One room, two different measurements
Flooring is bought by area. Everything around the edge of it is bought by length. Confusing the two is the reason people end up with enough boards and not enough beading, and the relationship between them is not intuitive: perimeter does not scale with area.
area = length × width
perimeter = 2 × (length + width)
| Room | Area | Perimeter | Metres of trim per m² |
|---|---|---|---|
| 4 × 4 m | 16 m² | 16 m | 1.00 |
| 8 × 2 m | 16 m² | 20 m | 1.25 |
| 16 × 1 m | 16 m² | 34 m | 2.13 |
| 6 × 6 m | 36 m² | 24 m | 0.67 |
Four rooms, and the trim needed per square metre varies by a factor of three. A corridor is almost all edge. A large square room is almost all middle. This is also why corridors cost more per square metre to floor than their size suggests — and why quoting trim as a percentage of area is always wrong.
Underlay
Underlay is bought by area, like the flooring, but it is not the same number. Rolls come in fixed widths — usually 1 m or 1.2 m — so you lose material to the offcut at the end of each run, exactly like wallpaper.
- Order 5-10% over the floor area for a simple rectangular room, more if the room is irregular.
- Underlay is butted, not overlapped. Overlapping creates a ridge that telegraphs through the boards and will be visible and audible.
- Run the underlay perpendicular to the direction of the boards. It makes the joints line up less often, which is what you want.
- Foam and fibreboard are not interchangeable. Check the thickness your flooring warranty requires — many laminate warranties are void with the wrong underlay, and 3 mm is the usual default.
- On a concrete subfloor you need a damp-proof membrane under or built into the underlay, even on an upper floor if the slab is concrete. Retrofitting it later means lifting the entire floor.
- Underfloor heating changes everything: you need a low tog underlay specified for it, and the flooring itself must be rated for it too.
Underlay thickness does not fix an uneven subfloor. A thicker foam under a bumpy floor makes the boards flex, which breaks the joints. Level the subfloor first.
The expansion gap, and why the trim exists
Floating floors move. Laminate and engineered boards expand and contract with humidity across the seasons, and if the floor is pinned at the edges it has nowhere to go — so it lifts in the middle. The fix is an expansion gap of 8-12 mm around the entire perimeter, including around pipes, door frames and any fixed obstacle.
That gap has to be hidden, which is what beading and skirting are for. The order matters: skirting goes on top of the flooring only if the flooring goes down first and the gap is left, and it must never be nailed through the boards. Beading is the alternative when you are keeping existing skirting.
- New skirting over the floor
- Cleanest result, most work. Remove old skirting, lay the floor, fit new skirting to the wall — never into the floor. Costs more and means redecorating the wall.
- Scotia or quadrant beading
- Fitted into the angle between the existing skirting and the floor, pinned to the skirting only. Cheapest and fastest, slightly less clean visually.
- Undercutting the existing skirting
- The floor slides underneath and no trim is needed at all. Best-looking result, requires a specialised saw and a steady hand.
Counting lengths, not metres
Beading and skirting are sold in fixed lengths, typically 2.4 m or 3 m. You cannot buy 17 metres — you buy whole lengths, and the offcuts are rarely usable because they end up too short for any remaining wall.
lengths = ceiling( total run ÷ length per piece ) + 1
The plus one is not padding, it is arithmetic. Every wall shorter than a full length wastes the remainder, and every internal corner needs a mitre — two cuts that must both be right. One spare length is cheaper than a second trip.
Subtract doorways from the run, since no trim crosses them, but do not subtract anything else. Radiator pipes, alcoves and chimney breasts all add length rather than remove it: an alcove 60 cm deep adds 1.2 m of trim, not zero.
Threshold bars
One per doorway, always. The expansion gap runs through the doorway too, and a floating floor should not continue uninterrupted from room to room — each room needs to move independently.
| Situation | Bar type |
|---|---|
| Same flooring, same height, both sides | T-bar |
| Different heights | Ramp or reducer |
| Flooring to carpet | Carpet-to-laminate profile |
| Open edge, step down | End profile or stair nosing |
Standard bars are 90 cm, which covers a normal internal door. Wide openings and patio doors need a longer bar or two joined, and the join is visible — measure before ordering.
A worked example
A bedroom 4.5 × 3.2 m with two doorways, each 0.8 m wide. Beading comes in 2.4 m lengths. Flooring packs cover 2.2 m².
area = 4.5 × 3.2 = 14.4 m²
packs = 14.4 × 1.10 ÷ 2.2 = 7.2 → 8 packs
underlay = 14.4 × 1.07 = 15.4 m²
perimeter = 2 × (4.5 + 3.2) = 15.4 m
trim run = 15.4 − (2 × 0.8) = 13.8 m
lengths = ceiling(13.8 ÷ 2.4) + 1 = 6 + 1 = 7
Plus two threshold bars. The shopping list is eight packs of flooring, 15.4 m² of underlay, seven lengths of beading and two bars — and the four items are counted four different ways.
Before you order
- Check the pack coverage in m² on the actual pack. It varies between ranges even at the same board size, and listings are often wrong.
- Let the flooring acclimatise in the room for 48 hours before laying, still in its packs, flat. Skipping this is the most common cause of gaps appearing a month later.
- Measure the room at both ends. Walls are rarely parallel, and the difference decides whether the last row is a full board or a 2 cm strip.
- Buy an extra pack rather than an extra metre of anything. Batch variation in wood-effect print is real and a pack bought later can be visibly different.
- If the room is not square, use the longer measurement for both length and width. Concrete floors do not forgive optimism.