Updated
Gaps Opening Between Floorboards
Gaps have opened along the length of original floorboards or an engineered wood floor, letting draughts and dust through.
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What's happening?
Solid and engineered timber move with the moisture in the air. Boards take up moisture in a damp summer and give it back in a heated winter, and because they move mostly across their width, that movement shows as gaps along the length of every board rather than at the ends. Original Victorian and Edwardian pine floors do this most obviously: they were laid in unheated houses at a much higher moisture content than a modern centrally heated room ever reaches, so they have shrunk permanently and continue to move seasonally on top of that. Gaps that close again in summer are normal seasonal movement. Gaps that keep widening year after year mean the room is running drier than the timber can cope with.
What usually causes it?
- Original boards laid at a high moisture content in an unheated house, now permanently shrunk by central heating
- Boards not acclimatised in the room before fitting, so they dried and shrank in place
- Room humidity running very low through winter, especially with underfloor heating
- Wide boards, which move more across their width than narrow ones for the same moisture change
- Boards face-nailed rather than secret-fixed, so each one shrinks away from its neighbour independently
- A previously damp subfloor drying out after a leak or a damp-proofing repair
- Underfloor heating run up too quickly after the floor was laid
Is it dangerous?
No, though a floor with open gaps over an unheated void loses a lot of heat and pulls cold draughts and dust into the room. Very wide gaps in an older floor can also let a heel or a chair castor drop in.
Can I fix it myself?
Do the easy part first: measure the humidity in the room over a winter and see whether the gaps close in summer. Seasonal gaps are best left, because anything rigid packed into them gets crushed when the boards swell back. Narrow, stable gaps take a flexible filler or a slim timber slip glued to one side of the gap only, so the board can still move. Draught-stopping strips designed to flex are the usual answer in an original floor.
When should you call a flooring fitter?
Call a flooring fitter when the gaps are wide enough to see the joists, when boards have cupped or lifted as well as separated, when the floor is engineered or a modern solid floor still under guarantee, or when you want the floor lifted, re-laid tight and re-finished. Closing an original floor properly means lifting and cramping the boards back together, which is not a job to start halfway through.
What will the flooring fitter actually do?
- Measure the moisture content of the boards and the humidity of the room before recommending anything
- Advise whether the movement is seasonal and should be accommodated, or permanent and should be closed up
- Fill or slip narrow gaps with a method that still allows the boards to move
- Lift and re-lay boards cramped tight, inserting new boards where the total shrinkage is too great to close
- Sand and re-finish the floor after re-laying, and set up underfloor heating commissioning where fitted
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