Withy Cottage
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as PDF Timber Frame & Straw Bale self build with thermal bridge free construction (other than door and window frames). Simple flat raft foundation on EPS.
Withy Cottage : 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 | - | - | 1528 kWh/yr |
|---|---|---|---|
| Natural gas use | - | - | - |
| Oil use | - | - | - |
| LPG use | - | - | 600 kWh/yr |
| Wood use | - | - | 8000 kWh/yr |
| Other Fuel | - | - | - |
| Pre-development | Forecast | Measured | |
| Primary energy requirement | - | - | 111 kWh/m².yr |
|---|---|---|---|
| Annual CO₂ emissions | - | - | 10 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 | - | 111 kWh/m².yr |
| Annual CO₂ emissions offset by renewable generation | - | 10 kg CO₂/m².yr |
Calculation and targets
| Whole house energy calculation method | |
|---|---|
| Other whole house calculation method | - |
| Energy target | Superinsulation design in 1995 |
| Other energy targets | - |
| Forecast heating load | 60 W/m² demand |
Airtightness
| Date | Result | |
| Pre-development air permeability test | 03 January 2006 | 1.38m³/m².hr @ 50 Pascals |
|---|---|---|
| Final air permeability test | - | - |
Project description
| Stage | Occupied |
|---|---|
| Start date | 24 December 2004 |
| Occupation date | |
| Location | Hereford Herefordshire England |
| Build type | New build |
| Building sector | Private Residential |
| Property type | Detached |
| Construction type | Other |
| Other construction type | Timber with staw wall insulation and blown celulose insulation |
| Party wall construction | |
| Floor area | 120 m² |
| Floor area calculation method | Approximate Floor Area |
| Building certification |
Project Team
| Organisation | |
|---|---|
| Project lead person | |
| Landlord or Client | Self |
| Architect | None |
| Mechanical & electrical consultant | None |
| Energy consultant | None |
| Structural engineer | Alan Pearce |
| Quantity surveyor | None |
| Consultant | friends informal chats |
| Contractor | Self plus Mike Whitfield, Dai Rees (el) and Steve Rann (plaster) |
Design strategies
| Planned occupancy | 2 people plus guests |
|---|---|
| Space heating strategy | Single woodstove with domestic hot water back-boiler. Towel rail in bathroom as heat dump otherwise no radiators, secondary heaters or other heat emitters. |
| Water heating strategy | Solar and woodstove compliment each other with very infrequent immersion heater backup. |
| Fuel strategy | Waste wood from local sawmill and timber from on-site woodland management. LPG hob and electric oven. |
| Renewable energy strategy | Disconnected after 7 years living off the grid. Emphasis on demand reduction. |
| Passive Solar strategy | DIY Solar thermal DHW, minimal passive solar because of uninformed fear about overheating in lightweight building. In fact behaves like a massive building due to insulation. |
| Space cooling strategy | Controled gains, night ventilation and high levels of insulation maintain very comfortable summer temperatures (peak summer temperatures 23-24C) |
| Daylighting strategy | Not optimised. Open plan living area with light from at least 2 sides in all rooms. One skylight in office and one in kitchen/dining/living area. Emphasis on animation and effect rather than DF. |
| Ventilation strategy | Simple passive stack cooker hood and thru' wall MVHR in bathroom. Trickle vents in office and bedrooms. Considering MVHR retrofit. |
| Airtightness strategy | Internal structure, 9mm ply air barrier behind 100mm structure/services layer. Continuous air barrier but unaware of proper airtightness tapes at time of build. Blower door tested after completion. |
| Strategy for minimising thermal bridges | Floating slab on 100mm EPS with 200mm edge insulation. Structure inside the insulation with rafters and gable support outside insulation layer. However windows and doors are major thermal bridge. |
| Modelling strategy | Basic spread sheet. |
| Insulation strategy | EPS under slab, local straw bales for walls and blown cellulose in roof. |
| Other relevant retrofit strategies | |
| Contextual information |
Building services
| Occupancy | 2 plus guests |
|---|---|
| Space heating | Wood stove only |
| Hot water | Solar plus wood stove back boiler (1kW) |
| Ventilation | Crude passive stack and trickle vents plus single room MVHR in bathroom. |
| Controls | None except thermostat on thermal store to dump heat to bathroom tower radiator if too hot. |
| Cooking | LPG and electric oven |
| Lighting | All CFL, linear T5 or LED spots. No incandescents. |
| Appliances | All best available at time of purchase. |
| Renewable energy generation system | Solar DHW |
| Strategy for minimising thermal bridges | Continuous layer of insulation with structure on inside. Floating floor slab with no penetrations. |
Building construction
| Storeys | 2 |
|---|---|
| Volume | - |
| Thermal fabric area | - |
| Roof description | 15mm plasterboard and skim, Self built 400mm truss rafters with cellulose insulation between, breather membrane, 50mm air gap, 18mm ply, MDPE membrane, 150mm turf from site. |
| Roof U-value | 0.11 W/m² K |
| Walls description | 12mm plasterboard and skim, 100mm service void in structural frame, 9mm ply air barrier, straw bales stacked up in thin orientation, breather membrane, air gap, douglas fir cladding. |
| Walls U-value | 0.20 W/m² K |
| Party walls description | n/a |
| Party walls U-value | 0.00 W/m² K |
| Floor description | polished concrete on 100mm EPS with 200mm edge insulation. Was seen as a lot of insulation at the time! |
| Floor U-value | 0.19 W/m² K |
| Glazed doors description | Self build by friend, oak frame and double glazed (IPlus with Argon and thermix spacer) |
| Glazed doors U-value | - - |
| Opaque doors description | Self build by friend, Oak, PU foam, birch ply air barrier. |
| Opaque doors U-value | - - |
| Windows description | Ecoplus stormproof with iPlus glazing. |
| Windows U-value | - - |
| Windows energy transmittance (G-value) | - |
| Windows light transmittance | - |
| Rooflights description | 2 x Velux with best available glazing at the time. |
| Rooflights light transmittance | - |
| Rooflights U-value | - |