Open AccessArticle

Timber Biogenic Carbon Stock in the Urban Environment: Santiago City as a Second Forest

Felipe Victorero

^1,2,*

and

Waldo Bustamante

^1,3

School of Architecture, Pontificia Universidad Católica de Chile, El Comendador 1916, Santiago 7520245, RM, Chile

Centro Nacional de Excelencia para la Industria de la Madera (CENAMAD), Pontificia Universidad Católica de Chile, Santiago 7820436, RM, Chile

Centre for Sustainable Urban Development (CEDEUS), Pontificia Universidad Católica de Chile, El Comendador 1916, Santiago 7520245, RM, Chile

Author to whom correspondence should be addressed.

Sustainability 2025, 17(2), 529; https://doi.org/10.3390/su17020529

Submission received: 8 November 2024 / Revised: 16 December 2024 / Accepted: 6 January 2025 / Published: 11 January 2025

(This article belongs to the Special Issue Timber's Green Revolution: Sustainable Construction from Start to Finish)

Download

Browse Figures

Figure 1
The study area consisting of 32 municipalities that make up the Santiago province (prepared using <a href="https://mapshaper.org/" target="_blank">https://mapshaper.org/</a> (accessed on 8 August 2024) with ©Mapbox and ©OpenStreetMap). "> Figure 2
Diagrams of structural wood for short and long historical walls. "> Figure 3
Diagrams of structural wood for short and long historical roof spans. "> Figure 4
Diagrams of structural wood for short and long traditional walls. "> Figure 5
Diagrams of structural wood for short and long traditional roof spans. "> Figure 6
Diagrams of structural wood for short and long contemporary walls with OSB panels. "> Figure 7
Wood volume per built square meter according to historical period and according to minimum, average, and maximum scenarios (city of Santiago). "> Figure 8
Material intensity of wood according to historical period and according to minimum, average, and maximum scenarios (city of Santiago). "> Figure 9
Weighted material intensity of wood over entire studied period, according to minimum, average, and maximum scenarios (city of Santiago). "> Figure 10
The annual wood-built surface area (bars) and growth rate (line) according to the average scenario during the study period (city of Santiago). "> Figure 11
The annual wood mass per year according to the average scenario (city of Santiago). "> Figure 12
The age of dry wood mass in the average scenario (city of Santiago). "> Figure 13
Annual biogenic carbon and CO2 storage per year according to average scenario. "> Figure 14
Temporal distribution of CO2 storage per municipality (city of Santiago), made with Microsoft Power Bi Desktop version 2.138.1452.0 64-bit (November 2024). ">

Versions Notes

Abstract

Urban environments significantly contribute to carbon emissions, both through operational processes and the embodied emissions of construction materials, thus exacerbating climate change. Nevertheless, urban timber structures offer a viable alternative by acting as carbon sinks, capable of sequestering carbon for decades or even centuries. This study develops and applies a methodology to quantify the biogenic carbon stored in Santiago City’s timber-based buildings, conceptualized as a “Second Forest” that transfers and preserves the carbon capture capacity of trees in the built environment. The analysis estimates that Santiago’s urban timber constructions have expanded their wood-built surface area by 192,831 m² over the past eight years, reflecting the growing adoption of timber in urban construction. During the same period, biogenic carbon storage increased from 199.78 kt to 202.73 kt, equivalent to 10.84 kt of CO₂ under average conditions. These findings highlight the potential of urban planning strategies, such as promoting taller timber buildings and adopting circular timber practices, to enhance carbon sequestration and reduce reliance on carbon-intensive materials. This research highlights the fundamental role that timber buildings play in urban climate change mitigation, positioning them as active contributors to global carbon management efforts.

Keywords:

biogenic carbon stock; urban wood structures; sustainable urban planning; carbon sequestration; timber urban resources

1. Introduction

Harvest wood products, sourced from sustainably managed forests, have proven to be a renewable alternative with a lower environmental impact compared to materials that are intensive in fossil fuels and contribute to climate change with higher greenhouse gas (GHG) emissions [1,2,3]. Additionally, their potential to capture carbon dioxide from the atmosphere during photosynthesis and tree growth presents a unique opportunity as a material in which wood product manufacturing can store biogenic carbon over its lifespan. In simplified terms, for every two kilograms of anhydrous wood, approximately one kilogram of biogenic carbon can be estimated, around 50% of its mass, which is equivalent to storing approximately 3.67 kg of carbon dioxide from the atmosphere when considering the mass of carbon and oxygen involved [4,5]. This condition remains in time, unless the carbon is released through combustion and oxidation or degraded by biological agents, mainly being released as carbon dioxide and methane.

This potential for atmospheric carbon dioxide storage over time depends directly on ensuring that any wood product remains in the environment for as long as possible and prevents the release of carbon, whether accidental or deliberate. This can be achieved through the manufacture of long-lasting products, reuse, and, to a lesser extent, recycling or modification for other uses, considering that any recycling or modification process tends to lose some material and release stored carbon to some extent.

Consequently, wood products used in construction, especially in structural applications, offer buildings the potential to store substantial amounts of biogenic carbon for decades, or even centuries [6]. Moreover, the lower GHG emissions and reduced environmental impact associated with wood construction offer a substantial potential for decreasing the environmental impact of this sector. Currently, the construction industry is responsible for approximately 37% of atmospheric GHG emissions [7]. Additionally, traditional construction materials such as concrete and steel currently account for approximately 11% of global GHG emissions due to their production processes, in which it is difficult to reduce emissions, and their global production volumes. In fact, approximately 70% of the planet’s anthropogenic mass currently consists of materials such as concrete and aggregates, and it is expected that by 2040, concrete by itself would exceed the entire earth’s biomass [8]. Moreover, these materials are increasingly scarce, requiring transportation over long distances for processing, resulting in emissions and environmental impacts associated with their extraction [9].

By contrast, forest resources are abundant in many regions worldwide and have the potential to grow even further through reforestation and afforestation strategies, offering substantial potential for combating climate change [10]. This is especially important in countries that consider forests and wood products as strategic resources for achieving GHG emission reduction targets and meeting raw material demands. Moreover, durable wood products harvested from sustainably managed forests can effectively help prevent CO₂ emissions, even when sourced from younger forests. For example, newly planted forests, when managed with a focus on denser planting schemes and rapid growth strategies, can capture CO₂ more effectively than older forests [11]. And although older forests capture less CO₂ overall, individual mature trees capture more CO₂ than several young trees; more importantly, they may have stored CO₂ for a longer time, potentially even predating the industrial revolution [12]. Therefore, cutting down old trees in mature forests can have a higher impact on CO₂ release compared to cutting young trees in young forests, where reforestation plans can help capture new CO₂.

Likewise, if the destination of wood products involves a life in construction elements, where the materials’ duration in the built environment could span several replacement tree growth cycles in the environment, any release of carbon dioxide could eventually be compensated. Thus, it is desirable that the useful life of any wood product exceeds the time it took the tree to capture the stored biogenic carbon. Furthermore, forests with rapid growth and carbon dioxide capture, such as those with a regeneration cycle of just a couple of decades, are more appealing from this perspective than forests that are centuries old, where the slower regeneration of carbon capture may outweigh the benefits.

In this context, wooden constructions within the urban environment of a specific city act as a biogenic carbon stock that endures over time and varies depending on the longevity of wooden construction elements in the built environment. Moreover, the integration of new wooden buildings can potentially offset carbon released into the atmosphere or increase urban carbon storage. Furthermore, if wood surpasses the replacement rate of equivalent carbon harvested from the original tree through the planting of a new tree, it could provide a long-term benefit to the global carbon balance. This not only represents a transfer of biogenic carbon from the forest to the city but also creates a carbon reservoir independent of the original forest stock.

