CO2 impact of mass timber

Question: properly harvested timber can be carbon negative, so more should be better. I could pack my design with more timber than I need and it would be better for my building’s GWP numbers. Right?

This does not make sense to me. We should be reducing the amount of material we use, even timber. My sense is that we should only be increasing timber to reduce other materials, not just as a carbon sink. If that were the case I could offset the concrete in the building with a 40m3 unusable block of timber in the basement.

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Yes and no - there are ways to sequester carbon in the long term, but the most effective methods use short rotation crops, e.g., grains and bamboo. The argument for timber is that by removing the grown tree and ‘storing’ it, there is space for a new tree to grow, the balance kind of works, but only for plantation timber, and only if the cycle is optimized, these days the rotation times are being shortened, but in fact should be lengthened.
Your point illustrates the ludicrous market of ‘offsets’, to offset your concrete you need to sequester carbon that otherwise would not have been sequestered, I am not aware of any realistic way to achieve this, at least at the scales required.
Anyway, please join the biogenic materials happy hour tomorrow, it’s on the calendar here: CLF Community Calendar

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there are may people here who know a lot more than I do on this topic (and hopefully they chime in) but i want to briefly underscore your point that will picked up on and draw a comparison to energy use.
we should of course optimize our structure to the greatest extent possible, whatever the combination of wood, steel, and concrete. there is also good wood and bad wood. if we replace concrete and steel with good wood, that’s great! if we replace it with bad wood, there isn’t much environmental benefit at all and it can actually be worse.
if we think about a parallel to energy use, we could have a single building that uses as much energy as half a city but offset all of it with PV panels and technically it is a ‘net zero energy’ building. however, PVs should be used only once we have done other things (passive design strategies, systems optimization, etc) to reduce the required energy as much as possible in the first place.

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I kind of agree with the sentiment of these email trail. I think the best answer is “it depends”, I just saw a comparison between different structural types and some of the concrete types were equal or even have less CO2e than the lowest of the high level of wooden structures.

Hi Will,
Sorry to have missed the happy hour… I will try to make them in the future. Sounds like a good forum to discuss random stiff like this.

Sid and Jeremy,
Thanks for your input.
I’d like to understand how I (as an architect) can best specify for low carbon timber. I’d like to find or create a best-practice specification guide. The same applies to concrete (and steel/aluminum for that matter). How to other architects approach this?

According to the standards EN 15804 and ISO 21930, and the timber PCR, EN 16485, the carbon sequestered into biomass and stored in timber products is considered as a removal in Module A1 and needs to be considered at the end of life as well, as a balancing emission whether the timber is burnt, used for energy recovery, or recycled or reused. For recycling/reuse, the carbon is transferred to the next product system, so reported as an emission in the product system (in C3) and a removal in the recycled/reused product. For landfill, the carbon is either emitted or transferred to nature (reported as an emission). Thus, for a building, there is no net benefit in the reported GWP over the life cycle from the sequestered carbon stored in products, using EN 15804, ISO 21930, EN 16485, EN 15978 etc.

There are benefits from storing carbon for long periods in buildings, but these are recognised using different metrics, for example the removals from increases in Harvested Wood Product used in national GHG accounting or the measurement of radiative forcing over time.
As you say, using timber inefficiently is not sustainable, and there is no benefit at building level, or globally, in using more timber than is needed in buildings. Where timber reduces impact by substituting other materials, then if a given timber quantity can be used in to substitute other materials in a larger number of biuldings by using it more efficiently, then there will be greater benefit. if one building uses unnecessary timber to “take advantage of sequestration” then substitution will be lower and the amount of sequestration will be the same whether it is in one building or many.
My motto is “more buildings in timber, not more timber in buildings”.

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Hi Jane,
If I understand your comment and can relate it to my understanding of carbon reduction goals, then properly harvested/grown timbers have very little long term sequestration benefits. However, due to the immediate need to reduce our carbon footprint the use of timber over concrete and steel (as currently produced) provides the immediate reductions we need to meet reduction goals such as those in AIA 2030 and SE 2050.
To address the above discussions, optimization of a structural system is a given and the use of the term offset refers to carbon sequestration rather the “Offset Credits” trading market which I agree is a potential avenue for greenwash, though I would caution has it’s place given a more robust regulatory oversight.
Afforestation is turning out to be a complicated issue but I get the feeling that properly managed and regulated plantation type harvests still have their place in the carbon reduction puzzle. I don’t fully understand that aspect yet but 3rd party certification is key.

