Comprehensive UK Roofing Glossary

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Abutment

The junction where a sloping roof meets a vertical surface like a wall or chimney. Proper damp proofing including flashing is needed at abutments to prevent leaks. For example, where an extension’s roof connects to the house wall, lead flashing and a cavity tray are used to waterproof the abutment.

Aggregate (Roof Ballast)

Crushed stone or gravel used on flat roofs to hold down membranes and protect them from UV rays. In the UK, bitumen flat roofs often have a layer of stone chippings added as aggregate. This ballast also helps shield the roof from temperature swings and mechanical damage.

Apron Flashing

A specific type of flashing at the base of an abutment. It’s a strip of lead (or other metal) that covers the joint where the top of a lean-to or porch roof meets the wall. The upper edge of the apron flashing is usually tucked into a mortar joint or groove in the wall, while the lower edge overlaps the roofing material. This creates a waterproof “apron” over the top of the sloped roof, directing water away from the wall.

Asphalt (Roofing)

In UK roofing, “asphalt” usually refers to mastic asphalt, a traditional hot-applied bitumen material used on flat roofs. Mastic asphalt forms a seamless, waterproof surface when spread in molten form and cooled. It’s extremely durable and often found on balconies, walkways, or flat roofs (sometimes lasting 50+ years with proper maintenance). Asphalt shingles – the bitumen-based felt shingles common in North America – are also used in the UK but mainly on sheds or low-cost roofs.

Barge Board

A board (wooden or uPVC) fixed along the gable end of a roof, following the slope of the roofline. Barge boards cap and protect the exposed ends of roof timbers at the gable. They provide a neat finish and guard the verge (roof edge) from wind and rain. Decorative barge boards are common on older buildings, sometimes carved or shaped, whereas modern homes often have plain uPVC barge boards for low maintenance.

Batten (Roof Batten)

A thin, horizontal strip of timber (typically 25×50 mm, pressure-treated) that is nailed across rafters to support roof tiles or slates. Roof tiles are attached to the battens (either hung or nailed), so the spacing (gauge) of battens must match the tile overlap. Modern battens must meet BS 5534 standards – they are graded for strength and marked with their dimensions and treatment. Using proper roofing battens ensures the roof covering is securely fixed and can withstand wind uplift.

Bedding (Mortar Bedding)

In roofing, “bedding” refers to the mortar that secures certain components in place. For example, ridge tiles or hip tiles on older roofs are often bedded in mortar – a sand-and-cement mix that hardens and holds the tiles to the ridge line. Verge tiles at a gable might also be bedded onto a mortar strip or an undercloak. This traditional “wet” bedding fixes tiles and also seals the gaps against wind-driven rain.

Bitumen

A thick, black, tar-like petroleum product used in many roofing materials. Traditional roofing felt is coated in bitumen, and flat roof membranes often consist of layers of bitumen felt bonded with hot bitumen. Bitumen is waterproof and flexible when warm. It’s used in bituminous paint, DPCs, and as the key ingredient in asphalt roofing. However, pure bitumen can become brittle in cold weather and soften in heat, so modifiers are often added to improve its performance.

Blue Roof

A specialized flat roof designed to attenuate rainwater rather than shed it quickly. A blue roof temporarily stores rainwater in rooftop layers or controlled flow outlets, releasing it slowly to the drainage system. This helps prevent flooding by smoothing out peak runoff during heavy rain. Blue roof systems often involve a void or crate system and an outlet control that only lets water drain when it reaches a certain level.

Box Gutter

A square or rectangular gutter usually set between two roof sections or behind a parapet, rather than at the eaves. It’s “boxed in” by constructions on both sides. Box gutters (also called internal gutters or trough gutters) are common where a roof abuts a wall or between roof pitches on a valley between parallel roofs. They are lined with metal or membrane to be watertight, and have outlets (or downpipes) to drain water.

Breathable Membrane

A modern roofing underlay that is waterproof but also vapour-permeable. It’s laid under tiles or slates in pitched roofs. Unlike old bitumen felt, breathable membranes allow water vapour from inside the roof to escape through them (reducing condensation), while still shedding external water. They are typically synthetic sheets (polypropylene or polyester) with micro-perforations. Breathable membranes have largely replaced traditional felt in new construction.

BS 5534

This is the British Standard “Code of Practice for Slating and Tiling” in the UK. BS 5534 sets out best practices and technical requirements for pitched roofs – such as the minimum overlap of slates/tiles, how roof battens should be graded and fixed, nail specifications, and resistance to wind uplift. Roofing contractors follow BS 5534 guidelines to ensure durability and compliance with Building Regulations.

