Issuu

BUILDING IN TIMBER W I T H I N N AT U RE ’S L I M I TS

MAIN AUTHORS

Adrian Campbell (Change Building), ORCID 0000-0002-9384-0484 Hana Svatoš-Ražnjević (ICD Institute for Computational Design and Construction at the University of Stuttgart), ORCID 0000-0002-4622-5403 Alastair Ogle (Waugh Thistleton Architects)

ACKNOWLEDGEMENTS

Supporting authors: Hans-Jakob Wagner and Achim Menges (ICD) Harry Mortimer and Kirsten Haggart (Waugh Thistleton Architects) Contributors: Arup, CONFOR, Elliot Wood, Evolving Forests, Soren Jensen Engineering and The Royal Society of Forestry. Peer reviewer: Dr Morwenna Spear of the Biocomposites Centre at Bangor University.

The research was supported with grant funding from Built By Nature (grant G-0033).

Published under Creative Commons CC BY-NC-SA 4.0

IMAGE COPYRIGHTS

C I TAT I O N

A. Campbell, H. Svatoš-Ražnjević, A. Ogle, H. J. Wagner, A. Menges, H. Mortimer, and K. Haggart, Using Wood Well: Building in Timber within Nature’s Limits. Stuttgart, Germany: ICD University of Stuttgart, Change Building, Waugh Thistleton Architects, 2026. doi: 10.18419/opus-19343. v1.1: Published September 2026 Publisher: ICD University of Stuttgart, Change Building, Waugh Thistleton Architects Accessible at: https://doi.org/10.18419/opus-19343

“we measure what we care about… and care about what we measure”. -Donella Meadows1

USING WOOD WELL

B U I L D I N G W I T H I N N AT U

APPROACH TO THE RES

THE METRICS

R E S U LT S

W H AT W E L E A R N T

AVAI L AB LE O UTPUTS

REFERENCES

URE’S LIMITS EARCH

B U I L D I N G W I T H I N P L A N E TA RY L I M I T S

B U I L D I N G W I T H I N N AT U R E ’ S L I M I T S The identification and assessment of Planetary Boundaries2 has significantly changed the understanding of sustainability over the last decade. The recognition of finite limits to earth system has informed approaches like Doughnut Economics3, supported revisions to longstanding definitions of sustainability 4and influenced regulation towards climate neutrality, the Circular Economy and construction regulations and strategies. However, quantification of the boundaries is complicated, tracking cumulative environmental impacts. The Using Wood Well (UWW) research proposes three projectfocused metrics that shifts the emphasis to the sustainable use of materials not just their initial sustainable supply. This requires changes in industry norms and a clearer and much needed direction for the industry to enable this shift.5 The metrics quantify bio-based material use on projects compatible with this recognition of nature’s limits. It adopts a model of ‘strong sustainability’6, to suggest ways of quantifying the longterm sustainable use of renewable materials. This would meet rising demand for timber, help preserve Critical Natural Capital7,8 and transition to ecologically informed construction9. The idea is not new. Herman Daly previously suggested tests to achieve this, in what are sometimes called the ‘Daly Rules’ (Box 2.1)10 to: 01

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1) Limit use of all resources to rates that ultimately result in levels of waste that can be absorbed by the ecosystem. 2) Exploit renewable resources at rates that do not exceed the ability of the ecosystem to regenerate the resources. 3) Deplete non-renewable resources at rates that ... do not exceed the rate of development of renewable substitutes. Whilst the research is focused on the second of these ‘rules’, together they identify the need to think critically about the scale of all materials used in building. This emphasis on resources, not just carbon, mirrors other work, such as on resource productivity11, ‘re-materialzation’ 12 and the importance of design for durability13. W E A K S U S TA I N A B I L I T Y

S T R O N G S U S TA I N A B I L I T Y

N AT U R E N AT U R E

MONEY

PEOPLE

MONEY PEOPLE

Figure 1: Weak sustainability vs. strong sustainability USING WOOD WELL

APPROACH TO THE RESEARCH

Figure 2: Aims of the research related to system leverage points 03

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A P P ROAC H TO T H E RES E A RC H