I thought this article was interesting: https://www.dezeen.com/2021/06/18/carbon-negative-solo-house-perkins-will-fred-bernstein-opinion/

It’s also apparent that only ~20% of the timber is used in long term products - which kind of throws the equations out of whack. Short rotation crops seem to be the only really effective measures, what structural grade products are out there that are made from cereal, grain agricultural waste, bamboo or similar?

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If you are not using FSC wood, you are not getting the carbon sequestration benefits of wood. Sometimes, it can be hard to get, especially if you are serious about the benefits of sequestration and don’t want mixed FSC wood. SFI is a Timber Industry certification product designed to get out the cut. Young trees do not sequester carbon at anywhere near the rate of older and mature forests as the industry claims. Think about the volume of a tree ring for old growth versus a sapling. Ecosystem services and ecosystem carbon outside the volume of product produced are considerable and ignored. Mature forests are one of the best carbon sinks that we have. The timber industry has repeatedly shown contempt for efforts to reduce climate change and throws lots of money at the deniers. Climate sustainability language is being co-opted similarly to how the nuclear industry touts itself as a climate solution. Also, if you can get FSC wood with an EPD using the SCS PCR, it will be much better than the UL PCR. However, the SCS PCR is not widely used. There was not a sincere effort to address important issues concerning regeneration times, ecosystem services, ecosystem carbon, etc in the recent revision of the UL PCR last year. Efforts were made to get a disclaimer included, but the result was not meaningful. Mass timber is the #1 marketing thrust of the timber industry right now with many millions of dollars behind it. It is conceivable to use small diameter wood from legitimate thinning for mass timber, but the typical path is to abuse it for clearcuts and more robust extraction. Currently there are also efforts to get FSC implemented for USFS wood as well.

Also, the big timber industry press for more and more wood of any type does a huge disservice to all the other types of EPDs being produced by other industries and skews WBLCA. Many feel that it very much deligitimizes all the rest of LCA when looking at the focus on net positive using uncertified wood.

As the article makes clear, size is an important consideration, but not just for the building itself. I would suggest that the scale of anything, be it a building or the firm that designs the building, is in many ways a significant factor in the sustainable function of the entity. Management of larger entities requires trade-offs that are not part of smaller ventures. Having grown up on a small dairy farm I like to think of it this way: if you can’t walk across your land in a day you can’t manage it by yourself.
Enter managers. Managers necessarily manage primarily with their heads and run the risk of a lack heart. I’m not saying managers are bad but rather that scale is the determining factor and there is the rub.
A small design firm cannot afford that best software, research personnel, and overhead time to produce top of the line LCA. A large firm can afford those things but has thousands of other things to manage as well as the impetus of a big name reputation to uphold. Again, neither firm is doing anything wrong.
I believe that the large firms involved in this space need to set aside time money, and human resources to produce workflows using accepted software and to develop best practices for LCA and then GIVE AWAY that knowledge. Membership and active participation in forums such as this should be mandatory (thank you CLF) and any lessons learned presented freely for all to use.
I don’t know the people involved in the design by Perkins and Will or in the response to the criticisms leveled in this article but it does appear that some obfuscation has occurred, though I suspect it may simply be part of the larger learning process we are all undergoing. I have great respect for the firm and hope that greater transparency is forthcoming so that we may move the incredibly important goal of reducing our carbon footprint forward as fast as possible with minimal mistakes.
We must not become a shadow of the fossil fuel industry, hiding behind lobbyists and lawyers and industry hacks. There’s simply no time.

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With all due respect, @hatscott I beg to differ. SFI, and other third party audited certifications provide equivalent carbon sequestration benefits. Also, SFI timber is NOT an industry certification. SFI is an independent, non-profit organization that is governed by an independent, three chamber board of directors. Happy to provide insight to you and anyone who would like to learn more.

