If you want to understand the benefits of having proper insulation before checking the 4 signs, you can also read our quick guide: Why Insulate Your Loft?
Over time insulation compresses because people store heavy items directly on top of the insulation, so the weight squashes the fibres and the insulation becomes thinner.
When loft insulation goes from let’s say 270mm thick to 80–100mm from being flattened, the air pockets disappear — and it’s the air pockets that keep the heat in the home. So compressed insulation can lose around 30–50% of its effectiveness.
Another reason for loft insulation compressing is people walking on it.
If you have a loft conversion, meaning your loft is an actual living space, people may not realise but walking on it over time will start to compress the loft insulation, resulting in the insulation thinning.
If you notice sudden unexplained increases in energy bills, then it’s very likely it’s because of your loft insulation. It’s not always something you have to visually see in your loft but rather in your bank account.
When insulation gets old, it loses its ability to keep heat within the home, like it originally did when you had it installed. The material installers used to use back in the day had a lower R-Value (that’s just a measure of how well insulation slows down heat loss). When the R-Value drops, the warmth escapes through the roof much faster.
This means your boiler has to do a lot more work to compensate for the insulation not holding the heat in. Your radiators will also be on more, and suddenly you notice your gas or electric bill has gone through the roof for no clear reason.
Modern insulation with top materials used by good installers keeps heat in homes for much longer, so your heating doesn’t always have to be switched on.
If you’ve noticed an unexplained jump in bills and nothing else in the house has changed, the problem most often can be traced back to insulation past its time.
Insulation should always be kept dry and never get wet. The moment it gets damp or wet you might as well say it’s finished. When insulation gets damp it makes the insulation material heavy and clumped together. This is what makes the insulation unable to trap warm air in the way it’s supposed to. Instead of acting like a puffy blanket, wet insulation just sits flat and cold.
There’s also the bigger problem: moisture in the loft is a perfect breeding ground for rot and mould, and musty smells can spread to timber or plasterboard if it’s left unresolved for too long.
A lot of Barking and Dagenham homeowners make a common mistake… many believe that wet insulation will just “dry out over time.” But it won’t. Once insulation becomes saturated it can’t go back to working properly. If you spot any signs of dampness, staining or sagging, the insulation needs to be removed and replaced by an installer as soon as possible.
Good insulation is meant to look fluffy, even and nicely spread out. If you go into your loft and see thin patches, dips, or areas where it looks completely flat, that’s a clear sign your insulation is no longer doing its job properly.
Insulation ages, and over time — usually after 10–15 years — insulation naturally compresses under its own weight. Once it flattens, it loses a lot of its ability to trap warm air, which means heat easily escapes straight through the roof. Gaps and low spots basically act like little chimneys letting warmth leak out.
Modern loft insulation in 2025 is usually installed at around 270mm depth, which creates a thick barrier that’s needed to keep the house warm efficiently all year round. If the insulation that’s in your loft is nowhere near that height, or looks worn out, it’s likely overdue for an upgrade.
Information in this guide is general home-energy improvement advice. For wider guidance, you can also visit:
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