Plain-English definitions of roofing terms — written by the team at Tonbridge Roofing Experts. Questions? Call 0173 224 1138.
These are the roofing terms we use most often when surveying Tonbridge properties. If a term on your quote isn't explained here, call us on 0173 224 1138 and we'll explain it plainly — no jargon, no pressure.
The progressive corrosion of the galvanised steel nails that fix concrete interlocking tiles to the roof battens. As the zinc coating fails after 40–60 years, the corroding steel expands slightly, cracking some tiles and losing grip on others. Tiles begin to slip down the slope. Widespread on Tonbridge's 1960s–80s estate housing across Cage Green, Trench Wood and Higham Wood.
A single-lap clay roofing tile approximately 265×165mm, the dominant historic roofing material of Kent. Each tile hangs from a single peg or nail through a hole near the top edge. The warm terracotta colour comes from iron-rich Weald clays fired at 1000°C. Design life is effectively unlimited where fixings and battens remain sound.
Lead sheet formed into waterproof junctions between the roof covering and vertical surfaces — chimney bases, parapet walls, dormer cheeks and valley junctions. Specified by code number (4 = 1.78mm, 5 = 2.24mm, 6 = 2.65mm). Code 5 is the minimum for chimney aprons and step flashings on exposed UK positions. Welted joints prevent lap failure.
The semi-circular or angular tile running along the apex of a pitched roof. Traditionally bedded in mortar (historically lime, later OPC cement which cracks under thermal cycling). Modern alternative is the dry-fix ridge system using mechanical clips and a ventilating undercloak — eliminates mortar maintenance and improves roof ventilation.
Glass Reinforced Plastic — a composite membrane formed by laminating fibreglass matting with polyester resin directly onto the plywood deck. The resin cures in situ, creating a seamless jointless waterproof shell. No lap joints means no lap bond failure, the most common fault on felt systems. Design life 20–25 years. Cannot be installed below 5°C.
A mechanical ridge fixing system using extruded plastic or aluminium clips to secure ridge tiles without mortar. The clips allow thermal movement and maintain mechanical security in high winds. Eliminates mortar maintenance — ridge mortar typically needs repointing every 15–20 years; dry-fix does not. Standard specification on all new concrete interlocking tile installations.
The waterproof layer fitted directly below the tiling battens and above the rafters. Original bituminised felt (pre-1990s) has a design life of 40–60 years and traps condensation. Modern breathable membranes (vapour-permeable underlays) allow moisture vapour to escape while remaining waterproof. Recommended on all re-roofing projects.
The lower edge of the roof where the slope meets the fascia board and guttering. The eaves detail — undercloak, fascia board height, gutter bracket position and fall — determines how well rainwater is directed into the gutter. Eaves ventilation (via perforated soffit or over-fascia vents) is required on cold roof constructions to prevent condensation.
Questions about your roof? Free on-roof survey — no call-out fee.
Call 0173 224 1138 today — or ring 0173 224 1138 · Mon–Fri 7:30am–6pm · Sat 8am–2pm · Emergency 24/7