Last edited 05 May 2020

Wood and carbon

1 Introduction
2 Net zero
3 Carbon neutral = Offsetting carbon = Carbon free = Zero carbon
4 Carbon positive = Carbon negative
5 Sequestered carbon = Carbon capture
6 Embodied carbon
7 Operational carbon
8 Taking action
9 Going beyond zero
10 From old to new
11 Zero = Hero
12 Related articles on Designing Buildings Wiki

[edit] Introduction

Net zero, carbon free, embodied carbon and offsetting carbon: each concept is a step in the right direction to tackle the climate emergency, but the terminology needs demystifying.

The article below explores each concept, how it is being implemented and what this means for the built environment.

[edit] Net zero

Since the UK government’s 2019 announcement to target net zero by 2050, the phrase has become the most well known term when it comes to reducing the impact of climate change.

Net zero is the balance between the emissions that are produced and the emissions that are removed from the atmosphere. Emissions are removed by offsetting carbon.

The net zero goal outlined below includes the ways to make it happen.

[edit] Carbon neutral = Offsetting carbon = Carbon free = Zero carbon

The journey to achieving net zero means knowing how to offset emissions. According to the Carbon Trust, carbon neutrality is achieved when the emissions produced are offset by carbon credits or natural carbon sinks.

Carbon credits are permits and work as part of a ‘cap and trade’ programme. Companies that pollute are given a limit, in credits, that they can pollute up to. Any unused credits can be sold to another company that is exceeding its limit. The aim is for companies that pollute to reduce their emissions and over time their limits for pollution are reduced.

Natural carbon sinks are ecosystems such as the ocean or forests. They absorb and store around half of the carbon dioxide (CO2) produced by human activity. However, these ecosystems are under threat due to increased emissions and deforestation.

Political awareness of the need to increase tree cover as a viable solution to reduce CO2 emissions has grown recently. This awareness also places responsibility on the timber industry and wider construction industry to ensure timber is sustainably sourced - particularly tropical timber.

To determine if a building or building product is carbon neutral, there is a standard to prove that it genuinely offsets carbon emissions and is not ‘greenwashing’. PAS 2060 can be used to prove carbon neutrality for buildings, product lines, manufacturing and more.

[edit] Carbon positive = Carbon negative

Confusingly, carbon positive and carbon negative initiatives both seek the same outcome: to remove more carbon from the world than they add. This is the next step after net zero.

[edit] Sequestered carbon = Carbon capture

To sequester carbon is to capture CO2 from the Earth’s atmosphere and store it. This can be done in a natural or manufactured way. Trees naturally absorb and capture CO2, acting as a natural store. Consequently, forests and woodland are considered to be the most efficient natural carbon sinks.

Carbon capture and storage (CCS) is a new technology to remove CO2 emissions from fossil fuel power stations and industrial processes that use or produce coal and gas. The CO2 can be captured in three different ways and in the UK, it is stored offshore.

Carbon can be captured or sequestered in buildings and building products made from wood.

[edit] Embodied carbon

Embodied carbon is defined by the UK Green Building Council as ‘the total greenhouse gas emissions generated to produce a built asset’. This means knowing how much CO2 is emitted from extraction, processing and manufacturing, transportation and assembly of every building product used. It extends to the lifecycle of each product so also considers end of life.

[edit] Operational carbon

Operational carbon is often measured alongside embodied carbon. It is the collective CO2 emissions produced in order for a building to run, from the energy and ventilation systems through to IT equipment.

[edit] Taking action

The UK built environment currently contributes around 40% of the country’s total carbon emissions. To reach the 2050 net zero goal, new homes need to be built to offset carbon.

Even with the most natural building materials, CO2 will be released before and during the construction process. By estimating embodied and operational carbon, designers can ensure this is offset through the materials, products and systems used.

[edit] Going beyond zero

The BaleHaus system uses prefabricated straw bale panels, ModCell and structural timber frame elements. This system works to Passivhaus principles and is made from locally available materials that are designed to be dismantled, re-used and recycled at the end of a typical 75+ year life.

It also has triple glazing, a biomass boiler and energy efficient electrical fittings and appliances. The careful design and specification of the BaleHaus reduces carbon emissions by almost 50% each year. It goes beyond zero carbon as it banks 22 tonnes of CO2, making it carbon positive (or negative) and a carbon capture.

[edit] From old to new

Older properties can be improved too. To reduce the built environment’s impact on the planet, the aim should be to reduce the number of new buildings, reuse as many buildings, materials and products as possible and recycle responsibly if there is no other option.

An example of this was the sensitive retrofit of a home on Walter’s Way, designed by architect Walter Segal. The timber-framed home had its windows replaced, the roof rebuilt and full insulation was installed including the roof. Solar PV panels were added alongside a new solar water heating system, passive ventilation and mechanical ventilation heat recovery, water-saving devices and low energy appliances and lighting.

Where possible, natural materials such as cellulose and wood fibre insulation were used. The result of the refurb was a reduction of 73% in carbon emissions.

[edit] Zero = Hero

The built environment has the tools and the knowledge to refurbish and create homes, offices, schools, hospitals and many other buildings that remove rather than contribute carbon emissions. It is a cultural and educational shift, but it is possible to make beautiful and practical buildings that have less of an impact on the planet.