There’s a corner of our eldest’s room where homework becomes an Arctic expedition. Desk under the window, cold line down his forearms, pencil like an icicle. I kept blaming “old house” until I did the boring checks: tissue test, incense stick, hand along the frame. The cold wasn’t the pane; it was a thin jet of air sneaking through the timber sash meeting rail and the latch side. Not romantic. Just a leak.
What I used (receipt on the fridge): EPDM self-adhesive foam strip, 6 mm wide, 3 mm thick, 10 m roll. £11.79 from the DIY shed. A microfibre cloth, a dash of isopropyl to clean the contact points, scissors. Twenty minutes and a chair to stand on.
Before numbers: room at 18.9 °C, skirting under the window at 14.2 °C (IR thermometer), CO₂ 780 ppm and steady. The giveaway wasn’t the temperature; it was the tiny plume from an incense stick pulling inward along the meeting rail even with trickle vents shut and the radiator ticking away. You could feel it with a damp knuckle.
Steps (the non-glossy version):
- Opened the top sash a touch, cleaned the flat faces the strip would touch. Old paint dust everywhere; wipe again.
- Test fit a 10 cm offcut. Too thick on the latch side—sash stuck. Swapped to a single run of the 6 mm foam there, doubled it on the top rail where the gap was bigger. Foam needs a continuous path; don’t hop gaps.
- Peeled and stuck in one pass, pressing hard with a blunt butter knife to seat it into the ripples of old paint. Corners get a little miter cut so it doesn’t bunch.
- Closed and opened the sash three times so the foam “learns” the shape. No squeaks, no drama.
After numbers (same meter, ten minutes later): room 19.0 °C, skirting under the window 17.6 °C, CO₂ unchanged. Incense plume no longer bending toward the frame; it lazily rises. The kid’s arms stop hunching. Radiator valve backed down a nudge because the room holds onto warmth instead of losing it through a slot the size of a library card.
Time and cost: 24 minutes, £11.79. About two metres of strip used today, eight left for the other window and the wobbly loft hatch that whistles when it’s windy.
Mistakes I made so you don’t have to:
- I tried a thicker strip first. Looked satisfying, jammed the sash. If you’re guessing gap size, err small and build up.
- I nearly stuck onto dust. Clean once, then clean again. Adhesive hates memories of 1987 gloss.
- I forgot the latch throws tighter at the top; different gaps need different runs. Mix widths if you have them. If not, double up only where the smoke tells you.
This isn’t a miracle. It’s a leak you can stop with a tenner and a quiet half hour. One less cold jet, one less argument about homework in a coat. Tomorrow I’ll take the same roll to the landing window and see if the stair chill is the same story in a different hat.
