Grove Cottage

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Extension & Refurbishment of Victorian Townhouse using Passivhaus methodology and CarbonLite guidance. Certified to the Passivhaus Institute's new EnerPHit (refurbishment) Standard. [NEW:Passivhaus Trust awards shortlisted project - presentation available on these pages].PHPP certification is based on 20 C, rather than the 21 C the house was heated to during 2010/11. Forecasts are based on a 'typical year' rather than the 'actual' year being monitored. Measured data here is from 2005/06 (before) and 2009/10 (after). Measured room temperatures show an average of 21 degrees centigrade during the heating season. Please note the final air leakage as certified under EnerPHit was an N50 of 1.0 ACH. When adjusted for 2010 average monthly temps.& an internal temp. of 21 C, PHPP predicted a space heat demand of 36kWh/m2.a whereas 35kWh/m2.a was measured.
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CO2 emissionsPrimary energy requirement
Energy target

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 4300 kWh/yr 2728 kWh/yr 3312 kWh/yr
Natural gas use24000 kWh/yr 6724 kWh/yr 6937 kWh/yr
Oil use- - -
LPG use- - -
Wood use- - -
Other Fuel - - -
Primary energy requirement 284 kWh/m².yr 108 kWh/m².yr 120 kWh/m².yr
Annual CO₂ emissions 55 kg CO₂/m².yr 22 kg CO₂/m².yr 25 kg CO₂/m².yr
Annual space heat demand - 25 kWh/m².yr 35 kWh/m².yr

Renewable energy

Electricity generationForecastMeasured
Renewables Technology--
Other Renewables Tech--
Electricity consumed by generation --
Primary energy requirement
offset by renewable generation
108 kWh/m².yr 120 kWh/m².yr
Annual CO₂ emissions
offset by renewable generation
22 kg CO₂/m².yr 25 kg CO₂/m².yr

Calculation and targets

Whole house energy calculation method PHPP
Other whole house calculation methodPHPP results (EnerPHit certification file) are based on 20 C internal temps and standrd 'typical year'.
Energy target EnerPHit
Other energy targets-
Forecast heating load 13 W/m² demand


Pre-development air permeability test--
Final air permeability test16 July 20100.88m³/m².hr @ 50 Pascals

Project description

Start date11 July 2008
Occupation date01 March 2009
Location Hereford Herefordshire  England
Build typeRefurbishment
Building sectorPrivate Residential
Property typeSemi-Detached
Construction typeSolid Brick
Other construction type
Party wall construction
Floor area 135
Floor area calculation method Treated Floor Area (PHPP)
Building certification  Passivhaus certified building Passivhaus certified building

Project Team

OrganisationSimmonds.Mills Architects
Project lead personAndrew Simmonds
Landlord or ClientAndrew Simmonds, Lorna Pearcey
ArchitectSimmonds.Mills Architects
Mechanical & electrical consultant Alan Clarke, Peter Warm
Energy consultantDavid Olivier
Structural engineerBob Johnson
Quantity surveyorNone

