but if the wall is being removed as part of a larger extension project, you may need to submit a Full Plans application instead. Your local authority's Building Control department will be able to confirm if you are unsure.

If you're planning on altering or removing a wall for the first time, heed the advice from a seasoned renovator and the lessons she's learned while knocking down walls.