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Design Guide Benefits!
There is no doubt that the most recent version of the SPRA Design Guide released in 2018 and the 7th edition in all, continues to add to the bank of knowledge in good single ply roofing design and practice. The first edition of this document was released in 1996 and the latest edition together with a suite of specific guidance notes on various related key issues are essential reference for all involved in single ply roofing.
Having been involved in major single ply roofing projects in the USA, Europe and Asia over the last 30 years I struggle to think of a more comprehensive range of reference guidance documents. Good knowledge is developed over many years and is an evolving process based on shared experience. As with most things there are aspects of both sound engineering principals derived through testing, certification and the like as well as the benefit of hindsight gained through experience of what does or does not work. The latter often allows the roofer to pass on the benefit of their experience to the industry and is also crucial in developing knowledge. Our Design Guide documentation seems to me to capture this knowledge and allow easy referencing.
This process continues to evolve and no matter how much we know or think we know there is always more information concerning our profession to be learned and knowledge to be gained. Any of you attending the recent Technical Committee meeting will know that we are already starting to file away topics for consideration in the next 2020, 8th edition of the Design Guide.
There is no substitute however for always referring to key principals in terms of single ply design and highlight from time to time some detailing or issue that the Design Guide gives sound advice on. With this in mind I would like to touch on a simple but effective and essential detailing issue in this blog referring to what DG (2018) actually says;
Perimeter membrane restraint or known by some as “base tie-in”
(SPRA Design Guide, 2018 p27)
The Design Guide says;
“Mechanical restraint of the single ply membrane is always required at the roof perimeter, at the bottom of changes of slope and around details. This can be achieved by one of the following, depending on the manufacturer:
A continuous bar (and cord) secured to the deck or upstand and covered with a flashing.
A row of individual fasteners secured to the deck or upstand and covered with a flashing.
Welding the field and vertical membrane to a membrane/metal profile secured to the deck.(SPRA Design Guide (2018))
Some manufacturer systems also approve a reinforced perimeter fastening strip secured to the deck or upstand by a row of appropriate individual fasteners beneath the waterproofing membrane. The reinforced strip is then cold jointed to the underside of the waterproofing membrane before it continues to be adhered to the upstand.
There are other methods of ensuring adequate restraint at this crucial point but the principal remains that the manufacturer and contractor should be able to demonstrate that adequate consideration and subsequent restraint has been allowed for in design and practice on site.
I raise this issue to members as having recently witnessed inadequate change of angle restraint that caused the membrane to “bridge” or peel away from the insulation. Future dynamic wind effects could have caused further issues with the particular detail witnessed. In fairness the installing contractor repaired the detail when the issue was highlighted.
Going back to the issue of adding to our technical knowledge based on testing and resulting experience gained. It is surely right that we can evolve our different methods of detailing and should be encouraged to do so as that enriches the single ply knowledge base. The proviso is that adequate testing is required as supporting evidence.
As always, your opinion matters and pleased to receive any comments.
Dr Ronan Brunton B.Sc MBA GMICE, Technical Manager
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