The short answer
Installed well in a suitable wall, cavity wall insulation should last as long as the building. Ofgem used a 42-year standard lifetime for cavity insulation backed by an appropriate guarantee, and the usual CIGA guarantee runs for 25 years. Fills fail early when the wall is too exposed, the cavity is narrow, or the installation left gaps or allowed the fill to slump.
On this page
The official figures
Two numbers are worth knowing, and they measure different things.
- Lifetime for the energy saving. Ofgem’s guidance on appropriate guarantees for the Energy Company Obligation gave cavity wall insulation a standard lifetime of 42 years where an appropriate guarantee is in place. That is a figure used to count the carbon and energy saving, not a promise about your wall.
- Guarantee length. The CIGA guarantee, which covers most cavity fill installed in the UK, is a 25-year guarantee. Ofgem’s list of reviewed guarantees names it as the CIGA 25 Year Guarantee.
In practice, a mineral fill or bonded bead that stays dry has nothing in it to wear out. The question is whether it stays dry and in place.
By type of fill
| Fill | What it is | How it ages |
|---|---|---|
| Blown mineral wool | Glass or rock fibre blown in loose | Stable if dry. Can mat down and hold water if the wall is exposed or bridged. |
| Bonded polystyrene bead | Beads coated with binder as they go in | Locks in place, does not wick. Long life when installed with enough binder. |
| Loose polystyrene bead | Beads blown in without binder | Can settle and run out of any opening, leaving voids at the top. |
| Urea formaldehyde foam | Foam injected wet, set in the cavity | Older installs. Can shrink and crack, opening paths for water. Historic England advises it only in moderate exposure. |
| Polyurethane foam | Closed-cell foam, used in narrow or flood-risk cavities | Durable; costs more and is harder to remove. |
What shortens the life of a fill
Exposure
Walls facing heavy wind-driven rain put far more water into the cavity. A fill that would last indefinitely on a sheltered terrace can be wet within a few winters on an exposed gable.
The cavity itself
Narrow cavities and those bridged by mortar or brick headers give water an easy path across. Historic England notes that walls tied with bricks across the cavity should be treated as solid walls.
The installation
Missed drilling points, too little material, no binder in bead fill, and debris left in the cavity all show up years later as cold spots and damp.
Maintenance
Pointing, gutters and downpipes. Guarantees generally expect the house to be reasonably maintained, so a failure traced to a long-blocked gutter may not be covered.
What happens after 25 years
The guarantee ends; the insulation does not. If it is dry and in place, there is nothing to do. If you are buying a house where the insulation is close to or past the guarantee, a borescope survey is the way to know its condition, and a lender may ask for one (see cavity wall insulation and your mortgage).
When fill has to come out
If a survey finds the fill wet, slumped or bridged, it does not improve with time. Extraction clears the cavity; whether to refill depends on why it failed, covered in removal and refill. Our removal cost calculator gives a typical budget.
Think your fill has reached the end? Tell us about the house and we will find a specialist to look.