A slate roof looks like a single sheet of stone, but it is hundreds of separate pieces, each hanging from a batten (a narrow timber lath running across the rafters). What holds each slate there is not its weight alone. It is a fixing, and the fixing is where most slate roofs fail first.
Roofers use two families of fixing. The traditional one is the nail, driven through a hole in the slate into the batten. The newer one is the hook, a bent metal clip that catches the bottom edge of the slate and holds it without a hole. Each has a place, and each has limits. This guide sets out what they are, how nailing patterns differ, what the 25 degree rule means for hooks, and what BS 5534 requires. If you want the story of a nail that has failed, our answer on nail fatigue covers it. For the broader service, see slate roofing in Stroud.
What a fixing has to do
A slate fixing has three jobs, and it does all of them out of sight, beneath the slate above. It stops the slate sliding down the pitch, particularly on a steep roof where gravity pulls it towards the gutter. It resists wind uplift, the suction that tries to peel slates off the roof, and it has to keep doing both without staining, cracking or corroding the slate over a very long time.
The standard that governs this is BS 5534, the British Standard that covers slating and tiling. Its 2014 revision, amended in 2018, sets out the fixing of slates according to pitch, exposure and slate size. We work to it and, because it is a code of practice and not a price list, it leaves a roofer to make judgement calls. Slate size, headlap and exposure all affect what is appropriate for a particular roof, and a competent slater will explain the reasoning behind each choice, which is why our guide to Welsh and Spanish slate is worth a look before you commit to a slate.
Why the metal matters as much as the method
Fixings sit in a damp, mildly acidic environment for generations. Iron and plain steel rust. Zinc coatings wear off. A nail that corrodes thins, loses grip and finally lets the slate go, well ahead of the slate wearing out. That is the heart of nail fatigue, and it is why material choice is the first decision on any slate job.
Copper nails and other metals
For slate, the best-regarded nail is copper. Copper does not rust, it stays strong in damp conditions and it is soft enough to grip the timber without splitting it. Aluminium and stainless steel are also used. Galvanised steel nails have been used in the past, but the coating can wear through in the long term, and that is a common reason older roofs lose slates.
| Fixing metal | Behaviour on a slate roof |
|---|---|
| Copper | Resists corrosion, widely used, a traditional match for natural slate |
| Stainless steel | Resists corrosion, strong, often used for hooks and in exposed spots |
| Aluminium | Does not rust, but can react with some timbers and treatments |
| Galvanised steel | Coating wears, which can lead to the fatigue we find on older roofs |
Two nails per slate
A slate is nailed with two nails, one either side. That keeps it square on the batten and shares the load. If one nail rusts, the second may still hold the slate for a while, which is why a roof can appear fine until several slates slip together.
The hole in the slate
The nail passes through a hole made by a holing machine or by hand. If the hole is too close to the edge or too large, the slate can crack at the hole. A hole in the wrong place changes the headlap, and a slate holed too high or too low will either leave a gap in the cover or sit proud of its row. On reused slates we check the old holes before reuse, because a slate that has already been nailed once often has a hole that no longer sits well on the new gauge.
Head nailing and centre nailing
Where on the slate the nails go matters. There are two long-established patterns.
Head nailing
In head nailing, the holes are near the top (the head) of the slate. The slate hangs from its nails like a coat from a hook, and the tail swings free. It is the common method on most roofs today, and it makes good use of each slate because less of the slate is buried under the one above. The trade-off is that a long tail has more leverage in the wind, so the fixing matters on exposed slopes.
Centre nailing
In centre nailing, the holes sit near the middle of the slate, roughly where it balances. With the nails nearer the centre, the tail is shorter and has less leverage to lift. The cost is that the slate needs a bigger headlap, because the nails are further down, so more of every slate is covered by the one above. Centre nailing is associated with larger slates and with sites where a roofer wants extra resistance to uplift.