In this regard, previous research has attempted to quantify the amount of wood in urban environments using various methods but has encountered challenges that have constrained the results [13,14,15,16,17,18]. Most of these challenges are associated with limitations in the availability of public data on the materials used in buildings, making it difficult to represent material quantities on a large scale and track their evolution over time [14]; the restriction of results to a specific range of building types within particular timeframes and spatial constraints [15]; or the use of material quantity indicators that need to be extrapolated from other contexts [17].

These limitations highlight the need for methodologies that address gaps in the quantification of urban wood use and reduce uncertainty, particularly in developing countries with limited data on construction materials and their environmental impacts. This study focuses on Santiago City as a case study due to its unique urban characteristics, including a growing use of timber in construction and its role as the capital of a developing nation with ambitious carbon neutrality targets. By examining Santiago, this research provides insights applicable to other rapidly urbanizing regions with similar constraints, offering a replicable framework for understanding the environmental potential of urban timber.

The concept of Santiago as a “Second Forest” reflects the premise that urban timber structures can replicate the carbon storage capacity of natural ecosystems. This concept suggests that urban environments, when designed with an emphasis on wood-based construction, have the potential to become significant carbon sinks, simultaneously reducing emissions while enhancing carbon storage. By envisioning cities as anthropogenic extensions of natural carbon storage systems, this study highlights the need for a paradigm shift in urban planning where built environments actively contribute to climate change mitigation by retaining part of the original forest’s carbon through harvested wood products while allowing the development of low-emission buildings in emerging nations.

Furthermore, this perspective emphasizes the broader potential of urban wood use in reducing reliance on carbon-intensive materials such as concrete and steel. Additionally, as a forest-rich country, Chile depends on the maintenance and expansion of its forests to offset at least 50% of its growing emissions and achieve carbon neutrality [19], underscoring the need for an industry that promotes long-lasting and renewable harvested wood products that foster sustainably managed forests. By integrating these principles into policy frameworks, nations like Chile could develop effective strategies to offset emissions while enhancing carbon storage. This approach positions timber construction not only as a sustainable alternative but also as a critical element in achieving carbon neutrality by 2050 and aligning with the nation’s commitments under the Paris Agreement.

The primary purpose of this work is to present a methodology for quantifying the biogenic carbon stored in wooden buildings within the urban built environment of a city, particularly in contexts with limited or no available data on wood material use and carbon storage. Additionally, a secondary aim of this research is to provide an initial understanding of how biogenic carbon is distributed in a large developing city, such as Santiago, Chile. Considering its significant expansion in recent decades and its pressing need for new infrastructure, this study examines the temporal behavior of biogenic carbon and identifies future research directions to improve projections of wood usage and biogenic carbon storage in the coming years.

2. Materials and Methods

2.1. Case Study: Santiago of Chile

Chile has positioned itself as a regional leader in Latin America in terms of sustainability and development in the construction industry. Despite being a developing country, Chile has adopted policies that promote energy-efficient buildings through the implementation of sustainable certifications, alongside tools designed to encourage a more circular construction industry. These initiatives aim to reduce the environmental footprint of the rapid urban growth the country has experienced in recent decades—a characteristic common to emerging nations that face the need to quickly expand their infrastructure. Furthermore, Chile has gradually begun to adopt more complex models for assessing environmental impact, laying the groundwork for the development of life cycle assessments in construction and the quantification of embodied emissions.

Chile is a strong advocate of international climate commitments, being a signatory to the Paris Agreement, which reflects its determination to achieve carbon neutrality by 2050. This goal is supported by a comprehensive strategy that includes significant progress in emission reductions, accounting for 50% of the projected reduction, and the sustainable management of its extensive forests, which cover 17.9 million hectares [20]. These forests are expected to act as natural carbon sinks, offsetting the remaining 50% of national emissions. Within this strategy, the construction sector accounts for approximately 31% of national emissions [21] and is projected to contribute, through sustainable building strategies, at least 17% to the national emission reduction plan.

Over the past two decades, Chile has emerged as an international leader in the adoption of renewable energy, particularly solar and wind energy, with more than 50% of the installed capacity in its electrical system coming from renewable sources. These energy sources have transformed the country’s energy landscape, significantly reducing greenhouse gas emissions associated with electricity generation and, consequently, the operational emissions of the built environment. While the country is expected to reach 100% renewable energy by 2050, and national industries like lithium and green hydrogen enable energy storage, the significant reduction in operational emissions from the built environment alone would not be sufficient. This is due to the construction sector’s heavy reliance on fossil fuel-intensive materials such as concrete. Within this Chilean context, it is essential to understand the carbon-storing benefits of materials like wood in the construction sector, alongside their advantages in promoting a forestry sector that produces sustainable wood products capable of storing carbon and reducing embodied emissions.

The city of Santiago, represented in this study by the 32 municipalities of the Province of Santiago (Figure 1), with a total area of approximately 2110 km² and a population exceeding five million inhabitants, serves as a representative example of national building and public policy trends in Chile. Like many cities worldwide, Santiago faces significant challenges related to urban densification, transportation, and resource consumption. Nonetheless, the city has implemented pioneering initiatives in green infrastructure, urban planning, and efficient public transportation, positioning itself as a model for other cities in the Latin American region. However, the impact of these policies on wood-based buildings and the urban biogenic carbon stock remains unclear. More critically, it is uncertain whether these policies are contributing to biogenic carbon storage or facilitating its release into the atmosphere.

2.2. Quantifying Wood in the Built Environment

Accurately quantifying the volume of wood present in buildings within the built environment is the key to understanding its extent and distribution patterns. This requires considering various factors, such as construction systems, building types, and wood species, among others. Moreover, the potential benefits of wood construction at the urban level can only be analyzed if its scope and variation in space and time are well understood.

However, determining how much wood exists in the built environment is not a straightforward task, and this information is not readily available in all countries. Various approaches can be used to obtain these data, including (i) data from national records, such as building permits or real estate property records; (ii) estimates made through sample surveys, such as censuses or sampling methodologies; (iii) approaches based on aerial imagery and model estimations; and (iv) commercial records of forest production and sales of wood products.

This study is based on the use of national real estate records to quantify wood in the built environment. The case study of Santiago in Chile benefits from tax records maintained by the country’s Internal Revenue Service, which detail the primary materials used in building structures for the purpose of a property tax assessment. This database includes multiple records that allow for the identification of built square meters according to the materials used in structural walls, the intended use of the building (e.g., residential, commercial, educational, or other), the year of construction, records of modifications over time, the quality of construction, and others that are not relevant to this research.

Chilean records have been available since 2018, with updates being made every six months, and they include public access data on demolitions, modifications, and new constructions [22]. These records are gathered using detailed manuals and assessments carried out by professional property appraisers. The eight-year measurement period is due to the system’s digitization in 2018; earlier records exist but lack the consistent structure found in the current dataset. Furthermore, while the Chilean National Statistics Institute (INE) keeps a record of building permit requests, which identifies the main materials used and conducts a national housing census that records the materials of surveyed buildings, these sources are less reliable than the real estate registry. This is because the former does not confirm whether the permitted building was constructed or modified, and the latter faces issues related to survey-based data collection, where residents may provide incorrect or incomplete information about the building systems they inhabit.

