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Roofing Glossary

Plain-English definitions of the roofing terms you'll come across when getting work done on your Guildford property.

Nail Sickness

The corrosion of the iron or steel nails fixing roof tiles or slates, causing tiles to slip over time. Common on Guildford's post-war concrete tile estates where zinc-plated nails installed in the 1960s-70s are now failing systematically.

Repointing

Renewing the external mortar joints in brickwork or ridge tiles. On Guildford's pre-1920 properties, lime mortar is the correct specification; Portland cement is too rigid and damages period masonry.

Lead Flashing

Weatherproof lead sheet used to seal joints where a roof meets a wall, chimney or abutment. Code 4, 5 and 6 lead is specified depending on exposure. A common failure point on Victorian and Edwardian Guildford chimney stacks.

EPDM

Ethylene propylene diene monomer - a synthetic rubber membrane used for flat roofing. Cold-applied and tolerant of damp installation conditions, making it well-suited to Guildford's Wey Valley suburbs. Lasts 35-45 years.

GRP

Glass reinforced plastic (fibreglass) - a seamless resin-and-glass flat roofing system. Requires dry substrate and temperatures above 5C to cure correctly. Rigid, walkable and durable, lasting 30-40 years in Guildford.

Breathable Membrane

A vapour-permeable underlay fitted beneath roof tiles that allows moisture vapour to escape while keeping water out. Standard on all modern re-roofs, replacing the older bitumen felt used before the mid-1990s.

Verge

The edge of a roof at the gable end, where tiles meet the wall. Traditionally mortar-bedded but increasingly finished with dry verge systems that require no maintenance.

Flaunching

The mortar fillet at the top of a chimney stack that secures the pots and sheds water. Cracks and erodes over decades, allowing water ingress into the stack - a common repair on older Guildford chimneys.

Valley

The internal angle where two roof slopes meet, channelling rainwater. Often lined with lead. The highest-risk drainage point on any roof and a frequent source of leaks when blocked or when the lining fails.

Soffit and Fascia

The fascia is the board along the roof edge carrying the guttering; the soffit is the underside board closing the eaves. Together they protect rafter ends and support gutters. Common replacement work on Guildford properties.

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