The research considers bio-based material use in buildings from a theoretical, methodological and practical standpoint. By clearly defining the purpose and more deeply rooted beliefs behind the work it provides a more rigorous basis for the development of the metrics for their application in practice. This approach is common when thinking about systems, identifying what are often ‘leverage points’14,15 to help scale the impact of the approach. The research therefore looks at issues that are less apparent to the day-to-day technical work of building design and questions established approaches. The research therefore considers: Purpose: methods compatible with strong sustainability principles and building within nature’s limits. Structures: a clear methodology for the quantification of metrics for sustainable wood use consistent with ecological principles. Patterns: trial the use of the metrics on the assembled project data to explore how much and how well wood is used in buildings. Practice: suggest industry design and assessment parameters that can be used to reduce building impacts.

USING WOOD WELL

APPROACH TO THE RESEARCH

HUMAN TIMESCALE

Figure 3: Scale for Renewable Materials - Using illustrative values. 05

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P L A N E TA R Y T I M E S C A L E

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THE METRICS

WUI EFFICIENCY This is a measure of the efÏciency of wooden construction products in buildings. volume of wood (m3) in products / building area (m2)

BIO CONSISTENCY This is an measure of the significance of biomaterials used in the building relative to other non bio-based materials within the same scope. It is defined as a percentage of: wood-based material by volume (m3) / all material by volume (m3)

URR SUFFICIENCY This is a measure of the sufÏciency and long term sustainable supply of resources and using materials for longer than they take to grow. time in use (years) of a product / harvest time (years) of the source material Figure 4: Using Wood Well Metrics 07

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THE METRICS The UWW project develops metrics for wood and other plantbased non-wooden materials in construction and compares this to other metal, mineral and fossil based materials. A bio-based materials are both ecologically and economically constrained (they can only grow so fast and there is competition for their use), they need to be used more effectively, in higher value products that last longer, and more efÏciently, in the right amounts to suit the needed performance.

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THE METRICS

WUI EFFICIENCY

This is a measure of the efÏciency of wooden construction products in buildings. volume of wood (m3) in products / building area (m2) WUI can be calculated for varying elements scopes: Floors - WUIfloor Superstructure frame - WUIframe Whole building - WUIgeneral / WUIbuild Areas will use both Gross Internal Floor Area (GIFA) and Gross Structural Floor Area (GSSA) to suit the focus of the designer. By knowing ranges of wood intensity across different structural systems it is possible to compare different materials approaches, and improve the design to reduce and manage costs.

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BIO CONSISTENCY

This is an approximate measure of the significance of biomaterials used in the building relative to other non bio-based materials within the same scope. It is defined as a percentage of: percentage of wood-based material by volume (m3) / all material by volumes (m3) The calculation does not determine the amount of biogenic carbon in products simply the ratio of living to non-living materials used. This value may change during the life of a building as systems and materials are replaced. The metric is used alongside WUI and URR in the project results to give context to their use and help indicate the scale of carbon storage within the structure.

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THE METRICS

URR SUFFICIENCY

This is an indicative measure of the sufÏciency using materials for longer than they take to grow. It is the ratio of: time in use (years) of a product / harvest time (years) of the source material The metric provides a lower (market) and upper (average actual) range of how long materials ‘last’ in a building. It can be calculated for: Material/products - URRmat Frame - URRframe Building - URRbuild Harvest time is assumed the average of available species growth estimates. URR is averaged by mass (kg) of elements. Ratios above 1.0 suggest using renewable materials within the limits of longterm sustainable supply. 11

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New Build Commercial

London, UK

GENERAL

W O R K S TA C K dRMM

WUIgeneral 2023

STRUCTURE TYPE Panel Timber - Steel frame M AT E R I A L -

ENGINEERED WOOD CLT

SPECIES Spruce

GSSA 1601 m2

TIMBER VOLUME 621 m3 Workstack Exterior

WUI

BIO

URR

Figure 5: Workstack data USING WOOD WELL

THE METRICS

L0 - 4718

L1 - 695

L2 - 56

L3 - 1

Figure 6: Numbers of projects at each level of data quality 13

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R E S U LT S Building data is defined in three ‘levels’ reflecting how much detail was available:

LEVEL 0 InsufÏcient data to make some assessment of efÏciency.

