RetroPHit 02 Medical Surgery, Hereford

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A 400m2 GP Practice in Hereford City, built 1978.
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RetroPHit 02 Medical Surgery, Hereford : 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

Measured data from renewable generation is not yet available.

Fuel use

Electricity use 40210 kWh/yr - -
Natural gas use53687 kWh/yr - -
Oil use- - -
LPG use- - -
Wood use- - -
Other Fuel - - -
Primary energy requirement 408 kWh/m².yr - -
Annual CO₂ emissions 87 kg CO₂/m².yr - -
Annual space heat demand - 40 kWh/m².yr -

Renewable energy

Electricity generationForecastMeasured
PV2999 kWh/yr -
Other Renewables Tech--
Electricity consumed by generation --
Primary energy requirement
offset by renewable generation
-19 kWh/m².yr -
Annual CO₂ emissions
offset by renewable generation
-4 kg CO₂/m².yr -

Calculation and targets

Whole house energy calculation method PHPP
Other whole house calculation method-
Energy target AECB Silver
Other energy targetsWe propose a phased retrofit plan aiming for a whole building energy performance target aiming to achieve a minimum of AECB Silver and a maximum of the Passivhaus EnerPHit. Aspirational fuel use forecasts for gas and electricity are based here on Silver.
Forecast heating load -


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

Project description

Start date
Occupation date
Location Hereford Herefordshire 
Build typeRefurbishment
Building sectorPublic
Property typeDetached
Construction typeMasonry Cavity
Other construction typeLightweight block inner skin, 50-70mm cavity, 100 facing brick
Party wall construction
Floor area 398
Floor area calculation method Approximate Floor Area
Building certification

Project Team

Project lead personRetroPHit
Landlord or ClientCantalupe Surgery
ArchitectSimmonds.Mills Architects
Mechanical & electrical consultant RetroPHit
Energy consultantRetroPHit
Structural engineerRetroPHit
Quantity surveyorRetroPHit
Contractorchosen from RetroPHit business list

