A2 Dominion- Northholt,

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This typical semi-detatched property has poor orientation for exploiting solar gain and the residents will remain in their home during the works, making this a particularly hard to treat property. The rewards however are great, with approx 5.9 million semi detatched properties in England which could be treated similarly. We aim to deliver a highly cost effective and replicable solution, using innovative solutions such as the solar shed , blown underfloor insulation, cork external insulation and bio-foam loft insulation in a holistic design approach. The proposals have been detailed and specified with a strong emphasis on UK based expertise and technologies.

Retrofit for the future ZA569T
Images Graphs Figures Description Strategies Building

A2 Dominion- Northholt, : 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 2029 kWh/yr 1236 kWh/yr -
Natural gas use2461 kWh/yr 136 kWh/yr -
Oil use- - -
LPG use- - -
Wood use- - -
Other Fuel - - -
Primary energy requirement 99 kWh/m².yr 41 kWh/m².yr -
Annual CO₂ emissions 21 kg CO₂/m².yr 9 kg CO₂/m².yr -
Annual space heat demand - 29 kWh/m².yr -

Renewable energy

Electricity generationForecastMeasured
Photovoltaic Array (1080W)933 kWh/yr -
Other Renewables Tech--
Electricity consumed by generation --
Primary energy requirement
offset by renewable generation
12 kWh/m².yr -
Annual CO₂ emissions
offset by renewable generation
2 kg CO₂/m².yr -

Calculation and targets

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


Pre-development air permeability test-9.06m³/m².hr @ 50 Pascals
Final air permeability test-7.59m³/m².hr @ 50 Pascals

Project description

StageUnder construction
Start date
Occupation date
Location London Borough of Ealing London  England
Build typeRefurbishment
Building sectorPublic Residential
Property typeSemi-Detached
Construction typeMasonry Cavity
Other construction typeBlock internal, 50mm (insulated) cavity, brick external
Party wall constructionSolid blockwork party wall
Floor area 80
Floor area calculation method Treated Floor Area (PHPP)
Building certification

Project Team

OrganisationBreyer Group PLC
Project lead personBreyer Group
Landlord or ClientA2 Dominion
ArchitectZED factory
Mechanical & electrical consultant DPS heatweb, Solar Empower & The Greener Alternative
Energy consultantDr Mark Gillot, University of Nottingham
Structural engineern/a
Quantity surveyorBreyer Group
ContractorBreyer Group

