Roofing terms explained: a plain-English glossary

Start with the structure and work outward.

• Rafters. The inclined timbers carrying everything above them, from the top of the wall up to the apex.
• Underlay. A sheet draped across the rafters under the covering, there to catch wind-driven water that slips past. Older roofs may have none at all.
• Battens. Slim timber laths nailed across the rafters, which is what tiles or slates actually hang from.
• Gauge. The spacing from one batten to the next, which fixes how much of each tile is left showing.
• Headlap. The amount by which a course of tiles or slates reaches over the course two rows down. Shallower pitches need more of it. Cupa Pizarras gives natural slate 500 mm long a headlap of 115 mm at 20 degrees for moderate exposure.
• Course. One horizontal row of tiles or slates.
• Covering. The outer layer: slate, clay tile, concrete tile or stone slate.

Most leaks start at a junction, so these are the words that appear most often on a repair quote.

• Eaves. The lowest edge of the slope, above the gutter.
• Ridge. The horizontal line along the top where opposing slopes join, capped by ridge tiles.
• Hip. The sloping line, standing proud, where two planes of roof join and run diagonally down to the eaves; hipped roofs have them in place of gable ends.
• Valley. The internal channel made by two slopes falling towards each other, lined with lead or cut slates and handling plenty of water.
• Swept valley. A valley where the stones or slates curve round the corner without a visible lead channel.
• Verge. The edge of the roof that follows a gable wall up the slope.
• Bargeboard. The board that finishes a gable edge.

BS 5534:2014 expects ridge, hip and verge fittings to be fixed mechanically, as mortar on its own is not trusted to hold them.

Where a roof meets something that sticks up, such as a chimney or a wall, the joint needs a seal.

• Flashing. Sheet metal, usually lead, bridging the gap between the roof and an upstanding wall or chimney.
• Stepped flashing. A flashing cut in steps to follow a sloping wall or brick courses.
• Soakers. Small lead pieces, one per course, tucked under the tiles or slates and turned up the wall. They are the traditional way to seal the side of a roof against a wall.
• Flaunching. The sloped mortar bed fixing a chimney pot in place and throwing off rain. It cracks as it ages.
• Lead code. A number for the thickness of lead sheet. Code 4 is 1.80 mm and is a common general choice; Code 5 is 2.24 mm and is used for heavier work, according to Leadworx.
• Pointing. The mortar between bricks or stones, which can be renewed without rebuilding.

Stone roofs have a vocabulary of their own, and some of it goes back centuries. Cotswold District Council's technical guidance explains much of it.

• Stone slate or stone tile. Roughly the same thing. The council says tile tends to be used in the south of the district and slate in the north.
• Diminishing courses. The slates shrink as they climb. Stone splits into many more small pieces than large, so the largest sit low down and the smallest are saved for the top.
• Cussoms. The largest slates, normally about 600 mm long but up to 750 mm, laid at the eaves in a double course. The next course is the followers.
• Short cocks. The smallest slates, a mere 150 mm long, for the top of the slope.
• Pegs. Wooden pegs, usually cleft oak, that hang each slate over a batten.

Water leaves the roof at the eaves, and several named parts deal with it.

• Fascia. The board running across the rafter ends below the roof edge, which normally carries the gutter.
• Soffit. The underside board that fills the space between wall and fascia, often fitted with vents.
• Gutter. The trough that gathers runoff at the eaves, laid to a slight fall towards its outlet; makers' guidance runs from about 1:600 to 1:350.
• Downpipe. The upright pipe taking water down to the drain.
• Rainwater goods. The trade name for gutters, downpipes and their fittings together.

MyBuilder's 2026 gutter guide puts guttering at about £30 to £70 per metre and fascia at £80 to £150 per metre.

A few more terms turn up on flat roof quotes and survey reports.

• EPDM. A rubber membrane, often laid as a single sheet across a flat roof.
• GRP. Glass reinforced plastic, or fibreglass laid in resin.
• Fall. The slope that lets a flat roof drain. BS 6229 recommends designing for 1:40 so the finished roof drains at 1:80.
• Dry-fix. A ridge, hip or verge system held by clips and fixings, covered by BS 8612, in place of mortar.
• Part L. The part of the Building Regulations covering energy efficiency, which can apply to roof renewal.
• Faculty. A permission issued through the diocese for building work to a church still in use.

On the planning side, our pages on Stroud's houses and their roofs and church roof permission use these words in context. If something goes wrong and you need to complain, the roofer complaint steps use plain language too.

If a word on your quote is not here, ask us. We explain every term on first use, and you can start from the Supreme Roofing home page.