Design Commission for Wales

• Location: Building Research Establishment
• Date Completed: 14th May 2008
• Client: Barratt Developments PLC
• Architect/designer: Gaunt Francis Architects, Cardiff Office
• Planning authority: Hertfordshire County Council
• Funding body: The Green House was designed by Gaunt Francis Architects as part of an open competition, short-listed by a panel of experts and selected by public vote through the Mail on Sunday as the design for 'The Home of the Future'. The design is supported by the National Centre for Excellence in Housing and the Building Research Establishment (BRE). Barratt Developments PLC implemented The Green House to widen their experience of building low carbon design houses.
• Contract value: Undsiclosed
• Project type: Detached house
• Full address: BRE Innovation Park, Garston, Watford
• Location type: BRE Innovation Park
• Number of dwellings: 1
• Dwelling type: Detached House
• Site area/ Density: The demonstration house was built as a detached house and achieves the requirements of the Code with the ratio of net internal floor area: net internal ground floor area being 2.5: 1. It can be implemented as a terraced, semi-detached and detached house in future to meet different site density requirements.
• Parking ratio: 1 car parking space is provided within footprint of site.
• Typical unit area: 9m x 9m = 81m²
• Cost per unit: Undisclosed

Images

Computer Generated Image House Model

Competition Image, CGI of 3 dimensional model. Copyright Glass Canvas

Computer Generated Image of Streetscape

CGI of terraced street of Barratt Green House types. Copyright Glass Canvas

Computer Generated Image Section

CGI of a section through the house with notes. Copyright Glass Canvas, Gaunt Francis Architects.

External View

As built external view of house. Copyright Peter White.

Front View

Front View of exterior of built house. Copyright Denis Jones.

Interior

Interior living space. Copyright Denis Jones.

Interior

Interior living space. Copyright Peter White.

Interior

Interior stair and landing. Copyright Denis Jones.

Interior

Interior top landing. Copyright Denis Jones.

Interior

Interior bathroom. Copyright Denis Jones.

Interior

Interior bedroom three. Copyright Denis Jones.

Rear view

Exterior view of the rear of the built house. Copyright Denis Jones.

Introduction

Following the win of the Mail on Sunday, 'The Home of the Future' competition, the Cardiff office of Gaunt Francis Architects Green House has been implemented by Barratt North London Division as a detached demonstration house on the Building Research Establishment (BRE) Innovation Park in Garston.

The Green House is designed as a three storey, three bedroom family home, including through living dining-kitchen space; downstairs cloakroom; games/play room; home office; family bathroom; and en-suite to the main bedroom of the three provided. All rooms are reasonably sized and serviced from a central hallway, which starts from the front door and covered car port area and terminates at the second floor external terrace.

In addition to being a family home, the Green House is also designed to achieve the UK government's Code for Sustainable Homes (CfSH) Level 6 (the highest level) of performance, and will therefore emit no carbon on average over the course of a year. The house is designed to achieve the Treasury's Stamp Duty Exemption definition of 'zero carbon', and achieves an Energy Performance Certificate rating of A (part of the domestic Home Information Pack). It is furthermore designed to achieve Lifetime Homes and Secured by Design standards. Gaunt Francis' design for the show home uses thin coat render and pre-patinated (hence green) copper cladding on the walls, as a deliberate statement that sustainable houses do not have to be clad in timber. The roofs are made from a combination of south facing single ply membrane (to be covered with photovoltaics) and a north facing roof covered with vegetation (sedum) and trimmed with copper. Whilst these external finishes give the show home a stylish, modern appearance, the house type itself is intended to be capable of receiving alternative external treatments that are tailored to the local vernacular and planning constraints of future sites.

Design Process

Whilst the competition brief was for a zero-carbon house designed to meet the requirements for Level 5 of the CfSH, Barratt Developments stepped up the target for the implementation of the project and wanted the house to be designed to meet CfSH Level 6.