Design strategies

Planned occupancyFor the SAP and PHPP modelling an occupancy of 2.1 people has been assumed as per the TSB competition requirements. For the hot water assumptions for sizing the solar thermal system an occupancy of 3 people was assumed which we feel is a more realistic figure for a 3 bedroom house.
Space heating strategySubstantial reductions in space heating demand have been achieved by bringing the building fabric close to Passive House / CSH Level 6 standards, with an MVHR unit to minimise ventilation losses and particular attention to detailing for airtightness. Triple glazed windows with fibreglass frames achieve a Uvalue of 0.9. An oversized solar thermal array is proposed for the "solar shed" in the garden, with vertically mounted arrays to optimise winter gains. This will meet approx 53% of the propertys' combined space heating and water heating needs. A boiler with flue gas heat recovery has been proposed with an efficiency of 95.1% to meet the shortfall. The existing radiators will be retained with TRV's added for extra user control.
Water heating strategyThe space and water heating stategies have been developed as one wholistic solution. The solar shed with oversized solar thermal will ensure that 100% of the Hot Water demand of the property be met by free, renewable energy. The gas boiler and solar thermal will both feed into a UK manufactured thermal store designed specifically for this application, optimising the efficiency of the heating system and reducing its phantom electrical loads.
Fuel strategySolar and gas. The overall shortfall of thermal demand will be approximately 4000 kWh, meaning annual space and water heating bills of just 120 (assuming gas price of 3p / kwh). This illustrates the benefit of the improved building fabric and solar thermal array not just reducing CO2 emissions but also fuel poverty; particularly in the light of rising fuel costs.
Renewable energy strategyThe innovative "solar shed" concept allows for the installation and ideal orientation of solar arrays on less favourable properties. This also minimised disruption to residents whilst providing them with extra covered amenity space in their gardens. The locally produced Douglas Fir timber framed structure can be pre-manufactured off-site and erected on a patio slab in 1 day. This also avoids disruption of the roof structure, health and safety issues of maintaining a roof mounted array, and can be installed with minimum disruption to residents.
Passive Solar strategyThe passive solar aspect of the design has remained as existing, but with improved window specification. The orientation of the properties do not allow for a more ambitious passive solar strategy without major alterations to the street side of the property, which could become a contentious planning issue. This is something we felt was unrealistic for the wider roll out across the UK. The higher performance windows and building fabric will ensure that thermal demands are minimised. External insulation allows the internal thermal mass to be retained, hence retaining heat from solar gain and internal sources.
Space cooling strategyThe results of the Passive House (PHPP) model shows that there is no risk of overheating on these properties, with the proposed alterations. This is achieved by the retained levels of thermal mass internally and the ability for secure ventilation whilst residents are out at work. The MVHR unit also has an over-ride function which allows increased ventilation without heat recovery if required during the summer.
Daylighting strategyIt has not been considered appropriate to alter the window sizes and locations due to planning considerations. Current lighting levels are felt to be adequate.
Ventilation strategyThe proposed Mechanical Ventilation with Heat Recovery (MVHR) unit is one of the most efficient systems available at time of writing. The "Itho HRU ECO 4" unit has a SAP appendix Q rating of 0.46 W/L/sec, with a 91% efficient couterflow heat exchanger. The system is also to be integrated with the cooker hood which incorporates an innovative "air curtain" to the perimeter, increasing the removal of odours directly from the cooking area.
Airtightness strategy Airtightness has always been a key consideration of ZEDfactory's design approach, and we have applied our experience in this field throughout the detailing process. All key junctions have been drawn and detailed as existing and proposed, with a red line indicating the airtightness line (see example in the image section). The walls airtightness is achieved by the external insulation system, returning at windows to a double silicone seal (internal and external). In the roof we are proposing a new product; a bio-foam insulation, which is spray applied around joists in the loft, providing a single homogenous airtight line, whilst still allowing timbers to breathe. This tackles the particularly complex junctions such as rafter to wall plate.
Strategy for minimising thermal bridges External insulation is specified with thermally broken fixings. Windows are located on the outside of the existing wall to minimise thermal bridging between window and wall insulation. The integral strength of the fibre glass windows also means that no steel fixing reinforcements are required. This reduces cold bridging but is not reflected in the Uvalue due to the standard calculation method. Bio-foam sprayed insulation ensures complete coverage in roof area and should be able to connect to the external wall insulation with minimal bridging. In the floor the only cold bridge is the internal leaf of blockwork, but since the wall cavity is already insulated this isn't considered a cost effective problem to remedy.
Modelling strategyThe project will utilise the Microwatt wireless eZone system for monitoring. The system will monitor the overall electricity (including individual power circuits and PV contribution), gas consumption, water consumption, external temperature & humidity and heat meter readings from the gas fired combi-boiler (seperately for space heating and hot water use). Internal environment monitoring will also be carried out for temperature, humidity, light, CO2 and occupancy sensors (hall & upstairs landing) to assertain occupancy patterns. Soil temperature probes will be used to evaluate the effect of the perimeter insulation and moisture probes and temperature sensors will be used to investigate thermal bridging details and changes in dew point location. Data will be collected and stored for 2 years and supplied in a CSV format to the EST at 5 minute intervals
Insulation strategyWalls: 200mm of external cork insulation, giving Uvalue of 0.16 W/m2'C. Roof: 100mm of Bio-foam sprayed insulation, then 200mm mineral wool on top. This approach gets the benefits of the Bio-foams airtightness and thremal bridge reduction, but taking it up to passive house levels of insulation with a more cost effective product. Floor: We are proposing an innovative use of polystyrene beads usually used for cavity walls, by blowing them into the floor void. This is far more practical than taking up the floor(with the residents remaining in their homes during construction), and more effective than perimeter trench insulation. We intend to monitor the moisture levels in the void to ensure condensation does not occur and prove this concept
Other relevant retrofit strategiesWhole house smart metering: A real time monitoring unit (from award winning UK company Onzo) will display real time data of energy use and energy generation of a range of appliances around the home. This should encourage behavioural change and engage residents with their new renewable energy installations. Whole house standby mode: A switch next to the door enables residents to disable any non-essential power sources (e.g fridge, washing machine) before leaving the house - reducing phantom loads. Efficient lighting and appliances: An allowance has been made to replace all tungsten and halogen lighting and supply each home with a highly efficient new fridge, washing machine and induction hob for cooking.
Contextual informationPlanning issues have been considered and it is felt that all proposals will fall withing Permitted Development rights. Confirmation is currently being awaited from Ealing Council planning department. In the event it is not classified as permitted development we have been informally advised that a full application would be viewed favourably and we have no serious concerns that planning would provide a barrier to the projects progress.

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