An Austrian company is building trailer homes that are designed not only to be compact, but with self-sufficiency in mind, too. Wohnwagon's trailers provide 25 sq m (269 sq ft) of living space and have their own off-grid electricity, water and waste systems. They can also be used as offices, guest rooms or cafes.

Wohnwagon was founded in 2013 and is currently building its fifth trailer. As with other typical tiny homes, the Wohnwagons are designed to make efficient use of space and resources. Measuring 10 x 2.5 m (32.8 x 8.2 ft), with a 3 x 2 m (9.8 x 6.6 ft) additional expandable section, they are built using natural and recycled materials and have a variety of sustainability features.

The outer shells of the trailers are made of larch wood and the inner panels are made of spruce or wood-fiber panels and clay plaster. The trailers are insulated by sheep's wool, which helps to regulate the interior temperature and humidity.

Four solar panels mounted on the roof deliver a peak output of 1.2 kW and surplus energy is stored in a 6 kWh battery-system installed under the floor. Wohnwagon says the system requires thoughtful use of energy, but provides enough output for comfortable year-round living. A monitoring system allows residents to keep tabs on their levels of energy usage.

The water system of the Wohnwagon uses a total of 550 l (121 gal), with 140 l (31 gal) of clean water stored in a tank under the floor. Water is heated using a wood-burning stove or the roof-based solar system and is recycled with perhaps the Wohnwagon's neatest trick.

A green roof provides additional insulation, but features marsh plants that naturally filter greywater run-off from the sink and shower. The greywater is pumped up to the roof and is purified naturally over the course of about 24 hours, after which it is reused for showers or washing. The Wohnwagon also has a bio-toilet that separates liquid and solid waste before turning each into fertilizer.

The trailers each cost in the region of €40,000 to €90,000 (US$45,000 to $110,000) and buyers are able to customize the design of their Wohnwagon prior to the build-stage. The current build is expected to be completed this coming October and will be installed at the Almdorf Seinerzeit hotel in Kärnten, Austria, as a bookable room.

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