Building Regulations (Roofing)

UK Building Regulations are statutory requirements for construction. Several parts of the regs apply to roofs:

• Part A (Structure): Roofs must be able to support loads (tiles, snow, etc.) safely. This affects rafter sizing, truss design, and bracing.
• Part C (Moisture): Roofs should prevent water ingress and adequately manage rainwater. Proper flashing, damp-proof courses, and ventilation to avoid condensation are required.
• Part L (Thermal): Energy efficiency – roofs need sufficient insulation.
• Part F (Ventilation): Ensures adequate ventilation of habitable rooms and roof spaces.
• Part B (Fire): Roof coverings near boundaries must meet fire-spread ratings.

Our building services team ensures all work meets or exceeds current regulations.

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Cavity Tray

A concealed DPC (damp-proof course) that sits within a cavity wall above a roof abutment or opening. At the junction of a roof and a wall, a cavity tray is installed about 150 mm above the roof line. This tray catches any water that might penetrate the outer wall and safely channels it out, usually via weepholes in the wall. In a typical scenario – where a pitched roof meets a masonry wall – you’d have stepped lead flashings on the outside and a stepped cavity tray within the wall.

Cold Roof (Cold Deck Roof)

A roof design where the insulation is at the ceiling level (above the top floor’s ceiling) rather than directly under the roof covering. In a cold pitched roof (typical attic), insulation is laid on the loft floor between joists, leaving the loft space above cold. This means the roof void must be ventilated (cold outside air passes through) to carry away moisture and prevent condensation on the cold roof underside.

Counterbatten

A vertical batten fixed on the roof, running down the slope (ridge to eaves), underneath the horizontal battens. Counterbattens are used when a roof is fully boarded or when a ventilation gap/drainage path is needed under the battens. For example, in a roof with sarking boards or a low pitch, you might lay a breathable membrane over the boards, nail counterbattens vertically, then nail the horizontal tile battens on top of those.

Course

A single row of tiles, slates, or other roofing units, running horizontally across the roof. Starting at the eaves, roofers install material in overlapping courses up to the ridge. In slating/tiling, the gauge (spacing of battens) and lap determine how much of each course is exposed. An “eaves course” is the first row at the gutter, sometimes using shorter tiles or doubled slates for extra thickness.

Dormer (Dormer Window)

A roofed structure projecting out from the main roof plane, containing a vertical window. A dormer has its own little roof (flat, arched, gabled, etc.) and walls (called cheeks) built up from the main roof. Dormers increase usable space and headroom in lofts by extending outwards, and they bring in light via the dormer window. Common styles include gabled dormers, hipped dormers, shed dormers, and eyebrow dormers.

Downpipe (Downspout)

A vertical pipe that carries rainwater from the gutter down to the ground drainage. Typically made of uPVC in modern homes (or cast iron on older ones), downpipes connect to the outlet of gutters at eaves or valleys. They channel water into drains or soakaways at ground level. UK practice often has one downpipe for every few metres of gutter, frequently at building corners.

Dry Ridge

A system for fixing ridge tiles without mortar. Traditional ridges were bedded and pointed with cement mortar (“wet” fix). A dry ridge uses screws, clamps, and sometimes a continuous plastic ridge roll/vent under the ridge tiles. Dry ridge systems have become very popular in the UK because they are storm-proof and maintenance-free (no mortar to crack). They also often incorporate ventilation along the ridge.

Dry Verge

A method of finishing the verge (gable edge of the roof) without mortar. Instead of a cement bedding to hold verge tiles, a dry verge system uses interlocking plastic (or concrete) pieces that cap the ends of the tiles. These pieces often clip over the tile edges and are screwed to the barge board or end of battens. The result is a clean, weatherproof verge that won’t crack or fall out like mortar can.

Drip Edge

A thin metal flashing installed along the eaves (roof edge) to guide water into the gutters. It usually has an L-shaped profile – one leg on the roof under the felt/tiles, and the other leg bent down over the fascia. The drip refers to a small projecting lip that causes water to drip off away from the fascia, rather than running down the soffit or wall.

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Eaves

The lower edge of a roof where it overhangs the wall. This is where rainwater drops off into the gutter. The eaves typically consist of the fascia board (vertical trim at the roof’s edge), soffit board (covering the underside of the overhang), and the exposed ends of rafters or the roof covering’s underside. Eaves serve to throw water clear of the walls and can provide shade for the upper parts of the house.

