How do I stop draughts from floorboards?
Sealing gaps between floorboards and at the skirting without stopping the underfloor ventilation a suspended floor needs.
- Difficulty
- beginner
- Time
- 3 hr
- Read
- 2 min
- Safety
- caution
Short answer
Fill the gap between skirting and floor with decorator's caulk, and fill board gaps with a flexible filler, slivers of timber, or a proprietary gap filler. Never block the air bricks that ventilate the space below — a suspended timber floor needs that airflow to avoid rot.
A suspended timber floor sits over a ventilated void, so cold air comes up between the boards and around the edges. Sealing the gaps is worthwhile and straightforward; the one rule is that the ventilation to the void itself must stay open.
Safety
What you'll need
- Decorator's caulk and gun
- Flexible floor gap filler or timber slivers
- Rugs and underlay
- Draught-proofing strips for boards (optional)
Step by step
- Check the air bricks outside are clear before doing anything inside.They are what keeps the void dry. Blocked air bricks cause rot in the joists.
- Seal the gap between the skirting and the floor with decorator's caulk.This is often the largest single gap and the easiest to fix. Caulk stays flexible as the timber moves.
- Fill gaps between boards with a flexible gap filler or thin timber slivers glued in.Rigid filler cracks out as boards move seasonally. Flexible products or timber move with them.
- For wide gaps, glue in tapered timber slivers and plane them flush.It is more work but it is permanent and looks correct on an exposed board floor.
- Work along the room in sections rather than trying to do it all at once.It is a slow, kneeling job. Sections make it manageable.
- Consider underlay and a rug rather than sealing every gap.A good underlay and rug cut both draught and heat loss substantially for far less effort.
- For a bigger improvement, insulate between the joists from below if you have access.From a cellar or crawl space this is far easier than lifting floorboards, and it is a significant heat loss.
- Leave the air bricks and any underfloor vents alone throughout.This is the one thing not to compromise on.
Tips
- Sealing floor gaps also reduces dust coming up from the void, which is a noticeable secondary benefit.
- In a room with an open fire, be careful about sealing too thoroughly — a fire needs combustion air.
- Rugs with a good underlay make an immediate difference to how cold a room feels underfoot, for very little work.
Common mistakes
- Blocking air bricks — The void under a suspended floor needs ventilation. Blocking it causes damp and rot in the joists.
- Using rigid filler between boards — Boards move seasonally and rigid filler cracks out within a year.
- Sealing a room with an open fire completely — Fuel-burning appliances need combustion air. Over-sealing is a carbon monoxide risk.
Questions people ask
Can I fill gaps between floorboards permanently?
Yes, with tapered timber slivers glued in and planed flush. Flexible fillers are quicker but may need redoing eventually as boards move.
Should I block the air bricks to stop the draught?
No. They ventilate the void under a suspended timber floor, and blocking them causes rot in the joists — a far more expensive problem than the draught you were fixing.