Design strategies

Planned occupancy2 adults and 3 children.
Space heating strategyPassive Solar + Mechanical Ventilation & Heat Recovery (MVHR) + replacement gas boiler inc. retention of existing radiators
Water heating strategyReplacement gas boiler + super insulated, solar ready hot water cylinder + all hot and cold water pipes insulated. Installed measures include a south facing roof area constructed to allow future installation of 4.5 m2 of solar thermal panels to feed into HWC
Fuel strategyNatural gas (minimised use of). Biomass not considered as appropriate fuel due to resultant air pollution issues (particulates etc) in a city residential area, combined with high capital costs associated with biomass equipment relative to low heat demand required.
Renewable energy strategyNo electricity generation technologies currently adopted.
Passive Solar strategyPassive solar gain maximised as far as possible mainly through creation of new South facing windows in existing house and new extension.
Space cooling strategyExisting house on N-S axis (main elevations East and West). Use of new & retention of existing thermal mass (blockwork / brickwork) within insulation envelope (i.e. use of external insulation). Windows - summer shading as result of window set back. MVHR has automatic summer bypass allowing automatic cooling at night during hot spells. More substantial rate of night time ventilation for cooling purposes also possible via openable windows (good arrangement for passive stack ventilation designed in).
Daylighting strategyExtensive daylighting to all rooms to displace electric lighting. Maximising daylighting through careful sizing and design of windows and internal colour scheme (favours light off white colours). Some windows with splayed reveals (opportunity arising with existing house) - increase light distribution and levels.
Ventilation strategyMVHR provides ventilation with openable windows if required, (good arrangement for passive stack ventilation designed in).
Airtightness strategy Existing house: external face of existing brick walls parged (thin layer of cementitious material used). New extension: internal plaster to blockwork walls + use of air-vapour barriers in ceilings and some limited wall areas where timber frame was required above brick/blockwork.
Strategy for minimising thermal bridges Adoption of 'thermal bridge-free' construction detailing for new construction and also in refurbishment work where possible.
Modelling strategyPHPP. Limited use of THERM.
Insulation strategy*Application of external insulation to solid brick and new blockwork walls*Insulation of existing suspended floor*Insulation of existing solid floor*New floor raft foundation with structural eps insulation below*Renewal of existing roof and placement of insulation above existing rafters. New roof uses fully filled I beams.
Other relevant retrofit strategiesFamily remained in house during all refurbishment and new build works.
Contextual informationHouse had limited architectural detail on street facade: Painted brickwork. (Decayed) stone subcills to windows: (Painted) stone lintels visible above windows. An original carved stone plaque was mounted on the house wall. The subcills and lintels details have been recreated in the new render. The street side entrance porch will be rebuilt in timber and roofed in original slates. The plaque will be recreated, updated and mounted as before.

Building services

OccupancyAs per stage 2
Space heatingVaillant natural gas non-system boiler with Alpha Pro 2 external circulating pump etc
Hot waterHWC details, insulated pipe details
VentilationPaul etc Heat Recovery Ventilation Unit, frost protection preheater.
ControlsSet for continuous heating - wall mounted Vaillant digital control and room thermostat and weather compensation
CookingExisting gas hob, electric oven, electric toaster maker with insulated jug, microwave.
Lighting100 % compact fluorescent.
Appliances*fridge: Baumatic BFE 25655 *washing existing appliances: AEG Oko-Lavamat 74630 *dishwasher: ISE DW51 *electric tumble drier - (now junked), MVHR serviced clothes drying cupboard. Also home office equipment; 2 laptops, 2 printers, router, office lighting. Home office is not separately metered.
Renewable energy generation systemNone
Strategy for minimising thermal bridges'Thermal bridge-free' strategy. For details - see uploaded documents

Building construction

Storeys 3
Volume 337
Thermal fabric area 446
Roof description Refurbished: fully filled I beams over old roof
Roof U-value 0.08 W/m² K
Walls description External insulation approach. Some very minor areas with internal insulation.
Walls U-value 0.12 W/m² K
Party walls description Party wall insulated by injecting foam into 25 - 40 mm variable gap between house gable wall and wall of adjoining house.
Party walls U-value 0.39 W/m² K
Floor description new extension floor
Floor U-value 0.13 W/m² K
Glazed doors description Internorm, Edition range. 3g with insulated frame. Not PH certified, rather 'passivhaus suitable' approach used here.
Glazed doors U-value 0.87 W/m² K uninstalled
Opaque doors description N/A
Opaque doors U-value - -
Windows description A range of sizes to fit existing openings and in new extension. U values range from 0.87 to 1.15 (average 0.98), with a glazed fraction per window/door ranging from 39% to 71%. Glazing area 18 m2 of total window and frame area of 29 m2.
Windows U-value 0.98 W/m² K uninstalled
Windows energy transmittance (G-value) 0.5 %
Windows light transmittance -
Rooflights description Fakro triple Glazed
Rooflights light transmittance 0.52%
Rooflights U-value 1.49 W/m² K

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