Roofing Formats

Random slates are produced with genuinely random lengths and widths between an agreed maximum and minimum length parameter and these slates produce traditional diminishing courses, with the longest slates laid at eaves and gradually smaller slates used up the slope to the smallest lengths at the ridge. This produces a pleasing visual perspective to the roof which makes intuitive aesthetic sense, with the biggest slates anchoring the bottom of the roof and the increasingly smaller slates helping the perspective of the roof as it slopes away from sight.

Sized slates are fixed in length but with genuinely random widths. This produces a more contemporary appearance with a constant (not diminishing) coursing yet retains a nod to the traditional random format and avoids the regular half bond of set sized (patterned) slates. Sized slates are quicker and more economic to lay than random slates as the Slater doesn’t need to size the slates into common lengths or calculate the setting out of the roof based on the random sizes.

Patterned Slates

Patterned slates are fixed in length and width and produce a regular half bond ‘pattern’ to the roof. This format of slate is less common in the north of the UK and more frequently used in the south.

Westmorland Green Slates

Westmorland green riven slates are only produced in traditional random sizes for laying in diminishing courses while Westmorland green calibrated slates can be produced in all three formats.

Traditional use of Burlington Slates in the Lake District

Historically Burlington blue/grey and Westmorland green slates were only produced in random sizes and the introduction of sized and patterned slates only came about in the late 19th and early 20th centuries with advances in sawing technologies. As such traditional areas such as the Lake District National Park are almost exclusively slated with diminishing course slates and the continued production of this format of local slates is vital to protect and maintain the traditional vernacular of the area and enshrine the built heritage of the National Park which does so much to maintain its unique sense of place.

Traditional use of Burlington Slates on Britain’s Built Heritage

Likewise, Westmorland Green and Burlington Blue/grey slates have been the slate of choice for centuries for architects working on many of the most important public buildings where making a statement of quality and permanence was important. Where you find these two slates on these traditional buildings at the heart of the UKs built heritage, the town halls, churches, schools, court houses, police stations etc., they are almost always random slates that have been laid in diminishing courses.