Designed to Passivhaus principles by Millar & Howard Workshop, Dursley Treehouse is a 200-square-metre dwelling sited on a heavily wooded plot in the town of Dursley, Gloucestershire. Conceived as a series of elevated and offset cantilevered ‘boxes’, the three-storey structure features a lightweight veranda that projects out into the tree canopy.
The brief was for an environmentally-friendly dwelling that would be highly sensitive to both its site and the wider community. More than 25 protected trees dictated the position of the house, with an elevated structure favoured to protect the roots, which were a condition of planning consent. The design also had to consider the position of the trees’ branches and their predicted growth.
‘We wanted to design a structure that was distinct from the trees, yet complemented their form, texture and pattern’, explains project director Tomas Millar. ‘We didn’t want to recreate a woodsman’s hut or a chalet. Our inspiration came from contemporary ‘treehouse projects, such as Jensen & Skodvin Arkitektkontorv’s Juvet Landscape Hotel in Gudbrandsjuvet, Norway (2008)’.
The desire to attain Passivhaus compliance posed a number of challenges – not least overcoming potential cold bridging from the steel frame that is used to support the building. This was resolved using specialist structural-thermal breaks. Equally importantly, the surface-area to volume-ratio had to be carefully considered to reduce heat loss. The windows and doors are positioned to both maximise views out and balance heat losses and gains through the glass. Elsewhere, MVHR is combined with high levels of airtightness and insulation.
The house is constructed from a double timber-stud frame supported by a steel structure. The latter sits on screwpiles, which are designed to keep ground disturbance to a minimum. Specialist forklifts and cranes with caterpillar tracks were used during construction for the same reason. The lower floor is clad with polished stainless steel sheets to reflect the surrounding landscape and defer visually to the upper stories, which are sheathed in untreated larch. Reclaimed items have been used for many of the internal and external components, including metal grilles on the bridge and some of the balconies, which were sourced from a disused local factory.