Slate fixings
Slate hooks or nails: which fixing is better?
Neither fixing wins everywhere. The pitch, the slate and the exposure decide, and one published limit rules hooks out on shallow roofs.
The short answer
The better fixing is the one the pitch and the site call for, and on any pitch below 25 degrees that excludes hooks, because Cupa advises against hooks below that angle. Above that angle both nails and hooks are used on slate, and the choice comes down to the slate, the battens and how exposed the roof is. BS 5534 provides the way to calculate the fixing specification for the site.
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What each fixing does
Every slate is held to a batten, the length of timber laid across the rafters at set spacings. A nail goes through the slate into the batten. A hook is a metal fixing that holds the slate by an edge instead, so no nail passes through it. Both do the same job: stop the slate lifting in the wind or sliding down the slope.
Cupa's guidance on the minimum headlap for fixing slates covers "nails or hooks", which shows the two are treated side by side, and that the lap is set by weighing the pitch of the roof, how hard the wind can lift a slate and how much rain is driven at it. A fixing is not chosen in isolation. It works together with the lap, the slate size and the batten behind it.
That is why a roofer who says "always one or the other" has not looked at your roof. The specification follows from measuring it, slope by slope, and from reading the maker's guidance for the slate that is actually going on. Photographs from the street cannot show the batten spacing, the lap or the fixing in use.
The 25 degree line
Cupa's advice is direct: hook fixings should not be used on any pitch below 25 degrees. The line sits beside the 20 degree minimum it quotes for a 500 mm natural slate lapped 115 mm on a moderately exposed site. Between them they split the pitch into three zones, and a roof can fall into any of them.
| Pitch | Nails | Hooks |
|---|---|---|
| Below 20 degrees | Check the data sheet | Not used |
| 20 to under 25 | Open | Not used |
| 25 degrees or more | Open | Open |
The first row is cautious on purpose: the 20 degree figure belongs to one slate size and overlap, so a shallower roof is checked against the product data. Open here means the fixing is not ruled out by pitch alone, not that it is approved for your roof. A 25 degree slope that is also exposed can still call for a closer spacing or a wider slate, so the table is a first filter and never the whole specification. Our answer on minimum pitch for slate goes through those figures.
Exposure and the fixing specification
On exposure, Cupa states: "Buildings positioned on slopes, hills or coastal areas as well as tall buildings will be graded with higher exposure." Marley describes BS 5534 as covering wind uplift formulas and a means of calculating fixing specifications, and says: "Installing to BS 5534 isn't required by law". It is a code of practice rather than a statute, yet it is the method the trade uses to calculate what a given roof needs.
On an exposed roof, that calculation can change the answer: a wider slate, a longer lap, a different fixing or a closer spacing. Two houses on the same street may not need the same specification if one is taller or sits higher on a slope.
At survey we note the slate size, the lap, the pitch and the exposure, then work out the fixing from those. A written specification goes with the price, so you can see what will hold each slate and why that fixing was picked. If you are comparing two quotes, it is the specification, not the headline fixing, that tells you whether they describe the same job. Ask for the slate size, the lap and the fixing to be written down, and compare those three lines before anything else.
Fixing choice and slipping slates
Swapping nails for hooks does not cure slipping on its own. Slates slip when their fixings have given way or the battens behind them are tired, so the first job is finding out which. MyJobQuote's cost guide notes that the nails often give out before the slate does, which is why a long-lived slate can still slip.
- One or two slipped slates with sound neighbours are refixed, often with a tingle or a clip.
- Slipping across a slope points to the fixings as a set, and to a re-slate.
- A re-slate renews the fixings throughout, chosen for the pitch and site.
A hook fixing is no more a cure than a nail is. Whichever is used, the batten has to be sound enough to hold it, and the slate has to be whole. Where either is in doubt, the specification waits until the timbers have been looked at.
Our answers on nail fatigue and on refixing a slipped slate show the two ends of that range. The slate roofing page sets out the job from first visit to written price.
More questions
Does BS 5534 say which fixing I must use?
Not as a choice between two. Marley describes BS 5534 as covering methods of fixing, wind uplift formulas and a means of calculating fixing specifications, and notes that "Installing to BS 5534 isn't required by law". The calculation for your roof decides the fixing, and we write it into the quote.
Can hooks go on a roof that was nailed before?
Only if the pitch allows it. Cupa says hooks should not be used below 25 degrees, so a shallow roof stays with nails. Above that, the slate, the battens and the exposure are checked first, and the specification for the site decides whether a change makes sense.
Tell us what's wrong with the roof.
You'll get one written total price.