Overcoming the Challenges of Narrow Natural Slates: Kytun’s Performance Plus Aluminium Continuous Slate Dry Verge Solution

For many years, the use of natural slates, especially those narrower than 300mm wide, has been slightly problematic for roof slaters when it comes to verges and side edge abutments, as the half width slate is narrower than 150mm as recommended by BS5534: 2014+A2:2018. The problem was solved with the use of a slate-and-a-half width slate at the verge edge or abutment.

In more recent times though, the solution of the “slate-and-a-half” width slate has become increasingly hard to obtain, and unfortunately, more expensive to buy.

Slating experts have provided alternative bonding patterns to help slaters around this issue, but these can be wasteful and time consuming.

Why does the roof slater need a “slate & a half” width slate?

BS5534: 2014+A2:2018, section 6.7.2 states the following:

NOTE Verges may be bedded in mortar or laid dry.

For natural slates:

1. a) verges should be detailed with a slate and either a slate-and-a-half or a half-slate (not less than

150 mm in width to ensure adequate strength) in alternate courses;

This guidance is to ensure that the half width slate, minimum 150mm wide would be strong enough to resist cracking as a result of the 2 nail holes required for fixing at the verge.

However, the British Standard also gives the following guidance with regards to mechanical fixings for perimeter roof cladding elements:

5.3.6      Minimum recommendations for mechanical fixings

5.3.6.1  General

When determining the fixings for roofing elements, the following recommendations should be met…

1. b) The perimeter roof cladding elements (see note 1) should be mechanically fixed using a minimum of 2 fixings (subject to meeting the wind loading recommendations), one of which can be a tile clip, adhesive or dry verge capping system where appropriate…

NOTE 1 “Perimeter” means the single element (e.g. tile, slate, shingle) at any discontinuity in the plane of the roof, including roof edges.

With the “dry verge capping system” solution in mind, Kytun commissioned independent testing with the BRE (Building Research Establishment) to demonstrate the suitability of their Performance Plus Aluminium Continuous Slate Dry Verge trims when used with half width, natural slates as narrow as 125mm.

The purpose of this testing was to establish the ultimate uplift resistance of the Kytun Performance Plus Aluminium Continuous Slate Dry Verge acting as the outermost mechanical fixing when subjected to simulated wind uplift forces.

Due to the variety of natural slates available, it was decided to use aluminium “slates” to determine the ultimate uplift resistance of the dry verge when used with the 125mm wide natural slate.

The results for this testing are incredible as can be seen in the BRE Report extract here:

The uplift resistance of our Performance Plus Aluminium Continuous Dry Verge profiles, C01 (T1) or C02 (T2), will be at least 10x that of the wind load forces likely to ever be encountered anywhere in the UK or Ireland.

This means that you can specify and fit the Kytun Performance Plus Aluminium Continuous Slate dry verge with half width slates at 500 x 125mm with the complete confidence that these verge edge slates will withstand any level of wind uplift forces likely to be experienced in and around the UK and Ireland.

In addition, the concern / risk that the narrow format, half width verge edge slate at 125mm wide, wouldn’t have enough residual strength when holed twice to resist cracking between the fixing holes is eliminated as the half slate only needs one nail hole, the outer edge is secured by the Performance Plus Continuous Dry Verge.

A full copy of the BRE test report is available on request.