BKE 3
BUILD ING KNOWLEDGE EX C HANG E
Complex roof designs: it’s all in the details
When it comes to complex roof designs, it is important to ensure that a reliable and indeed customizable roofing material is used in order to accommodate complex detailing without compromising secure fixing techniques. Slate is an incredibly versatile material that allows for a variety of designs and if fixed correctly, will last for a lifetime.
CURVED CONICAL SLATE EFFECTS
Curved slating may be defined as slating on a roof that has both a shape that is curved on a plan and a length of eaves and a ridge, since roofs that converge to a point at the ridge are classified separately as turrets or spires.
Individual slates should be taper cut along both sides in order to achieve curved slating - this can be done either on site, or ordered as such from a reputable slate supplier. To achieve the curved or conical effect, all slates in a given course should have the same dimensions but must be wider or narrower than the slates in contiguous courses, therefore the final size of any particular slate will depend on the shape of the roof and the position of the slate on that roof.
When it comes to fixing in this situation, nail holes should be positioned as close to the centre of the slate as possible, otherwise the weather protection offered by the slate can be compromised as a result of the slates being trimmed on either side to accommodate the curve. To that end, it is worth bearing in mind that slates should not be trimmed to a dimension less than twice the dimension of the end lap.
As a general rule, curved slating should therefore be laid at the steepest possible pitch in order to compensate for the reduction in side-lap cover.
RANDOM DIMINISHING SLATE EFFECTS
A traditional and increasingly popular slate specification is random slating. This finish gives the roof a cost-effective way of either reproducing traditional random slating during a restoration project or helps in creating a stunning aesthetic effect on a new roof.
Commonly, there are two random slating patterns: Random Width using roofing slates of the same length but in random widths, and Random Width in Diminishing Courses - using roofing slates of random width in courses of progressively shorter lengths towards the roof’s ridge.
SSQ NATURAL SLATE
When random sizes are required, natural slate is the ideal material to use thanks to its extraction process: it is within the interest of the quarry to use all pieces of the block, and some slate suppliers will be able to provide pallets of slate already prepared in random sizes.
In order to successfully create a random slate effect, a great deal of planning is required to ensure the roof is accurately marked up. In the first instance, the slates should be carefully sorted and graded by length and then by thickness. Once sorted, the number of slates of each length will determine how many courses using that length can be laid across the roof. When the number of courses is known, the gauge of the battens must be worked out to maintain the minimum headlap required.
If slates are being laid to create either a Random Width or Random Width in Diminishing Courses effect, an even and gradual reduction of the batten gauging from the eaves to the ridge must be introduced. In all random slating, care must be taken to adhere to the required minimum side lap between courses, determined by using a special formula.
Of course, to ensure that all elements of a complex roof are taken into account, it is wise to work under a guidance of a specialist slate supplier who would be able to provide a complete specification based on the requirements of the individual project.
(Our thanks to Lika Protsenko, SSQ Natural Slate, for this BKE article)
TEL: 0208 961 7725 13
WWW.SSQGROUP.COM
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