Retrofitting a post Decent Homes Standard, timber frame property to reach one-eighth of the existing energy use and carbon emissions.

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Fabric first retrofit of mid terraced 1970s timber framed dwelling, using innovative materials such as aerogel insulation, and technologies such as a compact service unit and waste water heat recovery system. Thermal bridging and airtightness will be radically improved in line with Passivhaus principles.

Retrofit for the future ZA564Y
Images Graphs Figures Description Strategies Building

Retrofitting a post Decent Homes Standard, timber frame property to reach one-eighth of the existing energy use and carbon emissions. : 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 - 3850 kWh/yr -
Natural gas use- 295 kWh/yr -
Oil use- - -
LPG use- - -
Wood use- - -
Other Fuel - - -
Primary energy requirement - 115 kWh/m².yr -
Annual CO₂ emissions - 27 kg CO₂/m².yr -
Annual space heat demand - 15 kWh/m².yr -

Renewable energy

Electricity generationForecastMeasured
Renewables Technology--
Other Renewables Tech--
Electricity consumed by generation --
Primary energy requirement
offset by renewable generation
115 kWh/m².yr -
Annual CO₂ emissions
offset by renewable generation
27 kg CO₂/m².yr -

Calculation and targets

Whole house energy calculation method OTHER
Other whole house calculation methodBoth SAP and PHPP modelled. SAP extension - Total PE consumption = 120kWh/m2/yr. SAP extension - CO2 Emissions = 19 kgCo2/m2/
Energy target Retrofit for the Future
Other energy targets-
Forecast heating load 26 W/m² demand


Pre-development air permeability test-6.37m³/m².hr @ 50 Pascals
Final air permeability test--

Project description

StageUnder construction
Start date01 July 2010
Occupation date01 January 2011
Location Hailsham East Sussex  England
Build typeRefurbishment
Building sectorPublic Residential
Property typeMid Terrace
Construction typeSoftwood frame
Other construction typePartially tile hung
Party wall construction
Floor area 87
Floor area calculation method Treated Floor Area (PHPP)
Building certification

Project Team

OrganisationHome Group Ltd
Project lead personLen Davies
Landlord or ClientHome Group ltd
ArchitectHome Architects
Mechanical & electrical consultant
Energy consultantBRE
Structural engineer
Quantity surveyor

Design strategies

Planned occupancy
Space heating strategyAir heating from compact service unit - integrated system that combines an air source heat pump, mechanical ventilation with heat recovery, and a thermal store.
Water heating strategyFrom compact service unit
Fuel strategyElectric
Renewable energy strategyNone
Passive Solar strategyMaximisation of gains via internal layout remodelling. Triple glazed windows primarily selected for heat retention, although g-value is reasonable allowing good solar gains to be made.
Space cooling strategyPassive cross ventilation; secure lockable night time ventilators will also be supplied.
Daylighting strategyFull daylighting audit and calculations to accurately specify required lighting levels. Internal layout remodelling to remove existing obstructions and facilitate light penetration within the dwelling. Light coloured decoration and finishes to aid light reflection around internal spaces.
Ventilation strategyMechanical ventilation with heat recovery
Airtightness strategy Comprehensive airtightness audit coupled with multiple air tests and smoke pencil diagnostics. Airtight membrane to walls, fully lapped with new DPM in replacement floor. Sealing to all surfaces and penetrations. Target to achieve 5m3/hr.m2
Strategy for minimising thermal bridges Installation of roof, wall and floor insulation at the internal surface ensures near continuous insulation at wall/ceiling and wall/floor junctions. Internal and external reveal insulation will minimise thermal bridging around openings. The most significant thermal bridges are at internal walls and the upper floor plate. These have been individually estimated by calculation within PHPP, then converted back into a global bridging value. The result is slightly better than y=0.04. As the project enters the next phase we will undertake full numerical thermal bridge modelling to accurately calculate individual psi values, and to effectively target the proposed remedial measures.
Modelling strategyFull SAP and PHPP calculations were carried out, including PHPP overheating calculation (0% risk). Retrofit for the Future extension spreadsheets were utilised to include appliances/cooking etc.
Insulation strategy80mm Spacetherm aerogel insulation board to walls; dedicated PU loft boards over 50mm mineral wool in roof void to maintain storage capacity, excavation and rebuild of solid floor incorporating 240mm PU below screed, to maintain thermal mass. Excellent bridge detailing in line with Passivhaus principles (see section above). Triple glazed windows and thermally efficient doors.
Other relevant retrofit strategiesShowersave waste water heat recovery system will be installed. Savings has been appraised via SAP Appendix Q scheme.
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