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As a newly-retired couple, the Youngs were keen to reduce the cost of heating and maintaining their home. After looking at several renewable and energy-saving sources, they felt it was time to downsize to a more energy-efficient dwelling. Mrs Young comments: “Our home was a vast, early Victorian house with several large rooms, high ceilings and fine sash windows. Although it was a beautiful home, with an elegant garden, it became increasingly costly to run and maintain. After retirement, we felt the need to plan for the future in a smaller and more energy efficient home.”
The couple had attended a presentation at the local Rotary Club about the past and future domestic architecture of Norfolk. It was here that Chris Parsons of Parsons + Whittley Architects introduced the future concept of Passivhaus. Re-iterating the principles, Chris explains: “Passivhaus is the foremost low energy and comfort standard delivering buildings that require very small amounts of space heating, whilst maintaining a very comfortable environment.
“Delivered through five principles of insulation, reducing thermal bridges, low air leakage, mechanical ventilation with heat recovery and modeling internal heat gains means that properties can remain comfortable for around 20% of the typical energy use of alternative modern homes.”
“The future Passivhaus concept outlined by Chris seemed to meet our needs in terms of a flexible build with extremely high energy efficiency,” comments Mr Young.
In order to reach a final decision on their build, the couple visited one of England’s first Passivhaus homes in Denby Dale. This confirmed their view that they would aim for a fully certified Passivhaus.
Build challenges
As the Youngs were fortunate to have a sizable garden with their property, the new home could be built on a part of the existing land. This meant the couple could stay in the community and enjoy their retirement.
The site itself, however, was not particularly large and it was dominated by a protected lime tree. This posed several challenges in the design stage, as Chris explains: “The protected lime tree dictated the form of the dwelling, being an annular segment centred around the tree, with the main garden space forming the tree’s root protection area. The shape in turn led to the resolution of the form, adopting a sloping monopitch roof, again centred on the protected tree.
“In addition to coping with the tree, ground conditions meant we had to use a piled concrete raft as both foundation and floor slab, and if that wasn’t enough, the site had a fairly restricted access.”
In total, the project took 28 weeks to complete. Three weeks of the build were spent constructing the inner aircrete shell. In order to help meet the Passivhaus standard, H+H’s Celcon Blocks were specified. Despite it being the first Passivhaus project for contractor Grocott and Murfit, the project team was confident all Passivhaus boxes were ticked with the H+H Celcon Block Standard Grade for the internal leaf and external leaf to the timber boarded elevations on the structure.
Speedy construction
Having looked at other alternatives, the contractors opted for H+H products due to their delivery time, speed of construction, stability and thermal mass. Faced with both brick and timber, the bungalow has an external U-value of 0.096W/m²K for the timber faced walls and 0.098W/m²K for the brick faced walls. H+H’s Celcon Block Standard Grade is a key contributor to achieving these results with a thermal conductivity of 0.15W/m²k.
Speaking of the product, Dan Higginbotham of Parsons + Whittley comments: “H+H provided us with advice on block types and their suitability for this Passivhaus project. Compared to a timber frame solution, the H+H products allowed for a faster build process, enhanced stability and better thermal mass qualities allowing us to reach Passivhaus standards. This was the preferred building material for the contractors at Grocott and Murfit whose previous experience and desire to build again using H+H aircrete was the reason we opted for the H+H solution.”
The choice of doors and windows was also instrumental in meeting the standards of Passivhaus, as Chris Parsons explains: “The doors and windows have a schizophrenic role in Passivhaus being both heat emitters and heat gainers. As a consequence, their performance is critical to the success of Passivhaus, as is their size and placement, all of which is modelled at the Passivhaus design stage.
Passivhaus performance
“In this instance we used an aluminium/timber composite window, manufactured by Internorm and supplied by Ecohaus Internorm, who are experts at delivering high performance products for Passivhaus performance.”
In spite of the challenges it posed throughout the initial design stage, the lime tree actually tackled the potential issue of overheating. “As with all good design, constraints became opportunities,” says Chris. “In Passivhaus design, it is important to provide summer shading to avoid overheating. We quickly realised that our protected tree was ideal for that purpose, providing shade when in leaf in the summer months, but allowing the sun’s heat through the main windows in winter when the leaves had fallen.”
Other key, and unique, elements of the project comprise the curved, sloping roof and larch cladding which together wrap around the lime tree. “The shape dictated the need for a roofing material that could cope with the circular slope so this led to the consideration of a standing seam zinc solution, with complementary zinc rainwater goods,” explains Chris.
“The tree and semi-woodland setting suggested the use of larch timber cladding on the inner faces, whilst the additional height of the taller north and east walls, as well as providing shelter, warranted a more robust solution leading to a brick facade in those locations.”
Satisfied customers
For the Youngs, their primary vision has been realised – a highly energy efficient and manageable home from which they can enjoy their retirement. Achieving an energy efficient home was the couple’s main concern, however the final structure has added a whole new dimension to the couple’s home and contributed significantly towards their satisfaction of the project, as Mrs Young elaborates: “Initially the actual design seemed to be of secondary concern, but now that we are in the house we can at last fully appreciate the high quality of the design.
“The curved outline may have been a pragmatic response to the lime tree but it has given our home a pleasingly embracing, unique building. The design details such as the sloping zinc roof, the bold windows and the clean internal lines with wonderful lighting, have created something we are delighted with and very proud of.”