The construction industry is a big polluter. The manufacturing of building materials – such as steel, iron, cement and glass – contributes to 11% of all global greenhouse gas emissions. A further 28% of emissions can be attributed to the powering of residential and non-residential buildings, totalling 39% for the construction industry. Whilst many countries have regulations to encourage sustainable materials and practices, decisions are often made in favour of cost-efficiency, to the detriment of the environment.
Alternatively, bio-construction aims to work with nature rather than against it. It is a sustainable form of construction that uses alternative building techniques with low environmental impacts. The materials used should, ideally, be readily available in your local area to minimise transportation and cost. Cob, adobe, plastic and glass bottles, local timber or bamboo, old car tyres and other repurposed waste items are a few examples of materials often used. The focus of bio-construction, however, goes beyond thinking about the materials used; it takes a holistic view of the entire space you are designing and aims to close the loop of water, energy and waste systems.
Some key design principles of bio-construction are outlined below, and relate to the 12 principles of permaculture set out by Bill Mollison.
- Use sustainable materials that are locally sourced, free of contaminants (e.g. PVC, asbestos) and allow the building to ‘breathe’ (i.e. moisture exchange).
- Integrate the design into the immediate environment by taking account of the local topography and vegetation, and the land-use of neighbouring plots.
- Optimise the layout of your design by locating and orienting services based on the microclimate of the terrain (e.g. taking advantage of solar patterns for light and heat).
- Capture and store natural resources for example using solar panels, collecting rainwater runoff or capturing wind for AC systems.
- Eliminate, minimise, recover and treat waste through systems such as recycling and composting, dry toilets or redirecting wastewater to irrigate plants.
An added benefit to bio-construction is that it can cut costs compared to conventional methods; cob is cheaper than concrete, for example. But in some cases, financial restrictions may limit the extent to which eco-friendly practices can be favoured. An example of this trade-off, which we observed in Guatemala, is the curing of bamboo; a common practice to extend its lifespan. The most eco-friendly method is to cure bamboo with Borax, but many opt for painting it with gasoline since it is significantly cheaper and more readily available, despite its worse environmental credentials.
Another common trade-off in bio-construction is the use of concrete. Even though concrete is a polluting and relatively expensive material, designs still need to be structurally stable and long-lasting. Ensuring the durability of your design is particularly important in areas at risk of seismic activity, like Guatemala. It is therefore widely accepted that concrete can be used in up to 20% of bio-construction designs for these reasons. [Note: To create concrete, combine two buckets of cement with one bucket of gravel and up to one bucket of water.]
During the 3 months we spent in Guatemala, we learned about multiple bio-construction techniques and had the opportunity to apply them. Below are three ‘recipes’ for how to use cob, car tyres and bamboo.
How to use cob to build walls or seating
- Construct the frame using wood or bamboo (ideally cured to avoid rot). Circular-shaped builds (see image above) have increased durability, important in earthquake-prone zones.
- Combine a ratio of 3 buckets of soil with 2 buckets of yellow sand or pumice and half a bucket of pine needles on a tarpaulin, breaking up any large clumps. If using cow manure, pine needles are not required due to the presence of plant fibres in the manure.
- Create a well in the middle of the dry mix, slowly add water and mix with your bare feet to create a dough-like texture. Add more water or dry material to get the right consistency. Occasionally fold the tarpaulin in half, like a taco, to make sure it is well mixed.
- Roll the cob into fist-sized balls. Then start building up the wall either by applying pressure to the balls to get them to stick or by throwing and splatting smaller balls onto the wall. Splashing water onto the wall helps them to stick.
- Consider leaving space for windows. You can also add glass or plastic bottles to allow sunlight to enter and increase the wall’s structural integrity.
- Once the wall is built, allow to dry for at least 48h (depending on the climate) before adding an outer layer and filling in any gaps that have appeared during the drying process.
- Alternatively, you can make cob bricks by filling a rectangular mould with soggy cob, lifting off the mould and drying the bricks in the shade (to avoid cracking) for at least 48h.
- You can also fill sandbags with a dry cob mix to build up the foundation of the wall, using 3 buckets of soil and 3 buckets of sand. Once filled and sealed, compact the bags on top of one another, either leaving them exposed or covering them with cob.
- Optional: Adorn the wall with a design using the cob and colour with natural paint.
How to use car tyres to build walls, steps, or seating
- If you are building a standalone wall, ideally flatten the ground beforehand. Otherwise, the tyres can be built into any topography.
- Line up the tyres in a row to create the foundation. Use a taught string as a guide.
- Place a thick sheet of tarpaulin or canvas across the inside base of the tyre to create a ‘bowl’.
- Fill with any type of soil available, compacting as you go. You can also add compacted rubbish such as plastic bottles.
- Once filled, use a mallet to push and compact the soil up into the curved rim of the tyre so that it is compact all the way around. Add more soil as you go.
- Use a spirit level to ensure the tyre is flat compared to the one next to it, pressing down on the tyre to account for any bubbles (since it will be weighed down once another tyre is on top). Correct any imbalances either by compacting more soil into the rim of the tyre or by inserting rocks or sticks underneath.
- Add the next tyre and continue. When you reach the next layer, ideally interlock the tyres like a brick wall. Fill in the space behind and in between the tyres with soil or cob.
- If water is likely to accumulate behind the wall, fill in this space with sand and gravel to drain the water and avoid erosion or pressure build up. Tyres are estimated to last 30 years in this state, depending on their exposure to the sun and the rain.
- Optional: Grow plants in the exposed tyres to make the wall more visually appealing.
How to make panels from bamboo for privacy, shade or shelter
- Position the bamboo cane vertically and divide the cross-section into equal segments using a marker pen.
- Cut out vertical strips by hitting a machete with a block of wood from top to bottom – it should split open easily.
- Thin the strips by shaving off the underside with a machete (see photo) until it becomes flexible.
- The strips may need to be cut using a saw, so they are of equal length.
- Space out a few strips vertically then weave strips in and out horizontally (see photo). The strips can then be nailed to thicker posts on either side of the panel.
If you need professional advice with a bioconstruction project, get in touch with Long Way Home who can consult on your design and send you blueprints. They also offer volunteering placements. https://lwhome.org/build-with-us The majority of the photos in this blog were taken in Long Way Home.