What vents are doing in the roof
Warm air rises. In a glazed room under the sun, hot air collects at the ridge with nowhere to go, so the room climbs in temperature. In winter the same high point collects moist air that then meets the cold roof and condenses. A vent at the top gives that air a way out, and an opening lower down gives fresh air a way in, so air moves through the room instead of sitting.
The effect is simple but real. Ventilation lowers the peak temperature on a bright day and removes some of the damp that causes drips on a cold one. It is not a replacement for good glazing or insulation, which deal with heat and cold passing through the roof. It handles the air in the room, and the roof structure deals with the rest.
If you want the full picture of what happens when moist air touches cold glass, our answer on conservatory roof condensation goes through it. A room that bakes at three in the afternoon and streams with water at seven in the morning is usually short of the same thing, a route for air to move.
Roof vents and trickle vents
The two names get used for different things, so it helps to separate them.
| Type | Where | What it does |
|---|---|---|
| Roof vent | High in the roof or at the ridge | Lets hot, moist air escape |
| Trickle vent | In a window or door frame | Lets a small steady flow of air in |
| Opening roof light | In the roof glazing | Gives a larger opening on demand |
A roof vent works best with an air inlet at a lower level, which is where trickle vents or opening windows come in. Together they make a flow of air through the room. A roof vent on its own can only draw air from whatever gaps there are.
Whether a vent can be added to an existing roof depends on the frame and the glazing. Some roof systems take a vent unit in place of a pane or panel; others are better ventilated through the walls. The survey sorts out which route suits the roof you have, and a vent is sealed into the roof so that it does not become a new leak point.
Ventilation in a solid roof
When a polycarbonate or glass roof gives way to a solid tiled one, the room is no longer open to the sky. Warm, damp air can reach the underside of the new roof build-up, so ventilation is part of the design from the start. The Planning Portal's guidance puts ventilation alongside structure and energy use as something a replacement conservatory roof must satisfy.
BS 5250:2021 is the current code for moisture control in buildings, and it is the reference behind the way a roof build-up is detailed so that moisture can leave rather than collect in the timber or insulation. For cold deck roofs, paragraph 6.11 of Approved Document C relies on ventilation of the deck. How that is arranged for a conservatory depends on the build-up, which is a matter for the specification and building control.
So a solid roof does not remove the need for ventilation. It moves the question into the roof itself, and the room below still needs openable windows for the summer. Our page on tiled conservatory roofs covers what goes into one, and building control signs off the result.
What to check on your own roof
Before you ask for a quote, a few minutes in the room tells you a lot.
- Count the openings: roof vents, opening roof windows, and window and door vents.
- Check that each one opens and closes, and that its seal is intact.
- Look at the room on a cold morning for beads of water, especially near the ridge.
- Note how hot the room gets on a bright day with the windows open.
If the room has no high-level opening at all and runs hot or drips, a vent is worth adding. If it has vents that are painted shut, broken or blocked by a blind, repair or clearing may be all that is required.
For the work on the roof itself, see our conservatory roofs service. The visit takes in the glazing seals, the gutters and the wall junction in one go. If you are choosing between a vented glazed roof and a solid one, the page on solid, glass or polycarbonate lays the options out, and either way you get a single written total.
