How Many Loft Boards Do I Need? Area, Thickness and Screws (UK)
Loft boards are laid across the joists to make a floor for storage. A 12 m² area takes 10 boards of 2400 × 600 mm, which covers 1.44 m² each, with 10% extra for cutting. The loft boarding calculator gives the boards and the screws for your size.
Boards by area
2400 × 600 mm boards, with 10% extra, over joists at 400 mm:
| Size | Area | Boards | Screws |
|---|---|---|---|
| 2 × 2 m | 4 m² | 4 | 48 |
| 3 × 2 m | 6 m² | 5 | 60 |
| 3 × 3 m | 9 m² | 7 | 84 |
| 4 × 3 m | 12 m² | 10 | 120 |
| 4 × 4 m | 16 m² | 13 | 156 |
| 5 × 4 m | 20 m² | 16 | 192 |
| 6 × 4 m | 24 m² | 19 | 228 |
| 6 × 5 m | 30 m² | 23 | 276 |
Thickness for your joists
| Joists at | Board thickness | Screws for 12 m² |
|---|---|---|
| 400 mm | 18 mm | 120 |
| 450 mm | 22 mm | 120 |
| 600 mm | 22 mm | 80 |
Measure from the middle of one joist to the middle of the next.
Boarding over insulation
- The recommended depth of mineral wool insulation is 270 mm, which is deeper than most joists (100 to 150 mm).
- Boards laid on the joists squash the insulation and let the heat out, so raise the boards on loft legs, or on timber battens fixed across the joists.
- Loft legs come in several heights, and the kit makes a platform with room for the insulation under it.
- Keep the insulation clear of the eaves, so that the air can move into the roof space.
Laying the boards
- Plan. Lay the boards across the joists, with the ends over a joist. Stagger the joins so that they do not all fall on the same joist.
- Fix. Use two screws at each joist, 50 mm long for 18 mm boards. Pre-drill near the ends so that the board does not split.
- Cut. Mark the cuts on the boards and trim them to fit around the hatch and the pipes.
- Wiring. Keep boards clear of cables, and lift the cables over the joists so that nothing is trapped.
- Light. Fit a light by the hatch so that you can see what you are doing.
Before you board
- Check that the joists are in good condition, and not wet or rotten.
- Think about the weight: store light things, and keep heavy items on the ground floor.
- Make sure the hatch is big enough and that there is a ladder you can use safely.
See also the loft insulation calculator and the stair calculator. These are estimates: check your joists and the quantities.
Frequently asked questions
How many loft boards do I need?
For 12 m² with 2400 × 600 mm boards and 10% extra, 10 boards. Each covers 1.44 m².
What thickness should loft boards be?
18 mm tongue and groove chipboard for joists at 400 mm centres, and 22 mm for joists at 600 mm.
How many screws do I need?
Two at every joist a board crosses: 120 for 10 boards over joists at 400 mm.
Do I need to raise the boards above the insulation?
Yes, if you add insulation to 270 mm: use loft legs to make a platform above it, so that the insulation is not squashed.
Can I board the whole loft?
You can, but it is not wise: leave the eaves clear for air, and remember that ceiling joists are not made to carry much. Board only what you need for light storage.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.