Getting Technical

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The benefits of using clay in roofing products

Clay is one of the most beautiful and versatile materials available. It offers many advantages over other roofing materials, and is very strong, in terms of material thickness. Clay’s versatility makes it an ideal choice for roofing. Many aesthetic features can be added to clay tiles, such as finished lower edges. The tails of clay tiles can be chamfered, rounded, square-edged and riven – the possibilities really are endless. What’s more, clay’s natural properties include being long-lasting, highly durable, more sustainable, and low maintenance, making it an adaptable and cost-effective option for customers.

Find out more about Wienerberger’s clay roof tiles at:


BS 5534 update – Roofing Underlays

In February 2018, the second amendment of the British Standards for Slating and Tiling, BS 5534:2014 + A2:2018 was introduced. For the first time, this includes a clear definition of air permeable underlays. The Standard now defines a low water vapour resistance (type LR) and air permeable underlay as having: “…a water vapour resistance not more than 0.25 MNs/g combined with an air permeability of not less than 20 m³/m².h at 50Pa.”

The ‘nominal’ 10mm underlay sag has also been redefined as a 15mm maximum drape, to avoid excessive ballooning damaging the tile fixings through wind uplift forces. It’s still important to ensure the drape is adequate to allow free drainage of water down to the eaves, to avoid potential damming behind the tile battens.

This Standard also references BS 8216, covering dry fixed ridge, hip and verge systems. Roofshield avoids the need to use these systems as it covers and protects the entire ridge, removing any risk of water penetration and delays to internal works.

Roofshield is recognised as one of the industry’s highest performing air permeable underlays and its endorsement by the NHBC, leading developers and major roofing contractors is evidence of its superior performance.


Performance assurance with W T Knowles & Sons

SIG Roofing has developed a Compliance Tracking System to give all their customers complete peace of mind when buying products. Being ‘SIG Assured’ ensures all products meet essential regulatory compliance.

Independent, family-run chimney pot manufacturer W T Knowles, not only meet but exceed these requirements.

As well as supplying Product Safety & Handling Sheets (fitting instructions), each individual Chimney Pot supplied to SIG Roofing has its own Declaration of Performance and detailed drawing.
The Declaration of Performance shows the product name, dimensions, intended use, compliance to harmonised Standard BS EN 13502, type classification, performance characteristics and essential markings, including CE Marking.

What’s more, W T Knowles have recently completed a full review of their Chimney Pot range with the help of British Standards Institute (BSI).

Standard BS EN 13502:2002 covers Chimneys and specifically the requirements and test methods for clay and ceramic flue terminals (Chimney Pots). The Standard defines and classifies terminals by type number.

W T Knowles now has 19 ranges certified as Type 0, 12 ranges as Type 1 and 13 ranges as Type 2.
You can download a Chimney Pot Classification guide from They recommend Type 0 and Type 1 pots for solid fuel, Type 1 (DFE) pots for multi-fuel and Type 2 pots exclusively on gas applications.