Future-proof Passivhaus homes in Harpenden
The suburbs of Harpenden are becoming an unexpected haven of eco homes and home to a growing number of pioneering Passivhaus schemes. The Deerings, certified in 2017, set Passivhaus in motion for Harpenden, with projects in the local area now proving more ambitious for both new build and retrofit.
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New build: Brambles Passivhaus Plus
Brambles is a detached 3-bed home completed and certified in 2020. The all-electric home harnesses addtional renewable energy through solar PV and a reversible electric heat pump. Per square metre, Brambles saves 80% energy compared to a typical UK home.
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Brambles use so little energy, that it generates 3x more over a year than it imports from the grid. This house demonstrates how we can build today to meet the ecological imperatives of our time. It will protect against a changing climate and will last several times longer than a power station. As such it will be a gift to future generations, not a liability.
Bere Architects
Key stats
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Construction
The home is constructed using a UK-manufactured frame made from Swedish engineered timber beams filled with cellulose insulation, chosen for its non-toxic properties.
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Floor Concrete slab (150mm) power floated and polished as finished floor EPS insulation (400mm)
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Wall Timber frame with cellulose insulation (310mm) Mineral wool insulation (100mm) Scottish larch rain screen cladding
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Roof Plasterboard ceiling, mineral wool insulation (45mm) Vapour barrier board (12mm), Timber frame with cellulose insulation (400mm) Multi-ply bituminous membrane roof.
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Predicted energy performance
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Airtightness |
0.3ach @ 50Pa |
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Thermal Energy demand |
13 kWh/m2.yr |
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Primary Energy demand |
129 kWh/m2.yr |
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Primary Energy Renewable |
34 kWh/m2.yr |
Key team
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Retrofit: Harpenden EnerPHit Plus
Originally a leaky 1960’s detached dwelling, the existing 4-bed family home was retrofitted into an EnerPHit Plus in November 2021. As with an EnerPHit classic, the project prioritises a fabric-fist approach to drive down energy demand, but also includes additional renewable energy generation. The home produces as much energy as the occupants consume and provides enough energy to operate the building throughout the whole year.
Retrofitting has cut our energy bills by 90 per cent. We have so much floor insulation we only need a very low level of underfloor heating, which is programmed to come on for just four hours at night when it’s cheapest. We don’t need any heating from late March until November. The standard appreciation on this house since we bought it would make it £1.3 million, but because of the retrofit it has been valued at £1.6 million. Estate agents have been asked if there are any houses like ours on the market.
The client, Harpenden EnerPHit Plus
Key stats
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Construction
Despite the challenges of retrofitting in a conservation area, the scheme successfully demonstrates the feasibility of achieving deep retrofit in keeping with the local vernacular. The existing structure consisted of cavity brick/ block flank walls which was externally insulated, with the original infill structure to front and back was replaced with site constructed timber insulated framing. As part of the summer comfort strategy, triple glazed windows include integrated blinds on southside of scheme. The ground floor was also replaced with a new insulated slab.
Floor |
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New floor slab in main house:
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New floor slab to rear extension:
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Wall |
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Retrofitted Wall:
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New Wall:
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Roof |
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Retrofitted pitched roof:
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Flat roof to extension:
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Predicted energy performance
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Airtightness |
0.6ach @ 50Pa |
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Thermal Energy demand |
23 kWh/m2.yr |
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Primary Energy demand |
84 kWh/m2.yr |
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Primary Energy Renewable |
35 kWh/m2.yr |
Key team
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Environmentally conscious clients were keen to give their 1970’s property a new lease on life through a holistic retrofit, and in the process, use their experiences to increase awareness among others. The main challenges of the project were to create an acceptable scheme in a conservation area, that aesthetically works in a row of almost identical houses. Harpenden EnerPHit Plus was the first Passivhaus project by the practice. It was also the contractor’s first retrofit project. Since this project, the practice has been working on several retrofit and Passivhaus projects.
Heather McNeil, Project Architect & Passivhaus Designer, AD Practice
Raising the bar for future-proof homes in Hertfordshire, these schemes are prime examples of self-build Passivhaus in the UK, providing optimum comfort and value, whilst driving down energy usage and fuel bills.
Feeling inspired? Discover more Passivhaus self-build schemes here. If you are interested in experiencing Passivhaus first-hand, the Passivhaus Open Days return this winter and offer an invaluable opportunity to experience Passivhaus projects for yourself!
Further information
Passivhaus Open Days 2022: Winter Edition
Brambles - iPHA Conference 2021
Harpenden EnerPHit Plus: 'Retrofitting has cut our energy bills by 90 per cent' - The Times
A beginner's guide to the Passivhaus Standard
1st October 2022
Get involved with the UK Passivhaus community
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