Which one to choose
The choice depends on slate size, pitch, exposure and the specification for the job. A listed roof may need the method it was built with. Our guide to slate sizes and headlaps shows how length and lap fit together, because the nail position and the lap are linked. We set the pattern out in the survey notes so you can see the method before work begins, and we are happy to talk through why one pattern suits your slope better than the other.
Slate hooks: what they are and where they work
A slate hook, sometimes called a hook fixing, is a strip of stainless steel or similar metal bent into a hook. It is nailed or screwed to the batten and curves round the lower edge of the slate, supporting the tail from beneath. No hole is drilled in the slate.
Why people use hooks
- No hole in the slate. Without a hole there is no weakness at the nail, and nothing to crack.
- Quicker to fit. There is no holing, which saves time on a plain roof.
- Useful on slates that do not take holes well. Thin or brittle slates sometimes split at the nail hole.
Where hooks do not belong
Cupa Pizarras is blunt about it: keep hooks off every pitch lower than 25 degrees. A roof under that angle sheds water slowly and leans on its nails to stay put. A hook that can shift is a poor fit there.
Hooks also look different. The hook shows at the tail as a thin line, which on a conservation roof may not be acceptable. On a listed house, or in a conservation area where the planning team cares about roof detail, ask before choosing hooks. Our guide to slate roofs on listed and conservation buildings explains how consent works.
Hooks and repairs
Hooks are also used for repair, and many slaters keep a few in the van for exactly that purpose. A single slipped slate can be replaced by sliding a new slate into the gap and fixing it with a hook or a tingle. That is often the neatest repair on a roof where the nails have failed across the slope.
The 25 degree rule and the pitch you actually have
Pitch is the angle of the roof to the horizontal, measured in degrees. Main roofs may be steep, but extensions, lean-tos and outbuildings are often shallower. A slate that suits a 40 degree roof may not suit a 20 degree one.
Cupa Pizarras, citing BS 5534:2014+A2:2018, indicates that the minimum roof pitch for natural slate is 20 degrees in moderate exposure with a slate 500 mm long and a 115 mm overlap, and NHBC guidance gives 20 degrees subject to headlap. Below 25 degrees, hooks are out. That leaves a band between 20 and 25 degrees where a slate roof is possible but must be nailed. Our answer on the minimum pitch for a slate roof sets out the limits.
Measuring the pitch
We measure the pitch on survey, either with a digital level on a rafter or from drawings, and we record it alongside the slate size so that the lap and the fixing can be checked together. Do not guess it. A roof that looks steep from the garden may be shallower than it seems, and an extension roof is nearly always lower than the main house.
Changing a covering
If you plan to change from tiles to slate, the pitch may rule out some options. A roof that carried concrete tiles at a low pitch may not take slate at all. A weight change of 15 per cent or more also needs Building Regulations approval. We check both at survey and say if a different covering would work better.
What a fixing choice does to the price and the roof
The method of fixing is a small part of the price of a slate roof and a large part of how well it lasts. A good fixing costs little compared with the slate, the scaffold and the labour. A bad one can undo the lot.
National cost guides do not price fixings alone. In MyBuilder's 2026 slate figures, a re-slate runs £100 to £180 per m² and a slater's day rate is £200 to £300. Those figures include the nails and hooks, but the guide does not separate them. If you are comparing quotes, check that each specifies the metal, the number of fixings per slate and the method, because a quote that does not say may be assuming something cheaper.
What goes in our specification
- The fixing metal and length, matched to the batten depth.
- Head or centre nailing, with the reason.
- Hooks only where the pitch and the look allow.
- The headlap for the exposure, taken from BS 5534 guidance.
- Fixings for ridge, hip and verge, mechanically secured under BS 5534:2014, since bedding mortar alone is no longer relied on to hold them.
You get the specification in writing as part of the written quote. Our slate roof cost guide has the full set of national ranges, and the fixing choice is one of the items we discuss when we talk through the survey. Our workmanship guarantee lasts 10 years and is given on paper; we also take away the old slate and packaging.