The roofing glossary

The timber structure carrying the whole roof: trusses, purlins and rafters. Once the roof is closed you never see it again, yet it decides whether the tiles can simply go back on or whether the deck must be rebuilt first. A sound frame shows straight lines when you look up from inside the loft.

See also rafter · purlin · boarded decking The related service

A timber running down the slope, ridge to eaves, at regular spacing. Rafters sit on the purlins and carry the roof decking. Where a rafter has lived under an old leak it goes black and soft in the middle — it is the first thing we probe once the tiles are off.

See also purlin · roof frame

A horizontal beam running across the slope, carrying the rafters. There is a ridge purlin at the top, intermediate purlins, and a wall plate at the bottom bedded on the masonry. A visible dip in a roof almost always comes from a purlin, never from a tile.

See also rafter · roof frame

Close-butted boards nailed across the rafters, forming a continuous deck under the covering. It is the traditional support for canal tiles in the Midi — closer to Scottish sarking than to the open battens common in England. Boards are replaced one by one: only what is damaged comes off.

See also rafter · tiling batten The related service

A membrane rolled out over the deck, beneath the tiles. It is the second line of defence: it carries to the eaves any water or fine snow driven under the covering by wind. Many old roofs have none at all — which is normal, and explains why they cope badly with a cross-wind.

See also air gap · counter batten The related service

A batten nailed down the slope, over the underlay and in line with the rafters. It creates the air gap that lets the deck breathe and dry between showers. Without counter battens, an underlay laid straight under the tiles traps moisture instead of letting it out.

See also air gap · underlay · tiling batten

A batten fixed across the slope, on top of the counter battens, which the tiles hook over. The spacing between battens is set by the tile’s gauge — and it is this setting-out that gives the courses their headlap and their alignment.

See also gauge · counter batten · headlap

The ventilated space held between underlay and tiles by the counter battens. Air comes in low, at the eaves, and leaves high, at the ridge. Block that path — a nest, a forgotten bag of mortar, a clogged ridge vent — and the timber stops drying out.

See also counter batten · vent tile · ridge vent closure

The tile of the Midi: a half-cone of fired clay, with no interlock and no nib, laid in pairs. It is the traditional covering of the Languedoc and the one required across most protected areas of the département. It works at low pitch, and it can be reused — a sound old tile beats a new one.

See also under tile · over tile · gauge The related service

The lower tile, laid hollow side up: it catches the water and channels it down to the eaves. The under tiles form the roof’s gutters. They go on first, set out on the battens, before their joints are capped.

See also over tile · canal tile

The upper tile, laid hollow side down, straddling the joint between two under tiles. It is what you see from the street, and what gives the roof its colour. On a re-roof it is usually the old over tiles that are reused: they carry a patina nothing else can imitate.

See also under tile · canal tile

The length by which one tile covers the one below, down the slope. Headlap is what makes a roof watertight, not the tile itself: the shallower the pitch and the more exposed the site, the more generous it must be. Too little headlap shows up in the first driving rain.

See also gauge · tiling batten

The part of a tile still visible once the course above is laid — in other words, what is not covered. Gauge and headlap are two sides of one setting-out: increase one and you reduce the other by exactly as much. This figure fixes the batten spacing.

See also headlap · tiling batten

The bottom line of the roof, where water leaves the covering. Everything that lands on the slope ends up here: it is the hardest-worked part of a roof, and the first place we look when a stain appears on a ceiling — even when the leak is elsewhere.

See also gutter · tile end · drip edge The related service

The half-round channel that collects water at the eaves and takes it to the downpipe. It is called “pendante” when hung from the roof edge on brackets. An overflowing gutter is not always blocked: it may simply be undersized, or have lost its fall.

See also gutter bracket · downpipe · eaves The related service

The ironwork that holds the gutter and gives it its fall. Brackets go up before the gutter, set to a line, falling gently towards the outlet. A corroded or loose bracket lets the gutter sag and hold water — usually invisible from the ground.

See also gutter The related service

The vertical pipe taking water from the gutter down to ground or drain. An undersized downpipe backs the gutter up in every summer storm — short, violent events that are common in the Aude and test a rainwater system far harder than winter rain does.

