Natural building: Bokrijk with a modern twist

A step beyond sustainable and even circular construction: Natural projects are emerging as the new hype in the construction sector. The focus will be on the use of biological materials. Back to basics, but with a modern, technical twist. Logically, the quality requirements must be respected. The question is whether it is possible and what challenges the contractors face…

In the world of construction, the concept of natural construction appears again more often. There is no strict definition, rather it is a collective name for a wide range of natural, rapidly renewable raw materials. “It concerns natural materials such as straw, wood, reeds, hemp, bamboo … and mineral minerals such as lime and clay,” explains Hilde Wijmeersch, driving force and founder of Woonder CV, a cooperative for natural construction. “We avoid using synthetic or cement-based components. We let the natural materials work for a good indoor climate. After all, they are particularly good at stabilizing the moisture content and temperature in the interior, at least if they are not combined with sheets or foils. Building is natural bio-based
or bioecological construction, but conversely, bioecological construction is not automatically synonymous with natural. Our northern neighbors are betting harder bio-based
building, so with materials that at least partially come from nature. These can therefore be mixed or bonded with synthetic components or cements.”

Limited climate impact

Why are builders now suddenly in natural or bio-based building interested? In the first place because of the climate impact. Traditional materials, such as concrete and metal, cause high levels of CO2emissions during production. Natural materials just store CO2 and also emits less CO2 when they are treated. In addition, mineral raw materials are becoming increasingly scarce. Just think of sand for the production of concrete, or drill for the production of glass wool and wind turbines. A final consideration is the favorable indoor climate. Unlike artificial products, natural walls are capillary active. They transport steam out into the open, so that the homes themselves get optimal humidity.

Design from the essence

Bio-based or natural design involves much more than simply ‘translating’ a traditional design into one with natural materials. “Everything is based on the circular philosophy: Don’t build what is redundant, reuse existing materials where possible…” Hilde Vanwildemeersch clarifies, “That principle also determines the layout of the house. Furthermore, it must be a modular concept – down on a material level – preferably multifunctional. Not only a room, but also a building must be easy to reuse. A good design ensures that you can do more with the space and perhaps therefore build less. A well-thought-out concept is also based on simple construction methods. It is perfectly possible to realize a simple monolithic wall by stacking straw bales or filling a timber frame with hemp concrete and then plastering everything inside and out. No complex details, sheets, foils or cloths are required. By the same token, the floor is not a complex structure of concrete, insulation and foils, but a layer of shells topped with lime hemp and a floor finish.Thanks to the shells’ anti-capillary effect, vapor from the ground cannot escape down to the floor. They also channel moisture around the foundation or from a leak to the ground, which keeps the structure dry.” Of course, it’s not difficult to build, but you can’t just put a straw bale in a classic wall, for example. A good natural design and the right detailing requires specific knowledge.”

Difficult certification

Only certified materials may be used, but it is not so obvious for now. “Certificates are certainly necessary from a quality and safety point of view, but obtaining them is an expensive affair,” says Hilde Vanwildemeersch. “Furthermore, more and more natural materials are added. Therefore, not all of them have a certification today. Many of the assessment methods are not geared at all or not at all for these products. For example, the comfort of an indoor climate cannot be measured. In some laboratory tests, natural materials, as opposed to synthetic ones, perform much worse than in practice. That is why we are in favor of not measuring the materials, but the finished homes and possibly certifying them.” In addition, it is not always obvious to find the materials and process them correctly. Players like Pixii, UHasselt, Woonder… have a wealth of information that they share through tailored training and guidance for architects, contractors and building owners. Buildwise also carries out tests and has ongoing research projects to expand knowledge about the use of natural materials. Remains though Bio-based still building a niche today.” training for around five hundred architects, contractors and builders.

Meanwhile, the price is competitive

Thanks to the growing popularity of natural materials, these are now easier to find and in greater numbers. “Some of them are already sold in the traditional building supply trade. There are also specialist retailers of organic building materials,” says Hilde Vanwildemeersch. Small industries have also been created around certain materials, such as building straw bales certified for home construction. These are ready in stock, so their availability is not seasonal. There are also prefabricated applications, such as wooden frames filled with straw. The advantage of this is the high quality because they are manufactured in a workshop and the fact that construction can be done very quickly on site. The key question, of course, is what the cost of such solutions is. Hilde Vanwildemeersch paints a positive picture: “Until the covid crisis and the war in Ukraine, bioecological construction was approximately 10% more expensive than the traditional approach. Current inflation, high energy prices and transport costs mean that both are competitive with each other today. After all, the natural materials are less subject to price drivers because they are produced locally.”

Available construction method

As a contractor, start with or switch to natural or bio-based building, initially requires the necessary knowledge. As previously mentioned, there are already various parties and agencies that offer objective, reliable information and training. Education is only relevant to acquire the necessary technical knowledge and insight, but also to be able to make well-founded offers. A company manager, calculator and/or project manager with the necessary knowledge is sufficient to take the first steps bio-based to build. Investments can be limited, existing construction cranes or telescopic cranes on a truck can also be used perfectly here. Finally, it is interesting to know: the guarantees and liability are identical to traditional construction.

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