The data provided by the real estate record and their uses in this work consist of eight files (from 2017 to 2024) that address urban areas and focus on parcels and building information. The details of the contents of the files can be seen in Table 1.

The Chilean real estate record also provides detailed information at the municipality, block, and property levels, with over 8 million entries nationwide. In this case study, 32 municipalities that make up the province of Santiago or city of Santiago are analyzed (the country’s most densely populated urban area). For the purposes of this study, analyses are conducted at both the city of Santiago and municipality levels, summing the square meters accordingly, to understand how wood and its associated biogenic carbon are distributed within the urban environment. For the same reason, the results and analyses are limited exclusively to buildings that list wood as their primary construction system regardless of whether it represents only a small part of a building complex that may include a greater proportion of square meters constructed with other materials, either before or after.

It is important to note that while the real estate record is the most reliable source of this type of information for this case study, it contains some inconsistencies and lacks detail. An example of this is that it might include properties that have not been properly regularized or have undergone undeclared modifications not identified by inspectors. Additionally, the registry does not specify the construction methods used for wood, making it impossible to distinguish between frame systems or mass timber, which could affect the quantification of the material.

2.3. Historical, Traditional, and Contemporary Construction Systems

Since the record of wooden square meters in the Chilean real estate database refers to the gross built surface area and not the volume or specific mass of the material, a methodology is developed to quantify the material intensity (MI) of wood per square meter. The MI is an indicator that represents the mass of various materials per surface area or volume, typically expressed in kg/m² or kg/m³. It is calculated by dividing the mass of a given construction material by the gross surface area or internal volume of the project that is being measured, which subsequently generates a record for the set of materials used [17]. In this way, by calculating the material in a project (whether based on design specifications, the material used during construction, or the material registered during demolition), it is possible to establish the MI for a specific material. In the case of wood, the mass depends on the equilibrium moisture content, so the MI of wood can be calculated either at the equilibrium moisture point or in a completely dry state.

{M I}_{w o o d} = \frac{V_{ω} \times ρ_{ω}}{G B A}

(1)

where

MI_wood: the material intensity of wood per gross built surface area (in kg/m²).

V_ω: the volume of the wood product at the specified moisture content (in m³).

ρ_ω: the density of the wood at the specified moisture content (in kg/m³).

GBA: the gross built surface area (in m²).

Alternatively,

{M I}_{w o o d - d r y} = \frac{V_{ω} \times ρ_{ω}}{G B A \times (1 + \frac{ω}{100})}

(2)

where

MI_wood-dry: the material intensity of dry wood per gross built surface area (in kg/m²).

ω: the moisture content of the wood, expressed as a percentage (in %).

The MI is commonly used by researchers to track the flow of construction materials within buildings, assess their lifespan, create inventories, study material recovery potential, analyze temporal–spatial identification, and evaluate environmental impacts, among other applications [15,17,23]. Materials associated with products that are prone to renovation, such as interior finishes or coverings, are more difficult to assess over time and to keep a consistent record of. Conversely, structural materials tend to exhibit fewer changes over time and remain throughout the entire lifespan of a building [24].

Since it is impractical to conduct an MI analysis of wood for every building in the case study, an assumed MI is proposed for different types of wooden construction systems. This is achieved by defining typical wooden walls and roofs linked to historical periods of construction in the country. Maximum and minimum MI indicators are proposed for the wood used in these structural elements. Considering that structural elements are the least likely to change over time and that the Chilean real estate registry primarily records load-bearing wall structures and their modifications, the focus remains on these aspects.

This study centers exclusively on typical construction systems based on sawn wood, acknowledging that this is the primary material used for the construction of such buildings in Chile. Engineered wood products, such as laminated timber, only gained significant market presence during the last decade of the 20th century—the first laminated structure is presumed to date from 1969, OSB products emerged in the early 2000s, and mass timber products like CLT only began to be used in the 2020s. While these products and construction systems may have higher MI values than frame-based systems, they are much less common and not representative of the historical wood construction practices in the country.

Thus, three historical periods are defined with the objective of evaluating the MI of wood in the case study: pre-1900 systems, those from the 20th century, and those from after the year 2000. It is important to note that while the real estate registry includes heritage structures dating back to the 17th century, most of the recorded built surface area is concentrated in the second half of the 20th century and the first decades of the 21st century. Additionally, an unknown number of historical wooden constructions in Santiago have been affected by fires, earthquakes, or have simply been replaced by masonry and reinforced concrete structures.

To facilitate the analysis of a large number of wooden architectures represented in the real estate record and to generate representative wood volumes for construction systems and historical periods, two typical wooden walls and two typical roofs are defined for analysis. These typologies assume building heights not exceeding three stories, in line with data collected by the INE in its building permit records [25]. This approach is also consistent with research conducted in Finland and other Northern European countries, which attribute nearly the entirety of wood MI in low-rise framed buildings to the walls and roof structures [15].

For the walls, a small wall of 2400 mm in length and a larger one of 7200 mm is defined, with a height set at 2400 mm. Although historical architecture often features taller ceilings than those found in constructions from the second half of the 20th century and the 21st century, due to variability depending on the project, a uniform and more conservative height of 2400 mm is used for all wall types regardless of the historical period.

Furthermore, to determine the volume of wood in walls per square meter of built structure, the wall density data from the floor plan are utilized. According to the literature, wooden structures should have a wall density in the floor plan between 3% and 6% [26,27,28,29], values that are higher than those found in equivalent concrete structures.

W a l l D e n s i t y = \frac{A_{w a l l}}{G B A} \times 100

(3)

where

Wall Density: the floor plan area of structural walls expressed as a percentage of the GBA (in %).

A_wall: the floor area covered by structural walls (in m²).

GBA: the gross built surface area (in m²).

Regarding the defined roof types, both are gable roofs with a 40% pitch. One case considers a smaller volume of wood covering a span of 3000 mm and a length of 2400 mm, while the second case involves a higher volume of wood, spanning 6000 mm with a length of 4800 mm. Horizontal structural elements, such as ventilated floors or intermediate floors, are not considered in this analysis because they cannot be identified in the real estate database. It is assumed that these elements are partially represented within the wood volume addressed by the roof cases.

2.3.1. Historical Systems

Regarding historical construction systems, the most common type corresponds to heavy timber framing and its variations. Examples of these systems include the “Quincha” of Latin American origin and some reinterpretations of European and North American systems, which were mainly imported during the 18th century [30,31,32,33]. For this type of construction, walls are considered to include studs, beams, top and bottom plates, and diagonals with cross sections ranging from 100 mm × 100 mm to 150 mm × 150 mm, while smaller elements like noggings are considered to have cross sections in the range of 50 mm × 50 mm to 70 mm × 70 mm (Figure 2). Additionally, the shorter wall of 2400 mm in length has studs placed every 1200 mm, and the longer wall of 7200 mm in length features studs spaced every 800 mm.

As for the roofs, simple and traditional trusses from the period that utilize the minimum and maximum amounts of wood for such constructions are considered. The “King-post” truss is used for cases with the least amount of wood, while the “Queen-post” truss is applied to those with the highest material intensity (Figure 3). Regarding the cross sections of the legs, ties, posts, and diagonals, sizes of 41 mm × 138 mm and 41 mm × 185 mm are used. For purlins, sections between 19 mm × 90 mm and 41 mm × 80 mm are defined. These trusses are evaluated with a spacing of 1200 mm for the roof with a lower volume of wood and 400 mm for the case with a higher volume.

