Ray Horwood CBE, chief executive of the National Federation of Roofing Contractors, discusses the impact of revisions to BS 5534 and the GRO code.
Given the pivotal role that architects and specifiers play in the design and specification of the building envelope, it’s imperative that they keep abreast of all developments within construction. As we all know, roofing impacts greatly upon the building envelope and in an ever-changing landscape of legislation for roofing, there have been two developments in particular that need careful consideration by architects – revisions to BS 5534 and the GRO code.
BS 5534 Representing the most comprehensive and far-reaching revision the roofing industry has seen in a long time, the recent changes to BS 5534 not only bring us closer to European practice, they help bring roofing into the 21st century in a simple and relevant way. The six-month crossover or co-existence period is fast coming to an end and the revised standard will become mandatory from the end of February 2015, so it’s wise to get smart.
Essentially, BS 5534 has been revised to make UK roofs more secure in the face of increasingly extreme weather events. It contains changes to the way we calculate roof tile fixing requirements, new minimum performance requirements for underlay have been introduced and there is no longer any reliance placed on the strength of mortar to resist wind uplift.
In brief, the theoretical wind loads used to calculate the mechanical fixing requirements of slates, roof tiles, ridge and hip tiles and roof systems have now increased and interlocking roof tiles now require fixings on every tile. One other change is that a manufacturer-approved adhesive will be considered a mechanical fixing. While it’s not the end of mortar – yet – the new standard also demands that all ridge and hip tiles are mechanically fixed. Mortar bedding failure has become a major issue, as it leaves the ridge or hip tiles vulnerable to dislodgement.
There are also now requirements to secure lightweight underlays and prevent ‘ballooning’ caused by wind deflection, which pushes on the underside of the roof covering, sometimes dislodging it. A new performance requirement and test method will be introduced for underlays for resistance to wind uplift.
New GRO code
A new and updated GRO code for green roofing has recently been unveiled. Instigated by the Green Roof Organisation (GRO) and supported by NFRC, the revised code aims to provide assistance for anyone who is involved in the design, specification, installation or maintenance of a green roof.
First published in 2011, the GRO code is intended to be a code of best practice and to serve as guide for behaviour and standards relating to all matters green roofing. This latest update contains more detailed information on meeting the requirements of the London Plan Policy, together with added guidance on substrate installation and waterproofing.
The revised GRO code reflects the growing movement by councils and local authorities throughout the UK, including the London boroughs, that now expect green roofs to be designed for new developments, where feasible. As such, it provides an enhanced technical report Living Roofs and Walls, supporting the London Plan Policy that was first unveiled in 2008. This document provides guidance in helping London combat the effects of climate change and recognises that green roofs have the potential to improve London’s resilience to climate change by reducing storm water run-off velocity and volumes, and by increasing the cooling effect during London’s hotter summers. They also bring many other wider environmental benefits.
Regarding green roof substrate installation, the revised Code also provides guidance on the size of substrate sacks required for certain projects and states that they should be disposed of once the substrate has been discharged at roof level. The method choice of lifting the substrate up to the roof level, and its subsequent dispersion of it across the roof, has significant access, budgetary and scheduling implications and is subject to the size of project. Substrate should be applied to the required depth (including the appropriate settlement volume) using grading bars. Depth checking should be undertaken throughout the installation.
When it comes to waterproofing, the revised code now states that in all applications the primary waterproofing layer is critical to successful performance of the roof as a whole, therefore its function and performance characteristics, and its suitability for use within a green roof system must be assured.
It is important that architects are brought up to speed with these two latest developments in order to bring improved best practice across all roofing disciplines and to deliver high quality, consistent and cost-effective results on all projects across the building envelope.
If you haven’t already done so, obtain a copy of the new standard – NFRC members can get discounted copies – and the new GRO code can be downloaded from www.nfrc.co.uk. So start protecting yourself, your practice and your roof today.