By Dean Knowles, Knowles Services Ltd · Updated 9 November 2026
I'm Dean, and I survey and insulate lofts across Essex and London myself. In older homes I find all sorts up there. This guide shows the common types of old insulation, how to spot them, and what a properly insulated loft should look like.
The drawings on this page are illustrations to help you recognise each type. The photos further down are from real lofts I've worked on.
If your loft was insulated decades ago, it probably has one of these. Some can be topped up. Others need clearing out first.
How to spot it: Yellow or grey fluffy rolls between the joists, often only 25mm to 100mm deep. Over the years they sink, go grey with dust and leave the tops of the joists showing.
What to do: If it is dry and clean, it can usually be topped up to 270mm. If it is dirty or crumbling, it is better cleared out first.
How to spot it: Loose fibres, rather than rolls, that were blown into the loft. They tend to drift, so you see deep piles in some places and bare ceiling in others, often pushed into the eaves.
What to do: The bare patches lose heat and fibres blocking the eaves can stop the loft breathing. It usually needs levelling or clearing, then re-insulating properly. Some very old loose-fill, especially blue-grey or whitish fluffy fibres, can be asbestos. If I'm not sure, I won't touch it until it has been tested.
How to spot it: Small, lightweight granules like gravel or pebbles, usually grey-brown or gold, poured between the joists. It was used in older homes, often decades ago.
What to do: Do not touch it, sweep it or disturb it. Some vermiculite contains asbestos. If I find it on a survey I will stop and tell you straight. It needs testing, and if it does contain asbestos it must be dealt with by a licensed asbestos contractor before any other work is done.
How to spot it: Grey, papery fibres, sometimes with flecks of newsprint. It is blown in loose, and over time it settles and can hold damp.
What to do: If it has settled or got damp it has lost much of its value. It usually needs clearing out and replacing.
How to spot it: Flattened, stained or dark patches, a musty smell, mould on the timbers, or droppings and chewed insulation from mice, rats or birds.
What to do: Wet or dirty insulation stops working. The cause (a leak, poor ventilation or a way in for pests) needs fixing first, then the old insulation is bagged up, the loft cleaned and new insulation laid.
How to spot it: Loft boards screwed directly onto the joists, with thin insulation squashed underneath and boxes stored on top.
What to do: Squashed insulation keeps far less heat in. Raised boarding on legs lets you keep your storage and still have the full depth of insulation underneath.
A properly insulated loft keeps the heat in the rooms below while still letting the roof space breathe.
What it is: The first layer fills the space between the joists. The second layer goes across the top at right angles, so there are no gaps over the timbers. Together they reach at least 270mm, the current recommended depth.
Why it matters: It is kept back from the eaves so air can still move through the loft, and it is cut neatly around pipes, cables and fittings.
What it is: A thin, layered foil insulation fixed across the underside of the rafters. It insulates and reflects heat, and with the joins taped it also works as a vapour control layer.
Why it matters: It is a good option where there is no roof felt, or the felt has failed, and for loft rooms and the eaves behind them, like my job in a Chingford loft room.
What it is: Boards raised on legs above the joists, with the full depth of insulation underneath.
Why it matters: You keep your storage space without crushing the insulation.
The current recommendation is at least 270mm of mineral wool, usually laid in two layers: one between the joists and one across them.
Yes, if the old insulation is dry, clean and lying flat. If it is damp, dirty, full of droppings or vermiculite, it needs dealing with first.
Mineral wool kept dry and not squashed lasts for decades. It stops working when it gets damp, dirty or crushed under boards and boxes.
Leave it alone and don't store things on it or sweep it. Book a survey and I'll tell you honestly what I see. If it needs testing or a licensed specialist, I'll explain that before anything else is done.
Most lofts are done in a single day, including clearing out the old insulation where that's needed.
I'll come and look, show you photos of what I find and explain it in plain English. The survey is free and there's no obligation.
Knowles Services Ltd
