How does cavity wall insulation work?

How does cavity wall insulation work in practice? This presentation looks at how to check whether you have cavity walls and how to spot if they’ve been filled, the choice of materials, the installation method, benefits and potential obstacles.

How to check whether you have cavity walls

One of the easiest ways to check whether you have cavity walls is to check the brick pattern. If you see the bricks in a stretcher pattern (laid end to end lengthways in one direction – there’s a good chance you have a cavity wall.

How to know if your cavity walls are already filled

The best way to check whether a cavity wall has already been insulated is to look at the bricks and see if you can see a small circle of mortar between three bricks where there has been some recent pointing. If the cavity has been filled there should be a similar circle of mortar 1 metre in each direction. Get a professional installer to check if you are unsure.

How a cavity wall is insulated

To insulate a property, a pattern of holes are drilled and mineral wool or polybead material blown into the cavity. Polybead has a higher performance value. Once the material is injected, the holes are made good with mortar. This is a job for a professional installer with specialist equipment.

When a cavity wall may be unsuitable for insulation

Cavity wall insulation may not be suitable for walls with high exposure to extreme weather conditions such as persistent driving rain. It can also be difficult to install it in properties that have adjoining structures restricting access to the entire cavity. It is important for the insulation to be spread evenly across the entire wall to get the desired thermal blanket effect.

Benefits of cavity wall insulation

Cavity wall insulation acts as a barrier, reducing the speed of transfer of heat across a wall.  It keeps heat in (or out) much more effectively than an unfilled cavity would. As a result, benefits include:

a) feeling warmer in winter (warmth stays in longer)
b) lower bills (thanks to the reduced heating requirement)
c) greater comfort in summer (provided you shut out the sun, insulation can also reduce summer heat gain)

Then, of course, there is the CO2 reduction from burning less fuel to heat your house, which means less environmental impact.

With thanks to Vincent Matthews of SIG Energy Management, sponsors of the SuperHomes project, for this presentation.

Also see:
Boarding a loft over insulation
Insulate a floor
Insulating a solid wall

eco renovation - talk to homeowners