Why I’m building an office out of straw
When we moved into our house, there was a shed in the garden. Its timbers were rotten, the floor had long since disappeared into the ground, there was no door, the window had fallen out and various creatures had moved in.
I decided to rebuild it out of a material that has been used around the world for hundreds of years, but is less commonly seen in modern buildings: straw bales. A year later, and the “work shed” is now nearly finished.
As sustainability assessment lead at Sheffield University’s Grantham Centre for Sustainable Futures, I wanted to make sure my garden office had the lowest possible embodied carbon (a term used to describe the amount of carbon contained, or “embodied” in the materials used to make a product), and low energy use once it was up and running.
That meant the office would need to be very well insulated to avoid using lots of energy to heat it, and made of materials with low carbon content.
Due to its structure, straw is a fantastic insulating material. It’s also cheap, easy to work with, and since the straw absorbs carbon dioxide from the atmosphere as it grows, straw buildings act as carbon stores. If we use this in a building, the carbon remains stored for the lifetime of the building, and can even be returned to the soil at the end of life.
My first real involvement with straw building was through the design of a low carbon cold room in Kenya, working with energy efficiency experts from the Energy Saving Trust and Solar Cooling Engineering, and architects from Switzerland and Kenya. A cold room is an easy-to-build and cheap alternative to a large fridge, enabling farmers in developing countries to store produce at a market, improving incomes and reducing food waste.
This cold room is now operating at Homa Bay market on the shores of Lake Victoria, Kenya. It has cement-free foundations, solar panels and batteries, water storage, low energy cooling units, a timber structure and straw bale walls. The project showed me that straw bale structures can provide good insulation without the environmental impact of expanded polystyrene.
Natural materials like mud, earth and dung, as well as fibrous materials such as straw were used to build homes for centuries.
Straw bale housing history
Straw in bale form has been used for buildings since the 1800s. After the invention of mechanical baler in the US, straw bales were used to construct homes in places where timber and stone were hard to find.
Some of these early buildings still exist, but most straw bale houses in the US were built since the 1970s. These buildings offer warm comfortable homes and were the inspiration for a new wave of UK straw bale builders in the 1990s.
Read more: How we can recycle more buildings
Straw works well for single or two-storey buildings, but requires careful design to avoid water leaking into it. Provided the bale buildings are protected from rain splash at the bottom and have an overhanging roof at the top, water isn’t really a problem. Fire requires oxygen and fuel, so a compressed straw bale is fire resistant, and straw bale buildings have met all fire, planning, and building regulations, and even achieved Passivhaus – extremely high standards of insulation, thermal performance and energy use.
My new garden office has 40cm thick walls and double glazed windows, it’s clad on the outside with reclaimed timber (some of which came from the original shed) and the roof, windows, doors and underfloor insulation are all secondhand. The final step is cladding the inside.
Here I’ve adopted another traditional building practice and used cob. Cob is a mixture of clay, water, sand and chopped straw. After digging the clay from our garden and mixing it, I’ve applied the cob by hand, via an incredibly messy but very satisfying process.
I know that the lifetime greenhouse gas emissions of my shed will be about 20 tonnes lower than they would have been if I had used expanded foam insulation and plasterboard.
People who live in straw bale houses talk about how the irregular shape and natural materials of straw bale buildings also have a positive impact on them, and say that buildings like my shed create a connection with the builder particular to the use of natural materials.
This concept, known as biophilic design, is challenging to quantify but I look forward to finding how it feels to sit inside it.
Stuart Walker is affiliated with The Grantham Centre for Sustainable Futures, University of Sheffield. He receives funding from the Grantham Foundation for the Protection of the Environment.