Does a solid conservatory roof need ventilation?

A glass or polycarbonate roof leaks warmth, and with it a good deal of moisture. Gaps at the glazing bars, thin panels and cold surfaces mean the room never quite seals itself. Swap that for a tiled or insulated solid roof and the room becomes much tighter. That is the point of the conversion, since it keeps heat in during winter. It also keeps in the moisture that people, wet washing, cooking from the kitchen next door and houseplants put into the air.

Warm, damp air looks for the coolest surface and condenses there. In a conservatory those surfaces are the glazed walls, the frames and, if the roof was built badly, the underside of the roof lining. Left alone, the result is streaming windows, black mould on the sealant and stained plasterboard. A solid roof does not remove that risk. It moves it, which is why ventilation is planned at the start of the job and not added after the first damp winter.

The first layer of ventilation is the room itself. Opening windows and doors let you clear stale air on demand, and trickle vents in the frames give a steady background change of air when the room is shut. Conservatories with only one small opening window and a fixed lantern tend to feel stuffy in summer and run with condensation in winter, because nothing sets up a draught through the room.

Two openings at different heights work best. Warm air rises, so an opening high in the room lets it leave while a lower one lets cooler air in. If the old roof had roof vents or an opening ridge light, keep them in the design or replace them with something equivalent. A fixed solid roof with no way for hot air to escape can make a south-facing room worse in July than the glass roof ever did. Tell the surveyor how the room is used. A utility room with a tumble dryer needs more air movement than a quiet reading room.

The second layer sits inside the roof. Roofers talk about a cold roof and a warm roof. A cold roof puts its insulation along the ceiling line and leaves a clear air gap above it, running from eaves to ridge, so any moisture that gets through is carried off. A warm roof takes the opposite approach: the insulation goes over or between the rafters with the right membranes, which keeps the timber warm and the whole build-up sealed rather than vented.

Either can work, but they are not interchangeable and they are not a mix-and-match job. A vapour control layer in the wrong place, an air gap blocked by insulation pushed hard into the eaves, or a warm-roof layout with a cold-roof detail can all trap moisture in the timber. For pitched roofs generally, Marley's guidance on cold roofs gives eaves ventilation for a high-resistance underlay of 25 mm at pitches of 15 degrees or less and 10 mm above that, which shows how specific the gaps are. Ask your roofer which type is being built and why, and have it written into the quote.

A solid conservatory roof needs Building Regulations approval. Planning Portal guidance asks for a sound structure, good energy performance and adequate ventilation in a new conservatory roof. Replacing a glass roof with a tiled one is a change to the structure, so it is not covered by the thresholds that let some re-roofing go ahead without an application.

You apply through the council's building control office or a private registered approver, and an inspector visits while the roof goes on. They will look at the frame and foundations, the insulation, the ventilation route and the way the roof joins the house wall. We explain which consents apply and deal with the building control notification where the job requires one. If you are comparing builders, ask each one who is making the application and when the inspections are booked. Our guide to Building Regulations for a solid conservatory roof goes through the process in order.

Some warning signs appear within the first season. Water beads on the inside of the glazed walls every morning, and mould speckles the silicone along the bottom of the panes. A musty smell lingers when the doors are shut. Paint blisters on the new ceiling lining, or a dark tide mark spreads out from the corners. In summer, the opposite sign shows up: heat that builds all afternoon and does not clear by evening.

Not every damp patch is a ventilation fault, and the wider picture sits on our conservatory roof replacement page. A drip from a failed joint looks similar to condensation, and the fix is different. Our page on conservatory roof condensation shows how to tell them apart. For summer heat, see why a conservatory gets too hot. Either way, we begin by surveying the roof, frames and openings with photographs, and then send you a written quote that gives one total price.