Will we build houses from mushrooms in the future?

Mr. Hebel, you are researching new basic materials for the construction industry. Are our current building materials not good enough?

In terms of their function, they are actually very good and perfectly developed for their unique use. Concrete, for example, can now be shaped into almost any form, is very resilient and is also relatively inexpensive. But its carbon footprint is poor, and after use we cannot yet recover the primary materials originally used; sand, gravel and cement. Many composite materials have not yet been developed to go into a second, third or fourth use. Take a building material such as wood, for example: When processed pure, it offers many advantages as it serves as a CO2 reservoir, can be used flexibly, and is very durable if properly protected. Ceiling beams from Wilhelminian-style buildings, for example, could be used in a new building without any loss of quality. In modern buildings, however, wood is often used in the form of glue-laminated beams or wood-based panels. This marks the beginning of the so-called cascade utilization, at the end of which is combustion. In the process, the stored CO2 is abruptly released again. In addition, toxic ash is produced that has to be landfilled instead of being used as a nutrient on fields, for example. And this is because our products often represent a mixture of biological and synthetic materials, which leads to varietal impurity.

How can we do better?

By building grade-pure: Different materials are no longer inextricably linked, but are intelligently incorporated into buildings. We have to plan for easy deconstruction at the planning stage. And we also need to research new, single-variety and consistent material classes. This offers great opportunities for industry: We have to test new, detachable joining techniques, invent novel binders and protective layers that may even be self-healing, similar to our skin. Numerous projects are also underway at KIT in this regard.

At the same time, you are also researching completely new building materials, for example, some made of mushrooms. How can houses be built with it?

We have not yet built entire houses with it, but that will come, I am convinced of that. Mushroom mycelium, i.e., the roots of mushrooms, can be used to make building blocks, panels and insulating mats that can be used in a similar way to conventional products. To do this, we use the root system of fungi: We let them grow on an organic material, such as grain husks or wood chips. The advantage is that the root threads of fungi bind together when they meet, thus forming a solid structure. We let this mesh grow in containers shaped like bricks, for example. After about a week, this cuboid is filled in. We then heat it briefly to kill the organism, and what remains is an organic structure that can also be used as a building material. Depending on the type of fungus, the admixed "food" or the growth period, the material is pressure-resistant, flexurally rigid, or porous, in which case it can be used as insulation. Mushroom mycelium can therefore be used in different ways and is a CO2 reservoir. And because the products have been consistently bred from the start, when they are no longer needed they can simply be thrown on the compost heap and become nutrients for other plants.