How to stop condensation on windows in an old house
Water running down the inside of the glass on a cold morning is condensation, and it happens because warm, damp indoor air is meeting cold single glazing. Wiping the sills is the least of it. That water is what feeds the mould around the frame, and given a few winters it is also what rots the timber.
The cause is a cold sheet of glass, so the fix is to stop the room side of the glass getting that cold.
Why full double glazing is not always the answer
Replacement double glazed units do solve it. They also cost a great deal, and in a heritage house they often mean losing the original sashes, which may not be allowed and is usually not worth it. Plenty of people want to know whether a room can be made comfortable before they spend that kind of money on it.
Add a layer of secondary glazing
Secondary glazing puts a second barrier just inside the existing pane and traps a pocket of still air between the two. That trapped air does the insulating. It lifts the temperature of the inner surface, which cuts the condensation and keeps more heat in the room.
Secondary Glazing Film does that for a small fraction of the cost of new glazing, which makes it the sensible first move for renters, for anyone mid-renovation, and for anyone working out which rooms actually need a bigger fix.
Fitting it takes an afternoon. Clean the frame, run the double-sided tape around the timber, stretch the film across and press it onto the tape, then shrink it tight with a hair dryer until it disappears. Done carefully you have to look for it to see it, and the difference on the first cold morning is not subtle.
Deal with the moisture as well as the glass
Warming the glass handles the symptom. Where the water comes from is worth a look too. Drying washing indoors, unflued gas heaters and long showers all put litres of water into the air of a house. Open something for a few minutes when you can, especially after a shower.
Draught-proofing helps hold the heat in, and the two jobs work well together, but leave a little controlled airflow rather than sealing a room completely. Air with nowhere to go just dumps its moisture on the coldest surface it can find.
If you want the permanent version later
Vacuum glazing puts double-glazing performance inside your original timber sashes, which is the work our parent company Sealasash does across Tasmania and Victoria. It is the endpoint, not the starting point. Film first tells you what a room is capable of, and it costs about as much as a takeaway dinner per window.
FAQ
Why do my windows have condensation in the morning? Warm indoor air meets cold single glazed glass overnight, and the moisture in that air condenses on the cold surface. Warming the inner surface reduces it.
Does secondary glazing stop condensation? It reduces it substantially by keeping the room side of the glass warmer. Combined with sensible ventilation it clears most everyday condensation.
Is secondary glazing film worth it? For the cost, yes. You get a noticeable jump in warmth and a real drop in condensation for a tiny fraction of the price of replacement glazing, and it suits rentals and heritage windows where you cannot alter the original.
Will it damage my window frames? No. The film fixes to double-sided tape on the frame and both come away cleanly, which is why it works for renters.
How long does the film last? A season at minimum, and often several if it is not knocked. Most people leave it up through winter and take it down for summer.
What you need for this job
- Secondary Glazing Film. Film and double-sided tape. All you need on top of that is a hair dryer and a clean cloth.
Sealing the gaps around the sash at the same time gets you most of the way to a warm room for very little money. If you want the permanent fix in the original sashes, ask us about vacuum glazing.