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Eco-friendly materials in a unique helicopter air base and

office facility.

Combining headquarters for the Cornwall Air Ambulance Trust (CAAT) and the operating base for its helicopter ambulance, this unique building includes a modern air hangar and office space for the charity’s fundraising staff. Completed in 2012, the building has many environmental features, including hemcrete walls.

Introduction

Truro

Exeter

Newquay

Cornwall Air Ambulance Trust

Key dates June 2010 : Project Manager, architect and engineer commissionedJune-Dec 2010 : £1M secured from ERDF Convergence Funding, planning applicationApril 2011 : Work commenced on siteFebruary 2012 : Cornwall Air Ambulance Trust moves into its new base.

Entrance - Photo © Graham Gaunt Photowork

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ContextWith its scattered rural population, air ambulance cover is vital to the Cornish community - the Cornwall Air Ambulance Trust gives lifesaving service across the Duchy funded entirely by donations and fundraising. The Trust is one of the most active and prominent charities in Cornwall and its new building is the focus of this activity, making it a hub of community activity as well as an operational air base. In 2010, the charity had outgrown its office facilities, and needed to update its helicopter base. A project was launched to build a combined facility on a well-connected site adjacent to Newquay airport. The

project progressed swiftly, with construction commencing in April 2011 and the Trust moving into its new base in February 2012. The design brief specified a building which minimised its environmental impact whilst providing efficient operating facilities and comfortable office accommodation. Features which contributed to this include; a compact building footprint which minimises external walls, building orientation which takes advantage of passive solar gain and shields workspaces from the noisy helipad and airport runway, design and

Plan © Chapman Workhouse Architects

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layout which maximises the use of natural ventilation and daylight. The building achieved a BREEAM rating of «Excellent».

Building overviewSet on a high and exposed site near the north coast of Cornwall, the CAAT building covers an area of 835 m², which includes a 590 m² hangar and 245 m² of office space. It is unusual in combining two very different functions, and this has led to the use of a range of materials and construction techniques. The hangar uses steelwork to achieve the necessary large clear span, with highly insulated walls clad in locally sourced corrugated fibre cement panels. The foundations, ground floor slab and helipad comprise 30% recycled aggregates in the concrete mix, sourced from the China Clay works near St Austell. The hangar is roofed with a highly insulated standing seam aluminium.

The use of natural materials is focussed on the smaller, more intimate office area. Here, the external walls are built from hemcrete, a carbon negative material composed from shiv (the woody core of the hemp plant) and a lime-based binder. The interior walls are timber studwork. The office area has a green roof insulated with

250 mm Cellotex. The building is heated by air source heat pumps, with hot water from a solar thermal panel.

The site is not connected to mains water, and due to long distances, connecting to the mains was prohibitively expensive; therefore standalone water and drainage services were required. A new borehole was sunk and the site provided with a bio-digester for foul drainage and a management system for water runoff. A 45000 litre grey-water tank provides recycled water for the fire service. A sustainable drainage system takes surface water from the car park and helipad; this includes a petro-chemical interceptor to prevent pollution from any oil spills. To conserve water, all toilets are fitted with dual flush cisterns and the taps and showers have flow restrictors to minimise consumption. This has resulted in net water consumption of 4.18 m3/person/year.

Ecology and biodiversity were considered throughout the design and build. An ecologist was employed to review the plans and monitor the construction process. New wildlife habitats were created by the green roof and the series of traditional Cornish hedges constructed to form the site boundary.

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Technical focus : Hemcrete and lime render on an exposed siteHemcrete was selected by the project architect for its low environmental impact, self-insulating and acoustic properties. The CAAT’s helicopter lands and takes off very near the office part of the building, and noise protection was thus an important issue. The architect and project manager visited a new build hemcrete house in north Cornwall as part of their research and were particularly impressed to find that it was heated only by solar gain and had excellent heat retention.The product used for the CAAT building was Tradical hemp, supplied and installed by «Back To Earth Ltd»

from Devon. The hemcrete was supplied as a dry mix of hemp with a lime binder and mixed with water on site. Shuttering was used on both sides of the building to hold the hemcrete in place whilst it dried. The external plastic shuttering boards were removed once the hemp had become solid. Internally, 9mm Multi Pro XS racking board was retained and treated with lime plaster to create the interior finish. Marine grade plywood was used to create studwork around window and door openings. The CAAT team found the hemcrete installation easy and straightforward. The work coincided with good weather during summer 2011 and the hemcrete dried out quickly. A self-coloured lime render was

