Why are my windows cold and draughty?

What this usually means

Standing near a window, you can feel cold for two different reasons. The first is radiant: the inner surface of low-performance glazing runs cold, and your body radiates heat to it, so you feel chilly even if the air is warm. The second is convective: air leaks in around the unit, the opening frame, or the gap between frame and wall (the reveal), and you feel that moving cold air as a draught.

These need different remedies. Radiant cold is reduced by better glazing — a warmer inner surface from improved units — or by addressing the whole window's performance. Air leakage is reduced by renewing seals and sealing the gaps around the frame and reveal. A window can be cold by radiation but not especially draughty, or draughty through leakage while the glass itself is reasonable, so identifying which dominates avoids spending on the wrong fix.

The reveal and frame-to-wall junction are commonly overlooked. Draughts felt 'at the window' often come from the gap where the frame meets the wall, or from an uninsulated, cold reveal, rather than through the unit. Sealing and, where needed, insulating these can transform comfort without replacing the window at all.

Common causes

Signs and symptoms

The inner surface temperature of glazing depends on its insulating performance: single glazing runs much colder on the inside than modern insulated units, so it both loses more heat and produces stronger radiant discomfort. Because the body exchanges heat with surfaces by radiation, a large cold pane lowers the mean radiant temperature near it, making you feel cold regardless of the air temperature. Warmer glazing raises that surface temperature and the comfort with it.

Air leakage at windows is convective and pressure-driven, like leakage anywhere in the envelope. Worn seals on opening lights, and gaps at the frame-to-wall junction, let air through under the stack and wind pressures across the building. Because these gaps are small and distributed, they are best found under the steady pressure of a blower door test with smoke, which distinguishes leakage through the unit from leakage around it.

The reveal is a thermal-bridge issue. A cold reveal both feels chilly and can fall below the dew point and condense, even when the glass is fine. Insulating and sealing the reveal raises its surface temperature and stops the draught and condensation there. Separating these three effects — glazing performance, air leakage, and reveal/junction detailing — with thermal imaging and a blower door test is what allows a targeted fix instead of a blanket window replacement.

How to fix cold, draughty windows

Treat the radiant cold and the air leakage separately, and don't overlook the frame junction and reveal. Diagnose which dominates before spending.

1. 01

   Separate the causes

   Use thermal imaging and a blower door test to distinguish cold glass from air leakage, and locate where the leakage actually is.

2. 02

   Seal the air leakage

   Renew worn seals on opening lights and seal gaps at the frame-to-wall junction — often the quickest comfort gain.

3. 03

   Address cold reveals

   Insulate and seal cold reveals to raise their surface temperature and stop draughts and condensation there.

4. 04

   Improve the glazing where needed

   Where radiant cold from the glass dominates, improve or replace the units — confirmed by measurement, not assumed.

5. 05

   Replace genuinely failed units

   Replace blown or rotten units and frames that have truly failed.

6. 06

   Verify comfort

   Re-check radiant comfort and draughts after the work.

How to prevent it coming back

• Maintain and renew window seals before they perish.
• Keep frame-to-wall junctions sealed.
• Insulate cold reveals during any window or wall work.
• Repair blown or rotten units promptly.