EPDM

A single-ply rubber roofing membrane, short for Ethylene Propylene Diene Monomer. EPDM is a synthetic rubber commonly used to cover flat roofs (like extensions, garages, and commercial buildings). It comes in large sheets (often cut to the full size of a small roof with no seams) and is glued down to the roof deck. EPDM rubber is very durable, UV-stable, and can last 25+ years.

Fascia

The long, straight board that runs along the lower edge of the roof at the eaves, fixed to the rafter ends. The fascia faces outward (vertical) and the gutters are usually attached to it. Traditionally made of wood (which needs painting and can rot), many homes now have uPVC fascias for zero maintenance. The fascia covers and protects the ends of the roof structure and gives a neat finish to the roofline.

Felt (Roofing Felt)

A traditional roof underlayment, also called sarking felt or underfelt. It’s an asphalt/bitumen impregnated sheet, usually supplied in rolls (often black or grey). On pitched roofs, felt is laid over the rafters (under the battens and tiles) as a secondary weatherproof layer. It catches any wind-blown rain or snow that gets under the tiles, and also reduces drafts.

Flashing

Thin pieces of waterproof material (usually metal like lead, zinc or aluminum) that are installed at roof intersections, joints, and edges to prevent water penetration. Flashings are critical at abutments (roof-to-wall joints), around chimneys, vent pipes, roof windows, valleys, and along roof edges. In the UK, lead flashing is most common due to its durability and malleability.

Flaunching

The sloping mortar bed at the top of a chimney stack, holding the chimney pots in place and throwing off rainwater. Essentially, it’s the concrete or mortar that’s troweled around the base of the chimney pot (or around a blanked-off chimney top). Good flaunching is smooth and angled to shed water away from the pot and chimney liner. Over time, weather can crack or erode the flaunching – if it fails, the chimney pot may become loose or water can seep down into the chimney.

Flat Roof

Any roof with a very low slope, typically not more than 10° (1:6) to horizontal. In practice, “flat” roofs are usually built with a slight fall (e.g., 1:40 or ~2.5%) to allow rainwater to drain toward outlets. Flat roofs are common on extensions, garages, commercial buildings, and mid-century modern houses. They require a continuous waterproof membrane since water may pond or drain slowly.

Fibreglass (GRP) Roofing

A type of liquid-applied flat roofing also known as GRP roofing (Glass Reinforced Polyester). This system uses a polyester resin (liquid) reinforced with fibreglass mat to create a solid, jointless membrane across the roof. It’s applied in situ: sheets of fibreglass matting are laid onto the roof deck (usually OSB3 boards), then saturated with resin, which hardens to a tough, plastic-like shell. GRP roofs are popular for garages and extensions.

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Gable

The triangular upper part of a wall that closes the end of a ridged roof. In other words, if a house has a pitched roof with two sloping sides meeting at a ridge, the ends of the house (where the roof doesn’t extend over) will have a gable – a flat wall that goes up to the ridge height in a triangle shape. The roof edges along a gable are called verges.

Gable Roof

A roof consisting of two sloping planes meeting at a central ridge, with a gable at each end. This is the typical “A-frame” shape. It’s the most common roof style in the UK for houses: imagine a simple pitched roof where the high point (ridge) runs along the middle and the roof slopes down to the eaves on two sides. The other two sides of the house are the vertical gable walls.

Green Roof

A roof that is partially or completely covered with vegetation, planted over a waterproof membrane. Green roofs (also called vegetative roofs or eco-roofs) have a layered build-up: starting with the roof deck, a waterproofing layer, a root barrier, drainage layers, a special lightweight soil (substrate), and finally plants. They provide insulation, reduce rainwater runoff, and promote biodiversity in urban areas.

Gutter (Rain Gutter)

A channel at the eaves or in a valley of the roof for catching and directing rainwater. Most houses have eaves gutters running along the fascia boards at the bottom of the roof slope. These are usually half-round or square-profile uPVC troughs that collect water dropping off the roof and funnel it into downpipes. Gutters prevent water from simply cascading off the roof edges.

Hip

The external angle formed where two roof slopes meet – specifically when they meet to form an external ridge, like on a hipped roof. If a roof has a hip, it means instead of a gable end, the roof planes slope and meet along a diagonal line. For example, a standard hipped roof on a rectangular house has four hips (two at each end, sloping from the ridge down to the corners of the building).

