Materials technology

The materials that buildings are made from are often given secondary importance to more eye-catching spatial and architectural qualities. But for us, the fabric of construction is always the first and most fundamental question; to be challenged, carefully weighed against environmental impacts and examined in molecular detail. How does it perform? Not just in isolation, but in real world complexity, over time and in different circumstances? Where does it come from? How is it produced? These are essential questions if, like us, you want to assess and minimise whole lifecycle carbon use and create genuinely affordable, healthy, more comfortable buildings.

And you really don’t need to dig very deep to discover that many mainstream construction products are not only bad for the environment and harmful to human health; they also don’t work very well.

Foamed plastics, for example, demonstrate excellent u values and are everywhere in the built environment, but perform poorly, apart from as thermal insulation. Because insulation values are only one aspect of a material’s capacity to contribute towards human health, comfort and well-being. Other more subtle (but easily measured) aspects of performance include vapour and thermal buffering, emissions of volatile organic compounds, properties of fire resistance and acoustic separation. These characteristics are important because they have a very direct bearing on the health of a building and its occupants.

Then there’s the question of what happens to a material over time and in different circumstances? So, for example, the thermal performance of mineral wool insulation is significantly reduced if exposed to moisture, which is a chronic problem in many typical wall and roof constructions. Moisture ingress can arise from a variety of sources, but the poor hygroscopicity and capillarity of mineral wool makes it an inappropriate insulation choice in many circumstances, because it doesn’t easily dry once wet.

And what happens to a material at the end of its life? Will it, one day in the distant future, be found floating in the sea or washed up on a beach? Gradually breaking up into millions of micro particles, to be consumed by animals and then by humans?

At Natural Building Systems we’ve simplified the choices, by avoiding all petrochemical derived or high embodied carbon products and materials that don’t lend themselves to re-cycling or re-use. Though this immediately rules out the majority of existing ‘off the shelf’ construction solutions, we don’t need to compromise, because the performance of plant-based materials is often far superior to their synthetic alternatives. And where we can’t find appropriate plant-based materials, we’re inventing new ones.

HempSil

Hempsil is a unique bio-composite, developed and patented in our laboratory. Comprised primarily of hemp shiv, it is similar to hempcrete (hemp + lime), but instead uses a low carbon binder to produce an insulating board with lower density and therefore better insulation properties. It has several advantages over hempcrete, in that it does not require intensive drying and produces a more robust, durable rigid insulation board. The pore structure of hemp shiv allows the material to absorb and desorb water vapour, regulating indoor temperature and humidity. These exceptional hygrothermal characteristics enable it to harness an effective thermal mass many times greater than its physical mass. In addition to outstanding thermal and acoustic insulation properties Hempsil is naturally fire retardant.

Why Hemp?

Hemp is a truly remarkable plant. Ready to harvest in 4 months, it absorbs around 11 tonnes of carbon per hectare per year. This makes it one of the most efficient carbon capture mechanisms available. In comparison, commercial forestry sequesters on average 4 tonnes of carbon per hectare per year. When grown for fibre it is used in a wide range of textiles, paper and many other products, while the woody inner core of the plant is processed into shiv.

As an annual crop, hemp integrates into rotation cycles, so it doesn’t compete with food supplies. In fact, hemp improves the yields of subsequent crops and so enhances food production. For example, winter wheat when grown after hemp shows a 10-20% yield increase.

Hemp can be grown without herbicides, pesticides or fungicides, therefore it’s good for biodiversity. The high planting densities suppresses weed growth, so pesticide and herbicide requirements are reduced for subsequent crops. The root system promotes soil health, as large tap roots penetrate deep into the soil facilitating aeration while simultaneously forming soil aggregates to prevent erosion.

MilaFoam

In most applications, plant-based materials meet and exceed the performance of synthetic alternatives. However, fire regulations in the UK now specifically exclude the use of bio-composites in the walls of residential high-rise buildings. Natural Building Systems is therefore developing a low-carbon, non-petrochemical and entirely non-combustible alternative to polyurethane derived foamed insulation. MilaFoam will have comparable thermal insulation properties and characteristics to PIR foam, but at a fraction of the environmental cost.