The initial competition winning design of Gaunt Francis' Green House was therefore further refined and developed with the input of various consultants forming a multidisciplinary design team together with the architects. During the design and development process the strong links between some of the individual aspects of the Code for Sustainable Homes soon became clear as changes made within one section often had an immediate effect on the scoring in other sections of the Code. In order to successfully meet the requirements of Code Level 6 in all sections it was necessary for all members of the design team to closely work together and understand the impact their own work has on the work of other team members.

After the majority of the design work had been completed the next step was taking the project to site. This posed a challenge to the workforce as they were unfamiliar with many of the proposed construction details and materials. Also the level of accuracy and precision required in building a house as airtight as the Green House is far beyond what is necessary to achieve current Building Regulation requirements. However, due to the method of construction chosen, i.e. the use of prefabricated elements for walls, floors and roof, the shell of the building could be erected in a very short time and air tightness issues could be minimised. This was followed by an extensive installation of building services before the internal finishes could be applied.

Sustainability Credentials

The Green House has a heavyweight structure with storey-high aerated concrete wall elements and precast concrete floor planks. The roof consists of Structural Insulated Panels (SIPs) and the building envelope is wrapped in 180mm of high performance Phenolic insulation. The use of prefabricated modules for the wall and floor construction as well as for the roof structure reduces on-site waste production, speeds up the construction process and reduces health and safety risks on site through the fabrication of elements in a more controlled factory environment.

The highly insulated heavyweight structure was chosen over a lightweight construction in order to achieve good thermal performance in terms of reduced heat loss through the building envelope and the maintaining of comfortable internal temperatures all year round. The thermal mass provided by the heavyweight construction absorbs heat from the air on warm days and releases it into the air again when temperatures fall at night-time. Together with the mechanical air-source heating and ventilation system this ensures a consistently comfortable air quality and temperature within the house at all times.

The mechanical air-source heating and ventilation system works in such a way that fresh air is drawn into the house and heated by the warm exhaust air from the kitchen, WC and bathrooms before it is supplied to the living room, study and bedrooms. During warmer months the fresh air drawn into the house bypasses the heat exchanger to avoid it being heated by the warm stale air that is driven out of the house. In the warmer months natural night-time purge ventilation will effectively cool down the internal air temperature when hot stale air is driven out of the building through open windows at the top of the staircase and replaced by fresh air that is drawn into the house at the bottom of the staircase, making use of the natural stack effect. This stack effect is also exploited for the drying of clothes at the top of the staircase, eliminating the need for a tumble dryer.

In order to further reduce heat gain, external shutters have been installed to shade the windows. In addition these shutters provide an increased level of security when they are closed at times the house is not occupied or the windows are open behind the closed shutters for night time ventilation. All energy used within the Green House is produced on site by photovoltaic panels.

To keep the energy demand as low as possible low energy light fittings have been used throughout the house along with A and A+ rated white goods. Whilst at peak times it might become necessary that energy is imported from the grid there will also be times when surplus energy is produced which in turn is fed back to the electricity network so that the house operates as zero carbon when seen over the course of the year. The hot water in the house is heated by a combination of solar heating, heat pump and electric immersion with the solar system taking priority over the other two and being capable of heating the majority if not all of the hot water over the summer months.

Rainwater is collected from the roof as well as from permeable paved areas and stored in a below ground tank. From here the filtered rainwater is pumped to a header tank in the attic space for use in the washing machine, toilets and green roof irrigation.

Code for Sustainable Homes: Code Level 6 Design Stage awarded; awaiting Post Completion Certificate.

Evaluation

The scheme has been selected because:

• The Green House is the first Zero Carbon house built by a volume house builder to CfSH Level 6 (design stage) in the UK, designed by a Welsh Architectural practice. It is therefore on the forefront of sustainable housing design and leads the way to achieving the Government Target for all new built housing to be Zero Carbon by 2016 (2012 for Wales).
• The Green House features a range of modern technologies from the use of renewable energy, automated heating and ventilation to rainwater harvesting. Rather than being bolted on and unsightly extras to a standard house these technologies have been neatly and inconspicuously incorporated into the design of the Green House underlining the holistic approach to sustainable design.