The climate impact of the buildings and construction sector is still headed in the wrong direction. Despite booming investment to increase energy efficiency and lower energy intensity, emissions and energy consumption from buildings and construction have rebounded from pandemic levels to an all-time high.

By the latest assessment, the sector accounts for 34% of energy demand and 37% of energy and process-related CO₂ emissions. Operational energy-related emissions reached ten gigatonnes (Gt) of CO₂ equivalent in 2021 – 5% over 2020 levels and 2% over the pre-pandemic peak in 2019. Similarly, operational energy demand for heating, cooling, lighting and equipment in buildings rose by 4% from 2020 and 3% from 2019.

Graphic by ECOS.

Decarbonising the sector is a priority if there is to be a chance of limiting global warming to even 2°C to avoid the most cataclysmic impacts of climate change. The sector desperately needs to further improve building energy performance, decrease building materials’ carbon footprint, multiply policy commitments alongside action and increase investment in energy efficiency.

Aiming to do just that, last month agriculture ministers in Germany’s states called for the use of wood in new housing projects to be made easier. The quota of wood in residential construction should be raised to 30% by 2030 (from 20% currently), they wrote in a joint letter, saying that forests and wood products make positive contributions to climate protection, resource efficiency and value creation.

Indeed, wood has a far lighter environmental footprint than other building materials like steel and concrete, and even locks carbon away from the atmosphere. A recent study by the Potsdam Institute for Climate Impact Research, found that if most of the new urban population were housed in newly built timber buildings, constructed with engineered wood (wood composite materials), it would save around 10% of the carbon budget needed to limit global warming to 2°C this century.

Sending construction back to its roots

Emissions from major raw material production for conventional buildings, such as cement and steel, accounts for roughly 10% of global greenhouse gas (GHG) emissions. However, according to a new report from the Environmental Coalition on Standards (ECOS), an international network of environmental NGOs, building using timber structures from sustainable forestry can significantly lower that embodied carbon footprint by factors ranging from 10% to 67%.

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Graphic by ECOS.

In fact, “using a wood building frame instead of concrete can reduce emissions by 75%, as well as reduce the whole life carbon of the building by 10–20%,” said Lauri Linkosalmi, director of product sustainability at Finnish wood and paper production group Stora Enso at a recent ECOS webinar.

The added benefit of structural timber – wood used as a building material for beams and columns – is its ability to store carbon for decades and sometimes centuries; potentially even matching the time needed to grow new trees. That could account for a vast amount of global carbon considering structural timber is 50% carbon by mass.

As trees are harvested, their sequestered carbon is transferred into a wide range of products such as building structures, furniture and window frames, but they can also be transformed into short-lived products like bioenergy, paper and single-use items such as cutlery, which depletes wood resources at a faster pace.

To be of most use to the climate agenda, storage should last as long as possible; both to delay the eventual carbon losses and to control demand for harvested wood products. To that end, timber building materials would need to be maintained through multiple reuse and recycling loops in line with the circular economy. ECOS proposes a “cascading” use of wood resources across the sectors that use wood – chemicals, construction, energy, furniture, packaging, paper and textiles – to both conserve forests and address the twin climate and biodiversity crises linked to forest harvests. Today’s timber buildings are not designed with this circularity in mind, and it would require a systemic shift in industry practice to improve longevity, modularity and ease of construction.

Graphic by ECOS.

Research shows that if such mass-timber construction (using engineered wood for load-bearing wall, floor and roof construction) were to become the norm by 2050, annual carbon storage could be as high as 700 million tonnes of carbon instead of just ten million tonnes in a business-as-usual scenario. This would, however, require an optimised use of wood to prevent forest degradation and loss.

“This transition requires a whole value chain collaboration,” said Linkosalmi. “Property owners and investors also need to demand more sustainable buildings, and we need to renovate our buildings so that they have less operational emissions.”

Planetary boundaries to timber construction

Nonetheless, there is a downside to mass-timber construction. Most net-zero scenarios, including those from the International Energy Agency and the Intergovernmental Panel on Climate Change, foresee a role for biomass in the energy transition, but if demand for forest products was to grow equally across the economy, there simply would not be enough biomass to go around.

“Timber buildings cannot be the green transition,” said Susanne Winter, programme director for forests at non-profit WWF Germany, at the ECOS webinar. “A green transition needs first to maintain the ecosystems and their functionality for the climate: the nutrient and water circle, and the biodiversity. We have to stop the overconsumption. We will degrade forest ecosystems by building houses with wood. The planetary boundaries have to be our default settings.”

According to a 2021 report from Material Economics, a consultancy, EU national climate plans forecast a 40–100% increase in demand for forest and agricultural products for energy and materials than will be sustainably available – due, in large part, to the planned increase in bioenergy demand. In fact, global wood consumption is already overshooting the lowest risk boundary of what global forests can sustainably provide by 67%, with this overconsumption only likely to grow, according to a recent WWF report. And this increasing demand for forestry products is cutting the carbon sink capacity of forests, even in regions where forest cover is growing, such as Europe.

Constructing future urban housing with engineered wood has two advantages: first, storing carbon long term in wooden structures; second, avoiding emissions from cement and steel production.

Abhijeet Mishra, Potsdam Institute for Climate Impact Research

This is both environmentally and economically unsustainable for a variety of reasons: increased demand for short-lived wood products and bioenergy re-emit sequestered carbon faster than the forest can grow back. While afforestation is necessary, creating new forests can encroach on land needed for people to live on and produce food, or on other vital ecosystems such as grasslands and wetlands. Such demand for construction timber cannot be solely met with local production and risks increasing deforestation.