LEVEL 1 Basic data with quantities of wood and building floor area sufÏcient to make some assessment of efÏciency.

LEVEL 2 Detailed data on the superstructure and built floor areas to undertake floor and frame assessment including URR.

LEVEL 3 Detailed quantities on all wood elements including frame, façade (skin), finishes (surfaces) and partitions (space plan). The following graphs show WUI and BIO metric applied to data at Levels 1 and 2. URR assessments are undertaken on Level 2 data only. They can be viewed at a larger scale and interactively using the data explorer platform.

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THE METRICS

L E V E L 1 - W U I G E N E R A L D ATA

Figure 7: Level 1 - WUI values for buildings shown by material type

L1 data only provides a quantity of wood used, not in what elements. However, it is more likely to be in the structural frame as this is the largest timber volume and easiest to quantify. WUI ranges are variable across the various framing methods and materials used. The data shows that timber is used in small and medium scale buildings under 15,000 m2 in total. 15

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L E V E L 2 - W U I F RAM E V S . F L O O R A R E A D ATA

Figure 8: Level 2 - WUI values for Structural frames shown by frame type

This provides further detail of WUI of the superstructure using GSSA (Gross Structural Slab Area) above DPC level as the basis. WUI ranges are similar to WUIgeneral. The drop off in WUI with area may just be that there are less all timber structures when the scale increases.

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THE METRICS

L E V E L 2 - W U I F R A M E V S . B I O % D ATA

Figure 9: Level 2 - WUI values for Structural frames sorted by BIO

WUI increases as the significance of timber also increases. This is fairly self-evident but emphasises that WUI should be stated with its corresponding BIO value and structural type. Data now suggests possible ranges to categorise timber buildings.

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L E V E L 2 - U R R F R A M E F O R F R A M E S D ATA

Figure 10: Level 2 - URR values for structural frames sorted by BIO

URR for wooden materials in structures is typically near or above 1.0 when considering average lifespans. This suggests softwood is being used sustainably in structures. Slower growing species can still achieve the threshold value of URR>1.0 and supports the use of hardwoods in long-lived structural systems (eg LVL, CLT or sawn elements).

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W H AT W E L E A R N T

The amount of resource used needs more consideration if material use is to be sustainable.

Use products for

SUFFICIENCY (URR)

AV O I D

longer and more than once

Optimise resource EFFICIENCY

REDUCE

(WUI)

carbon costs

Substitute timber

ECOLOGICAL CONSISTENCY (BIO%)

SHIFT

for higher impact materials

Develop carbon

BIOGENIC STORAGE (URR / BIO%)

use to reduce

STORE

pools using long lasting products

Figure 11: Resource reduction hierarchy 19

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RES OURCE FLOWS NOT JUST CARBON I M PAC TS N E E D AS S E S S I N G Overall demand for resources is increasing whilst material efÏciency is potentially declining.16 Whilst the decarbonisation of buildings is critical, achieving this is based on how much material is used over their service life, not just their relative initial environmental impact. The volumes of wood used over what period need more consideration, and how this is to be supplied. Quantifying resource flows provides awareness of the scale and the value of materials in building. The UWW metrics help promote discussions on alterative nonwooden resources that are available, how and where they might be adopted and how much and how long they might be used for. They help understand: - Reducing the scale of flows (WUI) - Slowing resource flows (URR) - The significance of resource flows (BIO) - The rate of development of built carbon pools (URR) Taken together, the metrics help assess the scale and significance of biogenic flows to non-renewable (minerals and metals), utilising constrained – if renewable – resources more carefully.

