Something New Under the Sun

An innovative, UV resistant roofing underlay with high water resistance opens up exciting alternatives to traditional roof coverings

Traditional pitched roofs call for traditional roof covering materials—classic thatch, slate and clay, and metals such as lead. They all completely cover the underlying breather membrane. Roofing felt breather membranes provide the necessary combination of water resistance to prevent any moisture entering the structures. Water vapour permeability allows moisture from the interior to disperse, preventing interstitial condensation damaging the building envelope. They work effectively under a closed covering system, where they are not exposed directly to precipitation, as, while they are water resistant, they are not impermeable. Nor can standard roofing underlays be exposed to sunlight for any length of time; typical installation instructions specify that breather membranes should not remain uncovered for more than two months while the roof is being installed. The damaging effects of UV radiation will cause the material to degrade and no longer be fit for purpose.

Until recently, the concept of using an openwork timber cladding system as a roof covering would be unheard of. Partially open timber cladding, as well as metal mesh and composite rainscreen systems are becoming increasingly common in modern façade design. But extending this cladding to the roof, giving an aesthetically pleasing effect for pitched and mansard roofs? Not possible. However, an innovative, highly water and UV resistant roofing underlay allows for creative exterior cladding design, not just limited to walls.

One project features this creative unified façade/roof concept. Designed by Robert Houmøller of Merrett Houmøller (initial design in collaboration with Eva Willoughby), their boathouse sits at the edge of a lake. The outer cladding of Japanese scorched timber extends up the walls and over the pitched roof.

The building was constructed using structural insulated panels, with Powerlon UV Colour façade membrane for the walls, and Powerlon UV Roof protecting the roof. These technologically advanced membranes protect the walls and roofs with exceptionally high UV and water resistance, combined with excellent water vapour permeability. Both are well suited for use with SIP construction, but are compatible with all substrates. They come with a ten-year warranty, when installed according to guidelines using proprietary adhesives and detailing accessories.

Powerlon UV Roof can be used on pitched roofs, including those with a shallow slope – greater than five degrees - and provides protection in even the harshest weather conditions. It can be used in both ventilated and unventilated roof installations, and can also be glued directly onto wood, metal or rendered supporting structures. Another feature of UV Roof is its extremely high nail tear resistance. UV Roof comes in two colours, brown and black, while the UV Colour façade membrane is available in eight colours.

Typically the UV Roof membrane has been used with timber rainscreen cladding, with gaps up to 40mm. UV Roof should be installed in conjunction with Powerlon Eco, an economical breather membrane suitable for roofs with a slope greater than fifteen degrees. Together, they allow for a complete water and UV protected installation with openwork timber panels.

Powerlon UV roof and façade membranes are offered by Industrial Textiles & Plastics Ltd, industry leaders in innovative building materials, including the FlameOut Breathe membranes (Euroclass B and Euroclass A2) which are suitable for both wall and roof installations.

Photo courtesy of IQ Glass

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