Hip Roof (Hipped Roof)

A roof where all sides slope downwards to the walls, so there are no gable ends. A typical hipped roof on a rectangular plan will have four faces: two large ones (front and back) trapezoidal in shape, and two smaller ones (the ends) that are triangular. All meet at a ridge or at a point. Advantages: hip roofs are more stable in high winds (no flat gable catching wind) and provide eaves all around.

Hip Tile

A special tile or fitting that covers the hip of a roof (the external ridge at the junction of two slopes). Similar to ridge tiles but designed for the hip angle. Common types in the UK are bonnet hip tiles (curved tiles that wrap over the hip like a bonnet) and arris hip tiles (angular tiles that meet the roof planes neatly). These tiles are secured either by mortar or mechanically (clips and nails in dry hip systems).

Hip Iron

A short L-shaped metal bar fixed at the foot of a hip rafter, projecting upward to support the bottom hip tile. It’s basically a “stop” to keep the lowest hip tile (or the mortar under it) from sliding down off the roof. Often made of galvanized steel or wrought iron, it’s built into the wood structure or securely screwed on.

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Insulation (Roof)

Material used to slow heat transfer, placed in the roof or loft to keep the building warm in winter and cool in summer. In roofs, common insulation materials include mineral wool (fiberglass or rock wool rolls laid between joists or rafters), rigid PIR boards (polyisocyanurate foam like Celotex or Kingspan, often between and over rafters), and polystyrene boards (EPS or XPS, used in some flat roofs).

Interlocking Tile

A type of roofing tile shaped with channels or lips so that each tile interlocks with its neighbor, both side-to-side and sometimes top-to-bottom. This allows for a single lap installation – meaning only one layer covering at any point (as opposed to double-lap where two overlapping layers are needed). Most modern concrete tiles are interlocking. They often have a pronounced profile and a lower pitch capability than plain tiles.

Inverted Roof

A flat roof construction where the usual order of layers is flipped – the insulation is placed above the waterproofing membrane. In a typical warm roof, you’d have deck → vapor barrier → insulation → waterproof membrane on top. In an inverted roof, you have deck → waterproofing → insulation on top of the waterproofing → ballast (often gravel or paving) holding the insulation down.

Jack Rafter

A shortened rafter that doesn’t run the full span from ridge to eave, usually because it’s cut off by a framing feature like a hip or valley. There are two kinds: hip jack rafters connect from a hip rafter down to the eaves, while valley jack rafters run from a valley rafter up to the ridge. Jack rafters support the roof decking/tiles in those hip or valley areas.

Jerkinhead Roof

Also known as a half-hipped roof. This is a hybrid between a gable and a hip roof. Instead of a full triangular gable at the end of the ridge, the upper part of the gable is “clipped” off and sloped back – forming a short hip – while the lower part of the wall is still a gable. The result is a truncated gable with a small hip on top.

Joist (Ceiling Joist)

A horizontal timber (or steel) beam that supports the ceiling below and, in a traditional roof, ties the feet of the rafters to prevent the roof from spreading. In a house with a pitched roof, the ceiling joists are usually the same pieces as the floor joists of the loft (if the loft isn’t a living space). They run parallel to the rafters, across the width of the house, sitting on the wall plates.

Kick-Out Flashing

A small but crucial piece of flashing at the bottom of a roof-to-wall junction that “kicks out” rainwater away from the wall. Picture where a roof slope ends as it abuts a vertical wall, just above the eaves gutter – water running down the last bit of the roof and along the wall flashing could otherwise spill behind the gutter or down the wall. A kick-out flashing is an angled flange that directs water into the gutter.

King Post Truss

A simple type of timber roof truss with one central vertical post (the king post) extending from the apex of the roof down to a horizontal tie beam. In a king post truss, you have two principal rafters (forming the sides of the triangle), a tie beam (forming the base), and the king post in the middle connecting the apex to the base.

Kerb (Rooflight Kerb)

In roofing, a kerb is a raised frame on a flat roof designed to mount something like a rooflight (skylight) or ventilation unit. It’s basically a box upstand that elevates the rooflight above the roof surface. The kerb can be built out of wood, PVC or metal, and is typically at least 150mm high above the finished roof to satisfy regs (keeping the rooflight above water level during heavy rain or minor ponding).

Lath

Thin wooden strips historically used in place of modern battens for fixing roof tiles or slates. Before the standardization of battens, roofers would nail split timber laths across rafters. Slates were then hung on these laths using pegs or nails. In old roofs (Victorian or earlier), you might see very narrow laths (maybe 1 inch wide) with irregular spacing.

