Conservation Area retrofit

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The project is to retrofit a mid-terrace Victorian house in a Conservation Area. The residents are to be occupation throughout. The proposal is to internally insulate most of the walls with aerogels, with the exception of the ground floor kitchen extension, which will be externally insulated. Air permeability will be improved to 5 m3/m2/hr. The space heating will be provided by an efficient gas boiler. Water heating will be delivered by a solar thermal system with a heat pump recovering heat from an integrated Passive Stack Ventilation system. Electricity will be provided by Solar PV and demand will be reduced by installing energy efficient appliances and low energy lighting.

Retrofit for the future ZA234Y
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Conservation Area retrofit : Project images

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CO2 emissionsPrimary energy requirement
Energy target
Retrofit for the Future

Energy and fuel use

Fuel use by type
Primary energy requirement
CO2 emissions

Measured data from renewable generation is not yet available.

Fuel use

Electricity use 1097 kWh/yr 1017 kWh/yr 1324 kWh/yr
Natural gas use25810 kWh/yr 4076.3 kWh/yr 2860 kWh/yr
Oil use- - -
LPG use- - -
Wood use- - -
Other Fuel - - -
Primary energy requirement 535 kWh/m².yr 119 kWh/m².yr 109 kWh/m².yr
Annual CO₂ emissions 98 kg CO₂/m².yr 24 kg CO₂/m².yr 23 kg CO₂/m².yr
Annual space heat demand - 43 kWh/m².yr -

Renewable energy

Electricity generationForecastMeasured
Photovoltaics530 kWh/yr -
Other Renewables Tech--
Electricity consumed by generation --
Primary energy requirement
offset by renewable generation
97 kWh/m².yr 109 kWh/m².yr
Annual CO₂ emissions
offset by renewable generation
19 kg CO₂/m².yr 23 kg CO₂/m².yr

Calculation and targets

Whole house energy calculation method PHPP
Other whole house calculation methodSAP Extension for Whole House. Performance estimates made with Extended SAP are based on the weighted average of two simulations
Energy target Retrofit for the Future
Other energy targets-
Forecast heating load 30 W/m² demand


Pre-development air permeability test-16.77m³/m².hr @ 50 Pascals
Final air permeability test-5.92m³/m².hr @ 50 Pascals

Project description

StageUnder construction
Start date02 August 2010
Occupation date02 August 2010
Location London London  England
Build typeRefurbishment
Building sectorPublic Residential
Property typeMid Terrace
Construction typeSolid Brick
Other construction type
Party wall constructionSolid Brick
Floor area 60.66
Floor area calculation method Treated Floor Area (PHPP)
Building certification

Project Team

Project lead personNic Wedlake - Peabody
Landlord or ClientPeabody
ArchitectFeilden Clegg Bradley Studios LLP
Mechanical & electrical consultant Max Fordham Consulting Engineers
Energy consultantRickaby Thompson Associates
Structural engineerTBC
Quantity surveyorTBC
ContractorWates Living Space

Design strategies

Planned occupancyTwo residents currently live in the house and the occupancy will remain the same during and after works. Both residents go out to work, but occasionally work from home.
Space heating strategyThe space heating strategy is to reduce heat losses to a level at which they can largley be satisfied by the internal and solar gains, especially in spring and autumn. Heat gains will be recovered by a heat pump from the ventilation exhaust, and redistributed via a thermal store that will also be used for water heating. Heat distribution will be via the existing radiators.
Water heating strategyHot water will be provided by roof-mounted solar collectors supplying heat to the thermal store. The store will also receive recovered internal heat gains, via the heat pump. When the temperature of the store is not high enough a small gas-fired combination boiler will be used to raise the temperature of the water to the required level.
Fuel strategyThe house has an existing gas supply. The proposed system will be largely electric, making use of a heat pump and solar photovoltaics, but a small gas-fired combination boiler will be used to bring the domestic hot water to the required temperature when necessary.
Renewable energy strategyThe house will make use of roof-mounted solar thermal collectors to satisfy approximately 50% of the hot water demand. Photovoltaic (PV) panels will be used to offset the electricity demand.
Passive Solar strategyThe project team has adopted a variant of the PassivHaus strategy, rather than a passive solar strategy. This makes the design substantially independent of orientation, which will be an advantage for replication of the improvements on this large estate and elsewhere.
Space cooling strategyNo cooling is proposed. The assisted passive stack ventilation system will operate year-round, and will be supplemented in summer by the occupants opening the windows. Upstairs windows will be opened on warm summer nights to counter overheating.
Daylighting strategyAlthough the existing windows will be replaced, no change is proposed to the daylighting of the house.
Ventilation strategyThe house will be equipped with an assisted passive stack ventilation system (with very low fan power). Supply air will be provided by humidity-sensitive trickle ventilators in window heads, and/or wall ventilators. Internal heat gains will be recovered from the passive stack by means of an electric heat pump, which will supply heat to a thermal store for space and water heating.
Airtightness strategy The target air permeability for the house is less than 5 m3/m2/hr @ 50 Pa; this is the best standard of air-tightness that the project team believes is realistically achievable for this old, solid-walled building. Air tightness will be achieved through careful attention to detailing and to construction on site. Particular attention will be paid to the continuity of the air barrier at corners and junctions between building elements. Where internal insulated dry-linings are installed internal electrical wiring, sockets, switches, etc, will either be relocated on internal walls or accommodated in wiring voids inside the air-tight membrane.
Strategy for minimising thermal bridges Thermal bridging will be minimised through careful attention to detailing and to construction on site. Critical details will be analysed usng Therm software to ensure an appropriate and cost effective approach. Internal insulated linings on external walls will be returned at least 600 mm along party walls. Subject to Therm analyses, consideration will be given to supporting the suspended floors internally and cutting off the ends of existing timber joists that bridge the internal insulated linings.
Modelling strategyThe performance of the house has been modelled using PHPP and Extended SAP, and the performance predictions below are based on the PHPP analysis.
Insulation strategyThe house will be insulated towards PassivHaus standards. External walls will be insulated internally using Spacethem aerogel-based lining boards, except for the single-storey kitchen wing at the rear, which wil be insulated externally. Loft insulation will be substantially increased. The suspended timber ground floor of the main house presents a challenge: the floor void will be filled with injected graphite-coated 'sticky bead' EPS insulation. Except on the front eleveation, windows will be replaced with new proprietary high-performance, triple-glazed low-emissivity argon-filled units. On the front elevation new double-glazed high-performance windows will be purpose-made to match the appearance of the existing windows.
Other relevant retrofit strategies
Contextual information

Building services

Space heatingNULL
Hot waterNULL
Renewable energy generation systemNULL
Strategy for minimising thermal bridgesNULL

Building construction

Volume -
Thermal fabric area -
Roof description NULL
Roof U-value 0.00 W/m² K
Walls description NULL
Walls U-value 0.00 W/m² K
Party walls description NULL
Party walls U-value 0.00 W/m² K
Floor description NULL
Floor U-value 0.00 W/m² K
Glazed doors description NULL
Glazed doors U-value 0.00 W/m² K -
Opaque doors description NULL
Opaque doors U-value 0.00 W/m² K -
Windows description NULL
Windows U-value 0.00 W/m² K -
Windows energy transmittance (G-value) -
Windows light transmittance -
Rooflights description NULL
Rooflights light transmittance -
Rooflights U-value 0.00 W/m² K