I plan to build an off-grid house. This page describes the basic outline of what I want to build. Linked pages go into more detail.
Update: House Sketch
- Off grid. That is, with no connections to mains power, gas, water or sewage. Telephone and internet access might be wired but would more likely be by some form of wireless connection.
- No combustion. Unlike many off-grid houses this one will, at least initially, have no stove or other form of combustion in the house. Depending on performance in practice, though, a small internal-combustion-engine generator or a small stove might be added as a backup to be used at most a few dozen times a year.
- Low energy use. This is, pretty much, implied by the off-grid status. The remaining points in this list mostly follow on from this.
- Optional energy use. Designed to be reasonably comfortable and usable with very low energy use for some period of time, e.g., during runs of dull, still winter's days, by deferring some activities until more energy is available.
- Active control. Computerized control system to coordinate making the most effective use of available energy, in particular tuning the use of the thermal mass.
- Evolveable. As there is little experience of designing houses of this type it's very difficult to predict the performance of the systems. It is therefore particularly important that it's possible to tune, update and experiment with the operation. There should be no expectation of a single point when the house can be considered to be "finished".
- Solar powered. All winter-time sun-exposed surfaces (south facing roof and east, south and west facing walls) covered with various forms of solar energy collectors: photovoltaic, windows (relatively small), evacuated-tube hot water and warm air used for domestic hot water and space heating. These collectors will be integrated into the design of the building forming the rain-screen cladding which is required anyway.
- Wind powered. One or two small wind turbines will be included to complement the PV.
- Highly insulated. In the region of three times better than required by current building regulations. About 300 mm of insulation in the walls and floor with somewhat more in the roof. Windows will be small compared with those in many current houses.
- Airtight. Avoid almost all uncontrolled air exchange to prevent loss of sensible and latent heat.
- MHRV. Mechanical heat-recovery ventilation to make best use of energy in out-going air.
- High thermal mass. Large quantity (many tons) of water in multiple tanks within the main thermal envelope of the house to store received solar thermal energy and to buffer temperature swings within the house. These tanks will be at varying temperatures and will have varying amounts of insulation from the rest of the house.
- Heat pump. A small water-to-water heat pump might be incorporated primarily to boost the temperature of part of the thermal store for domestic hot water purposes. This would act as a dump load for the the PV and wind turbine - i.e., it would cut in when the batteries are charged and there's no other higher priority use for available power.
- Rainwater Harvesting. The source of potable, bathing and other water will be rainwater harvested from the roof of the main house and the attached greenhouse. Probably a metal roof for the north side (where there aren't solar collectors) for this harvesting.
- Small. Designed for a single occupant (me), with occasional guests, for both living and working (office work). Mostly single-story 50 to 60 m² internal floor foot-print with open-plan kitchen, living room and office with a sleeping loft above the office and separate bathroom and mechanical room. Additional storage space, particularly a pantry, outside the main insulation envelope on the north side of the greenhouse.
- Attached greenhouse. To grow some fresh food to reduce shopping trips, to provide some semi-outdoor space and activity area particularly for poor weather, to extend the roof area available for rainwater harvesting, to provide a low-energy all-weather clothes drying space which doesn't result in extra moisture being released in the house, and to partially buffer the house (particularly the main entrance) from prevailing weather.
- Self build. I'll get professional help for any site leveling and for construction of the foundation pads. Beyond that I want to be careful in the design to make sure that I can construct the rest myself with the guidance of an architect, architectural technician or other suitably experienced and qualified consultant keeping any additional services required off the critical path as far as possible.
- Timber post-and-beam structure. Built above the ground, on individual foundation pads, in-filled with standard-size panels. Similar to Segal method houses but unlike the original Segal method houses, this one will have a sloped roof.
Simple form. Details depend somewhat on the site but my current thinking is that the footprint of the house will be a simple rectangle about 10 metres by 6 metres with a long side facing south. West to east, the semi-open-plan kitchen, living room and office with loft sleeping area above would be along the south side. East to west, the guest bedroom space at the back of the office, bathroom and mechanical room would be along the north side. The roof would have simple gable ends but be asymmetric with a steep (45° or more) south facing slope covered with solar collectors and a shallower north facing slope with a metal surface for rainwater harvesting. Beyond the 6 metres on the north side the roof would continue down below normal room height for about another metre or so to contain the thermal store water tanks.
The attached greenhouse will be to the west and its function will include buffering the main entrance into the kitchen. A garage/storage shed/workshop would be along the north side of the greenhouse.
Perfection is attained, not when no more can be added, but when no more can be removed. Antoine de Saint Exupéry