Next-gen cavity wall Passivhaus at Kirkburton
A self-build garden plot home nestles neatly amongst its neighbouring buildings through its flat roof design and use of local Yorkshire vernacular construction. It is one of a handful of UK Passivhaus schemes opening its doors to coincide with the 2021 UK Passivhaus Open Days.
PHT Patron Green Building Store led the Design & Build project, with its construction division working alongside PHT member Derrie O’Sullivan Architects and Passivhaus consultants PHT member Enhabit. The new-build home is a further evolution of Passivhaus projects using cavity wall construction built by the local design team.
The clients are keen gardeners who wanted a design that made the house feel part of the garden. The ‘upside-down house’ design took advantage of views with the location of the living space upstairs. For privacy from neighbouring properties, a flat roof was adopted.
Key Stats
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.jpg "Kirkburton Passivhaus, Image credit: Green Building Store") |
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Winter in the house was brilliant – that constant warmth that we’d felt at Denby Dale all through the house. We love the big windows and views of our garden, the clean air supplied by the MVHR system. The house is incredibly peaceful and quiet, with noise blocked so well from the outside sometimes we can’t hear the local church bells chime!
Occupant feedback, April 2021
A simple form, contemporary design with large-glazing and shading balconies in steel and timber use Yorkshire stone that harmonises with the traditional character of neighbouring buildings on the edge of the conservation area. The rectangular shape works well with the Passivhaus target, and fabric-first energy efficiency was a key focus.
Construction
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Wall Mineral wool insulation in cavity wall U-value: 0.118 W/(m2K) Floor PIR insulation on floor slab with screed on top, U-value: 0.106 W/(m2K) Roof Flat roof with plywood and PUR insulation U-value: 0.105 W/(m2K) |
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Building upon the project team’s previous cavity wall Passivhaus projects, Denby Dale and Golcar Passivhaus, the team wanted to improve the installation time for windows and doors within cavity walls. They wanted to explore the limits of thermal bridges at the window junction while still achieving Passivhaus certification. For cost and aesthetic purposes, the window detailing was simplified. It increased the thermal bridging and psi values which required designing some negative psi values on other junctions.
Previous strategies have involved locating the windows in the centre of the cavity, using plywood boxes for structural support and airtightness and bespoke aluminium cavity closers to cover the external gap. Putting the windows in the middle of the cavity minimised the thermal bridges and improved the psi values at these junctions.
At Kirkburton, the windows and doors were located further to the exterior, aligned against the stone-outer-leaf of the cavity wall. Placing the windows and doors next to the stonework worsened the thermal bridging and Psi values of the installation. However, it was modelled carefully in PHPP. Even with this detail, the project could still achieve Passivhaus certification without the need to increase the insulation specification from the most cost-effective mineral cavity wall insulation (with a lambda value of 0.037 W/mK), helping with the project team’s efforts to ‘value engineer’ the project.
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This new detail made it much easier to install. The team reduced installation time without the need for supply and installation of aluminium cavity closers - It meant that they could reduce costs, both by cutting out the material costs of supply of the external cavity closers, and saving on installation.
The project developed some new detailing at the foundation level and a flat roof, offering additional detailing examples for Passivhaus cavity wall construction.
Energy performance
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Airtightness (≤0.6ACH@50pascals) |
0.42 ACH@50pascals |
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Thermal Energy Demand (≤15kWh/m².yr) |
15 kWh/m².yr |
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Thermal Energy Load (≤10kWh/m².yr) |
11 W/m² |
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Primary E Demand (≤120kWh/m².yr) |
114 kWh/m².yr |
Low carbon heating options were initially explored, but a gas heating system was installed.
Lessons learned
During the project’s construction, it became clear that there was a greater potential risk for overheating than had first been modelled due to changes in shading guidance within PHPP. The team addressed this with a more robust shading strategy. Not all elements of the summer comfort strategy had been finalized with the clients before handover, so the first summer in the house did experience overheating.
The summer was challenging at times, but the large external blind, which is now automatic, plus the opening windows and the door onto the balcony, meant it was always comfortable. Good shading solutions are something that all Passivhaus dwellers need to consider carefully. We are lucky to have an upside-down house, so our bedrooms are on the ground floor and therefore cooler.
Occupant feedback, April 2021
It would have been preferable if the summer comfort strategy was agreed upon earlier with clients in the design. The project team might have pushed more on low carbon heating options, such as an air source heat pump.
Bill Butcher, Director of Green Building Store & Project Leader
Key teamClient: Private Architect: PHT member Derrie O’Sullivan Architects Contractor: PHT Patron Green Building Store Consultants: PHT Patron Green Building Store + PHT member Enhabit Passivhaus Certifier: WARM |
We are proud of our third certified Passivhaus in the Huddersfield area. The building team have got Passivhaus under their skin now and, it is second nature. We see the building team as operating our low energy building laboratory, and it was good to try out new ways on installing windows and improving on the Passivhaus cavity wall methodology at the Kirkburton project.
Bill Butcher, Director of Green Building Store & Project Leader
Do not miss the chance to visit! The scheme is generously opening its doors this November, exclusively to students, the day after the 2021 International Passivhaus Open Days.
All photos and images credited to: Green Building Store
Further information
Passivhaus Open Days 2021: Winter edition
Kirkburton: Phase I Submission Slides - 2021 UK Passivhaus Awards
1st November 2021
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