Grayshott, Surrey

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Refurbishment and extension of 1962 detached cavity wall house using external woodfibre insulation system, triple glazed windows, and mechanical extract ventilation.
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Grayshott, Surrey : 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 - - -
Natural gas use- - -
Oil use- - -
LPG use- - -
Wood use- - -
Other Fuel - - -
Primary energy requirement - - -
Annual CO₂ emissions - - -
Annual space heat demand 278 kWh/m².yr 35 kWh/m².yr -

Renewable energy

Electricity generationForecastMeasured
PV array3000 kWh/yr -
Other Renewables Tech--
Electricity consumed by generation --
Primary energy requirement
offset by renewable generation
-49 kWh/m².yr -
Annual CO₂ emissions
offset by renewable generation
-12 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 17 W/m² demand


Pre-development air permeability test30 July 20129.88m³/m².hr @ 50 Pascals
Final air permeability test02 December 20132.5m³/m².hr @ 50 Pascals

Project description

StageUnder construction
Start date15 January 2013
Occupation date16 February 2014
Location Grayshott, Hampshire/Surrey border Hampshire  England
Build typeRefurbishment
Building sectorPrivate Residential
Property typeDetached
Construction typeMasonry Cavity
Other construction type100mm block, 60mm cavity, 100mm brick. Part cavity filled.
Party wall construction
Floor area 152.7
Floor area calculation method Treated Floor Area (PHPP)
Building certification  AECB silver standard certified building AECB silver standard certified building

Project Team

OrganisationConker Conservation Ltd
Project lead personPaul Mallion
Landlord or ClientMr and Mrs Sims
ArchitectConker Conservation Ltd
Mechanical & electrical consultant -
Energy consultantConker Conservation Ltd
Structural engineer
Quantity surveyor
ConsultantKithurst Builders
ContractorContract Management Company

Design strategies

Planned occupancyTwo people, at work or working from home, with elderly relative living in annexe.
Space heating strategyHigh efficiency thermal mass wood stove.Trial of low energy electric radiant panels embedded into walls, on separate circuit to allow monitoring.
Water heating strategyDirect hot water cylinder with twin immersion elements, one linked to PV via Immersun controller to optimise solar heating of cylinder.
Fuel strategyWood heating, with electric radiant panels as back up, fueled by solar PV via Immersun.PV switch.
Renewable energy strategyPV
Passive Solar strategyProperty has perfect south front facade. South facing windows enlarged to capitalise. New west facing windows and doors added to gain late afternoon sun into living spaces.
Space cooling strategyCross ventilation provided by new windows at first floor, and large openable internal doors to create air flow.
Daylighting strategyVery well provided for as existing, being of partly open plan and large window as fashionable in 1960s. New west facing windows to replace north facing units, to balance heat losses.
Ventilation strategyConstant running individual low energy extracts in wet rooms.
Airtightness strategy Comprehensive survey done at commencement identified cavity as a leakage, along with defective windows. Replastering over airtight membranes, Siga and ProClima tapes and membranes used.
Strategy for minimising thermal bridges Careful assessment of each area from plans. Solutions include internal, external and cavity insulation.
Modelling strategyPHPP, with site specific climate data provided by BRE due to local conditions, height above sea level.
Insulation strategyExternal woodfibre insulation system by Steico with Lime Green render to existing cavity walls. New timber frame using 150mm wool between studs, woodfibre outside.PU insulation laid over existing floors. 300mm loft insulation. 100mm XPS to walls below DPC externally.
Other relevant retrofit strategiesAdditional thermal mass built in where possible, such as sun space floor slab. Electric solar PV fueled wall heating being trialled....
Contextual information

Building services

OccupancyAs design
Space heatingAs design, plus electric towel rails in three wet rooms, linked to timer and thermostat.
Hot waterAs design
VentilationAs design
ControlsIndividual switch and thermostatic control over radiant wall heaters.
CookingConduction hob and electric oven, and a good coffee machine, natch.
LightingMostly LED, small number of localised halogen spots, corridors using compact fluorescent.
Renewable energy generation systemPV array on main south roof slope
Strategy for minimising thermal bridgesDetails that have been previously approved on PH projects have been used, but not specifically calculated. Approximate but safe values used in calculations.

Building construction

Storeys 2
Volume 481
Thermal fabric area 456
Roof description Standard trussed rafters at 600mm centres, 2 layers of 150mm natural sheeps wool insulation
Roof U-value 0.14 W/m² K
Walls description Cavity walls filled with mineral wool, external 120mm woodfibre insulation. New walls 150mm timber stud insulated with 80mm woodfibre insulation externally, voids filled with wool, U value 0.18.
Walls U-value 0.25 W/m² K
Party walls description
Party walls U-value -
Floor description Existing concrete floor slab upgraded with 50mm PU insulation and floating floor.
Floor U-value 0.30 W/m² K
Glazed doors description Katzbeck timber clad timber framed units, triple glazed.
Glazed doors U-value 0.99 W/m² K installed
Opaque doors description
Opaque doors U-value - -
Windows description Katzbeck Linea aluminium clad timber framed units, tilt and turn with trickle vent in head.
Windows U-value 0.91 W/m² K -
Windows energy transmittance (G-value) 0.5 %
Windows light transmittance 0.6%
Rooflights description
Rooflights light transmittance -
Rooflights U-value -