Quick answer: The clearest sign is depth. If you can see the tops of the joists, your loft has much less than the recommended 270mm of mineral wool and is likely to need a top-up. Other signs point to replacement instead: insulation that is damp, matted, crushed, patchy, soiled by rodents or growing mould. Dry insulation in decent condition can usually stay and be topped up. Damaged insulation should come out first.
You don't need to be an expert to check. A torch, a ruler and ten minutes in the loft will tell you most of what you need to know. Only stand on the joists or on boards, never on the plasterboard between them.
Signs you need a top-up
You can see the joists
Ceiling joists in most homes are much shallower than 270mm. If the timber is visible above the insulation, there isn't enough. The standard fix is a second layer laid across the joists.
It measures well under 270mm
Push a ruler gently down through the insulation in a few places. Many lofts insulated years ago measure 100mm or less. Our guide on how thick loft insulation should be explains how to measure properly.
There are gaps and thin patches
Look for areas where rolls don't meet, where insulation has been pulled back for an electrician or plumber and never put back, and thin strips near the eaves and around the hatch. Gaps let heat escape and create cold spots on the ceiling below.
Upstairs rooms feel cold
Cold bedrooms or a heating system that struggles to keep the top floor warm can point to a poorly insulated loft. There can be other causes, but it is worth checking the loft first.
The hatch is uninsulated
A bare wooden or plasterboard hatch without draughtstripping is a weak spot in an otherwise insulated ceiling, and lets warm, moist air into the loft.
Signs the insulation needs replacing
It is damp or matted
Insulation soaked by a leak or by condensation goes flat and heavy, and doesn't insulate properly. Find and fix the cause first, then replace the affected area. Our guide to loft condensation and ventilation explains where moisture usually comes from.
It has been crushed
Boards laid straight onto the joists, or years of boxes stored on top, compress the wool. Flattened insulation loses much of its performance. If you want storage, raised boarding keeps the insulation at full depth underneath.
Mould, staining or a musty smell
Black spots on timber or stored items, dark stains in the insulation, or a damp, musty smell when you open the hatch suggest a moisture problem. The insulation may need replacing, and the cause needs dealing with.
Droppings, nests or tunnels
Mice and rats like to nest in loft insulation. Droppings, shredded material, tunnels through the wool or gnawed cables and pipes mean the insulation is contaminated. It should be removed safely, the entry points sealed, and new insulation laid. Our rodent proofing service deals with the access points.
It is very old, loose or a mix of materials
Some lofts have been added to over decades with a mix of rolls, loose fill and offcuts. Patchy, uneven layers are hard to top up well, and sometimes it is better to start again. If you find anything you can't identify, don't disturb it. Get it checked first.
Top-up or replace: how we decide
- Dry, clean and reasonably even? Keep it and add a layer across the joists to reach 270mm. That is our loft insulation top-up service.
- Damp, crushed, contaminated or badly patchy? Remove it, put right whatever caused the problem, then lay new insulation. That is our loft insulation removal service, followed by new loft insulation.
- A mix of both? It is common to replace a damaged section, for example under a leak or a nest, and top up the rest.
Things to check at the same time
- Pipes and the cold water tank. These should be lagged, because a well-insulated loft is colder above the insulation.
- The eaves. Make sure insulation isn't blocking the airflow at the edges of the loft.
- Light fittings and cables. Recessed downlights and cables need appropriate clearance or protection, not burying.
- Access. If getting into the loft is awkward, a fitted loft ladder makes future checks easier.
When to check your loft
There is no need to go up every month, but a quick look is worthwhile at a few points:
- when you move into a home, so you know what you have;
- after a roof repair, rewiring or plumbing work, in case insulation was moved and not put back;
- after a storm or a leak, to spot wet patches early;
- if you hear scratching or scurrying overhead, especially in autumn and winter.
Not sure what you are looking at?
If you would rather not go up yourself, or aren't sure whether what you have found is a problem, a loft inspection will give you a clear answer. We check the depth and condition of the insulation, ventilation, signs of damp or pests and access, and tell you what, if anything, needs doing. We carry out free assessments for homes across Teesside and the North East.
Every job starts with a free assessment and a written quotation that sets out the scope, materials and price before anything is agreed. The work is carried out by The Insulation Company or an approved installation partner. Call 0800 229 4668 (Monday to Saturday, 8am to 6pm) or request your free assessment online.