Jim Hart SBE0089

Written evidence submitted by Jim Hart

Introduction

Alongside my work as a sustainability consultant I am also a PhD candidate at Edinburgh Napier University, researching the role of biogenic (or nature-based) construction materials in a low carbon economy, so my answer mainly focuses on that question.

Questions & Responses

What role can nature-based materials can play in achieving the Government’s net zero ambition?

Nature-based materials undoubtedly have a role to play, and should be supported, but it is easy to overstate the extent to which material switching can solve our problems. Furthermore, complacency about the benefits of nature-based materials has the potential to lead to some negative outcomes, as a number of traps lie in wait, as follows.

• Many building products are composites of nature-based materials and synthetic or mineral binders and additives (such as bicomponent fibres, glues, flame retardants, etc.) with the additives in some cases having high embodied carbon, so the embodied carbon of each product needs to be evaluated.
• If we are considering a major shift towards timber-based construction, we should already be a long way into a domestic tree planting programme to support it (even though much of our current construction timber is imported). When a tree is harvested, not all of the carbon in the tree is retained in durable products, with a fraction being re-emitted to the atmosphere relatively quickly following use as packaging or fuel for instance. So a rapid increase in wood use will result in an initial decrease in the forest carbon stock (compared to the counterfactual), which is offset by an increase in the stock of carbon in buildings. Any such loss is not typically accounted for: in this respect at least, agricultural crop residues for instance have an advantage. Importing the additional wood from the UK’s current suppliers is not a solution either, as there is evidence that some such countries are already presiding over forest carbon losses. The need for tree planting to support any ‘more timber’ strategy indicates a requirement for a more strategic approach to land use, with enough land brought into forestry to meet the diverse needs not just of increased production, but biodiversity, ecosystem services, recreation, etc.
• There is a possible rebound effect associated with using ‘virtuous’ materials, in that if a material is viewed as being green, then there is a reduced incentive (leaving cost aside) to use it efficiently. This is especially true in the case of nature-based materials, which are often discussed as being ‘carbon negative’, implying (incorrectly) that the more we use the better. This runs counter to everything that is known about sustainability.
• More thought needs to be given to improving the account through life extension, reuse, and recycling. Energy recovery through combustion of waste wood is no better than landfill, as the environmental cost of the carbon release is not sufficiently offset by the value of the heat generated when wood is burned (which will, itself, reduce over time as energy networks are decarbonised).

Should the embodied carbon impact of alternative building materials take into account the carbon cost of manufacture and delivery to site, enabling customers to assess the relative impact of imported versus domestically sourced materials?

Yes absolutely. It is essential that as full a carbon account as is practicable is produced for all materials and products under consideration. In some cases this may uncover some unpalatable truths that need to be considered, such as shipment of materials (both biogenic and mineral materials) from Europe to the Far East for processing, and back again.

How should we take into account the use of materials to minimise carbon footprint, such as use of water harvesting from the roof, grey water circulation, porous surfaces for hardstanding, energy generation systems such as solar panels?

In the context of a whole-life carbon account of a building, the embodied carbon of solar panels needs to be evaluated just as the embodied carbon of insulation is. The challenge is the lack of data on the subject, and work is evidently required here. The other features identified (water harvesting, porous paving etc.) should also be included in the account: in such cases the environmental benefits associated with water resources will subjectively outweigh the carbon cost in the better designs, but – either way – the carbon cost should not be swept under the carpet. It would be difficult to quantify the indirect carbon benefits associated with such measures (e.g. the contribution to flood prevention and the destruction of property / resources), so there should always be room for discussion of such points alongside any quantitative analysis.

What can the Government do to incentivise more repair, maintenance and retrofit of existing buildings?

• Correct the imbalance in the VAT regime between new-build and retrofit etc.
• Focus on jobs in areas starting to be affected by blight / depopulation etc.

May 2021