Insulation: MATERIALS ENCYcLOPEDIA
The development of a foam-like insulation made from agricultural waste and mycelium (the roots of mushrooms) definitely ranks as one of the most exciting developments in green building.
The material is created by inoculating a blend of agricultural waste fibers (seed hulls, straw, etc) with mycelium. The mixture is placed into forms and allowed to grow until the form is full. The growth process does not require sunlight, water or fertilizers. The fully-grown insulation is then dehydrated and heated slightly to stop the root growth and prevent spore development.
In theory, this is an exceptionally clean and nontoxic way to create an insulation product that has many desirable qualities, including high R-values, rigidity and durability. Each cubic inch of material contains approximately eight miles of mycelium fiber, making it an ideal insulator.
The product can be used to make rigid insulation similar to conventional foam boards, and also to produce structural insulated panels (SIPs).
The product is nearing market-readiness as this book goes to press. Without being able to use it or read reliable reports from users, we could not present it here as a viable option. However, we hope it will soon become a very useful product for sustainable builders and show the way forward for more innovations that create valuable building materials in a more natural, environmentally friendly way.
Follow the development of this product at ecovativedesign.com
Wood fiber insulation is quite popular in Europe, and given the immense amount of wood production and manufacturing in North America it is surprising that it has such a small presence in this market. Wood fiber insulation can come in many forms, including cellulose batts (which are similar in appearance and performance to other forms of batt insulation) and rigid or semi-rigid panels used as insulated exterior sheathing boards. Opportunities exist to use recycled pulp and mill waste for these products, but the small market is currently held by European imports. It would be a positive development if these products were to find acceptance in the North American market.
In the past decade, numerous versions of prefabricated straw bale wall panels have been developed around the world. Though they vary in execution, they share a similar principle: the advantages of straw bale construction are best realized when the walls are assembled and plastered off-site and in a horizontal position. This approach combines the low material costs of straw bale walls with dramatically lower labor costs, and allows straw bale walls to compete with conventional options like wood frame construction in terms of overall cost while maintaining all the environmental and thermal performance advantages of bale wall systems.
A prefabricated straw bale wall system is much like other structural insulated panels (SIPs) on the market, offering ease of installation and excellent thermal performance, but without the higher costs and higher environmental impacts of foam-based SIPs.
The panels are created using forms. The wooden top and bottom plates of the form stay with the wall when it is transported and installed. The sides may be an integral part of the wall, or be removed after installation. The plaster for one side of the wall is placed wet into the form and the bales are inserted into the wet plaster. The exposed side of the bales are then coated with plaster, using the formwork as a screed to create a square, level wall surface. In this way, the plaster is applied in one horizontal coat, rather than two or three coats in a vertical position.
There are numerous ways of fastening the panels to different foundations, roofs and to one another, depending on the manufacturer’s system.
Straw bale SIPs realize the potential of combining natural building methods and materials with a more industrialized production methodology to provide building products that have minimal environmental impacts while meeting the expectations of modern house-building professionals.
The majority of straw in North America is baled into large rounds rather than the small rectangular bales used to make straw bale walls. The large round bales have a density far greater than the small rectangles, and this makes them well suited to act as structural columns.
Such columns were tested at Queen’s University in Kingston, Ontario, in 2007, and were shown to be able to have a working strength in excess of 120 kN.
Round bale columns were used to create the load-bearing elements of a performing arts center building in Madoc, Ontario, in 2008. The octagonal building used a stack of three bales, each 1.2 m wide x 1.2 m high (4 ft x 4 ft), for a total column height of 3.6 m (12 ft), at each of the eight points. A wooden roof beam joined the columns at the top.
The completed roof of the building was lowered onto the columns using a crane, and caused no measurable deflection of the columns. The walls between the columns were infilled with rectangular straw bales and the entire structure coated with earthen plaster.
The round bale structural columns proved to be very fast to build and very inexpensive. This structural system could have widespread applications for large buildings, where it would significantly lower costs, construction time and environmental impacts.
Round bales can be produced at diameters ranging from 70–120 cm (28–48 inches), with the smaller diameters being more adaptable to conventional construction methods.