How long does cavity wall insulation last and can it be topped up?

Cavity wall insulation is a relatively cheap way to increase the thermal efficiency and comfort of your home. If your home was built since the 1930s, it’s probably got cavity walls. If it has, it’s very likely they’ve already been filled. It is pumped in to the cavity through small holes made in the brickwork, where it expands and settles.

In theory, cavity wall insulation should last as long as your house. While this is true in many cases, there are a few situations in which this catch-all does not apply.

Cavity wall insulation can be rushed

There’s a chance your cavity wall insulation may not have been installed correctly in the first place, which can harm its longevity as well as its efficiency. Since the 1970s, there was a big drive in energy efficiency and various grants have been made available by the government to insulate cavity walls for free. The race to collect as much as possible before the grants dried up means that some installers rushed jobs, affecting their quality/durability. Over time, the materials sometimes move or degrade within the cavity, affecting the thermal effectiveness and potentially causing issues with damp.

Lifespan of cavity wall insulation materials

There are a few different materials used for cavity wall insulation: mineral wool, expanded foam and polystyrene beads.

It’s rare to have issues with mineral wool insulation boards. Now installed as standard in new builds, it would be very difficult to adjust or add to these.

Although rare, it’s not unheard of for these EPS beads to escape the cavity, e.g. through air bricks and vents. In some cases, it may be possible to top the beads up, but you’d have to have lost a lot of them to notice the difference.

Expanded foam insulation can shrink over time, and may become less effective over the course of several years.

Installing Cavity Wall Insulation

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