Floor & deck
Laying solid floorboards
From acclimatisation to expansion joints and trims
A solid wood floor moves with moisture, so acclimatisation, laying direction, staggered joints and expansion gaps all determine whether the floor lies flat and neat. The guide follows the laying from measuring up to skirting boards and explains why you must allow for the timber's shrinkage and use the covering width in the material calculation.
Acclimatise the boards
Leave the boards to acclimatise in the room according to the supplier's instructions, so the timber's moisture content approaches what it will have in use. Solid structural/floor timber is typically supplied with a moisture content of around 12 % ± 3 %, and in a heated indoor climate the equilibrium moisture settles lower — if you lay a floor that is too damp, it shrinks and opens the joints.
Moisture content on delivery (typical)12 % ± 3 %Measure up and calculate consumption
Measure up the room and calculate material consumption and running metres. Use the covering (effective) width — not the nominal size — for tongue-and-groove boards, as the tongue disappears into the neighbouring board. Add a waste allowance according to the room's shape and pattern; waste is not a fixed percentage. Use the calculators «Material consumption — area» and «Running metres of boards».
Always calculate using the covering width, not the nominal size — otherwise you will order too little.
Plan laying direction and starting width
Plan the laying direction (typically towards the incoming light) and calculate the width of the first and last boards, so you do not end up with a narrow strip along the last wall. If necessary, distribute the surplus so the first and last rows are roughly equal in width.
Lay the first row against a straight reference
Lay the first row along a straight, measured reference line — not necessarily along the wall, which is rarely completely straight. Keep an expansion gap to the wall, so the floor can move with moisture without buckling.
Stagger end joints
Stagger the end joints from row to row so the joints do not line up. This gives a stable, calm joint pattern and a stronger floor. Avoid very short offcuts out in the floor.
Fix according to floor type
Fix the floor using the method for its type: secret nailing/screwing through the tongue, face screwing or gluing. Follow the supplier's instructions for fixing method and spacing — it depends on board thickness and substrate.
Allow for shrinkage
Timber only shrinks and swells below the fibre saturation point (FSP ≈ 28 % MC). Shrinkage is greatest tangentially: for softwood approx. 2.5–3.0 mm/m per 1 % change in moisture content (radially about half). A wide floor that dries by a few percent can therefore open noticeable gaps — plan the joints so the movement can be accommodated.
FSP≈ 28 % MCShrinkage, softwood tangential2.5–3.0 mm/m per % MCFinish with expansion joints and skirting
Finish with expansion joints at all fixed surfaces (walls, frames, columns, pipes) and cover the joints with skirting or quadrant beads fixed to the wall — not the floor — so the floor can move freely. Also keep the moisture content down during laying: above approx. 18–20 % MC there is a risk of fungal attack.
Skirting boards are fixed to the wall, never to the floor — otherwise you lock the floor's movement.
Source
Based on Discebo's carpentry template «Process: laying floorboards», the article «Material consumption and waste», the shrinkage coefficients in the calculation module (Træ.dk «Fugtighed og træ») and the article «Moisture in timber structures».