Post Second World War suburban mid terrace house - 80% carbon emission reduction through whole house upgrade approach utilising established and innovative prototype technologies.

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Existing: brick/block cavity walls with cavity insulation and pebbledash; low pitch slate roof Proposed: Cavity walls overclad with insulation and render; Main roof insulation increased to 350mm; Insulation inserted between sloping ceiling rafters plus dry lining; Insulation inserted below living room & hall floors; Triple glazed uPVC windows (whole frame U=1.1); High efficiency gas boiler with flue gas heat recovery serving radiators; LED lights, 50k hours guaranteed max light output; Sun pipe to f/floor landing; Decentralised whole house ventilation; PV-T hybrid thermal panels; Shower water heat recovery; Reduced water consumption; Smoke alarm systems; AA++ appliances; smart metering with display

Retrofit for the future ZA491L
Images Graphs Figures Description Strategies Building

Post Second World War suburban mid terrace house - 80% carbon emission reduction through whole house upgrade approach utilising established and innovative prototype technologies. : 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 2223 kWh/yr 1278 kWh/yr 1839 kWh/yr
Natural gas use15811 kWh/yr 5388 kWh/yr 8807 kWh/yr
Oil use- - -
LPG use- - -
Wood use- - -
Other Fuel - - -
Primary energy requirement 396 kWh/m².yr 157 kWh/m².yr 245 kWh/m².yr
Annual CO₂ emissions 76 kg CO₂/m².yr 31 kg CO₂/m².yr 48 kg CO₂/m².yr
Annual space heat demand - 60 kWh/m².yr -

Renewable energy

Electricity generationForecastMeasured
PV-T equivalent to 2.2kWpPV1083.680054 kWh/yr -
Other Renewables Tech--
Electricity consumed by generation --
Primary energy requirement
offset by renewable generation
112 kWh/m².yr 245 kWh/m².yr
Annual CO₂ emissions
offset by renewable generation
20 kg CO₂/m².yr 48 kg CO₂/m².yr

Calculation and targets

Whole house energy calculation method SAP
Other whole house calculation method-
Energy target Retrofit for the Future
Other energy targets-
Forecast heating load -


Pre-development air permeability test-15.02m³/m².hr @ 50 Pascals
Final air permeability test-9.94m³/m².hr @ 50 Pascals

Project description

StageUnder construction
Start date01 March 2010
Occupation date16 April 2010
Location Dartford Kent  England
Build typeRefurbishment
Building sectorPublic Residential
Property typeMid Terrace
Construction typeMasonry Cavity
Other construction typeCavity insulated; external pebbledash finish
Party wall construction215mm brick plastered both sides
Floor area 60
Floor area calculation method Treated Floor Area (PHPP)
Building certification

Project Team

OrganisationPRP Architects Ltd
Project lead personPRP Architects
Landlord or ClientDartford Borough Council
ArchitectPRP Architects
Mechanical & electrical consultant N/A
Energy consultantPRP Environmental
Structural engineerConnaught Partnerships
Quantity surveyorConnaught Partnerships
ConsultantCDM Coordinator : PRP Project Services
ContractorConnaught Partnerships Ltd

Design strategies

Planned occupancyCurrently two adults and one child with a visiting second child
Space heating strategyGas fired boiler with flue gas heat recovery feeding radiators
Water heating strategySolar hot water with gas condensing boiler back up
Fuel strategySolar thermal hot water with mains gas back up, PV-T panels and mains electricity
Renewable energy strategy2.5sq.m solar thermal / 2.0kWp (16.7sq.m) PV-T equivalent
Passive Solar strategyThe house faces south and has some large windows at first and second floors. Fenestration patterns will change to accommodated larger pane tilt / turn windows and adjustments will be made to glazing g-values to compensate for potential overheating.
Space cooling strategyNatural ventilation via openable windows. Adjustments to glazing g-value to guard against overheating.
Daylighting strategyThe house already has good natural daylight through some large windows. Sun pipes are proposed to supply daylight to the internal landing at first floor level.
Ventilation strategyNatural ventilation via openable windows, plus a decentralised whole house system using continuopusly running low energy fans drawing air out through wet rooms
Airtightness strategy A combination of insulating strategies including overcladding present the opportunity for close fit and well sealed detailing. High performance seals to windows and doors. Draught sealing around the loft hatch. Ventilation equipment checked for air leakage prior to commissioning and careful detailing around socket outlets and other penetrations. Further investigation required around the detail and quality of existing finishes. Instruction to operatives on best practice at contract stage.
Strategy for minimising thermal bridges Minimisation of thermal bridges at design stage by careful detailing of all material and component junctions to ensure continuity of insulation and thermal performance. Continuation of overcladding to ground level or below where possible to protect ground slab edge. Instruction to operatives on best practice and careful monitoring on site during construction.
Modelling strategyWhole house modelling was undertaken using SAP (with NHER Plan Assessor software) in conjunction with the Extended SAP worksheet. AutoCAD produced plans and elevations were used to assist with visualisation and detailed design.
Insulation strategyGround floor - suspended timber - 150mm phenolic foam to U- value 0.17 W/m2K Exposed walls - 150mm Permarock external insulation to U- value 0.12 W/m2K Pitched roof with flat ceiling - -Existing 100mm mineral quilt between rafters increased to 350mm to U- value 0.13 W/m2K Pitched roof with sloping ceiling - 75mm Phenolic foam between rafters, plus 40mm Spacetherm drylining to U- value 0.17 W/m2K Windows - Replacement uPVC triple glazed low-e to U-value 1.1 W/m2K Doors - Replacement uPVC with triple glazed low-e to U-value 1.5 W/m2K
Other relevant retrofit strategiesOur proposals are designed to be carried out with the present resident remaining in occupation. Considering the wider application of Retrofit it will be neither practical nor economically viable on a large scale to decant residents while the work is in progress. Pre commencement discussion and engagement with residents, plus regular monitoring during and after the works, will help to minimise the degree of inevitable inconvenience.
Contextual informationThe location of this terraced house in an area of other similar terraces, most of which are privately owned, has influenced the choice of insulation strategies so that the house does not look strange and remains in character with its neighbours. Were a complete terrace to be upgraded, overcladding to produce a complete image change could be considered.

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