Construction goes Net Zero
Intro
In this article, I am going to talk about the carbon dioxide emissions of three building materials. All of the materials will have a major part to play in the construction industry In the future. Construction must decarbonises in line with the UK government’s net zero policies.
The materials I consider are concrete, steel and engineered timber (also known as CLT). I have not considered other carbon sequestering materials such as hempcrete because they do not have the off-site manufacturing advantages and structural strength of CLT.
I will look at their carbon emissions.
What the concrete and steel industries are dong to reduce carbon emissions in their manufacture.
And the natural advantages enjoyed by CLT panels.
Carbon Characteristics
As matters stand in early 2023:
· The manufacture and setting of concrete produces about 0.9 tonnes of CO2 for every tonne;
· The manufacture of steel produces about 1.24 tonnes for every tonne;
Carbon Dioxide Emissions & Climate Change
· Engineered timber (including CLT) sequesters 1.65-1.8 tonnes of CO2 for every tonne of timber.
In other words engineered timber is the only material under consideration which is carbon negative, and very significantly so, too.
By way of explanation of the timber numbers; timber is about 50% by weight carbon (technically referred to as the biogenic storage of carbon). When timber rots down or is burnt each individual carbon atom combines with two atoms of oxygen in the air to make 3.67 kg of CO2.
The carbon dioxide created in the manufacture of concrete and steel is released in the energy consumption required to make them. In the case of concrete in the chemical reactions in the manufacturing process and so is unrelated to any carbon stored in the material itself.
It is however clear from this comparison there is only one construction material that sequesters carbon. Building to net zero standards, can offset the inevitable carbon emissions in manufacturing. Other components in the building, the emissions in transporting materials to site and the energy used in constructing the building.
That material is engineered timber.
Whole Life Carbon Assessments and Carbon taxes
Whole Life Carbon Assessments (WLCA) are coming and will, I think, become ubiquitous in the relatively near future. WLCA’s look at both embodied carbon (the extent to which the construction materials and processes have emitted carbon dioxide in their manufacture, transport and assembly) and operational carbon (insulation, heating, cooling etc).
WLCA’s offer the promise of a standardised carbon emissions in the newly built environment and, a means of monitoring and reporting on those emissions in connection with our COP treaty obligations.
About 20% of Whole Life Carbon emissions relate to the construction of a building. The remainder relate to the operation of the building. To perform well on the WLCA, buildings will have to be low carbon both in build and in operation.
Engineered timber is carbon sequestering ie carbon negative and so will score well on the construction phase of the project. It will also perform well in terms of operating carbon as it is manufactured to very tight tolerances. Timber is also a naturally warm material and will need much less additional insulation than ,say, concrete.
Some local authorities already require WLCA’s to accompany planning applications. This is likely to become more widespread and may be mandated by central government in due course.
We also anticipate that building materials which are not carbon sequestering or carbon neutral, will suffer a carbon tax. The EU has already announced tariffs on the import of high carbon building materials. By 2026- it would make sense for the UK to follow suit.
The role of Carbon Capture and Storage (CCS)
CCS is being promoted heavily as having a huge role to play in converting steel and concrete to zero carbon materials. This is where the carbon dioxide created by the manufacturing process for these materials is captured and stored- often in worked out oil wells- or used to drive oil out of wells under pressure (ironically indirectly increasing carbon emissions!).
One of the ideas currently circulating is that the carbon dioxide stored can then be used in manufacturing processes including, potentially, the manufacture of synthetic petroleum fuel substitutes.
The trouble is that no-one has yet made CCS technology work reliably and efficiently. At present it is hugely energy intensive and expensive and can be dangerous.
While steel can be manufactured, at least notionally, with zero carbon emissions, by using renewable electricity sources, the manufacture of cement is more problematic because the carbon emissions come not only from the energy used in manufacture but from the chemical process itself.
Therefore CCS is absolutely essential to manufacture zero carbon concrete.
The concrete industry is claiming that they can push the technology even further and develop concrete that captures carbon. We have yet to see details of how this could work.
Despite the fact that CCS technology is unproven, expensive and hugely energy intensive, governments have committed very large sums to develop it. For example, the UK government has committed to spend £20 billion over 20 years to scale up CCS in the UK.
As is the case with much of the UK government’s net zero project, such as the widespread adoption of air source heat pumps, we think that the enthusiasm for CCS is likely to wane on contact with reality; once it becomes evident that the policy cannot be implemented, at least in the short term, with current technology.
CCS in Timber production
It seems trite to say it but timber is a natural product which has evolved over millions of years. In simple terms, trees grow when fed with sunshine, carbon dioxide from the air and water.
Trees emit oxygen in the process and produce a material, wood, which biogenically stores about 50% of the material’s weight in carbon.
So trees are natural CCS factories. capturing and storing carbon dioxide in their natural cycles.
The difference between trees and human CCS is that trees capture and store carbon 100% reliably and safely, for free and produce oxygen as a by-product. It is a real, proven, free reliable technology which produces useful wood and oxygen as by-products.
Cost and Other Implications
Building in CLT has now (2023) achieved cost parity with traditional builds. Moreover, it can be significantly less expensive when the speed of construction, finance, overheads and lost rents are taken into account.
We expect concrete and steel to become significantly more expensive as time goes by. The costs of CCS will be recouped in the pricing of the products. There will be tariffs and inevitable taxes applied to these materials if they do not meet zero carbon standards.
Further if, as we suspect, it will become mandatory to prepare a Whole Life Carbon Assessment when applying for planning permission, the argument in favour of building in CLT will become unanswerable.
End of Life
All of the materials under consideration can be re-used or recycled to a greater or lesser extent.
All can be left in situ and re-used, subject to condition of course. This can be a very low carbon solution.
Steel can often be unbolted, re-cycled or re-used (subject to inspection and safety considerations). This is not an option for concrete. If demolished it can only be used as aggregate after an energy intensive process.
Like steel frames, engineered timber is secured mechanically and can be dismantled for re-use. Misleadingly, until now some carbon assessments of engineered timber have assumed that the timber is burnt when the building has reached its end of life.
I think however that there will be a lively market in re-usable engineered panels or even whole buildings in the future.
Construction goes Net Zero
Conclusion
If CCS becomes a widespread technology, (and that is uncertain) the cost of concrete & steel will increase significantly. Engineered timber including CLT will become the cost leader. It is the quickest and easiest material from which to build structural envelopes.
If CCS technology proves to be a dead end, mass timber is likely to become the only material from which to build structural envelopes. It is the only material which has the ability to offset the carbon dioxide emitted by concrete, from which the foundations will still have to be made.
In either event, when preparing the Whole Life Carbon Assessment, the carbon sequestering, tight tolerance and insulating characteristics of engineered timber are compelling and should assist in obtaining planning consent.
Whichever way CCS goes, CLT is the clear winner. CLT combined with offsite manufacture is a great way to build. It’s negative carbon you can fill in your WLCA with ease.
We say Make CLT Mainstream, don’t wait to get with the direction of travel and join us on the journey.
Antony Fanshawe Director Lamella MMC 2023
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