2.3.2. Traditional Systems

For traditional construction systems built between 1901 and 2000, the walls are considered to consist of a light-frame construction with cross sections of 41 mm × 65 mm and 41 mm × 90 mm, with noggings spaced every 800 mm and 600 mm, and diagonals with cross sections ranging from 19 mm × 90 mm to 41 mm × 90 mm (Figure 4). The potential sheathing of the wall is not included in the volume calculation as it does not serve a structural function, since the rigidity is provided by the diagonals, and it is subject to possible renovations, especially in the case of exterior sidings. Studs are spaced every 600 mm for the smaller wall and every 400 mm for the larger case.

As for the roof systems used during the 20th century, two systems are considered to represent the minimum and maximum volumes of wood required for a gable roof (Figure 5). These scenarios are intended to reflect the various types of trusses found within the context of the case study. In the minimum case, spanning a three-meter width, a simple truss is used, where the beams are placed at a slope on the structural walls and rest on a ridge beam with purlins. In contrast, for the scenario with a higher volume of wood, a “Pratt” truss with purlins and roof sheathing is proposed. The cross sections for the top chords, ridge beams, ties, and posts, as applicable, range from 41 mm × 90 mm to 41 mm × 114 mm, while the purlins are considered to have sections of 41 mm × 41 mm, and the sheathing is 19 mm thick in the maximum case.

2.3.3. Contemporary Systems

For walls representative of structures built after the year 2000, the main variation is the introduction of OSB (Oriented Strand Board) panels into the market, which led to their structural use for wall bracing. This results in the reduction or elimination of diagonals and a decreased use of noggings (Figure 6). While the cross sections for studs, top and bottom plates, and blocking pieces remain between 41 mm × 65 mm and 41 mm × 90 mm, the diagonals are replaced by OSB panels, which can vary in thickness between 9.5 mm and 11.1 mm. In the case of buildings up to two stories high, these panels are typically installed on the exterior side of the wall, with the interior finish being provided by a gypsum board panel.

Regarding roofing systems, the truss structure remains similar to that of 20th-century cases, with the primary difference being that the roof sheathing can be replaced with OSB panels. In this regard, the sheathing thickness is reduced from 19 mm to 11.1 mm, which falls within the minimum and maximum volume of wood calculated for traditional cases.

Thus, the calculated minimum and maximum volumes of wood are found to be between 0.06 m³/m² and 0.14 m³/m² for “historical” cases before the 20th century, between 0.025 m³/m² and 0.086 m³/m² for “traditional” cases between 1900 and 2000, and within the range of 0.03 m³/m² and 0.085 m³/m² for constructions from the early decades of the 21st century.

2.4. Quantification of Biogenic Carbon

The methodology used to determine the biogenic carbon content in wood follows the guidelines established in the standard “UNE-EN 16449: Wood and wood-based products. Calculation of the biogenic carbon content of wood and conversion to carbon dioxide” [4]. The calculated volume of wood for each building and year recorded in the real estate database is used to estimate the biogenic carbon using the following formula:

C_{b i o} = c f \times \frac{ρ_{ω} \times V_{ω}}{1 + \frac{ω}{100}}

(4)

where

C_bio: the biogenic carbon stored in wood (in kg).

V: the volume of the wood product (in m³).

ρ_ω: the density of the wood at the specified moisture content (in kg/m³).

cf: the carbon fraction of wood biomass, where a standard value of 0.5 (50%) is used.

ω: the moisture content of the wood, expressed as a percentage.

Alternatively, for the purpose of this work, it can be expressed as

C_{b i o} = f_{c} \times {M I}_{w o o d - d r y} \times A

(5)

where

A: the built surface area of wood.

Meanwhile, regarding CO₂ emissions associated with biogenic carbon storing, UNE-EN 16449 presents the following equation:

P_{{CO}_{2}} = \frac{44}{12} \times C_{b i o}

(6)

where

P_CO₂: the amount of carbon dioxide emitted by the oxidation of biogenic carbon at the end of the product’s life cycle (in kg of CO₂).

44/12: the conversion factor from the molar mass of carbon (12 g/mol) to carbon dioxide (44 g/mol).

Additionally, since wood density can vary by species, the analysis considers two species that establish representative minimum and maximum values. From the second half of the 20th century onward, the period with the highest number of wooden constructions according to the real estate record, Pinus radiata (radiata pine) has been the most widely used wood species. Meanwhile, Nothofagus obliqua (Chilean oak) is one of the most common woods in the central–southern region of the country and represents the oldest constructions in the case study. Radiata pine, with a density of 450 kg/m³ (oven-dry), is one of the lightest local woods used in construction, while Chilean oak, with a density of 558 kg/m³ (oven-dry), is among the densest common construction woods [34]. The moisture content for both species is considered to be around 14%, in line with the equilibrium moisture content established for the climate in the case study [34], allowing for the determination of the carbon content per unit mass of wood.

While there is some debate regarding the carbon fraction associated with the dry mass of wood [5], this analysis follows the recommendations outlined by the UNE-EN 16449 standard. Therefore, the carbon fraction in the oven-dry state is established as 0.5, consistent with other similar studies [35,36]. This enables the quantification of both the biogenic carbon present in the mass of wood used in construction in the case study and its equivalent in carbon dioxide captured from the atmosphere.

2.5. Methodological Considerations

Although the methodology employed in this study offers an alternative approach for quantifying biogenic carbon stored in wooden structures within the built environment of Santiago, it has certain limitations. The reliance on real estate tax records, while based on a robust data acquisition system, can still introduce inconsistencies due to gaps in coverage. This is particularly relevant for properties with unregistered modifications, as the registry is updated semiannually, or for informal constructions/demolitions that fall outside the scope of data collection, especially in rural areas. However, given the sample size and its urban nature, it is expected that these unregistered cases follow the trends observed in the registry and represent a minor percentage of the study case.

The methodology used to identify the height of buildings and the presence of wood in them also depends on complementary analyses with other databases, such as the building permits registry. This is because the real estate registry cannot determine whether the square meters constructed with a specific material correspond to an entire building or just a portion of it (e.g., the top two floors). Consequently, the different methodologies used in each registry may lead to some taller wooden constructions being underrepresented in the analysis. Nonetheless, given the rarity of such buildings in the Chilean context, this underrepresentation is expected to be minimal.

Moreover, while the real state registry identifies the square meters constructed with a specific material, it considers only the predominant material used in bearing walls and does not provide the exact quantity of material present in the entire structure. Additionally, the registry does not include direct information about the specific construction system (e.g., post-and-beam or platform frame), making it difficult to estimate material quantities accurately. Similarly, it does not indicate the type of wood species used or whether engineered wood products are used, such as laminated timber, logs, or CLT.

Regarding the use of historical averages and generalized material intensity values to estimate the wood volume and biogenic carbon content, these may not fully capture variations in construction practices over time or across different geographic locations. Thus, the estimated wood quantity does not directly represent the mass of wood per square meter of structure, potentially leading to underestimation or overestimation. However, the proposed methodology also excludes secondary structural elements or non-structural components in its calculations, making the analyzed scenarios more conservative.

Additionally, for this methodology to be applicable in other case studies, it requires, at a minimum, adequate records of constructed areas by material for a given case, as well as relatively homogeneous wooden construction typologies, as presented in the analyzed case of construction systems. For this reason, urban contexts lacking proper records (either due to the absence of a data collection system or the age of the buildings) could hinder its implementation or result in significant errors.

