Why does my conservatory roof drip with condensation?

Every room has invisible water vapour in its air, and the warmer the air, the more it can carry. When that warm air touches a cold surface, it cannot hold all its vapour, and the excess condenses into droplets. A conservatory roof is a large, thin, cold surface hanging over a warm room, so it collects the droplets first.

The droplets run down the roof and gather at the bars, where they drip. Winter mornings are the worst, because the roof is coldest overnight and the room fills with moisture from breathing, cooking and the kettle. The same effect happens in any house with poor ventilation, but a conservatory shows it more because so much of the room is cold glass. BS 5250 is the standard that deals with moisture in buildings, and the idea behind it is simple: keep the air moving and keep the surfaces warm.

That also explains why a new conservatory can drip while the old one did not. Tighter seals and better window units keep draughts out, and with them goes the air change that used to carry the moisture away. A well-sealed room needs a planned way to breathe.

A leak follows rain. Water appears after a downpour, usually at the same spots, such as the ridge, the wall flashing or a bar joint, and it keeps arriving for a while after the rain stops. Moisture from the air follows the temperature instead. It shows on cold, still mornings, tends to be worst on the underside of the roof, and clears as the room warms up or the day dries out.

Look at the pattern as well, because it is the quickest clue you have. A light film on the whole roof points to condensation. A single steady drip, a stain below one joint or a damp patch at the house wall points to a leak. Our guide to a leaking conservatory roof lists the usual entry points. If you cannot decide, send us photographs taken at the time it happens, and we will help sort one from the other.

Sometimes the moisture is inside the roof itself. Multiwall polycarbonate has hollow channels that should be sealed along the ends. When the tape fails or a sheet is cut short, damp air gets in, and you see water or green algae growing inside the sheet. That cannot be wiped away from the room. The sheet has to be resealed or replaced.

Double-glazed roof units can fail in the same way. A unit with a failed seal mists between the panes, and no amount of ventilation clears it. The unit has to be replaced. Replacing one sheet or unit is often possible, but it depends on finding a close match. Blocked drainage channels in the glazing bars can also hold water against the glass, so we check them during the survey.

Ageing is another cause. Rubber gaskets harden and shrink, tapes lift, and the caps along the bars loosen. None of these is dramatic on its own, but together they let moist air reach cold surfaces that were once protected. A roof that has done well for years can start to drip simply because its seals have given up.

Start with the air. Open a vent or window for a short while each day, even in winter, so damp air can leave. Use extraction in the kitchen and do not dry washing in the conservatory. Keep furniture a little way from the walls so air moves, and think about how many plants the room holds, since they release water too.

A dehumidifier is worth trying on persistent mornings, and a heater on a low setting stops the glass from falling so far below the room temperature. A blind pulled across the roof shades the sun in summer, but it can trap damp air against the glass in winter, so open it on cold days. Our page on conservatory roof ventilation goes further.

If you have tried ventilation and the roof still drips, the roof is too cold. A better-insulated covering raises the temperature of the inner surface, so less water condenses on it. A solid roof does this best, and a modern high-performance glazed unit improves on older glass. Either option stops the drip at its cause instead of managing it every morning.

At the survey we look over the roof, record each problem in pictures, and give a plain verdict: ventilate, repair the failed seal, or replace the covering. A written quote follows, showing a single total. Read about conservatory roof insulation or go back to our conservatory roof replacement page.

If the drips are heavy, put a bowl or towel under them and protect any electrical fittings, since water and wiring in a ceiling do not mix. Take a photo of the roof each morning for a few days and jot down the day's conditions. That log shows whether we are dealing with moisture in the air or water coming in from outside.