SIG Design & Technology explores how single ply membranes can provide high-performance and cost-effective roofing solutions for wide range of building types

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Single ply membranes are traditionally associated with large flat roofs, particularly in the commercial sector where they are favoured for reasons of practicality and cost-effectiveness. But increasingly, architects are seeing the aesthetic and performance benefits of specifying this tried and tested roofing type on a much wider range of projects, including those in the public, residential and even historic sectors. So how do you innovate with single ply membranes? What are the advantages? And which products are worth considering?

Buildings.

What is a single ply membrane and how do I choose one?
Single ply is a flat, synthetic polymer-based roofing system that provides a waterproofing layer in a single sheet. Made from PVC, EPDM, TPO, TPE or PIB, the material is either homogeneous or contains a reinforcement layer. Sealed at the joints with heat, adhesive or mechanical means, it can be used on flat, pitched and green roof systems. Single ply roofs are lightweight, flexible, cost-effective, swift to install and safe. Different types of single ply roofing can be considered in terms of their track record and lifespan, sustainability credentials, cost and guarantee. The choice of roofing system should be based on design criteria, performance requirements and cost; and it is important to balance all three.

Pitched and curved roofs
Contrary to popular belief, single ply membranes are equally suited to pitched roof installations as flat ones. They also lend themselves to simple curved roof structures, as the following examples attest.

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Blacon Crematorium
Blacon Crematorium in Chester by KKA Architects is a £5m state-of-the-art facility that is crowned with a 1000-square-metre geodesic roof. An IKO Armourplan SG single ply membrane incorporating standing-seam profiles was specified to give the appearance of a lead/zinc roof. It also provided the client with an economical and quick to install solution that has proven long-term waterproofing integrity. Armourplan SG single ply membrane was fully adhered to the main field sheet areas, with Armourplan SM single ply membrane used on the upstands. The approved roofing contractor was Briggs Amasco.

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68-72 Worcester Park
Procured by a national house-builder, 68-72 Salisbury Road in Worcester Park, Surrey, comprises three blocks of terraced-style homes. FDT Rhepanol fk from SIG Design & Technology was chosen to waterproof flat roof areas, curved and barrel-vaulted sections, dormers, and balconies totaling 949 square metres. Specified in light grey with standing-seam profiles, the membrane is intended to mimic a lead roofing system.

In addition to its visual appeal, the system was favoured for its speed of installation and sustainability (it is the only membrane with a Full Lifecycle Assessment and is made from PIB). Some of the roofing elements utilise a Gripfix mechanical fixing system, while the remainder are adhered. The former attaches Rhepanol’s fleece backing to the Gripfix hook and loop system, making it safe and secure. A self-sealing chemically-welded seam between roofing sheets ensures immense tensile strength.

Imitating metals
Single ply membrane roofs are a cost-effective alternative to metal systems, which may be cost-prohibitive or at risk from theft. Among the advantages of single ply systems are that they can closely resemble the appearance of metal (particularly when used with standing-seam profiles and rolls); they are made from polymers which have no scrap value; they can incorporate special finishes, such as FDT’s decorative paint, which can be used to give a shiny copper or verdigris finish; and they are considerably cheaper than lead or copper alternatives.

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Guildford Crematorium
A good example is Guildford Crematorium in Surrey, whose copper roof was targeted by thieves. The stolen roofing to the visitor area and walkway has been replaced with an FDT Rhepanol fk single ply membrane. The roof features a copper paint finish, which is designed to resist cracking or peeling and comes with the same life expectancy as the membrane, as it is made with real flakes of verdigris copper suspended in the PIB. The reroofing work was carried out by Brayer Group.

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Lymington Shores
This waterfront residential development in Hampshire by AAP Architecture demonstrates how a properly designed and installed single ply membrane roof can closely resemble a metal roofing system. The project features 12,000 square metres of pitched roofs with standing seams, flat roofs, terraced areas and cold roof build-ups to bin stores and valley gutters. Performance and environmental requirements led to the specification of FDT’s Rhepanol fk PIB single ply membrane, which is 100 per cent recyclable and has a full life cycle assessment to ISO14040. The pitched roofs presented the greatest level of technical difficulty to the DATAC-accredited contractor and Rhepanol Ambassador Flat Roofing Membranes. Visible from every angle, ‘perfect’ execution of both field area and standing seam detailing was required to meet the objective of perfectly replicating a standing seam metal roof finish.

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Red Armourplan SG PVC membrane on a residential development in the Netherlands 

Colours other than grey
Single ply membranes are routinely specified in various shades of grey or black. What is less well known is that they can incorporate special paint finishes (as mentioned earlier) and be supplied in a wide range of colours. SIG Design & Technology’s bespoke coloured PVC membranes are made in the same plant as conventional grey membranes. The process is time and labour intensive (compared to making standard colours), so the amount of membrane required affects the price. The minimum amount usually ordered is around 5000 square metres. Below 4000 square metres, a bespoke roof membrane colour produces a considerable price difference to alternatives, although this isn’t always the case, as other factors may be involved.

Limitations in the manufacturing process mean that RAL colours cannot be matched exactly. A close match is the usual outcome. Last but not least, the manufacturer will need to make all of the coloured membrane in one batch to guarantee colour consistency and avoid additional costs. Specifiers should therefore plan for additional material to cover changes in the design, or repairs if required.

Waterproofing challenging environments
The long-term performance and sustainability of single ply roofing membranes make them ideal for protecting historic sites and/or buildings in harsh marine environments. They can also be used behind rainscreen cladding systems on object-like buildings that blur the distinction between wall and roof planes.

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Skara Brae 
Located on the largest island in Scotland’s Orkney archipelago, Skara Brae is a 5000-year-old human settlement comprising eight clustered dwellings. Despite having a grass roof, the interior of the best preserved house (number seven) and its Neolithic carvings were at threat from the island’s harsh climate. The solution adopted by client Historic Scotland and manufacturer FDT was to cover the dwelling with a watertight garden roof using Rhepanol hg. The lifespan of the PIB-based membrane is such that it can be left undisturbed for up to 50 years.

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Garnet Chapel
Perched on the side of Penkenjoch mountain in the Austrian Tyrol, Mario Botta’s Garnet Chapel was constructed in only three months using FDT’s PIB membrane Rhepanol fk. Externally, a series of perfectly aligned 300mm CorTen steel panels form a rainscreen with 10mm gaps. The interior is clad with similarly spaced larch slats. Behind the finished surfaces is complex system of cross-laminated timber panels, spacers and additional steel reinforcement. Central to the performance of the envelope is the Rhepanol fk waterproofing layer applied directly to the CLT surface. The membrane was chosen for long life span (Rhepanol’s predecessor is still waterproofing well after 50 years), flexibility at low temperatures, and environmental profile (ISO EN 14040-49).

Contact Details
For more information on flat roofing visit the SIG Design & Technology website.