Cladding & Sheeting

Aiming high with a Grand Design

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The Caravan Treehouse in Dursely, Gloucestershire features an envelope wrapped in a range of hi-tech DuPont building membranes to achieve high standards of sustainability, airtightness and thermal efficiency


One of the star turns on Grand Designs recently was the spectacular Treehouse project, built to meet passive house standards and set 40ft into the forest canopy. Designed as a much loved home and also to operate as a B&B, this blue-sky concept was naturally built to the highest standards of sustainability and efficiency. Steel and timber framed, with open-jointed timber cladding to blend into its environment, the design demanded the very best from its building envelope. Therefore, a range of DuPont Tyvek advanced building membranes and accessories were specified to both protect the structure during the build and to maximise airtightness and thermal performance once occupied.

Considering the location and style of the project, a key choice of membrane was the Tyvek UV Façade option, a totally black breather membrane designed to withstand exposure to sunlight. Fully certified and rigorously tested, this option is ideal for ventilated façades, allowing for the optimal combination of design freedom and peace of mind. Fitted at first floor level directly behind the timber cladding of the treehouse, Tyvek UV Façade will maintain its high performance for many years to come. Fitting a Tyvek membrane in this way also protects the insulation from the effects of windwashing – a process that is known to reduce its performance and which can increase a structure’s U-value by up to 80%.

At ground floor level, Tyvek Housewrap has also been applied externally to sit behind the steel cladding and act as a secondary water shedding layer while also diffusing moisture to the exterior. Watertight but naturally vapour-permeable, Tyvek membranes offer proven long-term performance in both these crucial functions.

In each application of the different membranes used here, all laps and penetrations have been carefully sealed (correct installation and maintenance being a key aspect of ‘performance as designed’) using UV Façade tape on the exposed areas and Tyvek tape to the areas protected by the Tyvek Housewrap.

Internally, in order to create an airtight seal and act as a moisture barrier, a systemised partnership has been installed consisting of DuPont AirGuard Smart AVCL and Tyvek Flexwrap to adapt to the more challenging sections (together with the appropriate specialised tapes and sealants.) The initial airtightness results have shown a figure of 0.32 ACH. DuPont AirGuard Smart AVCL is both fully airtight and water resistant and adapts its vapour resistance as humidity levels change, giving buildings maximum protection against structural damage caused by humidity.

Project owner Jon Martin said: “I was aware that there can be a big difference between the finished product and the design on paper and I was determined that the fabric of the building was correct. I knew that DuPont had a full range of both internal and external membranes but this is complimented with a wide range of accessories and tapes. These have been essential for the building to achieve our goal of it being the first passive tree house in the UK.”

DuPont Tyvek is distinctive in many key ways, from its hi-tech naturally breathable composition to its renowned long term functionality. Both DuPont AirGuard and DuPont Tyvek also come with expert technical guidance and with the added peace of mind of a comprehensive range of certification and full Building Regulation compliance.