Why is there a cold draught coming from under my skirting?
A cold draught at the bottom of the wall, where the skirting meets the floor, almost always means cold air from the void beneath a suspended ground floor is leaking up into the room through the gap there. Suspended timber floors are deliberately ventilated underneath by airbricks to keep the timbers dry, so the void is cold and breezy; where the floorboards meet the wall, and the skirting doesn't seal the junction, that cold air is drawn into the room — especially as warm air rises and escapes higher up, pulling replacement air in low down. It is a classic, very fixable air-leakage path.
Reviewed by George Sora, Certified Passive House DesignerUpdated June 2026Quick answer & key takeaways
6 min read- The draught is cold void air leaking up at the floor-wall junction.
- Suspended floors are ventilated underneath, so the void is cold.
- The skirting often fails to seal the gap to the void.
- Warm air rising elsewhere pulls cold air in low down.
- Biggest misconception: it's a wall draught. It's the floor void.
- RetrofitIQ's approach: locate and seal the junction while keeping the void ventilated.
What this usually means
Most older homes have a suspended timber ground floor: floorboards on joists over a ventilated void, with airbricks in the external walls keeping that void dry. The void is therefore cold and connected to outside air, and the perimeter — where the floorboards run up to the external wall behind the skirting — is rarely sealed. Cold air from the void leaks up through the gap between the boards and the wall, and out under or behind the skirting into the room, producing the draught you feel at ankle level along the bottom of the wall.
The stack effect makes it worse: warm air rising and escaping through the upper parts of the house lowers the pressure low down, actively drawing cold void air in through the skirting gap. The fix is to seal that floor-perimeter junction — sealing the gap between the boards and the wall and behind the skirting — and to seal gaps between the boards themselves, so the cold void air can no longer leak into the room. Crucially, this must be done without blocking the airbricks: the void still needs its under-floor ventilation to keep the timbers dry, so you seal the leak into the living space, not the ventilation of the void.
Common causes
Ventilated cold floor void
Airbricks keep the void cold and connected to outside air.
Unsealed floor-wall junction
The gap behind the skirting lets void air into the room.
Gaps between floorboards
Cold air leaks up through shrinkage gaps in the boards.
Stack effect
Warm air escaping high up draws cold air in low down.
Signs and symptoms
Cold draught at ankle level
Void air leaking in at the floor-wall junction.
Draught worse when heating is on
Stronger stack effect drawing in more cold air.
Cold floor near the walls
Void air chilling the perimeter of the floor.
Suspended timber floor
Construction that creates a ventilated cold void.
What most people check first
- Whether the floor is suspended timber over a ventilated void.
- Whether the floor-wall junction behind the skirting is sealed.
- Whether there are gaps between the floorboards.
- Whether the airbricks are kept clear for void ventilation.
What most people miss
- That the draught comes from the floor void, not the wall.
- That the stack effect drives it stronger when heating is on.
- That sealing must not block the airbricks.
- That the perimeter junction is the key leak.
The building physics
A suspended timber floor sits over a void deliberately cross-ventilated by airbricks to keep the timbers below the dew point's reach and prevent rot — so the void is effectively at outdoor temperature and pressure. The living space above is warmer and, through the stack effect, slightly depressurised at low level when warm air escapes high up, so air flows from the cold void into the room through any gap: principally the unsealed junction where the boards meet the external wall behind the skirting, and the shrinkage gaps between boards. The draught is thus an infiltration path driven by buoyancy and the void's connection to outside.
The remedy separates the two functions the floor must perform: it must keep the void ventilated (airbricks clear) while stopping void air leaking into the room. Sealing the perimeter junction and the inter-board gaps from above — or insulating and air-sealing the floor from below where access allows — closes the leak into the living space without compromising the under-floor ventilation. A blower door test with smoke or thermal imaging confirms the floor perimeter as the leakage path and verifies the seal afterwards. Done correctly, the draught stops, the floor's edges warm, and the timbers stay safely ventilated below.
How to stop a draught from under the skirting
Seal the floor-wall junction behind the skirting and the gaps between boards, while keeping the airbricks clear so the void stays ventilated.
- 01
Confirm the source
Check the floor is suspended and the draught comes from the perimeter.
- 02
Seal the perimeter junction
Close the gap between the boards and wall behind the skirting.
- 03
Seal board gaps
Fill shrinkage gaps between the floorboards.
- 04
Keep airbricks clear
Maintain the under-floor ventilation that keeps timbers dry.
- 05
Consider floor insulation
Insulate the floor from below where access allows.
- 06
Verify the seal
Confirm the draught is gone and the void still ventilated.
How to prevent it coming back
- Seal the floor perimeter, not the airbricks.
- Maintain under-floor ventilation to protect the timbers.
- Fill board gaps that let void air up.
- Treat low-level draughts as a floor-void issue.
How Retrofit IQ investigates this
We confirm the floor void as the draught source and detail the sealing without harming the under-floor ventilation.
Do not spend money fixing symptoms before you understand the cause — investigate first, then build with confidence.
Do I need a professional investigation?
If you feel cold draughts at the bottom of the walls, it is worth confirming the floor void as the source with a blower door test or thermal imaging. That locates the perimeter leakage precisely, so it can be sealed effectively while keeping the airbricks clear, stopping the draught without risking the timbers.
Where to go next
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Frequently asked questions
Why is there a cold draught coming from under my skirting?+
Almost always because cold air from the ventilated void beneath a suspended timber floor is leaking up into the room at the junction where the floorboards meet the wall behind the skirting. The void is cold and breezy by design, and warm air rising elsewhere draws that cold air in low down.
Should I block the airbricks to stop it?+
No — the airbricks ventilate the floor void to keep the timbers dry and prevent rot. Blocking them risks serious damp and decay. The fix is to seal the leak into the room — the floor-wall junction and board gaps — while keeping the airbricks clear.
Why is the draught worse when the heating is on?+
Because warm air rising and escaping higher up lowers the pressure at floor level (the stack effect), which actively pulls cold void air in through the skirting gap. So the warmer the upper house, the stronger the low-level draught.
How do I seal it?+
Seal the gap between the floorboards and the external wall behind the skirting, and fill shrinkage gaps between the boards. Where you can access the void, insulating and air-sealing the floor from below is even better — all while leaving the airbricks clear.
How do I confirm it's the floor?+
A blower door test with smoke, or thermal imaging, shows cold air entering along the floor perimeter at the skirting, confirming the void as the source and letting the sealing be targeted and then verified.
Stop guessing — find the real cause
Do not spend money fixing symptoms before you understand the cause. Every home behaves differently, and the only reliable way to know what is happening in yours is professional building performance diagnostics. At RetrofitIQ we verify buildings using the right combination of investigations:
- Thermal imaging
- Blower door testing
- Moisture & dew point readings
- Ventilation review
- Building physics assessment
- Passive House methodology