A pioneering low energy retrofit of a derelict farm building at Yorkshire Wildlife Trust’s Stirley Community Farm in Huddersfield has just become one of only a handful of projects in the UK to receive EnerPHit certification from the German Passivhaus Institut.
The design & build project, led by Passivhaus specialists Green Building Store, has transformed the dilapidated cow byre into an ultra efficient education centre, named the ‘Cre8 Barn’. A super-insulated timber frame ‘box within a box’ structure was built inside the existing stone building, which serves to shore up and preserve the outer stone wall of the barn, whilst offering exceptional airtightness and continuity of insulation. The project offers a useful template for low energy refurbishments of older and historic buildings, where it is important to preserve the outward appearance of the building. The Cre8 Barn recently won ‘The Legacy Award – Sustainability’ at Constructing Excellence Yorkshire & Humber Awards 2014.
EnerPHit certification: Elemental/ Component approach
The Cre8 Barn project is also the first EnerPHit project in the UK to be certified using the ‘elemental’ (or component) approach, which requires every element of the build to meet certain U value requirements, in addition to being modelled in Passivhaus Planning Package (PHPP) software. The elemental/ component approach was developed by the Passivhaus Institut for projects where the design team cannot control certain aspects of the build, eg orientation, size of window and door openings, roof height or treated floor area. This approach provides an alternative method for assessing building performance, where the usual Passivhaus heat load/ space heating methodology is not applicable, requiring instead ‘the consistent use of Passive House components in accordance with the requirements for Passivhaus Institut certification of components’.
Box within a box
The innovative timber frame ‘box within a box’ design aids energy efficiency & airtightness strategies on the project by effectively being a newbuild and so avoiding some of the difficulties associated with making older buildings meet exacting Passivhaus requirements, like dealing with thermal bridges in the existing building envelope.The inner timber frame structure has the additional advantage of helping to structurally support the original barn masonry walls, through a purpose-designed wall connector system, which uses specially-developed low thermal conductivity basalt wall ties.
Dealing with moisture issues
The project has been carefully modelled (using WUFI hygrothermal modelling software) to ensure that there will not be moisture movement between the existing masonry walls and the inner timber frame walls. The cavity between the two walls has been well ventilated and the design team is confident that there will not be any moisture ingression into the inner timber wall. For good measure, researchers from the Centre for the Built Environment at Leeds Beckett University are undertaking some research on the project and have sited moisture monitoring equipment at various depths within the walls. This data will also feed into AECB research on post retrofit environmental conditions in a range of constructions, such as behind and within internal and external wall insulation and below suspended timber floors etc. The monitoring data from the Cre8 Barn will help explore the effectiveness of externally ventilated cavities between the existing mass masonry walls and internal wall insulation systems.
Open to the public
The Cre8 Barn, which was funded by a grant of £300,000 awarded by The Veolia Environmetal Trust* through the Landfill Communities Fund as part of its Cre8 project, will be open to the public at various points during the year, including Stirley Community Farm’s Food Festival on 19/10/14 and during the International Passivhaus Open Days in November.
For more information, including a film and a FREE 30+ page technical briefing on all aspects of the Cre8 Barn retrofit, go to: www.greenbuildingstore.co.uk/enerphit.