Do I Need Tile Vents?

What a tile vent does

A tile vent looks like an ordinary roof tile with a grille or slot built into it. It lets air pass between the outside and the space under the tiles, and some versions connect to a pipe that vents a bathroom fan or a soil stack. In effect, it adds a controlled opening to a covering that would otherwise be sealed apart from the gaps at the eaves and the ridge.

There are two main types. A ventilation tile lets air into or out of the roof void. A pipe terminal tile allows a soil vent, extractor duct or flue to leave the house through the roof, with a collar that matches the tile profile. They are sold in versions for concrete interlocking tiles, clay plain tiles and slates, and the profile must match the roof around it.

Why roofs need ventilation

Houses produce moisture from cooking, washing, breathing and drying clothes. Some of it rises into the loft as warm, damp air, and when it meets cold timber or the underside of the covering it condenses. Over time, that wets the timbers, leads to mould, rots the felt and can reduce insulation performance. Moving air carries that moisture out before it settles.

The traditional approach was a gap at the eaves and a gap at the ridge, so that air could flow through. With a cold loft, that is often enough. In roofs where the ceiling is sloped, where the roof is long or interrupted, or where insulation has been packed tightly against the underside, the air has nowhere to go. That is when extra vents are added.

Breathable membranes change the answer

Many modern roofs use a breathable underlay, which lets water vapour pass through while keeping liquid water out. On a roof with that membrane, vapour can escape through the covering itself, and the demand for separate vents is reduced. It is not always zero, though, because the manufacturer's instructions and the build-up of the roof decide. Our guide on breathable roof membranes goes through the types.

If you are replacing the covering on a roof that previously had old felt, ask whether the new underlay is breathable, and whether the loft below is insulated. The two combined decide whether vents are needed, and what kind.

When they are usually added

Common cases include a loft conversion with a sloping ceiling, a kitchen or bathroom extension where the roof was altered, a roof with a hip and a short ridge, and a house where the eaves are blocked by insulation. A bathroom extractor fan that vents into the loft is a separate problem, because it should be ducted to the outside, and a terminal tile is a tidy way to do that.

Do not add vents blindly. Too many can let wind-driven rain or snow into the loft, and a vent in the wrong place can reduce the draw rather than increase it. Where a conversion or a re-roof falls under Building Regulations, your building control body (the council building control team or a private approver) can confirm the requirement. You can also read about related fixings in our guide to BS 5534 roof tile fixing.

Pipe and extractor terminals

Not every tile vent is about the loft air. A soil vent pipe that leaves the house through the roof needs a terminal that matches the tile profile, so that the pipe is sealed where it passes through. An extractor fan from a bathroom or kitchen should not simply blow into the loft, because the warm, damp air condenses on the first cold surface it meets. A duct to a terminal tile takes the moisture outside.

These terminals are fitted by replacing a tile and lapping the underlay correctly around the pipe, so rain that runs down the pipe stays on the surface. It is a modest job on an accessible slope, but it is easy to get wrong if the underlay is cut carelessly. A leak from a badly dressed pipe terminal can look like a general roof fault, which is why we check it from the loft as well.

How we decide

On a survey we look at the loft from inside as well as the roof from outside. Condensation staining on the rafters, a musty smell, black spots on the underside of the felt and blocked eaves are all clues. We tell you what we see, with photographs, and whether vents will help. Our overall tiled-roof service is described on our pitched roofing page.