Architect Sandra Lea-Murray and SIG Zinc & Copper Category Manager Simon Walker discuss best practice design for metal roofing on a private swimming pool extension with Architecture Today’s Technical Editor John Ramshaw.

In association with


Terence Smith

Located close to Cheshire’s picturesque Sandstone Trail in an Area of Special County Value, this striking residential extension scheme adds a swimming pool, sauna and gym to a converted farmhouse. The brief for architect Sandra Murray & Associates was to produce an understated elegant design with minimal visual impact. Central to this approach is the use of a highly refined, shallow-pitched, elZinc Rainbow Rojo/Red zinc roof from SIG Zinc & Copper. Architect Sandra Lea-Murray, in conversation with Architecture Today’s Technical Editor John Ramshaw and SIG Zinc & Copper’s Category Manager Simon Walker, explore the roofing design and specification process, including how the metal structure is protected from the humid spaces below.


 The elZinc Rainbow Rojo/Red roof has an organic coating which provides anti-corrosion protection

What was the concept behind the roof and why did you choose zinc?

SLM: I wanted the building to hug the ground and blend in with the natural colours of the surrounding earth, stone and landscape features. To minimise the impact of the building, I decided to opt for a low-pitched roof; the intention being to keep the ridge height below that of the adjacent tennis courts and ensure that the existing farmhouse was not dominated or overpowered in terms of scale. A metal roof would allow me to design a low pitch, and the use of a traditional standing seam detail would not be of unusual appearance in a countryside location. It was felt that the design could have a similar appearance to a traditional brick building but with more sophisticated styling.

I looked at several roof finishes before deciding to use zinc. elZinc Rainbow from SIG Zinc & Copper was chosen for its guaranteed appearance over time. This was important to the planning officer in terms of protecting the Area of Special County Value setting. elZinc Rainbow incorporates an organic coating to provide anti-corrosion protection. It also comes in a range of colours, and I selected Rojo/Red to imitate a weathered copper finish and to marry with the Cheshire red sandstone that can be viewed from the Sandstone Trail.

The fascias, gutters and downpipes are all formed out of the same zinc finish to maintain the simplicity and elegance of the roof design. This also reduces the number of materials in the palette, resulting in a strong, uncomplicated design that does not dominate in elevation.


 The roof build-up comprises elZinc Rainbow standing seam roofing with seam clips, a breather membrane, torch-on felt, fixing plates, and cellular glass insulation

How important was it to protect the roof from the humid environment below, and how is this achieved?

SW: A swimming pool is one of the most challenging applications for metal roofing, providing a potentially corrosive environment. The design of the roof system therefore needs to include an entirely reliable moisture-proof barrier situated under the metal sheeting. Cellular glass insulation is really the only option for this type of building, and we worked closely with the project subcontractor to design a solution. This comprises two layers of FOAMGLAS insulation, topped with a torch-on-felt and finished with a breather membrane. The resulting system produces the required U-Value of 0.16 W/m²K, with the reassurance of a robust water and vapour-proof barrier.


elZinc Rainbow is also used to form the fascias, gutters and downpipes, creating a strong sense of design unity

What was the specification route?

SW: We have worked with Sandra on a number of projects, providing technical support and make suggestions around product solutions. On this scheme the architect was responsible for producing the design drawings up to planning stage. Once approved, the project then went to tender as a Design and Build Contract with the main contractor RS Burgess & Sons subcontracting the roofing to specialist MH Midlands.

SIG was involved in the initial product selection and then worked with MH Midlands to produce the detailed design drawings for installation on site. elZinc is supplied in coils and profiling of the product is carried out on site by the contractor. Gutters and downpipes in this instance were fabricated from the same material by a specialist fabricator.


Garden elevation

Is the system warranted?

SW: The individual products used in this roof system come with manufacturer warranties, of course. However, the advantage of sourcing the products and the design advice from us is that the finished roof can be supplied with a system warranty from SIG of up to 30 years.

Contact Details
For more information, please visit the SIG Zinc & Copper website.