Bowmans Lea

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A 1978 mid-terrace townhouse in London has become the first certified step-by-step EnerPHit retrofit in the UK. The 3-storey property is both home and project of architect Harry Paticas, of PHT member Arboreal Architecture.Step-by-step EnerPHit is designed to facilitate long-term deep retrofit projects, by planning measures from the outset which will lead ultimately to achievement of all the usual EnerPHit targets, however many years the project may take to complete. Once the first step in the plan has been successfully accomplished, and demonstrable energy savings of a minimum of 20% (easily surpassed in this case) have been achieved, the whole project can be pre-certified.
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Bowmans Lea : Project images

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CO2 emissionsPrimary energy requirement
Energy target

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 - - -
Natural gas use- - -
Oil use- - -
LPG use- - -
Wood use- - -
Other Fuel - - -
Primary energy requirement - - -
Annual CO₂ emissions - - -
Annual space heat demand - 22 kWh/m².yr -

Renewable energy

Electricity generationForecastMeasured
Renewables Technology--
Other Renewables Tech--
Electricity consumed by generation --
Primary energy requirement
offset by renewable generation
Annual CO₂ emissions
offset by renewable generation

Calculation and targets

Whole house energy calculation method PHPP
Other whole house calculation method-
Energy target EnerPHit
Other energy targets-
Forecast heating load -


Pre-development air permeability test--
Final air permeability test--

Project description

StageUnder construction
Start date
Occupation date
Location London London 
Build typeRefurbishment
Building sectorPrivate Residential
Property typeSemi-Detached
Construction typeMasonry Cavity
Other construction typeBrick and block, part cavity wall
Party wall construction
Floor area 1
Floor area calculation method Treated Floor Area (PHPP)
Building certification  Passivhaus certified building Passivhaus certified building

Project Team

Project lead person
Landlord or ClientHarry Paticas
ArchitectHarry Paticas, Arboreal Architecture
Mechanical & electrical consultant
Energy consultant
Structural engineer
Quantity surveyor

Design strategies

Planned occupancy
Space heating strategy
Water heating strategy
Fuel strategy
Renewable energy strategy
Passive Solar strategy
Space cooling strategy
Daylighting strategy
Ventilation strategy
Airtightness strategy
Strategy for minimising thermal bridges
Modelling strategy
Insulation strategy
Other relevant retrofit strategies
Contextual information

Building services

Space heating
Hot water
Renewable energy generation system
Strategy for minimising thermal bridges

Building construction

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