Arboreal Architecture share details of their shortlisted entry in the New Forest, Sustainable Buildings category.

Congratulations to AECB members, Arboreal Architecture for reaching the shortlist in Hampshire’s Countryside Awards which has seen a record number of entries this year.

Now in their 11th year, the county branch of the Campaign to Protect Rural England run these awards to recognise and celebrate those working for a beautiful and thriving Hampshire countryside.

Harry Paticas of Arboreal Architecture saw the call for entries in our Network newsletter and shares below the details of their shortlisted project.

This project is a holisitic “deep-retrofit” and ground floor extension of a 1920’s semi-detached house in the village of Brockenhurst in the New Forest. The 3-bedroom house was designed to meet the AECB Silver Standard and the AECB CarbonLite Retrofit Standard. The design incorporates holistic insulation and airtightness measures that follow Passivhaus design principles with resulting low energy consumption, excellent air quality and high levels of thermal comfort.

The client for the project is the mother of the architect Harry Paticas (Arboreal Architecture) and has a large family with frequent guests to the home. The long back garden incorporates a play-space for grandchildren, a biodiversity orchard with winding cycle paths through and a demountable timber hut.

The walls have both cavity wall insulation and vapour-permeable internal wall insulation to achieve low u-values resulting in high levels of comfort throughout the year. The ground floor has vacuum insulated panels placed over the existing floor (thus avoiding having to break up the existing concrete and resulting landfill) and the roof has 500mm thick blown cellulose insulation. Windows have been detailed and installed with high-performance triple glazing and reflective membranes were installed in the roof to reduce summer overheating. The ventilation strategy employs simple mechanical extract vents in each wet room which pull air in through natural leakage and adjustable vents in windows. The materials specified included: locally sourced ash timber, vapour permeable paint capable of breaking down VOCs and kitchen counter/bathroom riles with high recycled content.

Since completion, the actual energy performance has been carefully monitored and has exceeded expectations – the project was designed to achieve 40kWh/m²/yr and the actual gas usage (adjusted for client absences) has been under 30kWh/m²/yr – the total gas bill for the year (heating and hot water) was only £169. The client has also reported year-round high air quality, cool summers and warm winters.

The ground floor extension has a carefully crafted, timber “Chinese-hat” roof which introduces an element of fun and provides a sheltered outdoor space at the back of the house. The ground floor and shower room extension has been designed to be fully wheelchair accessible to accommodate potential future client needs.

A local builder was employed as the main contractor (George Speechley) and toolbox talks were given to site workers to explain the low energy design principles. During construction in November 2014 an AECB local group meeting was led by the architect who explained the design, insulation and airtightness strategies. In March 2017 the New Forest Transition Group visited the house to learn about the measures and the project will be further engaging with the community through the Green Open Doors event run by the New Forest National Park. In 2015 Historic England installed a weather station and over 20 sensors in the loft as part of a wider loft hygrothermal monitoring study – this research is on-going and in 2018 will result in a publication of the results.

The Larch Hut, located at the end of the garden, was originally designed for and built in the grounds of an Umbrian farmhouse. To comply with the local planning requirements it was sized to the outbuilding foundations on which it was built and was designed to be fully demountable in one day. The exterior cladding is rough sawn to encourage lichen and moss growth while the interior surfaces are sanded smooth and finished with linseed oil. The interior spaces are formed from cross-beams that perform as a both structure and furniture at the same time. In 2014 the Larch Hut was de-mounted and transported from Italy to the UK where is was rebuilt on recycled foundations formed from the pre-cast concrete panels of an old garden shed.

To view all shortlisted entries, click here.