Sam Finnie, Supply Chain Specification Manager at SIG Design and Technology, discusses the design, specification, and installation of a complex and challenging single ply membrane roof on a mixed-use development in Kent, with Architecture Today’s Technical Editor John Ramshaw.

Designed by Richard Reid Associates, 11-13 Swanley High Street, Kent, is a new-build, mixed-use development comprising 10 apartments and two retail units. A complex and expressive roof structure consisting of both flat and pitched elements – all waterproofed with IKO’s Armourplan PSG membrane – forms an important part of the projects visual appeal and weather-performance strategy. Equally impressive is that the membrane has been cleverly detailed and expertly installed to produce a convincing standing-seam effect.

Sam Finnie, Supply Chain Specification Manager at SIG Design and Technology, in conversation with Architecture Today’s Technical Editor John Ramshaw, discusses SIG’s role in the project and how the company worked with both the architect and roofing contractor to design and deliver a high-performance membrane roof.

The roof incorporates both flat and pitched elements, all of which are waterproofed using IKO’s Armourplan PSG membrane (ph: Michael Cameron)  

What was the brief and how did this inform the design strategy?
The client was looking for a visually-appealing design to blend in with the vernacular style of the area and envisioned a zinc roof with standing-seam detailing. However, cost constraints and technical challenges led the architect and SIG Design and Technology to propose an IKO Armourplan PSG membrane roof, with the standing-seam effect created by the contractor using the same material.

The design comprises 480-square-metres of pitched and flat roofs, including terraced areas, laid over a Metsec construction. Alongside aesthetic considerations, Armourplan was chosen for its ability to create an effective interface between the flat and pitched roofed elements. This is achieved on site through a process of hot air welding.

While the gable ends would usually be finished with tiles, it was decided that a fully adhered Armourplan system would provide increased versatility, with the added benefit of being readily available from SIG D&T. This in turn meant that the project could progress more quickly.

The contractor created the standing-seam effect using the Armourplan membrane to SIG’s specification (ph: Michael Cameron)

What is the roof build-up?
The principal roofing system used on the project is a fully-adhered IKO Armourplan PSG 120 fleece-backed PVC single ply roofing membrane laid over 140mm PIR insulation broads. The latter were chosen for their high thermal performance, and reduced thickness (half) compared to other equivalent mineral-based insulation products. Time and cost considerations also drove the specification of both the single ply membrane and insulation.

On the flat areas, the roof build-up comprises a bituminous primer, followed by a self-adhered SIG Signature Vapour Barrier, then 140mm PIR flat board Insulation, also fully adhered, followed by the IKO Armourplan PSG 120 membrane. The majority of the Armourplan is bonded with Spectrabond Low Foaming PU Adhesive. On the vertical applications and pitched roof sections (with a slope of more than 20 degrees), the adhesive fixing was supplemented with mechanical fixings supplied by IKO Polymeric.

With metal roof beams and eave projections, detailing of the insulation to avoid thermal bridging was critical. Here, the architect relied on SIG’s technical team to specify the appropriate details. Overall, the warm roof construction achieves a U-value 0.18 W/m²K.

The finished roof achieves a U-value 0.18 W/m²K (ph: Michael Cameron)

How is the standing-seam effect achieved?
The contractor created the visual effect of a zinc roof with strips of membrane roofing using SIG’s specification. Given the varied nature of the roof, simply designing the geometric layout for the standing seams was complex, and all the detailing had be absolutely perfect to ensure a weatherproof performance.

How was the roof installed and what were the main challenges?
The material specification was undertaken by SIG and the architect. SIG then recommended roofing contractor Performance Roofing to carry out the installation. The latter is a highly experienced SIG Design and Technology Approved Contractor, with the DATAC scheme providing assurance that SIG single ply products, such as IKO Armourplan, are correctly installed on site.

A roof-mounted PV installation contributes to the building’s sustainability strategy (ph: Michael Cameron)

It might have been easier for the roofing contractor to fabricate some of the upstands offsite, but the company was insistent that the entire installation should be undertaken in-situ to ensure that each element was precisely detailed and perfectly resolved.

Another challenge arose from the requirement to install the roofing membrane to the gables. Working from scaffolding, site operatives used a series of ladders to reach various points on the gables – being careful not to damage the membrane and work safely at height. Overall, the complex installation was undertaken with great care and attention to detail, which is evident in the completed roof.

Contact Details
For more information, please visit the SIG Design and Technology website.