Roofconsult Website Devil’s Advocate is an Architect’s Greatest Ally by Steve Cleminson of SIG Design & Technology
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While architects strive to deliver great buildings, technical services manager Steve Cleminson at single-ply roofing specialists SIG Design & Technology explores how bringing in experts from the outset can avoid compromising the vision down the line.
Architects have a hard balancing act to maintain. Clients expecting a king’s banquet on a pauper’s budget. Problematic sites and locations prove difficult to design into. There’s complicated and, often, conflicting government legislation to work around while bureaucrats are lining up to pull plans apart. All of these create extra hurdles while trying to deliver buildings that perform on aesthetics, functionality and commerciality.
Not surprising, then, a building’s details are often the key to its success.
But if architects have to focus on balancing the overall picture and the devil is in the detail, getting the most out of a project relies on working with trusted, specialist partners who can help to design problems out of each element.
At SIG Design & Technology, we wouldn’t expect to come to a project and not add value in this way. We spend our lives focussing on a single aspect of a building and so we should be able to help to resolve issues, improve solutions and make the roof work much harder on any project.
Roof falls are a case in point. While British Standards stipulate that all single-ply roofs should achieve a fall of 1 in 80, it is often over looked that this recommendation is for an “achieved” fall and the standard goes on to say that in order to actually achieve this pitch we should be designing at a minimum of 1 in 40.
There are so many good common sense and technical reasons for working to the good practice code rather than the bare minimum on falls but more often than not the minimum standard is specified or at best a halfway house of 1 in 60.
Your main objective with any roof should be to get the water off as quickly as possible. Ultimately, you’re not designing a swimming pool, so while roof membranes will withstand torrents, water ponding can lead to the roof failing. It’s not the water itself that can lead to accelerated aging of roof coverings, but rather the build up of leaf litter, moss, fungus and algae growth. Picutre1
Also poorly drained roofs can lead to greater imposed loadings, increased levels of water ingress if the coverings are damaged, problems of icing during winter and the associated slip hazards during maintenance inspections.
Then, there are the building tolerances to take into consideration.
Designing at 1 in 60, even, is all very well as long as your building tolerances are perfect. But buildings are never 100 per cent perfect. Factoring in this inevitability will avoid problems further down the line.
Our membranes are designed to last for up to 40 years as long as they are installed in line with good practice and are looked after. Getting the most out of a membrane depends on the design and build being right from the outset and also ensuring that the recommendations regarding the periodic maintenance are adhered to.
Our star single-ply membrane, Rhepanol fk has been installed on some 90 million sq m worldwide over the last 50 years.
It’s been hailed as the world’s most advanced single-ply roofing membrane and it’s also the oldest. First developed in 1938, it has been adapted since to provide the architect with much greater flexibility, introducing options for green and photovoltaic roofs.
Based on polyisobutylene (PIB), it is the only single-ply membrane with the unique independent Life Cycle Assessment rating of DIN EN ISO 14040 part ff. It has a unique self-sealing edge and Gripfix system, so it can be installed quickly and with minimum fuss in three simple steps. The self-sealing edge forms an impermeable seam. There are no naked flames, installation is quick and simple, in no small part due to the factory produced self-sealing edge and preformed detailing accessories. And as the membrane is compatible with bitumen, it can be laid over almost any substrate which is structurally sound. Picutre2
But even with these credentials, durability is only as good as the design and installation.
Sure, you can drive a Ferrari at 90mph in first gear but you wouldn’t expect the dealer to pick up the tab when the engine blew up.
I understand the commercial pressure of value engineering a project. Architects are under increasing pressure to shave money off build costs. The first place to look is specification – but decisions do have implications so you have to make sure they are the right ones.
The best way to make sure you aren’t cutting corners in the wrong areas is to seek expert guidance and ask the manufacturer/supplier partner to look at where you can cut costs without designing in problems.
I much prefer to spend my time working together with architects to get things right at the beginning, even when there’s no immediate commercial gain, than trying to reach a compromise between the material requirements and the signed-off design.
It makes sound sense to bring a specialist in to design within the parameters of your overall vision. Not only will they research the products but they will also provide a design complete with calculations of U values, condensation risk analysis, acoustic performance and wind uplift calculations. Together, these not only combine compatible materials within the build up but also ensure interfaces are correctly designed with other building elements.
I come across a lot of projects where the main reason for not delivering best practice on falls is down to cost. Yet here again is an example of how by working with specialists you can find budget busting ways to achieve the ideal.
Commonly, roof falls are or can be achieved through the use of tapered insulation; this can be in the form of multiple layer build ups or even pre-bonded boards. However on large projects, where insulation thicknesses can become excessive, the use of screed to falls, firings or a slight alteration to the structural elements can deliver more effective and less costly ways of delivering the fall.
Falls are not the only topic in a whole matrix of things to think about. We often need to deal with issues around how the falls interact with the rest of the roof geography or other building elements – the parapet, windows, doors, or rooflights, for example.
We’ve had cases where on a refurbishment project the best way to achieve the required falls was to recommend the removal of a run of existing ribbon windows and replace these with shorter ones to allow a tapered scheme to be installed whilst still achieving the minimum 150 mm recommended upstand height at this interface.
The client in this instance wasn’t just interested in a meaningless “scrap of paper warranty”, he wanted a sound solution that complied with good practice and he acknowledged that to ensure the life expectancy of the coverings he needed to abide by the rules, common sense and good advice based on years of experience.
Location and building usage will also dictate the choice of materials used and sometimes there has to be a play-off between the two. It doesn’t always follow that where a material worked on one job, the same solution is suitable for the next.
For example, bonded membranes may be inappropriate for coastal areas because of the excessive wind uplift. This said, we wouldn’t normally recommend mechanical fixings over something like a swimming pool, because in a building of high temperature and high humidity, penetrating the vapour barrier may lead to condensation problems. This aggressive environment may also highlight / exacerbate problems of bimetallic corrosion between the metal deck, the structural elements and the metal fixings. So perhaps a combined approach of bonding and ballasting may be a more risk reduced, cost effective option, or even a green roof? Each and every installation needs to be analysed individually. There isn’t always a one-size-fits-all solution.
Whether it’s a 70sqm London townhouse or a Scottish ancient monument, we will always take the same approach: we will identify the criteria that will impact on design, hone them down to a sensible number of solutions so we can design it right, install it right and achieve the best solution for the building, project, location, client and end user.
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