Slate Hook Fixing

Slate hook fixing is a way of fastening natural or fibre-cement slates to roof battens using small metal hooks instead of nails. Each hook is fixed to the batten (or driven into it) in the gap between two slates of the course below, and its lower end curls up to hold the bottom edge, or tail, of the slate above. The traditional alternative is nail fixing, where each slate is holed and nailed near its head or centre.

Origins

Early slates were hung on wooden pegs. Two traditions developed from this: in Britain, nails replaced the pegs, while on the European continent S-shaped metal hooks were adopted. Hook fixing is widespread on the continent, and in the UK it is common in exposed areas such as Scotland, Cumbria, Wales, Devon and Cornwall.

Advantages

• Wind resistance: the hook holds the tail of the slate, which is where wind lift starts, and locks neighbouring slates together.
• Lower pitches: suppliers state that hook fixing can be used below 20° pitch, where nailing is not recommended.
• Narrow slates: nailed slates need a margin of about 25 mm (1 in) between hole and edge, which limits them to a minimum width of about 150 mm (6 in); hooked slates can be as narrow as about 100 mm (4 in).
• No holing: slates do not need to be holed on site, saving labour and waste.
• Repairs: a single broken slate can be slid out and replaced, and a slate that cracks across its width stays in place.
• No nail sickness: corroded nails are a common cause of slipped slates on old nailed roofs.

Disadvantages

The hook ends are visible on the roof surface, giving a less smooth appearance than a nailed roof, where every nail is covered by the slates above.

Hook materials

Hooks are usually stainless steel, often supplied with a black coating to reduce their visibility. UK industry commentators have recommended grade 316 stainless rather than 304 near the coast, after reports of rusting in salty air.