Lead (Leadwork)

Ubiquitous in UK roofing, “lead” refers to lead sheet used for waterproofing details – e.g., lead flashings, lead valleys, lead damp-proof courses, and entire lead roofs on bay windows or porches. Lead Flashings are malleable and long-lasting (properly installed lead can last 100+ years). They’re used around chimneys, roof junctions, etc., because lead can be shaped to complex profiles and stays put.

Lead Code (Code 3, Code 4, etc.)

A grading system for lead sheet thickness and weight. In UK roofing, common codes are 3, 4, 5, 6, 7, 8 (higher number = thicker/heavier sheet). For example, Code 4 is ~1.80 mm thick, 20.41 kg/m² – the most common, used for chimney flashings, general-purpose flashings, and vertical cladding. Many chimney step flashings and aprons are Code 4.

Lean-to Roof

A simple single-pitch roof that “leans” against a higher wall. It has one slope, with its high end abutting a wall and its low end at the eaves. Think of an attached shed or a small extension on the side of a house – often they have a lean-to roof. It’s basically half of a pitched roof (no ridge, just sloping one way).

Loft (Attic)

The space inside the roof above the top floor ceiling of a house. In UK usage, “loft” is more common than “attic.” It’s the void where you might store holiday decorations or where the cold water tank lives (in older systems). Lofts can be cold (insulation on the floor, so the loft is chilly) or warm (insulation at the roof, so the loft is part of the heated envelope).

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Mansard Roof

A dual-pitch roof with two distinct slopes on each side – the lower part is very steep (almost vertical), and the upper part is low-pitched. It’s like a roof with a knee: the steep lower sections maximize usable space within, creating an additional floor (often called a mansard loft), and the gentle top part is just for covering.

Membrane (Roofing Membrane)

A general term for flexible, sheet-like waterproofing material used on roofs. It can refer to underlays on pitched roofs or the primary waterproof layer on flat roofs. Examples include breathable membranes (pitched roof underlay), non-breathable felt (traditional bituminous underlay), single-ply membranes (synthetic sheets used on flat roofs like EPDM), and liquid membranes (coatings that cure to form a membrane).

Mortar

A mixture of cement (or lime), sand, and water used in roofing for bedding and pointing tiles, ridge caps, etc. In roofing contexts, bedding mortar is thick mortar that affixes ridge tiles, hip tiles, or verge tiles to the roof. The tile is pressed into the wet mortar which then cures, holding the tile in place (and sealing the joint). Pointing mortar is the outer fillet applied to seal and finish a joint.

Moss

A common growth on roof surfaces, especially in damp and shaded areas. Moss tends to colonize clay and concrete tiles and sometimes slates. While a small amount of moss is not immediately harmful, it can cause issues by retaining moisture, growing under tile laps and lifting tiles, and sliding into gutters when dried, contributing to clogs.

Nail Sickness

A term describing the deterioration of the nails holding roof slates or tiles, causing them to loosen or slip. It’s commonly associated with older slate roofs that used iron nails. Over decades, these nails rust and the cross-sectional area of the nail reduces to the point where it either breaks or no longer has a head. When enough nails fail, slates begin to slide out or rattle in the wind.

Nibs (Tile Nibs)

Little projections on the underside of certain roofing tiles (like double Roman or plain clay tiles) that allow them to hang on the battens without immediate nailing. Traditional plain clay tiles have two nibs at the top inner face – when you hang the tile on the roof, those nibs catch on the batten. This holds the tile in place by gravity.

Nogging

Although more of a general construction term, in roofing context a nogging (or noggin) is a short horizontal piece of timber fixed between joists or rafters to give stiffening or a fixing point. For example, if you have widely spaced rafters and need to mount a rooflight, you might put some noggings between rafters to form the support frame.

OSB (Oriented Strand Board)

A type of engineered wood board commonly used as roof decking (the flat surface to which roofing material is attached). OSB is made by compressing layers of wood strands (flakes) with adhesives in specific orientations, giving it strength similar to plywood but at lower cost. You’ll often see OSB3 used for roofing – this grade is structural and moisture-resistant (suitable for humid conditions).

Overlay (Roof Overlay)

Not a specific component, but a term describing adding new roofing on top of old without full removal. For example, a “felt overlay” might mean applying a new layer of felt over an existing flat roof membrane, or “overcladding” a metal roof with new sheets over old. In pitched roofs, an overlay could be putting a new shingle roof over an old one.