3. Results

The results are presented by first quantifying the wood usage per square meter in buildings from the case study and generating wood MI data, categorized by historical period. Second, these results are cross-referenced with the real estate database to identify average values for the entire case study and to determine their variation by the studied municipality. Finally, the results for biogenic carbon storage and the equivalent CO₂ amount are presented, both aggregated for the entire city and by municipality.

3.1. Wood Material Intensity

The maximum and minimum wood volumes per gross built area, calculated by the studied time period, range from 0.78 m³/m² to 1.04 m³/m² for “historical” cases prior to the 20th century, between 0.42 m³/m² and 0.52 m³/m² for “traditional” cases from 1901 to 2000, and in the range of 0.59 m³/m² to 0.64 m³/m² for “contemporary” constructions from the early decades of the 21st century (Figure 7). These figures yield wood material intensity values with a maximum of 91.56 kg/m² and a minimum of 30.88 kg/m² for buildings from the 19th century or earlier; a maximum of 54.75 kg/m² and a minimum of 12.67 kg/m² for 20th-century constructions; and a maximum of 54.05 kg/m² and a minimum of 15.29 kg/m² for 21st-century structures (Figure 8). These values are in accordance with the densities presented in the methodological section and the ambient humidity.

Similarly, by correlating material intensities by time period with the results from the filtered database, it becomes possible to identify that the weighted wood material intensity ranges between 54.69 kg/m² and 13.07 kg/m², with an average of 33.88 kg/m² across all declared periods (Figure 9). Additionally, the ratio between the wood material intensity of the roof and walls is 2:1 in the most material-intensive case and nearly 1:1 in the least material-intensive case. This observation takes into account the differences in the amount of wood established for each case according to the historical period.

3.2. Wood Temporal Distribution

From the processing of the real estate database, it is possible to isolate the square meters of wood construction per year, which increased from 13.4 million in 2017 to 13.6 million in 2024, with a growth of 192,831 square meters during the period (Figure 10). Additionally, these figures show an average growth rate of wood construction area of around 0.2% compared to the previous year. Moreover, a significant decline in new wood-built areas is seen in 2021, followed by a stabilization in the growth percentage between 2023 and 2024.

The variation in growth rate of the wood-built surface area in the case study (Figure 10) can be attributed to an expansion in construction at the beginning of the recorded period, which was abruptly interrupted by the effects of the COVID-19 pandemic in 2020 and followed by a limited recovery due to subsequent economic impacts. Similar effects have been observed in other economies worldwide, with recovery periods varying depending on the specific context.

Similarly, considering a minimum and maximum range according to the methodology presented, the volume of wood built in the case study varies between 0.3 and 1.2 million cubic meters of wood depending on the scenario (minimum, average, or maximum). This shows a ratio difference of approximately four times, with the average value varying between 0.75 and 0.76 million cubic meters of wood depending on the year. It is important to highlight that this volume of wood considers a 14% moisture content in accordance with the equilibrium moisture level of the case study and the methodology used for this work.

When considering the evolution of dry wood mass, the scenario in 2017 presents a minimum of 153,883 tons and a maximum of 645,219 tons, reaching 156,930 and 654,000 tons of dry wood, respectively, in 2024. Similarly, the average values increase from 399,552 tons to 405,468 tons of dry wood, representing a rise of 5914 tons over the 8-year recording period (Figure 11).

Upon reviewing the age of wooden structures, it is possible to confirm that the largest stock of dry wood was produced during the second half of the 20th century, with most of the wood’s age being concentrated in constructions from the 1960s to the 1990s (Figure 12). Thus, older municipalities located in the city center contain wood that has remained in the built environment for a longer time. In contrast, younger wood is represented by a large volume of buildings originating in municipalities that are part of the urban expansion in the late 20th and early 21st centuries.

3.3. Biogenic Carbon and CO₂ Capture

If we examine the biogenic carbon associated with the mass of dry wood, it can be observed that it has grown steadily on average from 199.78 kt to 202.73 kt, with a cumulative increase of 1.5% in the total mass over the 8-year measurement period (Figure 13). Similarly, the scenario with the minimum biogenic carbon stored in 2024 accounts for 78.47 kt, while the maximum reaches 327.0 kt.

As expected, we observe the same trend with the CO₂ captured in wooden buildings, varying from 732.51 kt in 2017 to 743.35 kt in 2024 (Figure 13). Similarly, in 2024, there is a variation between a minimum scenario of 287.71 kt of CO₂ and a maximum of 1199.00 kt of CO₂ captured by the built wood biomass. The oldest CO₂ is concentrated in the central districts of the city, while the newest CO₂ is found in the urban periphery, with intermediate municipalities showing lower CO₂ capture in comparison (Figure 14).

4. Discussion

Regarding the wood MI results, which range from 54.69 kg/m² to 13.07 kg/m² with an average of 33.88 kg/m², previous studies have established values for housing, considering variations in wall and roof structures, between 15 kg/m² and 50 kg/m² [15]. Also, these studies show similar wall/roof wood usage ratios. Meanwhile, studies addressing the full set of wood-based materials have indicated a range of around 50 kg/m² of wood being used for framed buildings, while maintaining the roof-to-wall ratio identified in the Chilean case [17]. In this sense, the upward variation in some case studies is due to the fact that these analyses do not only include structural elements. However, an average wood MI of 37 kg/m² has been identified in the context of European and Asian studies [17] in accordance with the results obtained in this work.

On the other hand, it has been identified that historical dwellings based on other construction methods with high wood usage, such as stacked log systems, could have a wood intensity of up to 135 kg/m² on average for Swedish homes and 88 kg/m² on average for traditional Japanese homes [17]. However, these types of buildings are rare in the Chilean context as they were not recorded during the data collection period and should not represent a significant correction factor for the results presented. It is recognized, however, that in the case of Chilean historical buildings, wood usage may be slightly underestimated due to the height used in the quantification of material in the defined wall types. This is because a review of projects from that era suggests that the heights of historical buildings are greater than those of contemporary buildings [32]. Nevertheless, due to the high variability in this aspect, a conservative height was chosen in alignment with modern structures.

Regarding the quantification of wood buildings in urban environments, as expressed in the methodology, several assumptions had to be made to obtain the presented results. This may lead to underestimations or overestimations, which are addressed by the sensitivity analysis that considers minimum and maximum ranges for wood mass estimation. In this case, the representative structural elements and the wall density factor present an alternative to previous research, which used representative building types or random samples [15,17,23,37,38,39]. However, since the methodology considers only basic structural elements and not the entire wood construction, and it also underestimates the wood usage in historical structures, overall, these results tend to be conservative in relation to the total wood carbon storage.

With regard to the specific results of the case study, it is also noteworthy that there was a decline in timber construction in 2021, following continuous growth in previous years. This effect has been seen in other countries across the entire construction sector and can be easily explained by the COVID-19 pandemic and associated restrictions [40]. Furthermore, although a recovery in wood construction growth is evident between 2022 and 2024, this recovery is quite modest due to a local building sector crisis that the country has been experiencing for the past four years, related to investment issues and bureaucratic delays in permits [41]. This clearly demonstrates how global economic events and local conditions can affect wood construction growth and its capacity to store carbon.

Also, regarding the case study, it is interesting to note that historical parts of the city retain older wooden buildings, while urban expansion in the periphery through small wooden houses also contributes to increasing the wood stock. However, the ring surrounding the downtown area, where the modern city is more consolidated, shows less wood usage. This might imply that, in this case, urban densification through taller buildings has displaced wood in favor of more common construction systems for tall buildings, such as concrete or steel. Nevertheless, further study is needed to draw conclusions on this matter, and new trends in tall wooden buildings may also alter this tendency in the future.