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W H AT W E L E A R N T

NOT TIMBER BIO <20% VOLUME

SOME TIMBER BIO 20 - 50% VOLUME

M O S T LY T I M B E R BIO 50 - 95% VOLUME

ALL TIMBER BIO >95% VOLUME

Figure 12: Timber building definitions 21

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TIMBER BUILDINGS NEED A CONSISTENT DEFINITION Timber is used in multiple ways in buildings and across many different sectors. Typically, composite and hybrid systems are used to project performance requirements that might be challenging to achieve in all timber systems. What makes a building a ‘timber building’ is subjective. The results of the metrics application emphasise this, showing a variety of ways different wooden structural systems and elements can be applied. A proposed hierarchy of timber buildings based on material volume was developed based on the scale of the volume of timber used. All timber: principally for all CLT and / or glulam frames Mostly timber: covering a wide range of hybrid uses Some timber: where timber is used only partially in the frame Not timber: where timber use is only marginal Although the emphasis is on the superstructure system, the amount of wood used in non-structural (facades, lining materials, partitions, etc.) can also be significant. Initial quantative thresholds for each category are informed by the data results (see WUI and BIO relationship below).

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%AGE

W H AT W E L E A R N T

AV E R AG E

MINIMUM

POTENTIAL

50-60

100-120

150-200

TIME years

Minimum criteria often adopted for safety, warranty provision or commercial criteria and often adopted in life cycle assessment methods e.g. in lifecycle costing

Average service lives assuming reasonable maintenance e.g. as a basis for more typical estimates of impacts.

Potential service life, a new aim for extended life achieved through careful design and construction and then diligent maintenance and selective replacement.

Figure 13: Approximate building life distribution diagram 23

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DESIGN AND SERVICE LIFE CRITERIA NEED CLARIFYING There are a bewildering number of terms used to define how long a building or component might ‘last’ in use. Over 40 were identified just for this project. Design lifespans and suggested replacement periods are currently based on market requirements and what is ‘economically reasonable’ to repair. There is no consideration of what may now be ecologically necessary. The timescales that are adopted often do not help identify either much shorter (temporary) use or longer building lifespans greater than typical structural design working life or WLC Reference Study Periods (RSP) of about 50 to 60 years. Assumptions also vary across countries. There is roughly a factor of two difference between B4 component replacement rates noted in the UK RICS Whole Life Carbon Assessment methodology17 and Danish average lifespan data compiled by BUILD for Danish WLC assessment18. Three possible lifespan criteria can be identified dependent on the motivation for their use, minimum, average and potential. The reference service life values noted in Declaration of Performance & Conformity (DoPC) certification should be clear on the intention of their use.

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W H AT W E L E A R N T

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U R R H E L P S D E M O N S T R AT E S T H E VA L U E OF BIO -BASED PRODUCTS Despite the variability in growing conditions and goals on harvesting periods (species type, intended product goal, local microclimate, soil type and management method etc) it is possible to identify broad timescales of renewability (including new very rapid, super and hyper fast groups) of plant-based resources and their use in construction products. URR values (see table) indicate the potential of wood and biobased non-wooden products to last significantly longer than they take to grow. They therefore satisfy the second ‘Daly Rule’ and the threshold that was originally set out. Using URR for product certification across a wide variety of forestry, farming and fishery resources may provide a useful way to emphasise their ecological value. This might support their increased utilisation, and form a useful basis for demonstration of use within nature’s limits not just being a renewable supply.

