With obsessive attention to preserving and restoring the original fabric of these two Victorian townhouses, and a commitment to shunning petrochemicals and using only natural materials, could this be the most wildly ambitious and sustainable passive retrofit ever undertaken in the UK?
Deep ecological retrofit of two Victorian townhouses
Completed: Autumn/winter 2018
Standard: Enerphit Plus
-£43 per year (estimated total energy costs)
This Victorian property in the centre of Chorlton had spent many years serving as 5 apartments. During this time many original features had been lost. The proposal is to return to the original use of two semi-detached homes and reinstate the beautiful original façade.
Beyond the traditional detailing is a modern eco-home which has been designed to go beyond the EnerPHit standard and create a home that has energy bills of less than £100 per year. This will be achieved through high performance windows, extremely high levels of air tightness and insulation, MVHR and clever detailing to avoid cold bridging. The exterior is renovated with new robust materials such as copper gutters to reduce maintenance and increase longevity. Adding to this a complete renewal of the interior finishes with environmentally friendly petrochemical free materials two sustainable 5 bedroom luxury homes are created.
Building type : Two Victorian semi-detached homes built in 1894, combined internal floor area of 374.3 m² (187 m² per house)
Budget: £1.9 million
Certification: Enerphit Plus certified (the two combined dwellings certified as one building, party wall not thermally insulated)
Space heating demand (after): 12.5 kWh/m2/yr
Heat load (after): 10.4 W/m2
Primary energy demand (after): 99.6 kWh/m2/yr
Renewable energy demand: 41.6 kWh/m2/yr
Overheating (PHPP): 0%
Energy bills (estimate, per house): Total space heating demand of 2,346 kWh according to PHPP. This is to be met using a combination of wood burning stove & excess PV electricity to post heater in the MVHR system.
Electricity demand of 2,039 kWh per year (PHPP). To be met from solar PV system & grid electricity.
Hot Water of 1,864 kWh per year demand (PHPP). To be met from solar PV system & grid electricity.
Biomass costs approximately £80 per cubic metre for unstacked logs. Assuming this amount is burnt each year, and each cubic metre provides 1,950 kWh (2,600 kWh burnt at 75% efficiency), remaining space heating demand after logs are burnt is 396 kWh, to be provided by electric post heater to MVHR system.
Electricity consumption remaining for space heating, water heating & electrics is 4,299 kWh per year. The solar PV system generates 4,370 kwh per year, and assuming 80% utilisation & 20% export of this, the house uses 3,496 kWh solar electricity per year. This leaves 803 kWh per year required from the grid.
The house’s Tonik renewable energy tariff is 12.68p per kWh plus a £73 standing charge, for an estimated annual electricity bill of £175. Adding the cost of biomass at £80, gives a total annual energy bill of £255.
However, the house receives a renewable energy feed-in-tariff of £172 + £45 for 20% PV export to grid (£217). This leaves an annual energy bill of £37. In reality one cubic metre of wood could easily be sourced for free, which would leave an annual profit on energy costs of £43.
Airtightness (at 50 Pascals): 0.9 ACH (working towards 0.6 currently) Please note there were 20 different U-values for opaque building elements on this project and the following are just some of the main elements.
