You can board a loft that has insulation in it, but not by laying boards straight onto the joists. Insulation only works because of the air trapped in it — compress 300mm down to 100mm and you lose most of its value.
On this page
- The problem with direct boarding
- How raised boarding works
- Cost
- Things to check before boarding
The problem with direct boarding
Standard joists are typically 100mm deep. Current guidance points to around 300mm of mineral wool. Board directly onto the joists and the insulation is squashed to a third of its depth exactly where you walk and store things, creating a cold bridge across the whole boarded area.
How raised boarding works
- A timber framework is fixed across the existing joists to raise the boarding level
- Full-depth insulation sits undisturbed beneath the framework
- An air gap is maintained between the insulation and the underside of the boards
- Chipboard loft panels are then fitted to the raised framework
Cost
Raised loft boarding is £55/m² with us, and it is common to board only part of the loft — the area you actually use for storage — while insulating the whole floor. See the price list for the full breakdown.
Things to check before boarding
- Ceiling joists must be adequate for the intended load — storage only, not habitable use
- Ventilation paths at the eaves must not be blocked
- Electrical cables should not be buried under insulation or trapped by framework
- Any downlights need appropriate clearance
Common questions
Can I lay loft boards directly on top of insulation?
No. Compressing mineral wool destroys most of its thermal performance. Boards should sit on a raised timber framework above the insulation with an air gap beneath.
How much does raised loft boarding cost?
LoftFix charges £55/m² for raised loft boarding, including the timber framework and chipboard panels.
If you would like an honest opinion on your own loft, send us your postcode and a few photographs. Most lofts can be assessed and quoted remotely using satellite imagery, and we will tell you if work is not necessary.
Related: Raised loft boarding • Price list • Project planner • Contact