Figure 14: Renewal Data Table - Data is derived from a review of construction products but not individual EPD. Product uses are derived from Timber Construction Manual19 and Manual of Multi-Storey Timber Construction20 for products species use. The uses in products are indicative only. USING WOOD WELL

W H AT W E L E A R N T

NOT TIMBER BIO <20% VOLUME

0 . 0 3 - 0 .1 1 W U I F R A M E Timber Features

SOME TIMBER BIO 20 - 95% VOLUME

0 . 0 7 - 0 . 2 4 W U I F RAM E Timber-Concrete Composite

M O S T LY T I M B E R BIO 50 - 95% VOLUME

0 . 2 3 - 0 . 4 3 W U I F RAM E C LT / G LT F r a m e w i t h C o n c r e t e P o d i u m

ALL TIMBER BIO >95% VOLUME

0 .1 4 - 0 . 4 8 W U I F R A M E C LT F r a m e

Figure 15: Typical timber building frame types using representative projects 27

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W U I A N D U R R C A N O N LY B E UNDERSTO OD WITH BIO The efÏciency of wood use measured by WUI is dependent on how much of the system is made of wood. It therefore needs to be understood with BIO. Although reasonably self-evident, as the percentage of wood increases, the intensity of wood use per m2 also increases. WUI is also impacted by design and performance requirements. Differences in WUI may be influenced by a building’s design requirements (structural type, floor loads, seismic performance etc) or the architectural form (longer spans, massing irregular plan forms to fit plot boundaries, cantilevers etc). The same applies to URR when considered at a building level. Higher URR values are associated with more wood in the framing system. Lower URR values reflect the reduced significance of wood use even if the URR of the wood material itself is still high. Whilst URR can be assessed at a building level, the values are significantly impacted by non bio-based material use as allocated by mass. This demonstrates the scale of the challenge of shifting to more ecologically based construction. Structural framing approaches can also identified with their relative WUI and inform early design targets and cost estimation. These values also help make early estimates of possible carbon storage. USING WOOD WELL

W H AT W E L E A R N T

D ATA R E P O R T I N G M E T H O D S S H O U L D A L I G N W I T H S U S TA I N A B I L I T Y A I M S Despite increasing industry digitalisation, and take up of BIM and LCA, reported data on timber buildings is often hard to come by and/or poorly and inconsistently assembled. This includes basic project information on the building area and the quantity and type of timber system used. Only 695 of 4718 data points collated had sufÏcient data (Level 1) to undertake even a basic assessment of the efÏciency or significance of wood use on projects. More detailed information (Level 2) data on structural framing was possible for 56 projects with significant manual development of data to fill gaps. 1 project was trialled with comprehensive data (Level 3) to demonstrate how it might be used. Publicly accessible sources were not that dependable, particularly when it came to what building areas had been measured. Data is also often available at different stages of the design process and across different members of the design team. To be useable and useful in practice, the UWW metrics try to reflect what is realistically available and can be generated by the relevant contributors. The mixed and limited access to building data on this project highlights the need for more regular, consistent and open data gathering that allows a clearer demonstration of the scale and suitability of wood use. 29

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UWW METRICS S UPPORT CHANGES IN CO NST RU C T I O N P O L I CY A N D P RAC T I C E The direction of EU construction policy towards carbon neutrality, resource efÏciency and circularity needs to be supported with quantified evidence. Whilst Wholelife Carbon (WLC) assessment provides assessment of carbon impacts, the UWW metrics provide much needed consideration of resource efÏciency, extended service life and carbon storage. The metrics, particularly URR, can be used to inform and support emerging carbon removal and carbon farming (CRCF) methodologies and the additional benefits within the sustainability section of the QU.A.L.I.TY criteria21 and estimates of prolonged carbon storage. The metrics support other industry initiatives, including Built by Nature’s Principles of Responsible Timber Construction22, by emphasising the efÏcient use of resources, understanding of service life and the timescales of potential carbon storage in buildings.

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AVA I L A B L E O U T P U T S

AVA I L A B L E O U T P U T S In addition to this project summary report, other information and datasets are available through the University of Stuttgart’s data repository, DaRUS and through the TDUK and Built by Nature’s websites.

D ATA E X P L O R AT I O N P L AT F O R M Available at: https://architools.drawingtable.net/ UWW/ This visualisation platform includes a selection of charts for better exploration and understanding of the undertaken work than from static representation alone. Users can explore the metric results and project data, search and filter by different criteria such as sector, framing type, height or location. A. Ogle, H. Svatoš-Ražnjević, and A. Campbell, Using Wood Well: Interactive Tools for Analysing Timber Usage and Material Composition in Construction Projects. 2026. [Online].

