Carbon storage in wood-timber 1/2

Storage (binding) of CO2 in wood/timber is a hot issue at the moment*. But how should that be calculated really? Before I go into more detail, a few preliminary remarks:

(the part on ‘calculating’ has been later added, and ‘CO2’ has been adapted)

Building in wood is always a good thing, even apart from CO2 storage: it is in any case lower in process energy consumption compared to other common materials/building methods. That has been proven often enough. Moreover, wood as a material is renewable and, if used properly, does not lead to exhaustion and degeneration of the system, as many other raw materials in current volumes do, (think of sand..), apart from other negative effects during extraction of alternatives. In addition, the construction adaptability is much greater and simpler, as well as a lighter foundation is needed, and could even be done on simple point foundations. Something I won’t go into here now.

But what about CO2 storage or sequestration in wood?

It took me a while to grasp the essentials, of all that juggling with CO2. Since if we want to calculate with storage, at least we should do it properly and honestly. And then the central question is: is the absolute change in CO2 emissions present for a certain activity, negative or positive? (The question is in principle general, applies not only to a building, but also to a ’table’ for example)

When building with new wood, it starts with felling a tree, and use it as a column for instance, at t=0. Was, at that first instant, CO2 emitted or extracted from the atmosphere? No, at that point only a tree has been felled and used for a beam or column. The CO2 in the wood had already been stored, nothing has changed at t=0 at that moment. (except for some energy for cutting and sawing perhaps, the embodied energy, but we’ll consider that separately).

conclusion: Collecting new wood for construction at t=0 does not capture CO2!

Next the house starts to lead its own life and a new planted tree can grow again. Suppose at t= 50 (for example, 50 years) that tree has matured and the house is still there: ergo, now CO2 has been stored in that tree during those 50 years, while no emissions have taken place from that felled tree used for construction in the house. You can then say that in an absolute sense CO2 has been extracted from the atmosphere, but at most as a dynamic calculation: growing CO2 storage over time, and only at t=50 in the same quantity of the wood felled at t=0.

There are however a few requirements that must be met:

1 There must be a new tree regrown, planted or the like, ( or the plot from which it has been harvested must have regrown).

2 that regrowth must also be insured and directly traceable and linked to that house/building. Some shady arguing like “no forest has been cut in the Amazon” doesn’t do (see the guardian story on this [1] )

3 the house is still there. If not, no CO2 has been stored. As well as no CO2 emitted, in principle. (I will come back to reuse of wood) .

4 That house must remain standing even after t=50. In the first place, when it is broken down and fired up, extra CO2 has been captured, but is destroyed at t=50. In that case at most there is balance, material has been used without positive but also no negative impact. But that applies to all materials or raw materials, the difference then lies in the processing, the production energy, the embodied energy.


When it comes to applying CO2 storage in building evaluations, as follows: Different phases in the construction process are defined by the tc350 guidelines: A: for mining or harvesting resources, B: for construction, C: operation and D: end of life phase. Internationally, when it comes to carbon in timber, its common to use the +1/-1 or the 0/0 approach . The +1/-1 approach is aimed at the A and D phases, , and states in fact: Yes you store CO2 at the start, but in due time it will be emitted. So we feel rich in the beginning, but in he end we get the bill. In 0/0 it says we don’t count it, not now and not later. Following the analyses in the beginning both fail: regarding +1/-1: you don’t store anything at the start, so the +1 is incorrect, but its also speculative to think the house/timber will be burnt in the end. With 0/0 the first 0 is correct, but 0 at t=50 is also not satisfying. The way to deal with this then should be the 0/+1 approach , but only if conditions 1-4 are met.


By the way, this is a building level evaluation. And a relative approach, because the remaining CO2 emission budget has an absolute limit (and it is ultimately about CO2 emissions, that’s what the whole analysis started with). And keeping the CO2 emissions within that budget requires an approach at a higher abstraction level, across the entire stock, and whether we can still build anyway. After all, also in wood construction, emissions are created at the start, because of the embodied energy, the energy needed for processing and building itself, of wood, but also of the other materials that are also needed in wood construction, foundation, glass, installations, etc. ***
In short: When we talk about CO2 emissions and storage, we should not stick to a building system boundary, but look at real-time absolute CO2 effects.


