The Oxlet
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as PDF The project is a single, detached dwelling on a 5 hectare site that is part of the Wye Valley Area of Outstanding Natural Beauty and is located on the northern fringes of the Forest of Dean.
The Oxlet : Project images
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Fuel use
| Pre-development | Forecast | Measured | |
| Electricity use | - | - | 11237 kWh/yr |
|---|---|---|---|
| Natural gas use | - | - | 492 kWh/yr |
| Oil use | - | - | - |
| LPG use | - | - | - |
| Wood use | - | - | - |
| Other Fuel | - | - | - |
| Pre-development | Forecast | Measured | |
| Primary energy requirement | - | - | 99 kWh/m².yr |
|---|---|---|---|
| Annual CO₂ emissions | - | - | 23 kg CO₂/m².yr |
| 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 | - | 99 kWh/m².yr |
| Annual CO₂ emissions offset by renewable generation | - | 23 kg CO₂/m².yr |
Calculation and targets
| Whole house energy calculation method | |
|---|---|
| Other whole house calculation method | - |
| Energy target | |
| Other energy targets | - |
| Forecast heating load | - |
Airtightness
| Date | Result | |
| Pre-development air permeability test | - | - |
|---|---|---|
| Final air permeability test | - | - |
Project description
| Stage | Occupied |
|---|---|
| Start date | 01 December 2003 |
| Occupation date | 04 June 2006 |
| Location | Bishopswood, Forest of Dean Gloucestershire England |
| Build type | New build |
| Building sector | Private Residential |
| Property type | Detached |
| Construction type | |
| Other construction type | |
| Party wall construction | |
| Floor area | 290 m² |
| Floor area calculation method | Approximate Floor Area |
| Building certification |
Project Team
| Organisation | |
|---|---|
| Project lead person | Neill Lewis |
| Landlord or Client | David and Felicity Wadge |
| Architect | Neill Lewis |
| Mechanical & electrical consultant | Conservation Engineering Ltd |
| Energy consultant | David Olivier of Energy Advisory Associates |
| Structural engineer | Allan Pearce |
| Quantity surveyor | Colin Jones |
| Consultant | Wall, James and Davies (Planning Consultants) |
| Contractor | Self-built |
Design strategies
| Planned occupancy | 2 occupants for the majority of the time. |
|---|---|
| Space heating strategy | Ground source heat pump feeding underfloor heating. |
| Water heating strategy | Dual immersion heaters with supplementary heating provided by evacuated tube solar hot water panels. Some adjustments to be made to heat pump to assist in heating hot water. |
| Fuel strategy | There are no mains services to the site apart from electricity and water, therefore electricity was planned to be the main fuel source. |
| Renewable energy strategy | The owners plan to install a 1.5 kW(e) micro-hydro generating plant, which utilises the 45 m height difference between the house and the stream entering the site at the top of the hill. It will be grid-connected. The upper reservoir will be the remnants of two 22 m3 former fish ponds. Between them, this reservoir is able to store about 3 kWh(e). |
| Passive Solar strategy | Window areas were larger on the south and east elevations and minimised on the north and west elevations. |
| Space cooling strategy | There is no active cooling system. In heatwaves, the windows are to be opened by night and closed by day. The curtains are also to be closed by day to reduce the level of solar gains entering the building. |
| Daylighting strategy | Some first floor spaces in the house are double-height and are lit from above by rooflights. |
| Ventilation strategy | Mechanical heat recovery and ventilation (MVHR) was proposed to deal with ventilation requirements. |
| Airtightness strategy | The main air barriers in the design are a wet plaster finish to the internal masonry walls and the vapour barrier on those sections of wall that are insulated internally. |
| Strategy for minimising thermal bridges | |
| Modelling strategy | |
| Insulation strategy | |
| Other relevant retrofit strategies | |
