In explaining the advantages and disadvantages of cellulose insulation, the idea was raised that if the thermal insulation properties of blown cellulose insulation are provided by the cellulose structure itself, then cellulose straw has equally good properties.
With the growing demand for sustainable building solutions, alternative materials are gaining more and more attention. Straw insulation and straw bale construction technology both promise environmentally friendly and economical solutions, especially in agricultural areas where straw production is in surplus. This article shows how straw chips and straw bales can be used as thermal insulation and highlights the benefits and challenges of the technology.
Use of straw chips as thermal insulation
Finely chopped dried straw shreds, which can function in a similar way to recycled paper blown cellulose insulation, can be made flame retardant and pest resistant by appropriate treatment and impregnation (e.g. with borax or boric acid). Such a material can be used as blown-in insulation, just like cellulose. Shredded straw also easily fills any voids in the wall structure, so it can be particularly useful where piping and electrical wiring are drained in the wall (insulation).
Besides boron derivatives, other flame retardants are also used. These include phosphate-based compounds, which are also effective in fire protection. In addition, water glass is also an option, although its use is less common as it requires special treatment to preserve fibrous structures.
Advantages of using straw:
- Environmentally friendly use
Straw is a rapidly renewable raw material that is available in large quantities as an agricultural by-product. - Cost-effectiveness
The raw material is available locally, reducing transport costs. - Good thermal insulation properties
Straw has a low thermal conductivity, effectively retaining heat in winter and preventing the home from overheating in the summer heat - Sound insulation
Straw is like cellulose – its structure is excellent at absorbing noise. - Sustainable solution
Shredding and handling can be done with simple technology. - Gap filling
The material fills all small gaps and cracks, preventing the formation of thermal bridges.
Challenges:
- Ensuring protection against moisture is key to avoid mould and rot.
- Strict treatment procedures must be applied to achieve good fire resistance.
Modern applications of straw bale masonry
Straw bale construction has a long history that can be further developed with modern technologies. Treating straw bales with borax or other flame retardants improves fire safety while maintaining the masonry’s insulation and sustainability benefits.
How does it work?
- Straw bales are placed in layers in the wall structure.
- The outer layer of the bales is reinforced with wire mesh and then covered with a protective covering.
- Modern impregnation materials are used to protect against weathering and pests.
Advantages:
- Extremely low cost of masonry
- Locally available materials
- Excellent air transmittance properties to help control indoor humidity.
Challenges:
- Strict standards and certification required to ensure fire and moisture resistance.
- Requires specialist construction skills.
Straw could open a new era in sustainable architecture
The use of straw bales in construction has also been a long-established solution, offering a natural raw material similar to cellulose. In folk tradition, straw bales have also been used for load-bearing purposes, but today’s building standards would impose strict requirements that would make the use of straw bales for load-bearing purposes much more difficult. For this reason, modern straw bale architecture prefers to use straw bales as infill masonry for timber framed structures, thus ensuring structural safety and ease of construction. Borax-treated straw bales can also be used as a modern thermal insulation material, especially in masonry structures where the use of natural and sustainable materials is a priority.
Thermal insulation and masonry solutions based on straw chips and straw bales are excellent examples of how agricultural by-products can be transformed into useful and sustainable building materials. With modern treatment technologies, these materials can provide a competitive alternative to traditional insulation systems while contributing to the protection of natural resources.
Tiling of prefabricated wood-straw panels:
This is quite different from stacking bales of straw on top of each other, or filling a woodpile with straw on site. Here the walls are made of prefabricated wood-straw panels, i.e. a modular timber frame filled with straw, prefabricated to size in a factory and the finished elements are delivered to the construction site so that there is no waste on site, and then craned from a truck directly onto the plinth.
These wood-straw panels offer a prefabricated, energy-efficient and cost-effective solution for building walls, roofs and floors, with a simple installation process.
Key positives:
- Prefabricated panels represent an innovative construction system.
- Versatile: Panels can be used for external and internal walls, roofs, gable ends and floors.
- Construction benefits: this system offers significant time and cost savings on construction sites.
- Easy installation: the installation process is quick and simple.
- Market alternative: these panels are a real alternative within the construction industry.
Disadvantage:
- Our country is not in the tree line on this one, and the straw is rotting outdoors due to our declining livestock production.
The website of the European Straw Builders’ Association lists hundreds of projects – none of them Hungarian.
Issues (fears) related to the use of straw in construction:
– Why straw?
Straw can become a key player in decarbonising the construction industry. It is not a new concept and has advantages over many other materials in terms of environmental sustainability. For example, the exterior walls of the Feldballe School extension were made of straw cassettes from EcoCocon, the straw panel manufacturer.
Building with straw is nothing new. In fact, straw, reeds, twigs and mud have been used in ‘construction’ for more than 10 000 years. Since then, the industrial revolution has completely changed building practice, introducing the mass production of steel, glass and, not least, concrete. However, the colossal climatic and environmental impact of industrialised building materials is as indisputable as their durability, and presents us with a crossroads that requires us to rewrite the end of history.
Straw has many advantages, such as being a renewable resource and biodegradable. As straw is a widely available agricultural by-product, building with it emits less carbon dioxide than composting or burning the material. In addition, straw avoids complex manufacturing processes and significantly reduces energy consumption in production and transport, effectively minimising its carbon footprint.
– What is the difference between straw and cane?
The reed is a tall, rigid and perennial plant that grows in wetland environments such as marshes, lakes or alongside weakly flowing water. Straw, on the other hand, is the dry stalk of cereals, such as wheat or rice, which remains after the grain has been harvested. Both reed and straw have advantages and are suitable for different environments and architectural styles. The choice between reed and straw can often depend on factors such as local availability, climatic conditions and desired aesthetics.
– Wouldn’t it be easier to stick to other, better researched and used materials?
It takes time and effort to bring “new” materials to the market. We must insist that industry moves towards low carbon solutions. We cannot solve the problems with the solutions that created them – and it may be challenging to move in new directions, but the long-term outcome of a sustainable future will certainly outweigh the current barriers.
– Straw is a highly flammable material, shouldn’t we be afraid of that?
Contrary to popular belief, straw is highly resistant to fire. Straw can be compressed to such a density that, when combined with clay or gypsum without oxygen to feed the fire, it can withstand a 1050°C flame for more than two hours, according to EcoCocon fire tests. Straw has a high silica content, which is a natural fire retardant. Straw buildings must also comply with local fire codes to ensure the safety of occupants in the space.
– How long can such a straw structure last?
Modern straw construction techniques date back to the beginning of the last century. Many structures made of wood and straw still exist today. By designing a dismountable structure (e.g. Feldballe School), you can replace individual panels if there is a leak or damage to a particular area of the building but if it is well maintained, it can have a lifespan of more than 20-30 years.
– Is straw a potential nesting site for insects and rodents?
Straw lacks nutritional value for rodents and does not attract them. In addition, it is heavily compressed and does not provide a favourable environment for rodents to build burrows or seek shelter.
Insects, including termites, are not attracted to straw.
Straw structures are subject to the same preventive measures as any other building material.
The questions and answers are based on henninglarsen.com.
Straw baling technology can also benefit those interested in natural building methods, especially in regions where sustainability and the use of local materials are a priority. Vapour proofing and waterproofing of such masonry walls deserve special attention, as does the use of modern materials (e.g. wire mesh, extra impregnation) to protect against rodents, rather than just earthen masonry.