combination of high humidity, drying screeds and plasters and cold temperatures creating moist conditions on site, especially if some or all of the build phase takes place over the winter months.

If the construction has limited drying potential to the outside, and the vapour control membrane does not then allow the moisture to ‘back dry’ to the interior when conditions allow during the warmer summer months, the moisture within the structure can become permanently trapped in the building envelope.

MEMBRANE SOLUTIONS To address these issues, the most effective specification methodology is to select a membrane that hinders the transfer of moisture into the building fabric during periods of high relative humidity, thereby limiting the root cause.

It’s also essential that the chosen membrane enables back diffusion of any moisture that does enter the structure, enabling it to escape to the inside of the building before it can cause structural damage. This is especially critical in scenarios where the exterior of the construction has limited drying capacity, such as where impervious layers like OSB or plywood are used on the outside. At pro clima, we have created a

term for this technology – ‘hydrosafe’ – and used this as a key element of the development of our airtightness membranes. One of these has recently achieved the Passivhaus Institute’s highest ever rating for airtightness during tests for Passivhaus approval. Hydrosafe technology ensures that the building envelope is much more forgiving because it provides humidity- variable moisture protection, particularly during the build phase when humidity levels are at their highest due to poured screeds and plastering. During periods of high relative humidity in the winter, when it is wet and cold outside and warmer and drier inside, the hydrosafe vapour check also provides excellent protection against condensation. Then, during the warmer summer months, when the relative humidity is lower,

Cembrit Plank brings life to bungalow

Water leaks are a distant memory for the owners of a bungalow in the Isle of Wight after Cembrit Plank was installed on the property to provide a new watertight cladding system. L J Teal Roofing Service was approached by the homeowners who were looking for a solution to fix a water ingress issue. Having heard about the recently launched Cembrit Plank, the contractor was confident that this weatherboard could provide a good cladding solution for the customer. Fibre

cement Cembrit Plank is low in maintenance, rot, rust, warp, crack, sun, heat, rain resistant, is non-combustible, providing a superior alternative to timber and plastic based alternatives.

Simply stunning! James Latham recently supplied 5m3

hydrosafe technology provides enhanced back diffusion capacity, enabling any moisture in the structure to dry out to the interior rather than remaining trapped.

The technology is based on building physics data, which has been used to measure ‘hydrosafe values’; a calculation to assess the vapour resistance of a humidity-variable vapour check at an average humidity of 70 per cent. For example, an average humidity of 70 per cent will be present if there is a humidity of 90 per cent inside the building and 50 per cent humidity on the opposite side of the vapour check, adjacent to the insulation between the rafters.

BEST PRACTICE As timber-framed buildings continue to increase in popularity in the UK, self- builders are faced with the challenge of achieving a building envelope that delivers the benefits of airtightness without the risks of trapped moisture. There are a host of CPD seminars to support architects and construction professionals in squaring that circle.

Niall Crosson is group technical manager at Ecological Building Systems, and Michael Foerster is engineer head of applications technology at pro clima

StrongFix - improved support from Norbord

SterlingOSB Zero StrongFix, from Norbord, is a precision engineered oriented strand board (OSB) with a special groove machined into the edge for metal C-studs at 600mm centres. SterlingOSB Zero is made from several layers of softwood strands, carefully layered and bonded under heat and pressure with a strong zero-formaldehyde resin to create a strong board. Superior to plywood, which contains knotholes, splits and cracks, OSB has a consistent density meaning you can attach fixings, hang

pictures or fit items of furniture securely anywhere on the panel. SterlingOSB Zero StrongFix is supplied in 18mm-thick, 2,400mm x 597mm panels with 50 sheets per pack.

of super prime grade Walnut to one of its customers who

have used it to create some spectacular doors as well as privacy screening for an outstanding, high-specification residential property in Lancashire. The project has seen twenty-three 2.7m high doors manufactured and installed by specialist bespoke handcrafted joinery company, Woodside Designs of Blackpool. Eleven of the doors are handle-less, incorporating grooves for handles, plus there are also 3D-hinges, and drop-down seals as well as top-end Swiss and German ironmongery throughout. In addition, a breath-taking, ‘living’ privacy screen has been created and framed in super prime Walnut which features lush foliage and dense greenery. Carl Hulme, Timber Sales Representative for James Latham Leeds, who supplied the timber commented: “The colour of super prime solid Walnut boasts a unique earthy brown hue which varies between cinnamon and chocolate and it also finishes beautifully, giving an excellent decorative appearance due to its outstanding grain, colour and pattern. This coupled with the bespoke workmanship on both the doors and screens have produced an outstanding interior space.” For more information, please visit the James Latham website. 36 november/december 2018

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