It is also interesting to note that although the case study includes buildings that are centuries old, less than 0.4% of the wood-built surface area is older than the 19th century. In this regard, 15.5% of the wood-built surface area dates to the 21st century, while 84.1% corresponds to the 20th century, mostly from the second half of it. This is particularly notable considering that the case study area has never been affected by a major city fire like in London or Chicago, or by significant war events. Moreover, earthquakes that commonly affect the city tend to impact rigid structures like masonry more directly than wood. Nevertheless, old wooden structures are rare as they have been replaced by newer and taller structures made from other materials.

To understand the potential of wood buildings for carbon and CO₂ storage in the built environment, it is important to compare them with other carbon sinks, such as forests. In this regard, Chilean forest land covers 17.9 million hectares, of which 14.8 million are native forests and 3.1 million are plantations [20]. According to the Chilean national carbon inventory, based on the IPCC methodology, native forests have sequestered approximately 67,474 kt of CO₂ per year, while plantations have captured around 74,935 kt of CO₂ per year, averaged over the most recent eight-year reporting period from 2013 to 2021 [42]. This means that, on average, native forests have captured 5077 kg CO₂/ha per year, and plantations 21,440 kg CO₂/ha per year. However, most of the carbon captured by plantations is assumed to be released later during harvest. In contrast, over the eight years of study, the wooden surface area in the case study has stored 1002 kg CO₂/ha per year. However, this figure could increase in some peripheral municipalities to up to 7607 kg CO₂/ha per year, while municipalities undergoing a densification process could release up to 3794 kg CO₂/ha per year due to the replacement of low-height wood buildings by taller concrete structures. This indicates that wood constructions in the built environment have the potential to retain annual CO₂ amounts comparable to a native forest in the case study scenario, although this potential may be significantly influenced by building trends.

That said, through its wooden constructions and the timber products used in its structures, the city of Santiago has managed to retain a significant part of the biogenic carbon originating from forests. The results have shown that this carbon may have been stored for a few decades in some younger municipalities and for up to hundreds of years in the case of downtown Santiago. Furthermore, the rate of wood construction in some expanding municipalities indicates that the annual CO₂ storage from new buildings may even surpass the per-hectare capture of native forests in the Chilean case. This highlights a temporal and quantitative potential for annual CO₂ capture, suggesting, to some extent, the city’s potential as a “Second Forest” in relation to its biogenic carbon storage capacity.

In a different context, while this work introduces an innovative approach to quantifying biogenic carbon in wood structures within Santiago’s built environment, it is not without limitations. These are primarily due to the type of information recorded in the database utilized and the lack of data specifically tailored for studies of this nature. Despite these constraints, the sample size and its predominantly urban character help to minimize the impact of such discrepancies. However, less homogeneous areas, such as rural locations, may exhibit a higher margin of error. Similarly, urban areas where mass timber buildings with higher material intensity are a predominant typology may be difficult to differentiate from lightweight timber frame buildings with lower material mass.

Additionally, considering the limitations of the proposed methodology and its extrapolation to other case studies, Santiago, being a relatively young city with an urban expansion primarily concentrated in the second half of the 20th century and a detailed record of its built environment, may present a more favorable case compared to older cities in other regions. This advantage arises from the ages of buildings in those areas, where structures can be hundreds or even thousands of years old with little or no data available, the variability of construction systems influenced by diverse cultural exchanges, and partial or interrupted records caused by historical events such as major fires or wars.

Moreover, although this study attempts to address these uncertainties through sensitivity analyses, the results remain conservative and may not fully capture the potential for carbon storage in urban wooden structures. Future research should incorporate more detailed data and advanced modeling techniques to improve accuracy and applicability across diverse urban contexts. This is particularly relevant given the global development of public policies aimed at promoting the use of wood in construction to reduce emissions and enhance carbon capture within the sector. In this context, information on biogenic carbon storage will become increasingly significant, as policies like France’s, which mandate that at least 50% of materials in state buildings must be bio-based, are expected to become more widespread. Similar initiatives have already been adopted in developed countries such as Croatia, Slovenia, and regions of Spain [43], and they are likely to emerge in developing nations like Chile in the coming decades.

5. Conclusions

This study presents a methodology for quantifying biogenic carbon and stored CO₂ in timber structures within the built environment. It has effectively assessed the city of Santiago’s potential to function as a wood carbon sink or “Second Forest”. Through the analysis of real estate tax databases, construction permits, timber building typologies, and carbon accounting models, this study quantifies the carbon stored in the city’s timber structures, revealing storage volumes comparable to those of native forest ecosystems in some urban areas. Additionally, the analysis shows that urban expansion zones tend to increase the use of timber in their constructions, while areas undergoing vertical densification tend to reduce the presence of timber. This finding is significant in terms of CO₂ storage in the built environment and the impacts of vertical densification using traditional materials other than wood.

Moreover, maintaining a record of CO₂ stored in the built environment not only improves the understanding of buildings’ carbon mitigation potential but also lays the groundwork for developing tools and public policies aimed at promoting low-emission, CO₂-storing construction practices. Data generated by studies like this are essential for creating regulatory frameworks that encourage timber construction, especially in taller buildings, thereby strengthening urban carbon storage strategies. Such methodologies also allow for extrapolation to other urban cases in countries lacking comprehensive material intensity records or timber use data within the built environment.

Finally, it is recommended that future studies focus on developing more accurate methodologies to quantify and characterize biogenic carbon storage in the built environment, particularly in regions where this methodology may not be suitable due to the stated limitations. Additionally, it would be valuable for future research to explore how urban planning trends influence the permanence of biogenic carbon in timber within the built environment, as well as to examine future scenarios for high-rise timber buildings and their potential impacts on urban biogenic carbon stock.

Author Contributions

Conceptualization, F.V.; methodology, F.V.; investigation, F.V. and W.B.; data curation, F.V.; writing—original draft preparation, F.V. and W.B.; writing—review and editing, F.V. and W.B.; supervision, W.B. All authors have read and agreed to the published version of the manuscript.

Funding

The authors want to acknowledge the support from Centro Nacional de Excelencia para la Industria de la Madera (CENAMAD, ANID BASAL FB210015). The authors also gratefully acknowledge the research support provided by CEDEUS under the research grant ANID FONDAP 1523A0004.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Real state taxation data can be found at https://zeusr.sii.cl/AUT2000/InicioAutenticacion/IngresoRutClave.html?https://www4.sii.cl/sismunInternet6/?caller=DETALLE_CAT_Y_ROL_COBRO (accessed on 8 August 2024). Building permit data can be found at https://www.ine.gob.cl/estadisticas/economia/edificacion-y-construccion/permisos-de-edificacion (accessed on 8 August 2024). Chilean forest carbon inventory data can be found at https://snichile.mma.gob.cl/sector-uso-de-la-tierra-cambio-de-uso-de-la-tierra-y-silvicultura/ (accessed on 8 August 2024). Any additional data presented in this study are available upon request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

