Roofing Glossary

Nail Sickness

The corrosion of galvanised steel nail fixings that hold roof tiles to the battens, common on 1960s-70s concrete tile roofs. Once the nails corrode, tiles are held by gravity alone and slip in wind. It affects most unmodified properties on Ashford's Bockhanger, Stanhope and Park Farm estates and is a primary trigger for re-roofing.

Breathable Membrane

A roofing underlay that allows water vapour to escape the roof void while blocking liquid water from outside. It prevents the condensation that rots battens and rafters under traditional impermeable felt. Breathable membrane has been the standard specification for new pitched roofs in the UK since the early 2000s and is used on all our re-roofs.

Nail Sickness vs Underlay Failure

Two separate end-of-life conditions on older roofs. Nail sickness is fixing corrosion; underlay failure is the perishing of the felt secondary waterproofing beneath the tiles. On Ashford's pre-1990 housing both often occur together, and when they do, re-roofing addresses the whole system rather than repeated repairs to individual symptoms.

Lead Code

The classification of lead sheet by thickness and weight. Code 4 (1.8mm) is standard for domestic chimney flashings and valleys with a 25-35 year life. Code 5 (2.24mm) is specified for exposed or coastal positions such as Folkestone and Hythe seafront properties, where salt air shortens the life of thinner lead.

Ridge Repointing

Replacing the mortar that beds the ridge tiles onto the apex of a roof. The mortar is exposed to freeze-thaw cycling on every winter and typically cracks within 15-25 years. Open ridge mortar allows wind-driven rain into the roof void. Repointing before failure is one of the most cost-effective roofing maintenance interventions.

GRP Fibreglass

Glass-reinforced polyester, a seamless flat roof system laminated over a plywood deck. It has no joints for water to penetrate, can be walked on, and lasts 25-40 years. GRP is our standard recommendation for domestic extensions and garages up to 40m2, though it requires temperatures above 5C to cure correctly.

EPDM Rubber

Ethylene propylene diene monomer, a single-piece rubber membrane for flat roofs. It is highly flexible, installs in colder conditions than GRP, and lasts 40+ years. EPDM is specified for larger flat roofs, complex geometries, and winter installations where GRP curing temperatures cannot be guaranteed.

NFRC

The National Federation of Roofing Contractors, the UK's principal roofing trade body. NFRC registration requires demonstrated competence, adequate insurance, and adherence to a code of practice, and is the most reliable single indicator of a professional roofing contractor. Our registration can be verified at nfrc.co.uk.