More timber will cost more. Carbon footprint is one parameter to optimize among many.

If sequestration is your goal, maximizing use of carbon-negative materials is an inefficient solution, as there are likely more cost-effective and future-proof ways. For $17/ton Nori.com will pay a farmer to change their farming practices in such a way that absorbs CO2 from the air and stores it permanently in the soil. At this price the entire footprint of some projects could be removed from the atmosphere for ~ $0.25/sf, or a fraction of 1% of project cost. This would be actual carbon removal, which is better than temporary carbon storage and supposed “carbon offsets”.

Haven’t heard many talk about doing this, but in my opinion prevention holds no moral high ground over a cure that is cheaper. Maximize value, minimize impact.

I would like to share this webinar (below) from 2019 with Jason Grant, I believe it was through the Sierra Club. He talks about the carbon impacts of different forest certification schemes. It was quite insightful. There seem to be quite some differences between FSC and other certification methods in regards to regeneration levels of carbon in above ground biomass and in the soil. This webinar was specific to the US. Does anybody have similar information for Canada?

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The issue is that you’re paying the farmer to sequester carbon and using those offsets to allow you to emit equivalent carbon - so you’ve not gained anything, and there is a limit to the land that’s degraded which can be used in this way. There is also the obvious fact that the farmland already has a carbon ‘debt’ through clearing and so you’re using the credit from paying off a debt to emit more.

Prevention is a much more effective solution, and doesn’t reduce the capacity of natural systems to absorb carbon from the atmosphere - whereas continuous logging and land clearing and not only emitting carbon but severely affecting the natural carbon cycle that we need to take the extra carbon from fossil fuels (and cement) and re-sequester them out of the atmosphere.

Your approach assumes the market is an efficient (and moral) measure to sequester carbon, but based on where we are at today this assumption doesn’t really bear out.

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You’re right that Nori’s agriculture-based carbon removal can only scale to so many buildings. But if the status quo is a building with an embodied carbon footprint 10,000 tons of CO2, and with today’s best green design techniques we can prevent 1/4 - 1/2 of that, say, then I think paying to sequester the remainder is a clear improvement. Less carbon in the atmosphere. More thoughts here.

Thank you everyone who has participated in this post chain.

My takeaway from this is “it’s complicated”.

  • Timber does reduce the overall embodied carbon, but is only truly carbon negative if you ignore the end of life. Still, way better than steel and concrete.

  • More timber is only better if it replaces worse materials, even if it does improve LCA results through sequestration. The idea of using more material in order to get better results is ludicrous.

  • Certified timber is important as it ensures replacement of the tree (“good wood”). Different standards have different priorities, and the differences between SFI and FSC, and the arguments for each, could fill a book. It’s not clear to me if one is better than the other purely in terms of CO2e, or if it would affect LCA results in the GWP category.

  • External offsets exist. They are available to counteract CO2 harm done elsewhere. Better not to cause harm in the first place. I don’t full trust offsets. Paying someone money so that I can continue a bad practice sounds a bit like indulgences to me. But better than business as normal. Also it’s a kind of carbon tax which should modify people’s actions. And I need to be clearer about the terms offset and sequester :blush:.

Jens, I’ll watch the video this weekend.

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The importance of the reuse of the timber at the end of the design life has not really been mentioned. In short, the longer the timber is in use, the greater the overall carbon store that can be built. If the timber is designed with deconstruction in mind then this can enable it’s reuse as a primary product and then be reused/recycled in a cascading principal beyond this. Not only does that prevent emissions from new materials being produced but it allows the overall carbon store to increase.

We just wrote an interesting white paper, ‘Our Green Downpayment: Fighting Climate Change by Turning Buildings into Carbon Sinks with Timber Bamboo,’ that compares wood timber with timber bamboo as carbon sinks. It may add some interesting answers to this conversation. I’m new here so if this is an inappropriate answer please kindly let me know.

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This is great, thanks for sharing Tobe. I wonder whether other fibre sources can be incorporated - agricultural waste from grain crops, or waste cotton?