Loft boarding: why raising it matters more than the boards

Most lofts we look in have a few boards laid straight across the joists with the insulation squashed underneath. It is the standard way it has been done for decades and it quietly undoes your insulation.

Why crushing it matters

Mineral wool insulates because of the air trapped in it, not because of the wool. Compress it to a third of its depth and you lose most of the benefit in that area. Current recommended depth is around three hundred millimetres, which is far deeper than a ceiling joist, so anything laid directly on the joists is sitting on compressed wool.

What raised boarding is

Plastic or metal legs screwed down onto the top face of the joists, battens across the legs, and the boards on top of that. The deck ends up clear above the insulation so the wool stays at full depth in the bays underneath and nothing bears on it.

What it will and will not take

Household storage. Ceiling joists are sized to hold up a ceiling, not to carry a floor. If you want a usable room that is a loft conversion, which is a different job with different structure and building control involved.

What to check before booking it

Whether the roof is trussed or cut, because trusses limit what you can store between them. Whether there are downlights below, since they need clearance. And whether the hatch is big enough for what you intend to put up there, because enlarging it usually means cutting and trimming a joist.