We shape our buildings; thereafter they shape us… (Part 2)

Part 2 of our blog post comparing natural and synthetic insulation materials…

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“We shape our buildings; thereafter they shape us…” Winston Churchill (1874-1965)


In Part 1 of this blog article I looked at the problems inherent in trying to reduce carbon emissions in the built environment by using huge amounts of synthetic materials to insulate our buildings. Synthetic insulation materials:

  • are often made from petrochemical materials themselves
  • have very high embodied carbon
  • tend not to be recyclable
  • often contain harmful chemicals that are better kept out of your living environment
  • stop buildings from “breathing”; causing damage to the building fabric and unhealthy indoor environments; and increasing energy demand, through ventilation requirements and damp (cold) walls

In contrast, natural, renewable materials (hemp, straw, timber – in the form of wood fibre insulation – earth, sheep’s wool etc.) – provide a natural, healthy, environmentally friendly way of adding thermal performance to our homes through insulation and/or thermal mass. All these materials are ‘produced’ (grown or collected) locally, and they all come from sustainable sources which can be renewed quickly with no associated increase in carbon emissions. Unlike synthetic insulations these materials can all be recycled at the end of the building’s life; “cradle-to-cradle” products, as they are known, or can be left to biodegrade safely without the cost (financial or environmental) from landfill disposal of hazardous waste.

Further benefits come from the fact that these natural materials, with the exception of sheep’s wool, are plant-derived and therefore have absorbed atmospheric CO2 during their life cycle, which is then locked away in the building’s fabric until such time as the building is demolished and the material is allowed to rot down. In most cases though, at the end of a building’s life, these natural materials can simply be re-used in a new building, so the carbon storage continues.

In particular, hemp shiv (the stalk of the hemp plant, used in hempcrete) sequesters a very high level of atmospheric carbon. This is due to the fact that it is a tall, spindly plant which has most of its branches and leaves at the top – to support this weight it needs to absorb lots of carbon from the air to create a very hard, tough stalk; a cellulose material very similar to timber. Because hemp grows very quickly (3.5 – 4.5 metres in around 4 months in the UK), this is a highly renewable source of insulation material, which also locks a huge amount of carbon away for the lifetime of the building.

In fact recent estimates suggest that even after accounting for all the CO2 emitted during the growing and harvest of the hemp; production of the lime binder; transport and construction on site, a hempcrete wall still stores between 110kg (sprayed hempcrete) – 160kg (hand placed hempcrete) of CO2 net, per m3 of hempcrete material. Developed countries are currently spending a fortune building complicated machines to capture carbon from power stations and factories, and then burying it deep underground. Every hempcrete building is achieving carbon capture and storage without even trying, as a side-effect of the construction process.

In new build these natural insulation materials can be used in combination with passive design principles; making the most of solar gain – storing natural heat from the sun (directly, or via the ground); reducing energy requirements through sensible siting, orientation and sheltering of the building and using passive heat circulation or passive heat recovery ventilation systems, to create the health and environmentally friendly buildings of the future.

In retrofit, especially when upgrading buildings built before 1919, natural, breathable insulations are an essential part of repairing and upgrading the building effectively and safely. They work in the same way as the original materials used in the building, ensuring that the vapour-permeability of the fabric is maintained. The mistaken use of synthetic, non-vapour-permeable insulation materials in such buildings effectively seals up the building, causing damp, unhealthy indoor environments, and cold, wet walls.

New-build projects using raw materials such as hemp shiv and straw should cost about the same as conventional construction methods, however some of the more processed natural insulation materials (e.g. sheep’s wool, wood fibre, or hemp fibre insulations) do currently cost more than synthetic equivalents. This is mainly because at the moment fewer people are using them, though this number is increasing all the time. Economies of scale, the fact that embodied carbon is not properly priced into materials, and tax breaks given by government to the powerful multinational chemical companies, all mean that synthetic insulation products remain cheaper at point of sale and that means many people still buy them, as they always have done, without thinking about the implications for their health, the building fabric, or the environment.

The situation is beginning to change though. Today we are shaping a new generation of homes and buildings, which in their turn will shape us. As we enter one of the most testing periods in human history, facing up to the realities of our survival on this planet, more than ever people are realising that the question isn’t: “can we afford to buy natural insulation materials?” The real question is: can we afford not to?

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