Soil insulation is also suitable for passive houses

The Building Physics research team of CTU UCEEB tested the use of mycelium thermal insulation boards in building envelopes. The tests were commissioned by the association MYMO, whose aim is to study this natural material in detail and find the widest possible use for it in the construction industry, where it could become an ecological alternative to, for example, polystyrene.

Mycelium products are new to the construction industry. It is a natural, environmentally friendly material created by growing mycelium on a suitable substrate such as wood chips, reeds, etc. Our task was to investigate the behaviour of mycelial boards with a bulk density of 200 kg/m3 in a complete envelope structure typical for modern timber buildings.

The tests were carried out in a small climatic double chamber in our laboratories in Bustehrad. On one side of the test specimen we simulated the conditions inside the heated building, on the other side we first created conditions typical for the outdoor environment in winter, and in the next step also the so-called winter design conditions with a temperature of −15 °C. Temperature, relative humidity and heat flux sensors were placed in the sample at several levels to get a complete picture of its hygrothermal behaviour.

The test results showed that mycelium boards are a sufficiently effective insulation material for building envelopes in our climatic conditions. With a thermal conductivity coefficient of 0.050 W/(m∙K), satisfactory values of the heat transfer coefficient can be achieved in all categories from conventional construction to passive houses with common insulation thicknesses.

The measured data also allowed us to quantify other important characteristics of the new material. Using inverse modelling, we were able to determine the shape of the sorption curve, the value of the diffusion resistance factor or the specific heat capacity. In terms of hygrothermal properties and behaviour, the mycelium-based composite can be classified among other building materials of natural origin, e.g. wood fibreboards or compressed straw products, which are already well established on the market.