Autonomous eco house design in Wales

David’s house is a low embodied energy, super insulated, timber frame construction using 300 mm Masonite I studs, joists and rafters. The house is conceived as an integrated closed loop system within the boundaries of the site and is self-reliant in terms of renewable electrical supply, space heating, hot and cold water supply, and biologically processes human waste streams to fertilise its edible landscape

We first worked with David to convert a coach house at Lam Rim Monastery into four meditation retreat apartments and then he asked us to design the UK’s first autonomous Masonite framed eco house.

It includes green oak structural timbers to the roof, super insulated breathing construction with one foot” of recycled newspaper cellulose insulation, a 2 storey triple glazed conservatory and a mixture of new and recycled local natural materials finished to a high specification.

Electricity comes from a wind turbine and solar photovoltaic panels. Cold water comes from collecting and purifying the rain. Hot water comes from the sun via solar hot water evacuated tubes. All foul water is naturally treated and recycled on site. Organic, non-toxic finishes where used throughout the house to create a healthy interior environment 

BUILDING FABRIC

The super insulated breathing vapour permeable walls, floors and roof have 300 mm of blown cellulose fibre made from recycled waste newspaper between Masonite I beams to give a consistent all over fabric U Value of 0.11 W/m2k.  The windows are Low E Scandinavian triple glazed to give a centre pane U value of 1.1 W/m2k.  Cold bridging is avoided with careful detailing around all reveals.

The Masonite I members comprise of solid 47 x 47 mm timber flanges and 8 mm hardboard webs.  This makes more use of a tree than does log conversion for solid timber and can utilise forest thinning’s and lower grade faster growing species.  The Masonite I members are guaranteed to be straight, strong, light, (using 65% less raw material than conventional timber) and energy saving giving a K value 15% better than a conventional wooden frame. All other timbers for external cladding, exposed structure and internal floors and wall cladding will be recycled from an existing chalet on the site or sustainable sourced indigenous green oak or Douglas fir from local Welsh woodlands 

 

Zero Carbon Eco House:in Wales
eco house design
eco timber frame construction

 

CENTRAL CONSERVATORY SPACE

The conservatory offers a passive solar heart to the house also providing the vertical circulation route and a raised seating platform to enjoy the distant views.

It is normally hard to justify an isolated conservatory space in cost and energy terms but if it is an integrated multi-function space it becomes not only a net solar gain asset but also a most beautiful place to relax for very little additional cost. Insulated internal shutters are provided to reduce heat loss during mid-winter and at night time.  A thick insulated concrete slab provides thermal mass to the glazed space retaining the suns latent heat.

HEATING SYSTEM

The conservatory pre heat buffer zone and supper insulation levels with minimal heat losses combined with thermal mass creates considerable thermal inertia eliminating the need for a full central heating system.

However for occasional use in extreme weather conditions a backup mini gas condensing boiler can provide background heat to a few small radiators. A 4 kW efficient Scandinavian wood burning stove fueled from timbers harvested from the 4 acre site provides a social focus to the living room and can complement the heat gains from the occupants and appliances.

RENEWABLE ELECTRICAL SUPPLY

The 20 m2  solar electric array of Solarex  2 kW photovoltaic panels are mounted on a simple garden timber trellis which permits optimum solar orientation without compromising the building and provides optimum performance by avoiding excess heat buildup, can be cleaned and maintained and can be easily extended if after the first year’s monitoring this appears necessary.

Due to the seasonal and day to day fluctuations in any solar array output the system is complemented with a matching 2.5 kW Scottish made proven wind turbine.

The combined wind and solar provision will give a more consistent and steady supply of renewable energy with the ability to adapt to seasonal variations. To ensure a backup electrical supply, if the sun isn’t shining and the wind isn’t blowing a 48V 12 kWh useable battery store is provided.

A mains connection will be maintained for the first three months of monitoring, after which the mains supply will be disconnected to allow total independence from the national grid.

LOW ENERGY APPLIANCES

All appliances have been carefully considered to eliminate unnecessary electrical demand and to optimize the efficiency of the required essential items, cooker, fridge, lighting etc.

Excess electricity produced from the renewables which cannot be stored in the battery pack will be dumped into the hot water cylinder to run in parallel with the hot water coil heated by the solar hot water panels.