Design strategies

Planned occupancyMedical centre housing GP Practice. Maximum occupancy: 9 Admin Staff, 9 GPs/Clinical Staff , 4 District Nurses and 21 Patients.
Space heating strategyExisting: heating is via 3 no. mains gas fired boilers feeding radiators + individual electric room heaters. In combination with extensive insulation measures: type, size and number of boilers to be assessed at detail design stage. Radiators can be run with greater efficiency and safety at a lower water temperature. Radiator layout and controls e.g., thermostatic valves (TRVs) to be assessed for required maintenance / replacement. Individual electric heaters to be replaced with additional radiators + TRVs if required.
Water heating strategyExisting: water heating via same 3 gas boilers (extent of hot water provision via boilers TBC) + electric point-of-use under sink heaters for hot taps. Pipe insulation to DHW pipework to be considered to improve speed of delivery of hot water to taps, potentially reduce use of expensive carbon intensive electrically heated hot water and to reduce summertime overheating from pipework in offices. Water use is recorded as typically 209 cu.m/yr, with a relatively low hot water use reported (TBC). South West facing roof space is occupied by PV panel array, with a smaller unshaded roof area still available to the South East. Mainly due to low hot water use solar thermal panels are not currently proposed, however an insulated and 'future proofed' hot water store will be investigated for both space and water heating purposes.
Fuel strategyExisting: natural gas via mains supply. To be retained as space (and water heating - see above) fuel. Existing mains electricity use is reduced by a recent PV installation. Strategy is to reduce whole building heat and power consumption through energy efficiency measures, whilst moving the proportion of fuel used away from electricity to natural gas as far as possible in order to reduce the Practice's overall carbon intensity.
Renewable energy strategyExisting: roof mounted PV system. No further PV proposed. Sub metering of PV output to be made more accessible/visible and to be reported / displayed separately to whole building electricity consumption. The role of other onsite heat and power technology will be assessed carefully at detailed design stage.
Passive Solar strategyThe main street elevation faces South West and this combined with the number of large windows relative to office size + the lack of shading leads to localised and general overheating from excessive (low angle) afternoon solar gain. The South East elevation is more shaded and has less glazing. Therefore the options for increasing useful solar gain appear limited and the issue of overheating should be tackled.
Space cooling strategyAn older air conditioning system is in use during the summer period to provide cooled air to a number of rooms. The energy consumption of this unit may be relatively high and there should be room for some potential improvement, however it needs to be assessed as part of the overall ventilation and passive solar control strategy (see ventilation strategy). Lack of significant/any insulation in the roofspaces also adds to overheating on the top floor from solar gain via the roofspace. Overall, increased wall and roof insulation will reduce the amount of heat during hot weather reaching the inside of the building. It is proposed to replace existing windows with 2+1 insulated frame windows with inetgral venetian blinds as an effective method of shading the westerly windows whilst reducing noise and heat loss. Improved cross building natural ventilation can be created via air vents (fire protected) though internal walls/doors to connect to rooms with openable windows on the North.
Daylighting strategyDaylighting could be improved through redecoration of certain areas with higher reflectance colour schemes. If the 2+1 windows are used, the integral blinds offer an ability to control solar gain/privacy levels with good daylighting control. Electrical lighting retrofit, including daylight sensitive lighting controls + upgrading existing luminaires with lowest energy types available offers an extremely cost effective way to reduce running costs and reduce emissions.
Ventilation strategyOption 1: full mechanical ventilation with heat recovery (natural ventilation backup). Benefits include comfortable temperature, consistently high quality air - potential use of finer, pollen grade filters if required. Heat recovery reduces heating costs and can be used at night during hot weather to slightly cool the concrete floor slabs / building structure ready for the next day. For significant nighttime cooling natural cross-ventilation is required through windows open in 'hopper' position. Security issues can usually be addressed. Higher capital and installation cost, ductwork could fit above suspended ceilings. Building may require more than one unit. Option 2: whole building mechanical extraction only (natural ventilation backup). Individual 'passive' air inlets (dampened against external noise) set through walls behind radiators to 'preheat' air drawn into rooms. Loft mounted unit extracting continuously with low power fan from wet rooms. Lower capital, installation cost.
Airtightness strategy Air leaks (draughts) from outside will be: through light fittings in the 2nd floor ceiling, and other service penetrations in this ceiling or walls generally: via window and doors - poor or missing seals: via the ventilated masonry wall cavity and through the blockwork where not plastered: The concrete intermediate floors may be solid (in situ) or precast solid concrete plank or hollow core concrete plank. The drawings indicate that they are built into, and bear onto the inner skin of blockwork which, unless potentially compromised by being hollow core planks, is an intrinsically airtight detail. However the airtightness of the wall relies on the plaster and to maintain this continuity the plaster should be taken up to the concrete ceiling and down to the floor slab. This is unlikely to be the case, so some air leakiness should be assumed as the blockwork is NOT airtight in itself. Therefore an airtight hi-performance injected cavity fill insulation is proposed for the walls.
Strategy for minimising thermal bridges Installation of cavity wall insulation can suffer from poor workmanship leaving unfilled areas. Using a highy quality installation company is proposed, combined with thermal imaging to assess final work. Linking the injected cavity wall insulation continuously with the proposed loft insulation is important for air tightness and to reduce thermal bridging losses. Thermal bridges will remain between window frames and cavity wall insulation however the detail will anticipate any future addition of external wall insulation in order to close to any replacement window frames further reducing thermal bridging and heat loss whilst improving comfort conditions close to windows. Thermal bridging generally will be improved.
Modelling strategyThe next stage in the RetroPHit process - detailed design, drawing and specification - uses the Passivhaus Planning Package to effectively model energy use, comfort and co2 emissions. Post retrofit whole building energy forecasts and running costs can be assessed more accurately during this next stage.
Insulation strategyGiven the role of the masonry cavity allowing uncontrolled air leakage into the building it is proposed to inject the cavity with a hi-performance polyurethane injected cavity insulation. The cavity appears to be 70mm wide. We have no concerns in principle with insulation filling the cavity using a closed cell foam of this type, which will not transfer moisture across the cavity to the inner blockwork during severe weather. It is not proposed to insulate wall internally nor the ground floor due to disruption and cost. External wall insulation may be added at a later date. It is proposed to use a thin layer of hi-performance spray foam from eaves (where the cavity wall insulation is accessible), across the attic floor structure to the oppposite eaves. Above this a cheaper mineral or natural fibre insulation maye be fitted to a greater depth.
Other relevant retrofit strategiesWe are planning to carry out the package of retrofit measures with occupants remaining in the dwelling during the proposed works. Peripheral switch off plug on office equipment. It is proposed to explore affordable monitoring of different electrical circuits to understand and aid management of electricity use for three key distinct areas: lighting; plug in equipment; hardwired building services (ventilation,cooling,pumps,fans). In addition the use of individual wall mounted power monitors adjacent to each room entrance is proposed. Energy monitors in certain rooms to inform and influence occupant behaviour.
Contextual informationThe building is in a conservation area. It took 6 months to gain permission for the recent installation of PV panels. All but one option for the energy efficiency measures proposed will be unseen on the public face of the building. The option to replace the westerly windows should not in our opinion pose an issue with planning. This can be explored with the LA at the next stage.

Building services

Space heating
Hot water
Renewable energy generation system
Strategy for minimising thermal bridges

Building construction

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
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Windows description
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Windows energy transmittance (G-value) -
Windows light transmittance -
Rooflights description
Rooflights light transmittance -
Rooflights U-value -