Harpenden EnerPHit Plus
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as PDF Deep retrofit of a 1960s detached house in Harpenden and the addition of a small rear extension. This project was constructed to meet the EnerPHit Plus criteria as well as going gas free; by using an air source heat pump and harnessing renewable energy with an entire roof pitch dedicated to solar pv. The existing brickwork walls were externally insulated using wood fibreboard and finished with a painted render and the curtain walls were removed and replaced with new highly insulated timber I beam walls with cellulose insulation and clad in western red cedar. The rear single storey extension was also constructed in this way and finished with either render or timber cladding. The existing ground floor was removed and replaced with a new highly insulated slab with underfloor heating.
Harpenden EnerPHit Plus : Project images
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Energy and fuel use
Measured data from renewable generation is not yet available.
Fuel use
| Pre-development | Forecast | Measured | |
| Electricity use | - | - | - |
|---|---|---|---|
| Natural gas use | - | - | - |
| Oil use | - | - | - |
| LPG use | - | - | - |
| Wood use | - | - | - |
| Other Fuel | - | - | - |
| Pre-development | Forecast | Measured | |
| Primary energy requirement | - | - | - |
|---|---|---|---|
| Annual CO₂ emissions | - | - | - |
| Annual space heat demand | - | - | - |
Renewable energy
| Electricity generation | Forecast | Measured |
|---|---|---|
| Renewables Technology | - | - |
| Other Renewables Tech | - | - |
| Electricity consumed by generation | - | - |
| Primary energy requirement offset by renewable generation | - | - |
| Annual CO₂ emissions offset by renewable generation | - | - |
Calculation and targets
| Whole house energy calculation method | PHPP |
|---|---|
| Other whole house calculation method | - |
| Energy target | EnerPHit |
| Other energy targets | - |
| Forecast heating load | - |
Airtightness
| Date | Result | |
| Pre-development air permeability test | 10 December 2019 | 8.39m³/m².hr @ 50 Pascals |
|---|---|---|
| Final air permeability test | 08 November 2021 | 0.59m³/m².hr @ 50 Pascals |
Project description
| Stage | Occupied |
|---|---|
| Start date | 13 January 2020 |
| Occupation date | 13 February 2021 |
| Location | Harpenden Hertfordshire England |
| Build type | Refurbishment |
| Building sector | Private Residential |
| Property type | Detached |
| Construction type | Other |
| Other construction type | Two types: retrofitted cavity wall and new infill curtain wall |
| Party wall construction | |
| Floor area | 151 m² |
| Floor area calculation method | Treated Floor Area (PHPP) |
| Building certification |  Passivhaus certified building |
Project Team
| Organisation | |
|---|---|
| Project lead person | Heather McNeill, A D Practice Ltd |
| Landlord or Client | Private - carried out own BMS/home automation design |
| Architect | Heather McNeill, A D Practice Ltd |
| Mechanical & electrical consultant | M&E Spec & MVHR: Enhabit Ltd; Solar PV: GB-Sol Ltd; ASHP: Solid Renewables |
| Energy consultant | Heather McNeill, A D Practice Ltd and Guy-Pitts Crick, Heatflux |
| Structural engineer | |
| Quantity surveyor | |
| Consultant | Certifier: Kym Mead, Mead: Energy & Architectural Design Ltd |
| Contractor | Jigsaw Design & Construction Ltd |
Design strategies
| Planned occupancy | Two people (and two cats) working from home or office-based |
|---|---|
| Space heating strategy | Air source heat pump with underfloor heating downstairs and dual fuel radiators in bathrooms. |
| Water heating strategy | Air source heat pump heating hot water tank with extra immersion element powered by solar pv. Waste water heat recovery from showers. |
| Fuel strategy | Gas free. Electricity, as much as possible generated on site |
| Renewable energy strategy | Full front roof pitch of solar pv (8.10kW) array helping to run ASHP and heat hot water as well as powering the house and charging cars. |
| Passive Solar strategy | Southern-facing rooms with large windows to maximise solar gain. |
| Space cooling strategy | Fan coil unit with ducted cooling into upstairs rooms. *Continuous use of MVHR with night purging in hot weather. *Electrically opening rooflights in rear extension and above stairs for stack effect purge ventilation linked to building management system. |
| Daylighting strategy | Large windows providing lots of natural daylighting as well as rooflights over the dining/garden room area and skylight over stair void, flooding staircase, hallway and landing with light (previously very dark). |
| Ventilation strategy | Comfort ventilation with heat recovery (winter) *Openable windows (summer) *Electrically opening rooflights in rear extension and above stairs for stack effect purge ventilation linked to building management system. |