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02 W O R K E D E X A M P L E Available at: https://doi.org/10.18419/opus-19394 This explains how to calculate and apply the three metrics using an example of a CLT frame on. steel podium as an example. A. Campbell, H. Svatoš-Ražnjević, A. Ogle, H. J. Wagner, A. Menges, H. Mortimer, and K. Haggart, Applying the Using Wood Well Metrics to Your Building: A Worked Example of Charlton WorkStack. Stuttgart, Germany: ICD University of Stuttgart, Change Building, Waugh Thistleton Architects, 2026. doi: 10.18419/opus-19394.

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AVA I L A B L E O U T P U T S

03 B U I L D I N G D ATA S E T Available at: https://doi.org/10.18419/DARUS-6284 This dataset contains basic project information used to calculate and compare WUI, URR, and BIO% values. it excludes sensitive or confidential building projects. For academic and industry research purposes only. Data is sourced primarily from publicly available sources and has not been independently verified. It is not intended for commercial use. H. Svatoš-Ražnjević, A. Ogle, and A. Menges, Multi-Level Dataset of Using Wood Well Metrics on 695 Timber Buildings. DaRUS, 2026. doi: 10.18419/DARUS-6284.

04 D ATA S U B M I S S I O N If you would like to contribute additional data to this project please complete the follow the guidance in this document and complete the data form at this location: https://air table.com/appT7MnQnpFCtoxQk/ pagZXTqI5hVPo7ERM/form

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05 H A R V E S T L O O K U P D ATA Available at: https://doi.org/10.18419/DARUS-6285 This dataset contains a selected sample of harvest data showing estimates of ranges and the assumed average renewal rates. It contains initial product applications for both wooden and non-woodenbased species. It is intended to demonstrate how URR might be assessed at a building not material level using assumed average values for various materials and their uses in products. A. Campbell, Assumed Data for Building-Level Use to Renewal Ratio (URR) Assessment. DaRUS, 2026. doi: 10.18419/DARUS-6285.

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REFERENCES

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E. Neumayer, ‘Weak versus Strong Sustainability: Exploring the Limits of Two Opposing Paradigms, Fifth Edition’, in Weak versus Strong Sustainability, Edward Elgar Publishing, 2025. Accessed: Feb. 23, 2026. [Online]. Available: https://www.elgaronline.com/monobook-oa/book/9781035327898/978103532 7898.xml

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P. Ekins, S. Simon, L. Deutsch, C. Folke, and R. De Groot, ‘A framework for the

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practical application of the concepts of critical natural capital and strong sustainability’, Ecol. Econ., vol. 44, no. 2, pp. 165–185, Mar. 2003, doi: 10.1016/S0921-8009(02)00272-0. [8]

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Lehmann,

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H. Schandl et al., ‘Global Material Flows and Resource Productivity: Forty Years of Evidence’, J. Ind. Ecol., vol. 22, no. 4, pp. 827–838, 2018, doi: 10.1111/ jiec.12626.

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[20] ‘Manual of Multistorey Timber Construction | Hermann Kaufmann, Stefan Krötsch, Stefan Winter | 2018 | BIRKHÄUSER’, Birkhauser. Accessed: Sep. 21, 2023. [Online]. Available: https://birkhauser.com/books/9783955533953 [21]

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Setting metrics for timber use on projects based on a belief that nature has limits.

Built by Nature (BbN) is a not-for-profit organisation, with a mission to lead a global transformation of the built environment by accelerating the responsible use of timber and biobased materials. BbN connects demand-side construction industry leaders across Europe – from city ofÏcials and developers to architects and investors – fostering collaboration and knowledge sharing to drive systemic change. Its funding enables innovative cross-sector initiatives that overcome challenges and amplify the role of biobased materials in decarbonising construction for the benefit of climate, nature, and people