Front walls: Storm dry brick cream on 110mm Victorian facing brick externally, followed inside by 38mm cavity, 13mm Fermacell board, 145mm timber I-joists fully filled with Steico floc blown cellulose, 80mm Steico Protect Dry wood fibre insulation, 10mm Thermalime plaster. U-value: 0.175 W/m2 K
Side walls: 14mm Thermalime render on 80mm Steico Protect Dry externally, followed inside by 240mm Steico floc blown cellulose between Steico I-joists, 250mm double layer of Victorian wire cut bricks with finger cavity, 10mm Thermalime plaster internally. U-value: 0.116 W/m2 K
Rear walls (ground floor): Organowood cladding externally followed inside by 1mm façade membrane, 300mm timber I-joists fully filled with Steico floc blown cellulose, 1mm Proclima Intello or Siga membrane, 13mm gypsum plasterboard. U-value: 0.132 W/m2 K
Rear walls (upper floors): Organowood cladding externally followed inside by 1mm façade membrane, 300mm timber I-joists fully filled with Steico floc blown cellulose, original nine-inch brick walls, lime plaster. U-value: 0.125 W/m2 K
Floors (after): 22mm Reclaimed pine chevro with lime-based grouts & adhesives, followed below by 18mm Magply magnesium board, 1mm Proclima Intello or Siga membrane, 175mm Steico floc blown cellulose & floor joists, 80mm Steico protect dry. U-value: 0.165 W/m2 K
Roof (after): Welsh slate externally on 50x35 battens/counter battens, followed underneath by 1mm breathable roofing membrane, 60mm Steico Special Dry wood fibre board, 145mm to 300mm timber I-joists fully filled with Steico floc blown cellulose, 75mm rafters fully filled with Steico floc blown cellulose, 1mm Pro Clima Intello or Siga membrane, 13mm gypsum plasterboard U-value: 0.108-0.148 W/m2 K
WINDOWS & DOORS
Before: PVC 1980’s double glazing. Overall approximate U-value: 3.0 W/m2 K
After: Viking Windows AS SW14 & DK88 triple glazed timber windows: U-value of 0.68 W/m2 K (uninstalled), SW14 and DK88 doors: U-value of 0.72 W/m2 K (uninstalled)
Roof windows: Fakro U8 thermally broken triple glazed roof windows with thermally broken timber frames. Overall U-value: 0.81 W/m2 K
Before: Gas boilers and radiators
After: 2kW electric post heater on Paul Novus 300 MVHR system, DiBT accredited Wiking log burning stove. Domestic hot water electrically heated in Mixergy 300L tank. Electricity fed from PV on roof.
Before: No ventilation system.
After: Paul Novus 300 heat recovery ventilation system. 93-94% heat recovery (PHI certified)
Green materials: Wood fibre and cellulose (recycled newspaper) insulation; lime plaster/ render; timber frame hybrid construction; breathable magnesium construction boards; breathable flooring materials: Tuscan marble, hardwood; copper detailing for ultra-durable rainwater and coping goods; FSC certified hardwood cabinetry; Welsh slate kitchen worktops; CO2 absorbent lime-graphene paint by Graphenstone.
Electricity: 60 square metre solar PV array across the two properties. Comprising 36 x 330-Watt Panasonic HIT modules over two systems. Each system being 18 modules, and with each module having a Tigo voltage optimiser connected to efficiently manage any shading effects, and to maximise the total output of the systems. The total installed capacity is 11.88kWp. Each 18-module system has been wired in two strings, one string of 11 modules (3.63kWp) and one string of 7 modules (2.31kWp). This configuration is to allow the later addition of on-site energy storage. A Solar IBoost water heater controller is also installed on each system. These controllers monitor the electricity consumption in the house and as soon as any of the PV generated electricity is not being used and begins to export, this PV electricity will be diverted into a circuit of choice. In Zetland Road this circuit of choice is an immersion heater in the hot water cylinder. As the two houses consume so little electrical energy, a large proportion of domestic hot water will be generated from using PV electricity.
Selected project details
Developer, contractor, project manager, M&E engineer & passive house consultant: Ecospheric (Kit Knowles)
Architecture: Guy Taylor Associates and Ecospheric
Civil & structural engineer: Studio One Consulting
Passive house certifier: MEAD: Energy & Architectural Design
Electrical contractor: Environmental Building Services Ltd
Airtightness tester: Ritchie & Ritchie
Airtightness contractor: Ecospheric and ColdProof
Wall, roof & floor insulation & build
system: Steico UK
Thermal breaks: Schöck Ltd
Airtightness products: Ecological Building Systems / Siga
Windows & doors: Viking, via Ecospheric Windows & Doors Ltd
Roof windows: Fakro, via JJ Roofing Supplies
Organowood cladding: Ecochoice Ltd
Kitchen fit-out: John George Fine Cabinetry
Magply: IPP Ltd
Roofing: SIG Roofing
Permeable paving: Sudstech
MVHR: Paul, via A+ Ventilation supplies
Wood burning stove: Wiking, via Woodburner Warehouse
Domestic hot water system: Mixergy
Solar PV: Environmental Building Services Ltd
Water saving toilets: Caroma, via Sanlamere
Water saving fittings: Bristan, via Grahams Plumber Merchant
Cast-iron bath: Cast Iron Bath Company
Paint: Ecosphere, via the Graphene Company
Heritage lime plaster: Mike Wye & Associates