Alain Richard, Technical Manager at SSQ, discusses natural slate fixing methods. In the past, slates were fixed to the roof with wooden pegs. Nowadays, there are two methods for fixing natural roofing slates – the modern hook method, widely used in mainland Europe and the traditional nail method, which means that the slate has to be holed, either at the quarry or on site. This information is not intended to steer you to using either, but to explain the ‘pros and cons’ of both methods.

Effective design of a slate roof must take into consideration a number of inter-related factors including site exposure, the pitch of the roof and the type of slate selected. These factors may determine your decision to use the hook or nail fixing method.

There are many different types of roof, of varying pitch, shape and size and may include windows, or even turrets. These design features all need to take into consideration the size and shape of the slate. The hook method allows you to use slates that can be as narrow as 100mm wide. This width of slate can be utilised on special features such as swept valleys, cones, domes and eyebrows. If the nail fixing method is used the minimum width is 150mm, which does not provide the same design flexibility.

The hook method provides good resistance to wind lift as it locks the slates together more securely and if wind causes the tail of the slate to lift, the hook helps to snap it back into place.

In addition the hook method reduces wastage as holing of the slate is not needed. If the slates are delivered un-holed and are then holed on site, this process wastes between 3 and 5% if the slates are of average quality and wastage can increase to 10% if the slates are brittle. However when using the hook method it is important not to overlook the sorting of the slates which, when using the nail method is instinctively done while holing.

Aesthetically the nail fixing method is generally preferred as it does not leave any fixing detail on view. The slate laid on the row above overlaps and covers the nail heads on the slate below. The hooking method leaves the heel of the hook on view, which does not provide such a smooth appearance to the roof.

Hook fixing has been widely adopted in parts of the UK where severe exposure is an important factor when specifying slate ie Cornwall or Scotland. In Europe, 90% of double lap slating is fixed with hooks, mainly because they use smaller size slates.

At SIG Roofing Supplies we stock nails and hooks because we recognise that both methods have their merits and we want to give the customer the best and most informed choice.