| Airtightness strategy | SmartPly over existing masonry structure linked to SmartPly layer in new curtain walls. *Intello Plus membrane to underside of roof.Membrane under concrete screed. *All taped together and into windows/doors |
| Strategy for minimising thermal bridges | Thermal bridging analysis undertaken for all primary junctions interfaces. *Continuous insulation maintained throughout. *Geometric thermal bridges minimised. *External insulation wrap maintained as far as possible and compensatory insulation overrun at junctions where this is not possible. *External insulation below ground to top of foundations to prevent thermal bridging to floor/existing cavity walls. |
| Modelling strategy | Whole house modelling was undertaken in PHPP with thermal bridges modelled by consultant in Therm |
| Insulation strategy | Natural insulations as far as possible (not below floor slab) *External woodfibre insulation to retained cavity walls (to achieve U-value of 0.13 W/mK) *Blown Warmcel insulation in between I-studs in new curtain walls (to achieve U-value of 0.12 W/mK) *Existing floor slab renewed with 160mm PIR insulation below slab (to achieve U-value of 0.13 W/mK) *Extension floor slab with 260mm PIR PIR insulation below slab (to achieve U-value of 0.11 W/mK) *Retrofitted pitched roof with 30mm woodfibre sheathing, 240mm woodfibre insulation between rafters, 60mm woodfibre insulation below rafters (to achieve U-value of 0.135 W/mK) *Flat roof to extension with 300mm woodfibre insulation over joists (to achieve U-value of 0.12 W/mK) *EPS insulation used below ground to insulate base of walls to top of foundation level |
| Other relevant retrofit strategies | |
| Contextual information | Conservation area |
Building services
| Occupancy | Two people (and two cats) working from home or office-based |
|---|---|
| Space heating | Air source heat pump with underfloor heating downstairs and dual fuel radiators in bathrooms |
| Hot water | Air source heat pump heating hot water tank with extra immersion element powered by solar pv. Waste water heat recovery from showers. |
| Ventilation | Balanced ventilation system with heat recovery, enthalpy heat exchanger; heat recovery efficiency 86% |
| Controls | Loxone system providing whole building management system |
| Cooking | Induction hob with electric oven |
| Lighting | 100% LED |
| Appliances | A+ rated appliances as minimum |
| Renewable energy generation system | Full front roof pitch of solar pv (8.10kW) array helping to run ASHP and heat hot water as well as powering the house and charging cars with capacity for future battery installation. |
| Strategy for minimising thermal bridges | Thermal bridging analysis undertaken for all primary junctions interfaces. *Continuous insulation maintained throughout.*Geometric thermal bridges minimised.*External insulation wrap maintained as far as possible and compensatory insulation overrun at junctions where this is not possible. *External insulation below ground to top of foundations to prevent thermal bridging to floor/existing cavity walls. |
Building construction
| Storeys | 2 |
|---|---|
| Volume | 375m³ |
| Thermal fabric area | 503 m² |
| Roof description | There are two types:1) Retrofitted pitched roof:30mm woodfibre sheathing; 240mm woodfibre insulation between rafters; 60mm rigid woodfibre board; Airtight membrane; Service void; Plasterboard and skim 0.135W/m2K. 2) Flat roof to extension:100mm rigid woodfibre insulation; 200mm rigid woodfibre insulation over joists; Smartply; Service void; Plasterboard and skim 0.103W/m2K |
| Roof U-value | 0.12 W/m² K |
| Walls description | There are two types: 1) Retrofitted cavity wall:200mm woodfibre EWI; Existing insulated brick and block cavity wall; SmartPly; Service Void; Plasterboard and skim 0.129W/m2K. 2) New infill curtain wall: 80mm woodfibre sheathing; 300mm blown cellulose insulation between I studs; SmartPly; Service void; Plasterboard and skim.0.109W/m2K |
| Walls U-value | 0.12 W/m² K |
| Party walls description | N/A |
| Party walls U-value | - |
| Floor description | There are two types: 1) New floor slab in main house: Concrete slab; 160mm PIR insulation; Concrete screed with UFH; Floor finish. 0.127W/m2K. 2) New floor slab to rear extension: Concrete slab; 260mm PIR insulation; Concrete screed with UFH; Floor finish 0.080W/m2K |
| Floor U-value | 0.11 W/m² K |
| Glazed doors description | Internorm HF310 inward opening. g: 0.50; Ug: 0.53 |
| Glazed doors U-value | 0.86 W/m² K installed |
| Opaque doors description | Internorm front door. Moralt Passiv Ferro |
| Opaque doors U-value | 0.85 W/m² K installed |
| Windows description | Internorm HF310 and HV450 (front and rear bedroom windows) |
| Windows U-value | 0.86 W/m² K installed |
| Windows energy transmittance (G-value) | - |
| Windows light transmittance | - |
| Rooflights description | Fakro DEF DU8 (flat roof extension) and Fakro FTT U8: g: 0.38; Ug: 0.40. Fakro FTT U8: g. 0.35; Ug: 0.30 |
| Rooflights light transmittance | - |
| Rooflights U-value | 0.80 W/m² K |