75 Whitwell Way, Coton - Extension and Thermal Upgrade

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Adding a single-storey extension and applying thermal upgrades to a 1945 council-built semi.
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75 Whitwell Way, Coton - Extension and Thermal Upgrade : Project images

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CO2 emissionsPrimary energy requirement
Energy target
AECB Silver

Energy and fuel use

Fuel use by type
Primary energy requirement
CO2 emissions

Renewable electricity generation This project has used the contributions from renewable electricity generation equipment to either meet the Retrofit for the Future target or otherwise reduce the Primary energy requirement and CO₂ emissions associated with the project.

Measured data from renewable generation is not yet available.

Fuel use

Electricity use 3617 kWh/yr 2200 kWh/yr 1841 kWh/yr
Natural gas use7362 kWh/yr 2000 kWh/yr 2005 kWh/yr
Oil use- - -
LPG use- - -
Wood use- - -
Other Fuel - - -
Primary energy requirement 223 kWh/m².yr 99 kWh/m².yr 88 kWh/m².yr
Annual CO₂ emissions 46 kg CO₂/m².yr 22 kg CO₂/m².yr 19 kg CO₂/m².yr
Annual space heat demand - 25 kWh/m².yr -

Renewable energy

Electricity generationForecastMeasured
Solar PV2500 kWh/yr 2900 kWh/yr
Other Renewables Tech--
Electricity consumed by generation --
Primary energy requirement
offset by renewable generation
19 kWh/m².yr -4 kWh/m².yr
Annual CO₂ emissions
offset by renewable generation
3 kg CO₂/m².yr -3 kg CO₂/m².yr

Calculation and targets

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


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

Project description

Start date02 July 2018
Occupation date
Location Coton Cambridgeshire  England
Build typeMixed
Building sectorPrivate Residential
Property typeSemi-Detached
Construction typeMasonry Cavity
Other construction type50mm cavity in existing walls
Party wall construction
Floor area 78.59
Floor area calculation method Treated Floor Area (PHPP)
Building certification

Project Team

Project lead personBart Hommels
Landlord or ClientBart Hommels
ArchitectECO Design Consultants - Milton Keynes
Mechanical & electrical consultant
Energy consultant
Structural engineerWatson Hallam
Quantity surveyor
ConsultantGreen Building Store - MVHR

Design strategies

Planned occupancyOccupied during upgrade
Space heating strategyWet Underfloor heating from mains gas boiler using weather compensation controls. Low Temperature radiators on first floor.
Water heating strategy210 litre Heat Bank with proportionally controlled solar powered immersion element, with gas boiler backup
Fuel strategyMains gas, Mains electricity
Renewable energy strategy2.88 kWp roof-mounted solar PV array (SSE orientation, 42 deg inclination)
Passive Solar strategyWindow and roof light positions and shading optimised using PHPP
Space cooling strategyMVHR
Daylighting strategyWindow and roof light positions and shading optimised using PHPP
Ventilation strategyMVHR. All windows openable.
Airtightness strategy Extension: all transitions between build elements (walls, floors, roof) taped before wet render/plaster applied.Existing: floor taped to walls. Masonry wet plastered. Masonry in floor voids parge coated where accessible.
Strategy for minimising thermal bridges Continuous insulation kept throughout: EWI joined with extension cavity insulation. EWI to extend 400mm under DPC, limited by footings depth.Trimming of stone cill under entrance door. 50mm celotex perimeter insulation along all walls internally.
Modelling strategyWhole-house PHPP with options report to reach AECB Silver, EnerPhit standards.
Insulation strategy* All floors U=0.11 or better: screed on top of XPS, EPS or Celotex.* All walls U=0.14 or better: 200mm fully filled cavity in extension, 200mm EPS EWI on existing* Ceilings U=0.11 or better through warm roof with 110mm Celotex in between, 110mm over rafters for extension. Existing ceilings: loft insulation (rockwool) to 270mm
Other relevant retrofit strategiesExtension and refurb undertaken under self-management and contributing to the work. Occupation maintained during entire project. Minimising cost of improvements without compromising on quality.Use of low-embedded CO2 building materials where possible: Glulam beam instead of steel, low-CO2 slates for extension roof, wood for external cladding of extension walls.
Contextual information

Building services

Occupancyfamily comprising 2 adults, 1 child
Space heatingA-rated boiler driving underfloor heating directly through weather compensation controller. Separate zone for upstairs radiators.
Hot water210 l thermal store fed by solar energy (PV and immersion element controller) and boiler coil.
VentilationMVHR: Paul Focus 200, Lindab rigid ducting. Installation yet to be completed.
ControlsWeather compensation for boiler with own outside temperature sensor. MVHR with three settings.
CookingA rated induction hob and oven
LightingLED lighting throughout
AppliancesA(+) rated fridge, freezer, dishwasher and washing machine. Latter 2 on timers to make optimal use of solar PV energy.
Renewable energy generation systemRoof-mounted 2.88 kWp Solar PV Array. SSE facing, 42 degree inclination. MCS projection 2550 kWh/yr.
Strategy for minimising thermal bridges

Building construction

Storeys 1
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 -