See also gutter The related service

The lower end of a tile, the part oversailing the gutter. With canal tiles the ends form the row of half-moons you see from the street. It is also a check on the setting-out: a ragged line of tile ends gives away battens that were reset in a hurry.

See also eaves · drip edge

Whatever forces water to fall into the gutter instead of creeping back under the tile by capillary action — either a metal strip at the bottom of the slope, or simply a properly judged tile overhang. Without it, water works back under the covering and rots the rafter feet.

See also eaves · tile end

A tile with an opening that lets air in under the covering, supplementing the eaves ventilation where that is not enough. The French name means “cat flap”, which describes the shape rather than the use: it is meshed, and lets in neither bird nor dormouse.

See also air gap · ridge vent closure

The high line where two slopes meet, and the row of tiles that caps it. It is the most exposed part of a roof: in the Aude the tramontane gets underneath it and lifts whatever is not held down. A moving ridge is the most common failure after a blow.

See also ridge tile · ridge vent closure · hip The related service

The tile capping the ridge line, straddling both slopes. It used to be bedded in mortar; today it is more often laid dry on a ventilated closure, which keeps it demountable and lets air out. Both methods turn up in the same village — sometimes on the same roof.

See also ridge · ridge vent closure · mortar bedding

The flexible strip laid under the ridge tiles, sealing the top of the roof against birds and rain while letting the air gap exhaust. It is what makes a dry ridge possible. A crushed or clogged closure kills the high-level ventilation: the roof breathes in and never breathes out.

See also ridge tile · air gap The related service

The outward angle where two slopes meet on their way down, on a hipped roof. It is a sloping ridge: same tiles, same wind loads, plus a run of cut tiles on both sides. A badly closed hip lets water in right in the middle of the roof.

See also ridge · valley The related service

The mortar holding a ridge tile, a hip or a verge tile in place. It is the traditional method and still the majority on older roofs in the département. Mortar moves with frost and eventually cracks: crumbling bedding is repaired properly, not patched over.

See also ridge tile · verge

The side edge of the roof, stopping over the gable wall. After the ridge, it is the second most wind-exposed zone, because the tramontane gets in from the side. A verge is closed with mortar, with a purpose-made verge tile, or with a génoise, depending on the house.

See also génoise · mortar bedding The related service

The cornice of canal tiles corbelled out at the top of a wall, in one, two or three courses. It is the signature of Languedoc building — you count it in courses, and the number once said something about the owner. It throws water clear of the façade as much as it decorates it.

See also verge · eaves

The vertical board fixed to the rafter ends, closing the overhang and often carrying the gutter brackets. It is in the front line: facing full south on an Aude elevation, an unprotected fascia greys, splits, and then lets its fixings go.

See also gutter · gutter bracket

The inward angle where two slopes meet in a trough. All the water from both slopes converges here: it is the most heavily loaded point on a roof, and the least forgiving. A valley is formed in metal or in tile — never in mastic.

See also soaker · hip The related service

A small metal piece slipped between two tiles to carry water from an awkward point back onto the covering. Soakers are used along a valley, against a wall, around a chimney. They lap one over the next like scales: it is the lap that seals, not solder.

See also valley · flashing

The part of the chimney standing above the roof. It pierces the covering, so it interrupts it: with valleys and wall abutments, it is one of the three places we look first for a leak. You judge a stack by its flashing, not by its brickwork.

See also flashing · apron flashing The related service

The weathertight junction between the covering and anything vertical: a stack, a wall, a dormer. It may be mortar or metal. It is the single most common cause of a long-standing leak, because it takes both the building’s movement and the roof’s concentrated run-off.

See also cover flashing · apron flashing · soaker The related service

A metal profile let into a chase cut in the wall, covering the top of the flashing so water cannot get behind it. This is the detail that separates a junction that lasts from one that will leak: without a chase in the masonry, water always finds the joint eventually.

See also flashing

The metal piece at the downslope foot of a stack, throwing water that has run down the wall back out onto the tiles. It is the low point of the junction, so it takes everything. An apron that is too short, not clearly lapping the covering, drives water under the next course.

See also flashing · chimney stack