Plant based building

We all know that a vegan diet is one of the single biggest things most people can do to fight climate change, but do you know that plant based materials are the equivalent, game changing solution in the building industry? Current mainstream construction is part of the problem, but with education and open minds this can be reversed with plant based building. Plant based buildings can be beautiful, they are part of our shared human tradition, and in addition to helping fight climate change, they can be healthy and comfortable too!

Currently, the building industry “contributes 20% of New Zealand’s emissions”, and embodied carbon alone accounts for “9%” of this, according to the New Zealand Green Building Council. High embodied carbon building materials include; reinforced concrete, steel, aluminium, many types of insulation, glass, as well as the many fossil fuel derived plastics used in a typical building. The mining, manufacture, transportation and installation of these materials is the ‘embodied carbon’ component. It is important to note that the full emissions from these materials i.e. 9% of NZ’s annual emissions, are realised on, or before the first day of the buildings completion. Our conventional buildings then go on to create additional carbon emissions during their lifetime, via lighting, appliances, and artificial heating and cooling systems for example. Plant based building can tackle both of these carbon emission components i.e. both the embodied and operational emissions.

Nature’s building blocks

Obviously, plant based building uses plants in construction. More specifically, plants are used in the framing, cladding, insulation, or finishing elements of a structure. They have been one of the most common building materials throughout human history along with minerals. As such, plants form a big part of our built heritage. Evidence of this can be found in the regionally based, vernacular dwellings in many places throughout the world. Such buildings speak of culture and place, and I believe they are very beautiful. It is only in recent history i.e. after World War II (WWII), that this tradition largely died, and natural materials were typically replaced with plastic and synthetic alternatives. So for all, or most of human history, up until WWII, we were pretty much exclusively building with plants and minerals.

The most common plant based building material is timber. As you will all be aware, the typical kiwi home is currently, and has mostly been, built with this material. Timber is often used for framing, flooring, foundations, cladding, lining, and finishing in this country. Along with timber, bamboo is also often used for structural building purposes in many other parts of the world.

Although not commonly done at this stage, we can also make good use of plants for insulation. Plant fibres, such as wood shavings, straw, and hemp can be coated in a clay binder to form the light earth material. This can then become the insulation, and a backing for plaster finishes in timber framed homes. If you mix hemp fibres with a lime or magnesium based binder, and install it in a similar method to light earth, it becomes hempcrete. Alternatively, straw bales can be tightly packed into a timber frame, to also become the insulation and a backing for plaster finishes.

You can also go down the plant based insulation path with more conventional, industrially made materials such as, prefabricated straw structurally insulated panels (SIPs), wood fibre insulation, and cellulose insulation for example. There are also new products coming to the market, such as mycelium insulation panels, although fungi aren’t technically plants!

Thatch is a common and historical plant based roof and wall cladding material used in many parts of the world. The best examples use water reeds, and will last around 30 years in the UK, Ireland and Europe. Another common historical plant based building material is wattle and daub. The ‘wattle’ is a woven timber or bamboo lattice work, that is then ‘daubed’ with a mineral based material such as clay, along with straw. This can then become the infill in a timber framed structure.

Building for the climate

So how does all this help the environment you say?

As plants grow, they take in carbon (CO₂), and transform this into cellulose and starch via photosynthesis. If we then use the plant in our buildings, this stored carbon becomes locked in, or sequestered. As long as the building stands and is sound, the carbon is removed from the atmosphere, thereby helping to reduce the climate changing effects of too much carbon up there. So in contrast to conventional buildings, that cause ‘X’ number of emissions, plant based buildings can have ‘-X’ emissions i.e. they can sequester more carbon than was emitted in their construction. This way they can become part of the solution, rather than a big contributor to the current climate crisis.

Another important environmental consideration with building, is what happens at the end of the structures life. Ideally our buildings would be occupied for hundreds of years, as they often were historically. After WWII, many societies starting substituting ‘forever’ products with disposable products, and many of our buildings were no longer consider permanent structures. So in the event that a building is going to be dismantled, it needs to be done so in an environmentally friendly manner. Plant based building materials can simply be composted after decommissioning.

Transportation of materials to the construction site is also a contributor to ‘embodied carbon’. With plant based building, it is often possible to use local materials, and thereby reduce this component. In contrast, many industrially manufactured materials used in NZ, are actually made in other countries. Furthermore, plant based materials need little processing, so this side of the ‘embodied carbon’ equation can also be reduced.

Plant positives

Operational energy is the other aspect of building emissions. Many plant based wall building systems are highly insulating. They can also have a component of thermal mass and hygroscopicity. This is unique among insulation materials, and can lead to very high performing buildings if designed with good passive solar principals. The high insulation can reduce heat loss in winter, and heat gain in summer. This influences the amount of artificial heating and cooling required to maintain occupant comfort levels, and hence reduce operational energy consumption. The thermal mass side of the equation acts as a heat and ‘coolth’ battery, allowing the wall to perform much better than conventional walls with a similar insulation value (R value), but lacking thermal mass. Thermal mass allows a material to store midday heat during winter, and then release it in the evening. Conversely in summer, the heat from the day can be purged at night, allowing the wall to be a source of ‘coolth’ during the day.

The hygroscopicity of plant based materials, allows them to absorb moisture in the air, during times of high humidity, and then release this during dryer periods. This gives the wall good ‘hygrothermal’ properties, and helps keep the interior environment in the safe and comfortable humidity zone for human occupants. As well as helping to maintain comfort levels, this also promotes occupant health, as it reduces moisture associated issues such as dampness, condensation, mould, as well as increasing thermal performance.

Plant based materials can also be vapour permeable, or ‘breathable’. This allows moisture in the air to freely pass through them, rather than condensing on the surface. This also contributes to a healthy home, with less problematic, moisture associated issues.

Plant based building materials are generally safe for us. We have evolved with them, and they are typically non-toxic, and do not off-gas dangerous chemicals, as do many conventional building products. The exception to this is when chemicals are added to the plant based material for some specific reason. The main example of this is chemically treated timber. However, there are alternatives here, such as using naturally durable timbers, or the safe non-toxic acetylation treatment instead. Other examples include the chemical treatments added to cellulose insulation, or the glues used in wood fibre insulation, and if these are a concern, you may want to consider other plant based materials that do not contain added chemicals, such as light earth, straw bale, or hempcrete for example.

If we really want to take responsibility for the climate changing effects of our buildings, then we need to reduce the high embodied energy materials we use, and substitute them with carbon sequestering, plant based materials wherever possible. In addition to this, we need to reduce the amount of energy our buildings consume during operation. Plant based building can do this, with it’s unique combination of high insulation, hygroscopic, vapour permeable, and thermal mass properties. In addition to these climate change fighting qualities, wider use of plant based building will also have added positive effects to our health and comfort, and they can look and feel pretty good too!

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