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Brunton’s Blog – New SPRA Wind Loading Protocol
Wind loading assessment in the roofing industry is one of the most important tasks necessary to ensure the safety of individuals, property and robustness of any project design. Getting wind load assessment wrong can also have catastrophic consequences for all involved in the design and building phase as well as life threatening to anyone in the vicinity of a failing roof in a windstorm. Costs involved in repair are understandably high with major inconvenience and disruption to the building occupants or processes. Some argue that climate change has increased the frequency, and often the intensity of, storm conditions.
This underlines the necessity to focus on wind load assessment protocol and the importance of reviewing this documentation on occasion to provide up to date guidance on the subject. SPRA have always taken the wind load assessment of buildings to receive a single ply roofing system as a critical element of design and have produced guidance over the years on this important subject including: S11a-16 (Wind Loading- A guide to reduced risk; A checklist of the parameters required for calculation) and S11b-17 (Wind Load-Design requirements).
S11a-16 ensures that all the required parameters are available in the correct units and as the title of the document indicates, it is a checklist which includes guidance notes for the person supplying the parameters required for calculation.
S11b-17 highlights SPRA best practice guidance with respect to membrane and insulation attachment requirements, to provide resistance to wind uplift. It supplements guidance provided within the ‘SPRA Design Guide’ and offer references to other appropriate industry documents to ensure that SPRA members are fully informed of the appropriate design and installation requirements.
The recent and ongoing competency debate across the construction industry also highlights the need for a competent person providing the collection of data and carrying out such calculations.
In line with continuing to update and provide additional information, SPRA is on the verge of releasing the latest guidance in this subject area, S11b-18 (Wind loading; protocol for calculation). This new document is designed to be used in conjunction with S11a-16, adds guidance in the form of a complete protocol to further assist in attempting to reduce risk and enhance robustness of UK wind load design for flat roofs. The completion of this work represents a milestone in guidance development having consulted the industry widely with input from SPRA members, standards institutions and private consultants to deliver the most up to date comprehensive guidance of it’s type. This latest document provides further essential guidance with dedicated sections on key issues including; calculation software and competency, essential input data, as well as safety factors. The different methods of attachment (mechanical, adhered and ballasted applications) each get a dedicated section providing specific information pertinent to attachment method. This assists in providing the necessary detail while also ensuring that a holistic approach to the issue has been taken covering all means of single ply attachment.
A very worthwhile addition in the new protocol package is a separate document on ‘Site pull-out protocol for flat roofs’, the introduction section positions it’s importance alongside S11b-18 and states;
European Assessment Document (EAD) 030351-00-0402 Systems of Mechanically Fastened Flexible Roof Waterproofing Sheets was introduced in February 2019, replacing ETAG 006, Guideline For European Technical Approval of Systems of Mechanically Fastened Flexible Roof Waterproof Membranes which has subsequently been withdrawn. This SPRA protocol on site pull-out testing will replace the guidance offered by the former Appendix C of ETAG 006 which has not been reproduced within the new EAD 030351-00-0402 standard. This protocol should be read alongside the SPRA protocol for wind load calculation for which site pull-out testing forms an important task required in the determination of the fastener pull-out admissible design value (Wadm).
SPRA will be emphasising the importance of these documents to all involved in single ply flat roofing design and installation in the coming months. It is also critical that competence is evident in those who will use these new protocols. To this end it is proposed to run a one day course later in the year and more if necessary, to ensure that participants are clear in their understanding in the correct use of the documents and have achieved the necessary level of competence. There will be more information from SPRA on any competence training in due course.
Finally, it would be amiss of SPRA not to recognise the effort that many have given in getting these documents ready for publication. Individual members both in, and consultants external to SPRA, as previously mentioned, have made a tremendous contribution. Current SPRA Chair, Martyn Holloway, coordinated the work within the SPRA Technical Committee chaired by Nigel Blacklock and the then SPRA Technical Director, Jim Hooker, began the process back in 2017.
Dr Ronan Brunton B.Sc MBA GMICE, Technical Manager
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