The CO2 calculation is also another calculation as a ‘wood as raw material’ analysis! At t=50, CO2 , while the tree is growing, is indeed increasingly fixed (under the conditions mentioned), but that does not apply to wood as a raw material!! From t=0 there is even less raw material available, temporarily: only at 50 years the (wood) balance is restored and only after those 50 years will there be a net benefit , for both wood as available stock or as forest as added forest area. (wood ‘stored’ in the house is no longer available as stock)


The above is the analysis with regard to new wood and new construction. What about ‘old wood’ then? Its not guaranteed hat the old wood, and the CO2 stored in it, has actually been supplemented and regrown during the lifespan of that former building: that wood may also have come from clear felling for plantations. So the old wood does not come with included CO2 storage, and therefore has no effect on the absolute emission calculations. And since no wood was harvested for construction of the 2nd building, nothing was planted, and there is therefore no growing CO2 storage during the 2nd lifespan.

By the way, not building today at t=0 , in whatever material, and planting more forest**, is in all cases still better, with regard to the short-term absolute CO2 targets.

Th arguing and outcome might not lead to a popular approach,  but fundamentally I cannot see another way of arguing…



PS: will be followed soon by a part 2/2 , with the relation of biobased resources to land-use and time.



*: energy instead of CO2

Disclaimer: I am not in favor of calculating in CO2, which is an end of pipe approach, treating consequences instead of causes. The cause is our energy consumption (especially for materials for our extravagant consumption), fueled by the idea of limitless capitalism) and it is therefore better to calculate in energy sec, of whatever origin: because energy is also limited and always causes an impact, if not in CO2 then in material exhaustion and pollution.

And suppose we have made the energy supply CO2 emission-free at some point, and CO2 storage has become less opportune, then less energy consumption is still a highly relevant factor, because that makes a difference in the construction of energy generation, and the materials required.

Calculating in CO2, (focusing on 1 consequence) leads to the fact that we start building an alternative energy supply like crazy, to keep all our wealth upright with the dream that if everything is made of renewable energy, it no longer matters what we do. Well, that’s just problem shifting. That is with blinders on focusing on only 1 part of all cycles. About that another time.

** forests

Viewed from a forest (-stock), nationally, it is important to know whether all the wood harvest is already used as wood and therefore lready claimed as CO2 storage in the long term…? I didn’t specifically look at that. Because in that case the question is how to deal with new wood demand due to new construction? Is it based on existing forests, which have already been completely claimed? Or are those forests not fully utilized, and is there natural decay with CO2 emissions, which are then prevented by harvesting…?


The foregoing mainly concerns the CO2 emissions of a building in relation to the raw material wood. However, the intention is to gain control over CO2 emissions, and then we have to enlarge the scope. Added to this is of course the embodied energy of the processing and construction itself, and although these are lower for a wooden building than for alternative materials, there are indeed CO2 emissions from that building, right from the start. The embodied energy is somewhere around 4-6 GJ per m2 building, and depending on the production method, this is all fossil energy, and therefore CO2 emissions. A wooden building therefore also starts with CO2 emissions. Certainly in the first instance, new construction therefore increases our CO2 problem.

And even if timber construction is preferable, I the case of comparing buildings, what matters is that we have to reduce CO2 emissions quickly, and then it is not the relative better or worse compared to other buildings that counts, but the absolute emissions, from whatever origin. We should be at 0 by 2050, according to current policy, but if we look at the budget ( to have a chance to stay close to 1,5 degree), it will be in just a few years’ time. [2] An argument such as “we have avoided emissions because we do not build in concrete” does not hold, we still have absolute emissions.

Also calculating in reductions compared to a normal situation then no longer makes sense, there is no time. Building, both actual construction, as at stock level, must therefore be in relation to the absolute CO2 emissions, and ensure that these remain below a certain level, as a whole, and then there is only limited activity possible, even so for timber construction.

Of course, timber construction does lead to less of a problem. And if the aforementioned conditions are met, you could therefore gradually calculate a proportional part of negative emissions each year, whereby the actually emitted emission of embodied energy must first be compensated, after which a possible net negative balance can be established, which should in any case be achieved before 2050, but in fact much earlier, given the absolute budgets. In any case: as long as there are still net emissions at the start of a project, this will only increase our problem, while we should already have achieved a 50% reduction by 2030, knowing that we will also be renovating existing buildings on a large scale, with the necessary emissions as a result.

It is therefore necessary that we keep an absolute and cumulative CO2 accounting, about the entire construction task (and of course also for other sectors).


[1] Carbon offsetting is not warding off environmental collapse – it’s accelerating it

George Monbiot, Guardian, 26-01-22


Author: ronald rovers