Interface Support Products for Existing Technologies

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The proposed retrofit has been designed to be done to a property in Balham, London. This is a 3 bedroom house owned by Family Mosaic housing association, which sits on the edge of a conservation area, The proposal addresses a whole building solution by focusing on the fundamental energy consumption issues - namely a very high heating load and a higher than necessary electrical consumption. The large heating demand is due to the construction type of the house which we have proposed to adjust in the following ways : adding insulation to the walls (external insulation at the rear and internal insulation at the front) floor and roof and renewing the windows and installing MVHR.

Retrofit for the future ZA332B
Images Graphs Figures Description Strategies Building

Interface Support Products for Existing 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 2684 kWh/yr 1277 kWh/yr -
Natural gas use33051 kWh/yr 6456 kWh/yr -
Oil use- - -
LPG use- - -
Wood use- - -
Other Fuel - - -
Primary energy requirement 422 kWh/m².yr 100 kWh/m².yr -
Annual CO₂ emissions 79 kg CO₂/m².yr 20 kg CO₂/m².yr -
Annual space heat demand - 18 kWh/m².yr -

Renewable energy

Electricity generationForecastMeasured
PV array1000 kWh/yr -
Other Renewables Tech--
Electricity consumed by generation --
Primary energy requirement
offset by renewable generation
76 kWh/m².yr -
Annual CO₂ emissions
offset by renewable generation
14 kg CO₂/m².yr -

Calculation and targets

Whole house energy calculation method SAP
Other whole house calculation methodPHPP was used to used model the proposed project. The result are reported in the Phase 2 application submission. While they were
Energy target Retrofit for the Future
Other energy targetsOur main focus was to reduce heating demand as far as possible.
Forecast heating load 6.9 W/m² demand


Pre-development air permeability test-17.01m³/m².hr @ 50 Pascals
Final air permeability test-1.23m³/m².hr @ 50 Pascals

Project description

StageUnder construction
Start date01 March 2010
Occupation date30 June 2010
Location London London  England
Build typeRefurbishment
Building sectorPublic Residential
Property typeMid Terrace
Construction typeSolid Brick
Other construction type
Party wall constructionSolid brick
Floor area 106
Floor area calculation method Treated Floor Area (PHPP)
Building certification

Project Team

OrganisationPrewett Bizley Architects
Project lead personPrewett Bizley architects
Landlord or ClientFamily Mosaic
ArchitectPrewett Bizley architects
Mechanical & electrical consultant The Green Building Store
Energy consultantPrewett Bizley
Structural engineerNabeii Consulatancy
Quantity surveyorPrewett Bizley
ConsultantStructures Dept Greenwich University
ContractorManby contracting

Design strategies

Planned occupancyThis is a family house and we expect a couple with 2 children to take occupancy.
Space heating strategyThe space heating has been minimised by insulating the house very well and controlling the ventilation. However, we intend to locate small radiators in each room fed by a combination boiler. All pipe work will be well lagged. The heat emitters will be controlled by a programmer and thermostatic valves. It is unlikely that the radiators will be necessary in all but the coldest months.
Water heating strategyThe water heating will be done by a combination boiler. All pipe work will be well lagged to reduce losses.
Fuel strategyThe heating and hot water will be run on mains gas. Everything else will use grid electricity.
Renewable energy strategyA south facing PV array will be installed that should yield around 1000 kWh energy per year.
Passive Solar strategySome passive collection naturally forms part of the calculations. However as this project is low impact in terms of the elevations we have not actively adjusted window openings, but instead focussed on reducing heat demand.
Space cooling strategyThe house can be well cross ventilated and we don't anticipate over heating being a sigificant problem. PHPP calculations support this conclusion.
Daylighting strategyAgain we have worked with the existing window pattern which provided very good levels of daylighyt generally. We will return one opening to its original (larger) size to jmprove daylight to that room. Elsewhere, daylight levels were very good.
Ventilation strategyThe house will use an MVHR system and will have very high levels of air tightness to ensure that it works well. We intend that the system works in extract mode during the summer when windows will allow air to flow in and cross ventilation to occur. The system will be one of the new Paul units and its installation will be designed and commissioned by the Green Building Store.
Airtightness strategy The air tightness strategy will rely on continuous plastering to all masonry elements internally. These will extend through the joist zone. Where necessary we will use Proclima tapes to achieve interfaces between wet and dry systems of construction. We have achieved air permeability rating of around 1m3/m2h on similar retrofit work in the past. We will use ALDAS to run the tests and provide guidance on where matters can be improved.
Strategy for minimising thermal bridges We tried to eliminate cold bridging wherever possible, through good detailing. Where this has been impractical we have extended extra insulation 'socks' over fabric or into the ground to reduce the effect of the bridge as much as possible. We have analysed most of the interfaces with THERM software to achieve the best possible results. This has resulted in a very low entry for psi values within our PHPP and SAP analysis.
Modelling strategyWe ran the existing and proposed house through SAP model and then used the extension sheet to test for compliance with the competition. We also modelled the proposed condition using PHPP software supported with THERM for psi values. We used this model to tweak the design for optimal performance.
Insulation strategyFront wall internally insulated. Rear wall externally insulated
Other relevant retrofit strategiesWe developed details for 2 interface details: -gutter extension to act as a stop to external rendered insulation -decoupling device to get end of timber joist out of front wall. These detail prototypes were developed to reduce thermal bridging and ensure that the proposed development would be robust and sound for many years to come. This strategy addresses concerns we have with how some retrofit work may compromise the building fabric that it is supposed to enhance.
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