Incentives for low carbon timber buildings proposed
Friday 5 Apr 2019
The TDS Management Committee is promoting this incentive in support of the government’s One Billion Trees programme to encourage more forestry on marginal lands, and the Zero Carbon Act to reduce the use of fossil fuels. Both initiatives rely on carbon sequestration in forests, and both can be enhanced by encouraging low carbon timber buildings. Such timber buildings will keep more New Zealand grown wood in the national economy, rather than exporting logs overseas.
As trees grow, the process of photosynthesis absorbs carbon dioxide (CO2) from the atmosphere, and carbon is stored in new wood. When trees are cut down, the sequestered carbon stays in the wood and wood products for some time, extending the life of the pool of carbon. The wood components of a new timber building can store significant amounts of carbon for hundreds of years, until the wood eventually decays or is burned.
The eventual goal must be to phase out fossil fuels, because this is the only long-term way to achieve a zero-carbon economy. Forestry is a short-term step to buy time as larger steps are implemented.
According to Dr Andy Buchanan, Professor Emeritus at the University of Canterbury, new forests on unforested land are needed to increase the pool of carbon in New Zealand’s forests. These new forests can be permanent forests (mostly native), or managed forests (mostly exotic). In permanent forests, the amount of sequestered carbon levels off as the forest matures, eventually reaching a steady state. In forests managed for wood production, the amount of sequestered carbon rises and falls during forest rotations, with the average long-term pool about half that of a permanent forest.
To enhance the carbon benefits of forestry, the owners of new buildings should be encouraged to use wood rather than traditional structural materials. A financial incentive could be based on credits for the carbon stored in the wood, paid to the building owner. The benefits of low carbon construction can be quantified.
About half the weight of dry wood is carbon, so one cubic metre of wood which weighs half a tonne (500kg), sequesters a quarter of a tonne of carbon (250kg). This is equivalent to almost one tonne (920kg) of carbon dioxide (CO2) in the atmosphere. Carbon credits and carbon taxes are usually related to equivalent tonnes of carbon dioxide, not to tonnes of carbon.
A typical 200 m2 timber house contains 30 cubic metres of wood, and stores carbon equivalent to 27 tonnes of CO2. The three-storey NMIT Arts and Media building in Nelson contains 460 cubic metres of wood and stores 425 tonnes of CO2. With carbon credits trading at $20/tonne, the building owner would have received a modest cash incentive of $8,500.
Dr Buchanan suggests that the incentive should be a one-off cash payment to building owners at the time of construction, because a single payment for selected timber buildings is much easier to administer than a long-term compliance system for all wood users. In Hamburg, Germany, for example, building owners receive €0.80 for each kg of timber used in new commercial construction.
Structural timber is beginning to compete worldwide with steel and concrete in attractive and functional new buildings, with no increased cost and similar or better safety and performance. The New Zealand construction industry has been slow to adopt new timber technology. Even a small financial incentive based on carbon credits could make a difference. The main markets are commercial, educational, and cultural buildings, as well as offices, hotels and apartment buildings up to 10 or 15 storeys tall. Some timber buildings contain many hundreds of cubic metres of wood.
A further benefit of timber buildings is that wood processing is carbon neutral. The manufacturing processes for materials like steel, concrete and aluminium pump large amounts of CO2 into the atmosphere.
Many building owners are looking for green, renewable, and low carbon construction. Even a small financial incentive may tip the balance towards timber. The benefit to the government will be a small but significant contribution to the national carbon budget. Sustainable timber construction will provide many other benefits of to the national economy, including more forestry jobs, more local wood processing, and regional development.
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