PASSIVE VENTILATION

Mechanical ventilation has been avoided in favour of a healthy breathing wall construction and a Passivent system which naturally draws air through ducts from dry rooms through wet rooms (bathrooms and kitchen) and vents stale moist air through roof ridge vents.

LOCAL RAIN WATER SUPPLY

All house hold drinking and washing water requirements are met by collected rain water from the main roof via copper gutters and down pipes and stored in a 8 m3 integral tank in the storage undercroft.  Water is then plumbed through a 5 micron cartridge filter and a UV steriliser to a 200 litre holding storage tank in the roof loft.

 

passive house interior
oak staircase
passivhaus exterior

WASTE STREAMS

Presently we spend an enormous amount of energy and money collecting and purifying fresh water to a high EEC standard suitable for drinking.  We then urinate in it and defecate in it only to flush it down the loo back to where it came from to begin the entire process again.  In doing so we negate the hard work required to purify the water.  We throw away the potentially valuable nutrients in our urine and faeces and create unmanageable levels of pollution as the sewage is pumped into our rivers and seas.

There is something clearly tragic and wrong with this scenario and our collective reluctance to deal with our own waste.

David’s house uses Ifo Sanitar Cera dual flush WC’s which are at present the most water efficient flush toilets available with a minimum flush of 2 litres. This may be compared with a 9 litre flush which is commonly found in standard UK WC’s.

Given that flushing the toilet accounts for over 40% of our average water use the low flush Ifo WC’s can reduce a families consumption from 65,700 litres per year to 20,440 litres  per year. All black and grey water are feed to an existing septic tank on the site with a reed bed secondary tertiary system to absorb leaching liquids. Solids after an extensive settlement period will be extracted from the septic tank and distributed among the hedge rows and fruit trees to retain the valuable nutrients within the boundaries of the site.

If an existing septic tank infrastructure was not already present on site a dry composting system would have been more seriously considered.

Kitchen wastes and garden debris material will be composted and then returned to the land as an invaluable nontoxic fertiliser.

The above experiments demonstrate that human wastes do not need to become toxic pollutants of our rivers and seas but can be recycled and reused within an integrated eco system to become an invaluable resource furthering new life within the boundaries of the site.

EMBODIED ENERGY

Cradle to grave embodied energy costs are difficult to determine, but concrete and brick masonry buildings rely on excavating from the earth finite natural resources which cannot be replaced.

In comparison timber is a totally renewable resource if it is carefully and sustainably managed.

At David’s house ten times the number of trees used to make the house will be planted on the site to ensure that overall there is a net environmental resource gain.  This clearly cannot be replicated with heavy weight masonry buildings.

For a typical masonry house the embodied energy measured in delivered energy is about 6.5 J/per m2 and only 1.2 J/m2 for a timber frame house, which compares with consumption in use for a mid terrace house predicted as 39.8 GJ/per annum.  (Davis Langdon Consultancy 1997).

HEALTHY-INTERNAL ENVIRONMENT

The breathing construction where the vapour barrier is removed and the permeability of the layers in the fabric reduces toward the outside, creates a vapour hydroscopic envelope without the risk of condensation.  Scatter rugs over waxed timber floors, organic paints and stains to walls, avoidance of formaldehyde and equivalents combined with natural materials and a Passivent natural ventilation system will lead to a healthy internal air quality.

ENERGY PERFORMANCE

The house has a calculated Standard Assessment Procedure rating ( SAP ) of 100 and a National House Energy Rating ( NHER ) of 10 both of which are the maximum rating achievable on the scale. The building fabric heat loss at 21 degrees internal temperature and a 0 degree external temperature is 2.55 Kw. The house has a Building Energy Performance Index of 241 and a calculated per annum Carbon Dioxide Emissions of 5.0 tonnes / year and 29.6 kg / sq. m. / yr.

CONCLUSION

The super insulated timber frame construction following Scandinavian and Canadian best practice indicates that it is suited to sustainable autonomous housing in our temperate climate.

The improved embodied energy figures and quick thermal response of timber construction can however be offset against the improved thermal mass characteristics of heavy masonry construction.