References

Churkina, G.; Organschi, A.; Reyer, C.P.O.; Ruff, A.; Vinke, K.; Liu, Z.; Reck, B.K.; Graedel, T.E.; Schellnhuber, H.J. Buildings as a Global Carbon Sink. Nat. Sustain. 2020, 3, 269–276. [Google Scholar] [CrossRef]
Hildebrandt, J.; Hagemann, N.; Thrän, D. The Contribution of Wood-Based Construction Materials for Leveraging a Low Carbon Building Sector in Europe. Sustain. Cities Soc. 2017, 34, 405–418. [Google Scholar] [CrossRef]
Zhang, L.; Yu, C.; Cheng, B.; Yang, C.; Chang, Y. Mitigating Climate Change by Global Timber Carbon Stock: Accounting, Flow and Allocation. Renew. Sustain. Energy Rev. 2020, 131, 109996. [Google Scholar] [CrossRef]
UNE-EN 16449; Wood and Wood-Based Products. Calculation of the Biogenic Carbon Content of Wood and Conversion to Carbon Dioxide. AENOR: Madrid, Spain, 2014.
Van Shaik, T.; Doraisami, M.; Martin, A.R. Carbon Fractions in Wood for Estimating Embodied Carbon in the Built Environment. Sci. Total Environ. 2024, 921, 171095. [Google Scholar] [CrossRef]
Ramage, M.H.; Burridge, H.; Busse-Wicher, M.; Fereday, G.; Reynolds, T.; Shah, D.U.; Wu, G.; Yu, L.; Fleming, P.; Densley-Tingley, D.; et al. The Wood from the Trees: The Use of Timber in Construction. Renew. Sustain. Energy Rev. 2017, 68, 333–359. [Google Scholar] [CrossRef]
2023 Global Status Report for Buildings and Construction: Beyond Foundations—Mainstreaming Sustainable Solutions to Cut Emissions from the Buildings Sector; United Nations Environment Programme: Nairobi, Kenya, 2024; ISBN 9789280741315.
Elhacham, E.; Ben-Uri, L.; Grozovski, J.; Bar-On, Y.M.; Milo, R. Global Human-Made Mass Exceeds All Living Biomass. Nature 2020, 588, 442–444. [Google Scholar] [CrossRef]
Watari, T.; Cao, Z.; Serrenho, A.C.; Cullen, J. Growing Role of Concrete in Sand and Climate Crises. iScience 2023, 26, 106782. [Google Scholar] [CrossRef]
Griscom, B.W.; Adams, J.; Ellis, P.W.; Houghton, R.A.; Lomax, G.; Miteva, D.A.; Schlesinger, W.H.; Shoch, D.; Siikamäki, J.V.; Smith, P.; et al. Natural Climate Solutions. Proc. Natl. Acad. Sci. USA 2017, 114, 11645–11650. [Google Scholar] [CrossRef]
Pugh, T.A.M.; Lindeskog, M.; Smith, B.; Poulter, B.; Arneth, A.; Haverd, V.; Calle, L. Role of Forest Regrowth in Global Carbon Sink Dynamics. Proc. Natl. Acad. Sci. USA 2019, 116, 4382–4387. [Google Scholar] [CrossRef]
Stephenson, N.L.; Das, A.J.; Condit, R.; Russo, S.E.; Baker, P.J.; Beckman, N.G.; Coomes, D.A.; Lines, E.R.; Morris, W.K.; Rüger, N.; et al. Rate of Tree Carbon Accumulation Increases Continuously with Tree Size. Nature 2014, 507, 90–93. [Google Scholar] [CrossRef]
Churkina, G.; Brown, D.G.; Keoleian, G. Carbon Stored in Human Settlements: The Conterminous United States. Glob. Chang. Biol. 2010, 16, 135–143. [Google Scholar] [CrossRef]
Reyes, N.; Rodríguez, B.; Wiegand, E.; Zilic, F.; Ramage, M.; Bukauskas, A.; Debnath, R.; Shah, D.U.; Colman, T.; De Wolf, C.; et al. Achieving Zero Carbon Emissions in the Construction Sector; Cambridge University Press: Cambridge, UK, 2021. [Google Scholar]
Nasiri, B.; Kaasalainen, T.; Hughes, M. Estimating the Material Intensity of Wooden Residential Houses in Finland. Resour. Conserv. Recycl. 2023, 198, 107142. [Google Scholar] [CrossRef]
Kalt, G. Carbon Dynamics and GHG Implications of Increasing Wood Construction: Long-Term Scenarios for Residential Buildings in Austria. Carbon. Manag. 2018, 9, 265–275. [Google Scholar] [CrossRef] [PubMed]
Gontia, P.; Nägeli, C.; Rosado, L.; Kalmykova, Y.; Österbring, M. Material-Intensity Database of Residential Buildings: A Case-Study of Sweden in the International Context. Resour. Conserv. Recycl. 2018, 130, 228–239. [Google Scholar] [CrossRef]
Arehart, J.H.; Hart, J.; Pomponi, F.; D’Amico, B. Carbon Sequestration and Storage in the Built Environment. Sustain. Prod. Consum. 2021, 27, 1047–1063. [Google Scholar] [CrossRef]
Gobierno de Chile. Estrategia Climática de Largo Plazo de Chile; Gobierno de Chile: Santiago, Chile, 2021. [Google Scholar]
Poblete Hernández, P. Anuario Forestal 2023; INFOR: New York, NY, USA, 2023. [Google Scholar]
del Río Arteaga, M.; Contreras Biekhert, J.L.; Rojas Pinochet, E.; Tokman Ramos, C.; Valenzuela Benavides, A.; Romero Cocuy, C.; Miranda Toledo, R.; Stipo Antiao, D.; Krell Loy, R. Comisión Nacional de Productividad: Productividad En El Sector de La Construcción; CNEP: Santiago, Chile, 2021; Available online: https://cnep.cl/estudios-finalizados/productividad-en-elsectorde-la-construccion/ (accessed on 23 October 2024).
Servicio de Impuestos Internos Detalle Catastral y Rol de Cobro. Available online: https://zeusr.sii.cl/AUT2000/InicioAutenticacion/IngresoRutClave.html?https://www4.sii.cl/sismunInternet6/?caller=DETALLE_CAT_Y_ROL_COBRO (accessed on 21 October 2024).
Schandl, H.; Marcos-Martinez, R.; Baynes, T.; Yu, Z.; Miatto, A.; Tanikawa, H. A Spatiotemporal Urban Metabolism Model for the Canberra Suburb of Braddon in Australia. J. Clean. Prod. 2020, 265, 121770. [Google Scholar] [CrossRef]
Kalcher, J.; Praxmarer, G.; Teischinger, A. Quantification of Future Availabilities of Recovered Wood from Austrian Residential Buildings. Resour. Conserv. Recycl. 2017, 123, 143–152. [Google Scholar] [CrossRef]
Instituto Nacional de Estadísticas Permisos de Edificación. Available online: https://www.ine.gob.cl/estadisticas/economia/edificacion-y-construccion/permisos-de-edificacion (accessed on 23 October 2024).
Estrella, X.; Guindos, P.; Almazán, J.L.; Malek, S.; Santa María, H.; Montaño, J.; Berwart, S. Seismic Performance Factors for Timber Buildings with Woodframe Shear Walls. Eng. Struct. 2021, 248, 113185. [Google Scholar] [CrossRef]
Carcamo, S.; Valdivieso, D. Morphologic Study of Hybrid Tall Building Towards an Interdisciplinary Design. In Proceedings of the World Conference on Timber Engineering 2023 (WCTE2023), Oslo, Norway, 19–22 June 2023. [Google Scholar]
Cárcamo Chávez, S.I.; Caamaño González, J.L.; Cid Olivares, A.A. Interdisiplinary Design for the Light Timber Frame System: Recommendation for a Good Structuration. In Proceedings of the World Conference on Timber Engineering, Vienna, Austria, 22–25 August 2016. [Google Scholar]
Berwart, S.; Estrella, X.; Montaño, J.; Santa-María, H.; Almazán, J.L.; Guindos, P. A Simplified Approach to Assess the Technical Prefeasibility of Multistory Wood-Frame Buildings in High Seismic Zones. Eng. Struct. 2022, 257, 114035. [Google Scholar] [CrossRef]
Chile, M.E.; Schmitt, C. Lecciones de La Tradición Constructiva En Estudio de Obras Patrimoniales Del Siglo XX; Pontificia Universidad Católica de Chile, Escuela de Arquitectura: Santiago, Chile, 2020. [Google Scholar]
Acevedo Oliva, R.M.; Broughton Weine, J.; Carrillo Zuñiga, O. Construcción En Quincha Liviana Constructivos Sustentables de Reinterpretación Patrimonial; Ministerio de Vivienda y Urbanismo: Santiago, Chile, 2019; Available online: https://csustentable.minvu.gob.cl/wp-content/uploads/2020/03/CONSTRUCCION_CON_QUINCHA_LIVIANA_1a_edicion.pdf (accessed on 21 October 2024).
Patrimonio Construido En Madera: Manual Para Su Valorización e Intervención, 1st ed.; Schmitt, C., Ed.; Ediciones UC: Santiago, Chile, 2023. [Google Scholar]
Tomasi, J.; Bellmann, L. La quincha y los sistemas de entramados. Estructuras 2018, 1, 28–34. Available online: https://revistas.unc.edu.ar/index.php/estructuras/article/view/24741/24011 (accessed on 8 August 2024).
NCh1198:2024; Timber—Timber Constructions—Calculation. Instituto Nacional de Normalización—INN: Santiago, Chile, 2024. Available online: https://ecommerce.inn.cl/nch1198202488155 (accessed on 8 August 2024).
Hoxha, E.; Passer, A.; Saade, M.R.M.; Trigaux, D.; Shuttleworth, A.; Pittau, F.; Allacker, K.; Habert, G. Biogenic Carbon in Buildings: A Critical Overview of LCA Methods. Build. Cities 2020, 1, 504–524. [Google Scholar] [CrossRef]
Pittau, F.; Krause, F.; Lumia, G.; Habert, G. Fast-Growing Bio-Based Materials as an Opportunity for Storing Carbon in Exterior Walls. Build. Environ. 2018, 129, 117–129. [Google Scholar] [CrossRef]
Han, J.; Xiang, W.N. Analysis of Material Stock Accumulation in China’s Infrastructure and Its Regional Disparity. Sustain. Sci. 2013, 8, 553–564. [Google Scholar] [CrossRef]
Tanikawa, H.; Fishman, T.; Okuoka, K.; Sugimoto, K. The Weight of Society over Time and Space: A Comprehensive Account of the Construction Material Stock of Japan, 1945–2010. J. Ind. Ecol. 2015, 19, 778–791. [Google Scholar] [CrossRef]
Tanikawa, H.; Hashimoto, S. Urban Stock over Time: Spatial Material Stock Analysis Using 4d-GIS. Build. Res. Inf. 2009, 37, 483–502. [Google Scholar] [CrossRef]
ILO Sectoral Brief. Impact of COVID-19 on the Construction Sector; ILO: Geneva, Switzerland, 2021; Available online: https://researchrepository.ilo.org/esploro/outputs/encyclopediaEntry/Impact-of-COVID-19-on-the-construction/995219336302676 (accessed on 8 August 2024).
Forbes Staff Iconstruye: Industria de La Construcción En Chile Atraviesa La Crisis Más Aguda En 30 Años. Available online: https://forbes.cl/actualidad/2024-08-12/iconstruye-industria-de-la-construccion-en-chile-atraviesa-la-crisis-mas-aguda-en-30-anos (accessed on 24 October 2024).
Ministerio del Medio Ambiente Sector UTCUTS. Available online: https://snichile.mma.gob.cl/sector-uso-de-la-tierra-cambio-de-uso-de-la-tierra-y-silvicultura/ (accessed on 24 October 2024).
Chalupovitsch, M.; Buhary, N.; Gesley, J.; Figueroa, D.; Umeda, S.; Hofverberg, E.; Feikert-Ahalt, C. Mass Timber Construction; The Law Library of Congress, Global Legal Research Directorate: Washington, DC, USA, 2022. Available online: https://www.loc.gov/item/2022666107/ (accessed on 24 August 2024).