| Contextual information | The site had a chequered planning history. This included several refusals for barn conversions or holiday let(s). The owners first planning application, in 2001, proposed to demolish the existing cottage and milking shed and to replace them by a single much larger stone and rendered house, built partly into the steep east-south-east-facing slope. This position was felt to be more suitable than siting the replacement house within the curtilage of the original stone cottage, which was very close to the B road. The planners were sympathetic to this scheme. Subject to numerous conditions, it gained approval under their delegated powers. |
Building services
| Occupancy | Predominantly as designed - 2 people. |
|---|---|
| Space heating | A Kensa ground source heat pump supplies underfloor space heating. There are fewer pipes in the screed than normal thanks to the reduced heat load. For a house with 290 m2 of treated floor area, the M&E engineers calculated a peak space heat demand of 6 kW(t) at -1C, based on continuous cold weather heating. This low loading of 21 W per m2 compares well to previous UK low-energy projects, such as the Elizabeth Fry Building at UEA. |
| Hot water | The main DHW tank is 0.165 m3. It is insulated with 50 mm of PU foam and has one solar coil and twin electric immersion heaters. A further 0.56 m3 heat dump store, with the same level of insulation, accommodates output from the solar system at times of surpluses. The factory level of insulation is felt by the owners to be a bit inadequate, but it was all that was available at the time. The owners have fitted loose mineral fibre jackets on top of the foam. So the effective overall level of insulation is probably equivalent to 60-65 mm PU foam. The DHW pipes are insulated throughout the house with 19 mm of foam insulation. |
| Ventilation | A Regavent 650 DC MVHR system with electronically-commutated DC motors. |
| Controls | |
| Cooking | Mostly LPG, two 19 kg bottles per annum, each containing c. 250 kWh. Gas hob and electric oven. |
| Lighting | Extensive use of 7 W compact fluorescent downlighters. |
| Appliances | A+ models were purchased wherever possible. There were some, even in the early 2000s. |
| Renewable energy generation system | |
| Strategy for minimising thermal bridges |
Building construction
| Storeys | 3 |
|---|---|
| Volume | 725m³ |
| Thermal fabric area | - |
| Roof description | Reclaimed Welsh slate, felt and battens, breather membrane, 250 mm deep OSB-webbed I beams on 600 mm centres, filled with 250 mm blown cellulose fibre. Polyethylene membrane for airtightness, sealed meticulously at all seams and sealed to the plaster on the walls. 38 mm PU foam internally, bonded to 12 mm plasterboard, skim coat of plaster. |
| Roof U-value | 0.13 W/m² K |
| Walls description | Wall type 1: 13 mm dense plaster, 100 mm dense concrete block, 70+50 mm Kooltherm phenolic foam slab, 25 mm residual cavity, 135-150 mm local sandstone. (U-value 0.16 W/m2K)Wall type 2: 13 mm dense plaster, 100 mm dense concrete block, 200 mm blown cellulose fibre between TJI I beams on 600 mm centres, 9 mm Panelvent sheathing, breather membrane, 50 mm cavity, 20 mm render on stainless steel lath. (U-value 0.21 W/m2K) |
| Walls U-value | 0.21 W/m² K |
| Party walls description | |
| Party walls U-value | - |
| Floor description | Basement: 75 mm sand-cement screed, 100 mm EPS insulation, DPM, 150 mm concrete slab, 150 mm hardcore. (U-value 0.31 W/m2K)Intermediate: 50 mm sandstone flags, 75 mm sand-cement screed containing underfloor heating pipes, 175 mm beam-and-block floor, 38 mm softwood battens, 90 mm Kingspan Thermopitch TP10. |
| Floor U-value | 0.31 W/m² K |
| Glazed doors description | Ecoplus brand supplied by Green Building Store Ltd. There is an insulated wood-faced panel and the glass above is warm edge, low-e, argon-filled double glazing. |
| Glazed doors U-value | 1.40 W/m² K uninstalled |
| Opaque doors description | |
| Opaque doors U-value | - - |
| Windows description | Danish oak-framed windows, by Vrogum, with 16 mm argon-filled low-e double glazing. |
| Windows U-value | 1.40 W/m² K uninstalled |
| Windows energy transmittance (G-value) | - |
| Windows light transmittance | - |
| Rooflights description | Velux double-glazed argon-filled low-e |
| Rooflights light transmittance | - |
| Rooflights U-value | 4.80 W/m² K |