Sustainability on stilts
The landscape around Stoke-on-Trent in northwestern England is known for its lakes and canals. On Westport Lake, a new Visitors Center (rated BREEAM Excellent) has just been completed by Walker Simpson Architects that combines natural ventilation, natural building materials (such as straw bales) and the natural cooling potential of the lake water.
Westport Lake Visitor Centre was commissioned by British Waterways, on behalf of Stoke on Trent City Council, with the object of creating a high-class visitor destination along the canal network. The site, a local Nature Reserve, is popular with anglers, bird watchers ramblers and cyclists. The Brief called for an exemplar sustainable design to symbolise the regeneration taking place citywide.
The Visitor and Field Study Centre provides much needed community facilities; flexible spaces that can provide a learning opportunity for schools, a seminar space, as well as a visitor’s café and viewing deck over the lake and canal. Shower and WC facilities for the canal users are provided to encourage boaters to make the lake an overnight stopping point along the canal network.
The design, by Walker Simpson architects, was intended to challenge conventional environmental typologies. The main building accommodation is set on an elevated deck, supported by a series of slender oak columns articulated by steel pin joints at the base and head. The massive brick walls of the workshop and store support the part of this deck at lower ground. The tenant, Staffordshire Wildlife Trust, envisage this space being utilized by universities and schools for wildlife courses and practical training. An inlet is formed under the deck and a large timber sliding door opens from the workshop at the waters edge.
Visitors approach the building along a gentle ramp and over a steel pedestrian bridge, which links the building to the surrounding landscape. Vistas over the lake are immediately presented to the visitor as they approach the glazed entrance doors, connecting the visitor to the water upon arrival.
The form of the upper floor was conceived as a crustacean opening up to the lake and canal enclosing the space with floor to ceiling glazing. The rising curve of the deck, parallel to the canal, is mirrored by the curved roof overhang. The roof provides shelter for outdoor activities adjacent to the meeting rooms and café. Thick lime-rendered straw bale walls wrap the south and west elevations, contrasting the precision of the glazed curtain walling. Oak trims the corners of the straw walls and frame the deep reveals of windows creating a defined edge to the natural render.
The building is orientated to maximise natural north light and minimize solar gain and a roof light brings natural daylight into the centre of the deep plan. Natural ventilation is achieved by opening windows on two sides of the spaces bringing in cooled air from the lake; stale warm air is then exhausted out through the skylight.
The building envelope is specified with high levels of insulation and natural materials from sustainable sources. Straw bales were chosen for their low embodied energy and super insulation. The building has a glulam structure on a steel and engineered timber joisted floor and the cladding is untreated Thermowood. Lime render is used to finish the straw bales both internally and externally, which is a breathable natural material.
The roof is covered with a sedum mat, which enhances the insulation and provides storm water attenuation. The zinc roof edging is an 80% recycled material and the lower ground base is constructed in over 18,000 reclaimed red and Staffordshire blue bricks.
The building meets an air tightness of 4.7m3/h.m2 at 50 Pa to prevent heat leaking from the building.
Once the building fabric is optimized in terms of heat loss and natural ventilation, the residual energy required for space heating and hot water is met by the active environmental systems, comprising three sources of renewable energy; lake source heat pump, solar thermal panels and a 6kWp array of Sunpower monocrystalline photovoltaic panels part funded by the Low Carbon Building Programme.
Heating is provided by under floor heating. The lake source heat pump extracts heat via the 600m of pipe work at the bottom of the lake, which supplies low temperature flow and return achieving maximum efficiency for this system.
Domestic hot water is provided by solar hot water heating, supplemented by the lake source heat pump a 6m2 array is sized to provide 1700 kWh of hot water per annum.
Water use is minimised with low flush toilets, waterless urinal and low flow fittings. A rainwater recycling system collects rainwater from the main roof and the deck. The rainwater is utilized for flushing toilets.
Electric lighting is provided by energy efficient fluorescent fittings with daylight switching. The amount of electricity saved by the PV panels on the building equates to 3400kg of CO2 per year.
The renewable energy contributes to 47% of the estimated energy requirement of the building; a wind turbine has also obtained planning permission and if this is installed will increase the percentage further.
A display panel in the foyer records the amount of electricity generated at any given time, this raises awareness of the building’s environmental credentials and encourages responsible energy use in occupation.
Text: Walker Simpson Architects