Traditional Scottish slating is not recommended on roof pitches less than 25 degrees, but they can be laid up to 90 degrees. However, it should be remembered that at lower pitches side lap becomes increasingly critical and that sufficiently wide reclaimed slates may not be available. It may be preferable to consider a new SIGA 32s Random Width slate to replicate original Scottish slate where side lap is a concern.

Our recommended head lap tables according to exposure, roof pitch and slate size can be found in the SIGA Slate Guide. Detailed guidance on wind load calculations is given in BS 5534:2014+A2:2018 and BS EN 1991-1-4:2005+A1:2010.

Scottish Slating Practices

For a detailed description of the process of roof slating, reference should be made to BS 5534:2014+A2:2018, the code of Practice for Slating and Tiling for pitched roofs and vertical cladding and BS 8000-6:2013, Workmanship on Building Sites. In addition, the NFRC Technical Bulletin 43 provides additional guidance on Scottish slating practice.

A short guide to the basic steps in slating to Scottish roofing practices are below.

  • Slates should be sorted into at least three groups of equal thickness.
  • The size of slate, the head lap and hence the holing gauge should be selected to conform to BS 5534. These should be checked to ensure they provide adequate side lap.
  • Where required, slates should be holed with the thicker end as the tail, and in addition from the underside to the topside as laid, to provide a small counter sink in the face of the slate.
  • The roof should be covered with square edged sarking boards covered with the underlay (specified by the architect).
  • Mark out the roof to the correct gauge.
  • Check the actual width of slates and mark out perpends allowing a maximum of 5mm joint gaps between the slates to accommodate variations in the slate width.
  • Load out the slates onto the roof so that the thickest slates are in the lowest courses and the thinnest near the ridge.
  • The under eaves course should be laid to give the required overhang to the gutter or tilting fillet and with the dressed edges face down.
  • Slates should be laid with the dressed edge face up. Slates of equal thickness should be laid in any one course, with the thicker slates in the lower courses grading down to the thinner slates in the upper course.
  • Fix the slates to perpend lines. To maintain adequate laps and allow proper fixing, slates must not be cut too narrow. In general, no slates should be less than 150mm wide.
  • At all verges and abutments, alternate courses must be started either with half width slates or with slate-and-a-half widths to maintain bond. If the half-slate would be less than 150mm, slate-and-a-half widths must be used.
  • At valleys, hips and other places where slates must be cut on the rake, it is essential that slates are of an adequate width to accommodate secure fixings.
  • All slating should be mechanically fixed in accordance with BS 5534.

It should be noted that traditional Scottish slating practice will fall outside the scope of BS 5534 and that regional variations may apply. Where regular-sized slates which are centre nailed or hooked are used, then all calculations and clauses in BS 5534 will apply.

For more information on Scottish regulations for slate visit