Foto: Vojta Herout, www.vojtaherout.com
Almost Self-sufficient Straw Bale House
Czech winner of the Our home 2020 category
You can build houses using metal, glass, brick, wood or panels. Or large-format straw blocks. And that is exactly the material that the owners chose for their house in almost passive standard in Dobřejovice in the Central Bohemia. It was important to them that the materials used burdened the surroundings as little as possible. The straw was therefore supplemented with wood, clay or cellulose. And for the running of the house to have the smallest possible impact on the environment, the owners use rainwater both in the house and in the garden, the green roof and thought-out outside window blinds help cool down the house. The building demonstrates the way a house can be built with unique quality, even for those who do not have large resources.
The Adaptation Journey
The positive impact
Man is a species closely connected to the Earth and its limits. On the other hand, man is a species brave enough to discover new methods and approaches. The combination of these two ideas has inspired a house standing near Prague in Dobřejovice. The owners built the house in a way to be easily demolished thanks to the consistent use of natural materials and selected construction methods. So that the house does not burden its surroundings, they used a number of measures that also help reduce the negative impacts of climate change in the locality. The house is now almost self-sufficient.
How does it work?
In the house, the owners used old time-proved measures, which are being replaced by energy-intensive ones in the current construction industry. But the owners wanted to avoid that.
They used large-format straw bales to create the walls of the house, which they reinforced with wooden beams. They used cellulose for insulation and created plaster from clay. Clay plaster and heavy concrete floors help to stabilize the interior temperature.
They shaded the windows of the house by wooden roofs in the mezzanine and the roof extending wide over the walls of the house. In addition, they use simple external blinds that shade the windows when the sun is lower above the horizon. They do not need external blinds or air conditioning for cooling.
They collect rainwater in an underground tank and use it in the house to flush toilets and in the garden. A large part of the land around the house remains as grass and allows water to seep in. The green roof protecting against overheating covers not only their house but also their garage. It is possible to heat and have hot water here without electricity, thanks to the gravity connection of the fireplace insert. The house is connected to the water supply, but with a domestic water system and a filter, it would be possible to use water from the roof as well as drinking water.
The building is designed in an energy passive standard. The house operating was thus financially reduced to a minimum. The house is almost self-sufficient, to achieve full self-sufficiency it would be enough to connect a battery. However, according to the owners, this would be very expensive, so they decided against this measure.
Originally there was a garden on the building plot for the house.
Operation and maintenance
Thanks to the quality of the execution, the owners expect maintenance cost to be in thousands of crowns a year including necessary repairs. The operation of the house alone costs thousands of crowns a year.
Obstacles and challenges
The biggest challenge and obstacle was the original design of the building made of load-bearing straw. Due to an error in the calculation of statics, the structure sank irregularly a few centimetres, so grooves for inserting load-bearing wooden posts were milled into the straw. However, it turned out that the later insertion of the posts was not more difficult than if the projection had been carried out this way from the beginning.
The other challenge was that the owners decided to build the house themselves. During the construction, the number of hours worked jumped to thousands.
How much did it cost?
The investor calculated the total cost of building the house at 5-6 million crowns (189,226-227,071 EUR). The owners built the house from their own resources and by themselves.
Neither the return nor the savings during construction can be assessed. A similar house can be built for more with significantly worse energy qualities. The comfort and financial independence of the residents of the new house cannot be quantified either.
Rainwater flushing now saves 35 cubic meters of drinking water per year.
Heat savings are also significant. Over 80 years of service life, the savings on heating will reach approximately 936 MWh compared to a normal building of a similar extent (heat demand for heating 15 versus 80 kWh / m2a).
The service life of the building is expected to be 80-120 years. The technical equipment of the building has an expected life span of 50 years.
Family and apartment houses Water purification and recycling Use of rainwater Heating Green roof Shading Heat waves and thermal island Lack of water and drought Green energy Energy savings