Wood products as carbon storage – the Hiilijemma project studied the responsible use of wood in construction

The Hiilijemma project was launched out of a desire to provide clarity to the discussion around the use of wood in construction. As part of the project, SYKE (the Finnish Environment Institute) produced a study on how an increase in wood construction might impact emissions from construction and the carbon balance of Finnish forests.

Text: Aila Janatuinen
Read the article in Finnish: Puutuotteet hiilivarastoina – Hiilijemma-hanke tutki puun vastuullista käyttöä rakentamisessa

Construction and the use of buildings are a major source of CO2 emissions, which is why there is an urgent need to find quick ways to reduce their carbon output. Meanwhile, there is a heated public debate about increasing the carbon sequestration in forests, also known as carbon sinks. Even professionals find it difficult to follow the discussion.

The Ministry of Agriculture and Forestry of Finland dedicated part of its “Hiilestä kiinni” funding programme to the “Hiilijemma” communications project, which was conducted by the Federation of the Finnish Woodworking Industries, the Finnish Sawmills Association, and Tapio Oy. The project’s goal was to clarify key concepts to make these discussions easier to follow. SYKE (the Finnish Environment Institute) played a key role in the project by conducting a study on how much an increase in wood construction could reduce emissions from construction and affect forests’ role as a carbon sink.

Research data and international agreements

The report outlines scientific studies on the climate impact of wood construction and presents a number of calculations made in various contexts. This information and an assortment of case studies were used to calculate the reductions in CO2 emissions that can be achieved with different levels of wood construction. Tarja Häkkinen, D.Sc., who works as a research scientist at the Finnish Environment Institute, conducted the aforementioned part of the study.

Sampo Soimakallio, D.Sc. and head of unit of the Finnish Environment Institute, covered the decisions, calculation methods and modelling related to climate policy. Climate policies are decided at international climate conferences, and their targets are set at a global level. Inevitably, the processes are simplified in individual countries.

In Finland, we have already collected a hundred year’s worth of excellent data on our forests’ past. The future is more difficult to model because natural processes are strongly tied to weather phenomena and climate change. Changes in legislation and other possible policies on forestry resource use are a third factor.

Wood use is part of the carbon cycle 

Wood is produced from carbon dioxide and water by solar energy. The formula for photosynthesis is simple: a tree absorbs carbon dioxide from the atmosphere as it grows, storing the carbon and releasing oxygen. The carbon stored in the wood is retained in the resulting wood products for their entire lifetime. Wood lasts a long time in buildings, enduring for decades and sometimes even centuries. The carbon stored in this manner is removed from the atmosphere for this entire time. The production of wood products requires little energy from fossil fuels, which means the carbon footprint of construction products is quite low when they are manufactured from wood. In turn, this means that increased wood use will reduce overall emissions from construction products since the carbon footprint of many other materials is higher.

Reducing emissions and increasing carbon sinks

Forests and wood products are part of greenhouse gas emission calculations. As much as reducing emissions and increasing carbon sinks are important, their value varies for different actors depending on the type of regulations that will be applied in future and how they will affect the development and economic value of emissions and sinks. This is one of the reasons why the discussion in so heated.

All building materials have the potential to reduce their CO2 emissions, but some require expensive and time-consuming investments in R&D. Low carbon options will still take some time to enter the market and become competitive, and from a climate perspective, emission cuts need to be quick.

Wood construction cuts emissions quickly

The current Finnish government recognises that increased wood construction is a way to reduce carbon dioxide emissions, and this is why its programme supports developments in construction.

Because wood-based construction products have such a low carbon footprint, increasing the share of wood construction offers a quick way to cut CO2 emissions. The Federation of the Finnish Woodworking Industries commissioned Granlund Consulting in 2020 to calculate how much potential there was for cutting emissions by increasing the share of wood construction in accordance with the construction industry’s low-carbon roadmap. The resulting study included ambitious scenarios for increasing the share of wood construction

and also looked at its net impact. This meant investigating how much the increased wood construction in the various scenarios would reduce construction’s CO2 emissions. The study also assessed how a potential increase in the use of raw wood might affect the forests’ carbon sink. The review period was from 2020 to 2035.

Impact on construction emission reductions

Häkkinen examined the studies on reductions in emissions and the assumptions used to calculate these reductions. She confirmed that the growth in wood construction presented in the scenarios could amount to a reduction of up to 1.4 million tons of carbon dioxide.

Increasing the use of wood also raises the amount of carbon stored in Finland’s building stock. Häkkinen’s assessment notes that apartment buildings and sheltered housing have the greatest potential for increasing the share of wood construction.

The net effect can be deemed positive

Soimakallio used the existing models to examine how much the additional need for raw wood would affect the carbon sink provided by forests. If an increase in construction were to significantly increase the logging of trees, the carbon sink in Finnish forests would decrease. However, wood construction uses sawn timber, of which approximately 70% is currently exported. This is why three options were evaluated: increasing the amount of domestic logging to provide the increased amount of wood, redirecting the current production of wood products from the export to the domestic market, or expanding the base of raw materials to small logs and improving the efficiency of resource use in production.

Calculations indicate that net emissions will remain more or less unchanged between 2020 and 2035 if no more than about two-thirds of the additional wood needed comes from increased logging. Redirecting exports to the Finnish market has a neutral effect, as do redirecting the current volume of harvested wood to sawing and more efficient use of raw materials.


The study shows how even an ambitious increase in wood construction can be achieved while keeping the net effect on emissions positive. Diverting production to the domestic market and increasing processing are also good goals because these steps add value and create jobs. 

Thanks to the low volume of emissions from the manufacture of wood building materials, the use of wood rapidly reduces CO2 emissions from construction. And, rapid emission cuts are necessary to prevent average temperatures from rising. On a larger scale, this can all be accomplished through international agreements. In the case of the EU and Finland, regulations will play an increasing role in setting the course.

On a practical level, cuts can be made building one at a time. For example, the carbon footprint of a wooden apartment building constructed right now may be 30% lower than that of a corresponding concrete building. This is a choice that can be made today.

To see the Hiilijemma materials, visit https://tapio.fi/projektit/hiilijemma/.


Author Aila Janatuinen works as a senior advisor at the Federation of the Finnish Woodworking Industries. She has extensive experience in various advocacy positions in the wood products industry.