“Very often the ‘ecological benefits’ are restricted to the sequestration of carbon, but we also need the humidity and cooling of the forest; we need the forest biodiversity for human health and the ecosystem services,” says Winter. “In our study, we find that the sustainable limit of the forest harvest amounts to less than 50% of the annual growth, as we are already using way too much biomass.”

Using an open-source land system model, the Potsdam study assessed the impacts of increased demand for engineered wood on land use, and the associated CO₂ emissions, until 2100. Encouragingly, it found that if 90% of the new urban population were housed in newly built urban mid-rise buildings with wooden constructions, 106Gt of additional CO₂ could be saved by 2100 – about 10% of the carbon budget needed to limit global heating to 2°C. However, to achieve that, forest plantations would need to expand by up to 149 million hectares and harvests from unprotected natural forests would increase. Although it would be possible to do this without major repercussions on agricultural production, biodiversity would almost certainly suffer to some extent.

“On the decarbonisation side, constructing future urban housing with engineered wood has two advantages: first, storing carbon long term in wooden structures; second, avoiding emissions from cement and steel production – emissions we would make if we kept building with conventional materials,” the study’s lead author, Abhijeet Mishra, tells Energy Monitor.

“[But] a transition like this would come with a heavy loss to biodiversity due to either additional wood removals or conversion of unprotected secondary forests to commercial plantations – mostly driven by increased demand for engineered wood to be used in construction. This loss of biodiversity happens even after we explicitly prohibit any human activity in old-growth forests and biodiversity hotspots in our simulations in response to higher demand for engineered wood in the future.”

Ecological forestry

Indeed, debates around forestry and carbon often pit conservation against harvesting and replanting – but there may be a happy middle ground. Ecological forest management, such as ‘close-to-nature’ forestry, promotes a reasoned level of harvest to reap various rewards.

By extracting some timber while also considering what vegetation is left to grow, foresters can enhance certain forest traits and functions such as their adaptive capacity. After the felling, the remaining forest is allowed to continue growing, encouraging natural regeneration. This allows the carbon sequestration to continue, compensating for – and sometimes exceeding – the carbon removed in the harvest.

In fact, the largest stock of forest carbon is stored underground in the soil and other organic matter. By aggressively harvesting trees through destructive methods like clear-cutting – fully removing the stumps, brush and residues – the soil is exposed to the elements, leading to decomposition and the release of GHGs. This phenomenon only gets worse as global temperatures rise, creating a pernicious feedback loop.

Graphic by ECOS.

Forests, particularly old-growth and primary ones, need to be protected from this as they hold huge deposits of carbon that, if released, create carbon debts that cannot be compensated for with new growth for decades and sometimes centuries.

Furthermore, if forests are not managed correctly – such as the choice and diversity of tree species – they become less resilient to climate-related threats like pests, invasive species, heat drought and fires; once again, exposing the preservation of their carbon.

“We think that timber buildings are a promising climate solution, but only when they also contribute to ecological forestry that protects and restores forest ecosystems,” says Samy Porteron, programme manager at ECOS, and author of its recent report. “By ecological forestry, we mean a management approach that aims at restoring biodiversity so that the ecosystem is balanced to provide multiple benefits to both people and to nature.”

Europe cuts the path

Globally, Europe has been the bellwether when it comes to promoting use of sustainable timber in the construction industry. It has been a focus of the current Swedish EU Presidency – a country with 70% forest coverage.

“Sustainable timber buildings can certainly play a big role in the green transition,” said Sevim Aktas, policy officer at the European Commission’s Directorate-General for Climate Action, at the ECOS webinar. “By introducing a robust certification system, we will encourage responsible forest management. There are multiple work streams happening, with the Commission focused on reusing or recycling wood products at the end of their life and using timber as a feedstock. We are looking into what are the best practices, and which are the most productive ways of putting a policy framework together to support the process.”

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Although the EU has regulated operational emissions of buildings for more than a decade, the bloc still has to properly address buildings’ embodied emissions. Measures have thus far relied on a piecemeal range of policies on ‘whole life carbon’ (WLC) at the national level. However, the Commission is taking steps towards a systematic measurement and public disclosure of the carbon footprint of construction products, and of WLC emissions of buildings, in its legal proposals for a revised Energy Performance of Buildings Directive, as well as through a revised Construction Products Regulation – to take effect in 2030. When it comes to enforcement, the World Green Building Council EU Policy Whole Life Carbon Roadmap has already provided embodied carbon benchmarks for different types of buildings, based on which limits could be set aimed at reducing overall building emissions by 40% by 2030.

There are still some gaps in the science, though. For instance, the path for incentivising the use of timber from sustainably managed forests as a carbon storage solution remains unclear, as data and methodological issues impede a realistic modelling of the carbon storage benefits, according to Porteron. Nonetheless, sustainable timber holds exciting potential to be a key component in improving the climate performance of buildings, prolonging their lifetimes and boosting circularity; and ecological forest management approaches can already support forest carbon storage and provide truly environmentally friendly wood products.

Strong governance and careful planning will be required to ensure any form of sustainable transition to timber cities, even if old-growth forests and biodiversity hotspots are protected. If there is an important lesson from the recent biomass sourcing scandals surrounding another panacea climate solution, bioenergy and carbon capture and storage, it is this: everything in moderation.

Winter, in fact, has an outlandish idea about how to achieve that moderation. “Build less new buildings,” she said, flatly, when asked for her key takeaway at the ECOS webinar. “We keep demolishing buildings to build new ones; instead, we should be improving the old ones. That would be a real step forward for the building sector.”