Figure 1. The study area consisting of 32 municipalities that make up the Santiago province (prepared using https://mapshaper.org/ (accessed on 8 August 2024) with ©Mapbox and ©OpenStreetMap).

Figure 2. Diagrams of structural wood for short and long historical walls.

Figure 3. Diagrams of structural wood for short and long historical roof spans.

Figure 4. Diagrams of structural wood for short and long traditional walls.

Figure 5. Diagrams of structural wood for short and long traditional roof spans.

Figure 6. Diagrams of structural wood for short and long contemporary walls with OSB panels.

Figure 7. Wood volume per built square meter according to historical period and according to minimum, average, and maximum scenarios (city of Santiago).

Figure 8. Material intensity of wood according to historical period and according to minimum, average, and maximum scenarios (city of Santiago).

Figure 9. Weighted material intensity of wood over entire studied period, according to minimum, average, and maximum scenarios (city of Santiago).

Figure 10. The annual wood-built surface area (bars) and growth rate (line) according to the average scenario during the study period (city of Santiago).

Figure 11. The annual wood mass per year according to the average scenario (city of Santiago).

Figure 12. The age of dry wood mass in the average scenario (city of Santiago).

Figure 13. Annual biogenic carbon and CO₂ storage per year according to average scenario.

Figure 14. Temporal distribution of CO₂ storage per municipality (city of Santiago), made with Microsoft Power Bi Desktop version 2.138.1452.0 64-bit (November 2024).

Table 1. Data available from the Chilean real state registry.

Column	Data in Real State Registry File	Use in This Work
1	SII Code of municipality	Identify Santiago’s municipalities
2	Block number	No use in this work
3	Parcel number	No use in this work
4	Number of construction line	Identify building information
5	Structural material of construction line	Identify wood buildings (predominant material in bearing walls)
6	Quality of construction line	No use in this work
7	Year of construction line	Identify the age of wood buildings
8	Surface area of construction line	Identify the gross surface area of wood buildings
9	Use of construction line	No use in this work
10	Special condition of construction line	No use in this work

The file format remains the same for the eight years of data used in this study (2017–2024).

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

© 2025 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Share and Cite

MDPI and ACS Style

Victorero, F.; Bustamante, W. Timber Biogenic Carbon Stock in the Urban Environment: Santiago City as a Second Forest. Sustainability 2025, 17, 529. https://doi.org/10.3390/su17020529

AMA Style

Victorero F, Bustamante W. Timber Biogenic Carbon Stock in the Urban Environment: Santiago City as a Second Forest. Sustainability. 2025; 17(2):529. https://doi.org/10.3390/su17020529

Chicago/Turabian Style

Victorero, Felipe, and Waldo Bustamante. 2025. "Timber Biogenic Carbon Stock in the Urban Environment: Santiago City as a Second Forest" Sustainability 17, no. 2: 529. https://doi.org/10.3390/su17020529

APA Style

Victorero, F., & Bustamante, W. (2025). Timber Biogenic Carbon Stock in the Urban Environment: Santiago City as a Second Forest. Sustainability, 17(2), 529. https://doi.org/10.3390/su17020529

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Menu

Timber Biogenic Carbon Stock in the Urban Environment: Santiago City as a Second Forest

Abstract

1. Introduction