Chester Road Passivhaus
| Location: Stockport | |
| Completion Status: 2021 | Occupancy: 2021 |
| Architect: Roger Burton, nvirohaus | Consultant: Roger Burton, nvirohaus |
| Contractor: MBC Timber Frame | Client: Roger Burton |
| Certification: 2021 | Certifier: MEAD |
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Commended in the UK Passivhaus Awards 2023 in the new build residential category. Designed by Passivhaus Designer & Architect Roger Burton as his own home, the house boasts all-electric heating and benefits from off-site timber frame construction approaches.
The four bed home was built using an off-site timber frame system and clad in locally-sourced larch cladding. Occupying a garden plot, the constraints of the site presented a few challenges. The project is off the gas grid and uses all-electric heating.
Key stats
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Design
The site constraints determined a compact, double aspect plan over two floors. The roof is a combination of pitched and flat, to optimise the performance of the photovoltaic panels.
The rear of the house features a loggia across the full width offering a peaceful relaxing space away from the road, which is open to the late evening summer sun and also provides for clothes drying in wet weather. Timber features strongly in the design, with the adoption of a largely timber construction and locally-sourced timber cladding.
Heating strategy
The design team aimed to reduce heating demand to the point where the heating system can be simplified. The resulting house has no conventional heating system and is off the gas grid. An all-electric home with a substantial part of the hot water needs of the house being satisfied by solar photovoltaics (PV).
The domestic hot water (DHW) demand outstrips that of the heating. A large roof-mounted arrav of solar PVs, 6.6Kwp, has been installed which, with battery storage, is anticipated will satisfy or exceed all of the home’s electrical requirements balanced over a full year.Coupled with a large domestic water storage cylinder, a ‘Solar iBoost’ system diverts solar energy to the hot water demand before export to the grid and thus maximises the capture of solar energy throughout the year. With a much reduced season, space heating is provided by simple, direct electrical heaters using on-site generated energy or from the grid. As an aesthetic feature, the PV panels are “counter sunk” into the roof tile area rather than sitting on top of the tiles.
The design team further sought to reduce resource demand and carbon emissions by employing water efficiency strategies. Compact plumbing design and smaller pipe sizes have been used to reduce draw times, water usage and standing losses.
Ventilation & summer comfort strategy
The house was designed to reduce the heating demand but also aimed to maintain a comfortable temperature in the summer, with Passivhaus Planning Package (PHPP) modelling suggests 0% overheating.
- The principal rooms face the cooler northern side of the house, with a loggia designed over a courtyard garden.
- Glazing to the south is a relatively low ratio of the façade. Overall the glazing is 23.5% of the Treated Floor Area (TFA).
- Night time ventilation (by opening windows on the first floor) has been assumed in the PHPP modelling.
- Provision has been made for the future retrofit of an awning to the southerly ground floor glazing, if required.
A log of room temperatures in the main living area has shown that the PHPP prediction has been largely proven in practice, with 25°C only having been exceeded briefly during July 2021, when the house was not occupied.
Construction
PHT Members MBC Timber Frame were chosen to provide an offsite engineered system which met the desired U-values for the walls, roof and ground floor slab and offering the quality of a product manufactured in a factory environment.
The system includes a thermally-insulated slab for the building to sit on. This raft foundation helps ensure a continuously insulated, cold bridge free thermal envelope. Once the slab was completed, the frame went up in less than two weeks. At a later stage windows and doors were installed and recycled cellulose insulation was blown into the continuous cavities.
Building performance
Overall U-values
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Floor: 0.105 W/m2K EPS raft foundation |
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Wall: 0.10 W/m2K Passive twin wall system, filled with cellulose insulation.
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Roof: 0.12 W/m2K Timber frame, filled with cellulose insulation. |
Designed energy performance
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Airtightness n50 (≤ 0.6ACH @ 50 Pa)
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0.5 @ 50 Pa
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Space Heating Demand (≤ 15 kWh/m².a)
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14 kWh/m².a
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Heating Load (≤ 10 W/m²)
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9 W/m²
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Primary Energy Demand (≤ 120 kWh/m².a)
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102 kWh/m².a
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Primary Energy Renewable Generation
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41 kWh/m².a
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Costs
The estimated construction cost of the project is around £1882/m2 and based on the design calculations, it is predicted that the running costs for 2022 will be in the region of £3.08/m2/a.
Challenges
The site constraints affected the home's form factor, orientation and determined a compact, double aspect plan for the house over two floors with a ratio of width to depth of around 3:2.
Lessons learned
- The project benefited from adopting off-site factory based construction in terms of both quality build and timescale, The insulated floor slab and superstructure were constructed and erected in a little over three weeks.
- The project set out to test the theory that a conventional heating system might be eliminated, along with its inherent lifetime costs. This was achieved using all-electric convector heating and solar PV panels. A future project undertaken by the project team is aiming for a larger PV array to be provided (c. 10 kWp), with a relatively larger battery of around 10 kWhrs to maximise the renewable energy consumed in the house before export. The heating system for the new project is proposed to use electric radiant panels instead of electric convectors.
Key team
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Further information
Roger Burton - MBC Timber Frame case study
Passivhaus overlay for the RIBA plan of work
Passivhaus benefits guide & costs research
