Materials that come from natural sources and are harvested sustainably are able to be infinitely replenished. Plants such as trees and hemp sequester carbon as they grow, resulting in carbon negative construction materials.

Hemp is a plant which grows rapidly (in 4 months) and sequesters a high amount of carbon as it grows. It does not require water, maintenance, herbicides or chemical pesticides and its deep roots help to absorb harmful chemicals left behind from previous crops. 100% of the crop can be utilised to create products for beauty and food industries and the stem is used to make insulation or building materials. Read more here.

Hemp fibre among other natural fibres as an insulation material has the added benefit of being able to retain moisture without affecting performance meaning it is able to release moisture when required and regulate internal humidity. As a result, many natural fibre insulation products are resistant to mould and damp, in contrast to industry standard synthetic insulation products which do not allow moisture to permeate and trap humid air within a building, fostering mould and damp. 

At our residential project in Hackney, timber and wood fibre insulation was used alongside a vapour control layer which allows moisture to permeate whilst maintaining airtightness to improve efficiency of the external fabric.

Care should be taken to specify materials from sustainable sources, for example FSC certified timber to ensure that resources are not being depleted faster than they are replenishing. If timber is to be used in construction works, consider the possibility of using felled or fallen timber which has naturally reached the end of its life and can be repurposed as construction material without disrupting the local biodiversity and ecosystem. Similarly, all parts of a tree should be considered to reduce wastage - wood chips could be made into board or terrazzo surfaces, wood fibre into insulation.

Using materials that are biodegradable and free from plastics or VOCs reduces the impact of a material once it does reach the end of its lifespan. Materials that biodegrade can be safely disposed of if it is no longer usable or can’t be repurposed, unlike plastic products which take thousands of years or break down into micro-plastic particles. Care should be taken when specifying materials to analyse their make up and any treatment that has been applied that might make recycling or disposal at end of life more difficult.

Cross Laminated Timber is an alternative to carbon intensive structural solutions such as concrete or steel. CLT is quick and easy to install and can be designed to be disassembled at end of life. Read more here.

Other natural building materials such as straw have been traditionally used in construction and signal a return to simpler construction methods. Straw is a by-product of farming and has high insulatory properties as well as being easy to construct with and handle.