Inside the hangar - Photo © Graham Gaunt Photowork

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applied to create the external finish. To minimise any potential damp problems, the hemp/lime walls are protected by an upstand at the foot of the wall. The building is also surrounded by a gravel border which prevents rainwater from splashing up onto the walls. Since completion in 2012, the lime render has weathered extremely well despite the building’s exposed position.

Barriers and solutionsMaintenance in an exposed siteThe building’s hardwood windows were originally treated with a natural

oiled finish, which in most situations would last for at least five years without maintenance. However the finish has proved inadequate in the exposed, coastal setting and a more durable product has been applied.The building’s green roof has been a success, but has also been subject to some trial and error in terms of maintenance. Within the first nine months, several saplings had self-seeded and grown to 3-4 feet tall. The self-seeded plants had out-competed the roof sedum and their roots had disturbed the substrate. A regime of six-monthly weeding has now solved this problem.

On-site trainingOn site standards were maintained

Meeting room - Photo © Graham Gaunt Photowork

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throughout the build through a site induction process delivered by the main contractor, and toolbox talks covering topics including the building’s environmental aims, waste management and ecology. Several visits to site were made by local schools and students from Cornwall College.

A comprehensive approach to construction management and building lifecycleA strength of the Air Ambulance project is that care was taken throughout the planning, design and construction to ensure the environmental impact of the building was minimised.

During the design phase, a Low and Zero Carbon Feasibility Study was undertaken to determine the most

Office space - Photo © Graham Gaunt Photowork

Hemcrete and lime render - Photo © études ET chantiers

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efficient systems for the building; this resulted in the selection of air source heat pumps for heating and solar thermal hot water which deliver 26% savings in CO2 emissions over traditional heating systems. The building is designed to maximise daylight and solar gain, avoid heat loss and prevent the need for air conditioning. In all areas of the building, materials were selected with consideration to embodied energy, durability and ease of maintenance, demolition and recycling.

The principal contractor set targets for energy and water consumption use during construction which were benchmarked to the most efficient

industry standards. These were followed up by strict monitoring to ensure the targets were achieved. Water saving measures were encouraged by the contractor which resulted in total consumption of 159 m3 which equates to less than 10 m3/ £100K, putting the project amongst the most efficient in the construction industry.

During construction the contractors implemented a rigorous Site Waste Management Plan, which minimised the amount of material sent to landfill and encouraged the re-use and recycling of site waste. The principal contractor participated in the Considerate Constructors scheme, achieving recognition for ‘Performance beyond compliance.’

Building in operation - Photo © Graham Gaunt Photowork

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StakeholdersClient : Cornwall Air Ambulance TrustProject Manager : Stephen Murdoch, Wagg ConstultantsArchitect : Chapman Workhouse, TruroEngineer : URS/Scott WilsonPrime contractor : Morgan Sindall LtdMechanical and electrical services : EIC Ltd, RedruthWindows and doors : Camel Glass, WadebridgeHemp and lime : Back to Earth Ltd, Devon

The highly insulated walls, roof and floor have limited heat loss throughout the building to <0.2 w/m²K. The test result for air leakage in the occupied part of the building achieved 4.6 m3/hr/m²@50Pa.

The project contributed to the local economy through its construction, with 65% of the value of the contract being placed with Cornish subcontractors. There is also a significant ongoing contribution; the new facility has enabled the Trust to employ seven new members of staff, representing an increase in Gross Value Add (GVA) to the local economy of over £860,000 by 2015.

The Trust, as a very active local charity, is focussed on engaging with and supporting the local community. Many aspects of the building were designed with this in mind and the new building facilitates flexible use for a wide range of meetings and community events. The hangar has even been used to host up to 200 people.

PerformanceSection © Chapman Workhouse Architects

ContactCornwall Sustainable Building Trusthttp://csbt.org.uk/