Keywords: Mass timber city, Sustainable forest management, smart cities, Vernacular, Local species wood
ABSTRACT:
The capital city of Nepal- Kathmandu, like many urban cities globally, is undergoing uncontrolled urban expansion, neglecting its natural-based construction heritage, particularly timber. This research advocates for a paradigm shift towards mass timber, particularly multispecies Cross-Laminated Timber (CLT), to address environmental challenges. Emphasizing a circular approach, the study identifies local species and delves into the ecological and economic dimensions of sustainable forest management. Unlike singular ideal species promotion, it champions the use of sustainably harvested species, discouraging mono-species plantations.
Despite smart city concepts attracting significant investments in Nepal, mass timber remains absent from discussions. Nepal has untapped potential in utilizing its 44% forest cover for wood-based construction. However, forest encroachment for urban growth necessitates a delicate balance between conservation and resource use. The thesis culminates in a worker’s housing community development, acting as the inaugural link in the mass timber value chain. Seamlessly connecting indigenous wood harvesting with market demands, the design features multispecies CLT load-bearing wall panels, prototyped and tested. Beyond Kathmandu, this framework holds global relevance, fostering awareness, empowering local manufacturers, and reshaping perceptions of wood in constructing modern “Bio Cities” with cultural values.
PROBLEM STATEMENT | GLOBAL CONTEXT
Rapid urbanization is causing cities to expand exponentially, leading to increased greenhouse gas emissions and the loss of biodiversity. To mitigate this crisis, there’s a need to explore alternative building materials. Mass timber emerges as a promising solution, capable of addressing both the demand for construction and reducing carbon emissions. By incorporating mass timber and green spaces, cities can transform into carbon sinks, fostering a closer connection between the built environment and nature.
Recognizing the significant role of the building sector in global carbon emissions, it’s crucial to go beyond carbon neutrality and actively turn urban areas into carbon sinks. Mass timber emerges as a transformative solution, offering numerous benefits for sustainable urban development. Apart from its structural advantages, mass timber has a remarkable ability to sequester carbon, aiding in the fight against climate change. By prolonging the life of timber elements through practices like reuse and upcycling, carbon sequestration potential is maximized, resulting in a more substantial and lasting impact. Research from the University of Canterbury suggests that a midrise steel or concrete building typically emits around 1500 tonnes of CO2, while the same building constructed with mass timber can sequester approximately 600 tonnes of CO2, highlighting the environmental benefits of mass timber construction.
Mass timber signifies a transformative approach to built environments, seamlessly blending nature into cities to mitigate environmental impact and enhance people’s connection to their surroundings. Its renewable sourcing and minimal carbon footprint make it a leading choice for sustainable construction, with faster and more efficient construction processes. Embracing mass timber enables cities to reduce environmental impact and progress towards circular construction principles, maximizing efficiency through material reuse and recycling.
Beyond its environmental advantages, mass timber offers remarkable structural properties. Despite its lightweight nature compared to concrete and steel, mass timber exhibits exceptional strength, making it suitable for load-bearing elements in buildings. Moreover, its prefabricated nature facilitates faster construction timelines, reducing labor costs and enhancing project efficiency. Mass timber offers exceptional structural strength despite its lightweight nature, facilitating faster construction and reducing labor costs. Its aesthetic appeal adds warmth and natural elements to architectural designs, enhancing comfort for occupants. Through biophilic design, mass timber fosters a connection to nature, promoting relaxation and satisfaction. Despite wood’s combustibility, mass timber products like CLT demonstrate good fire resistance. Moreover, by utilizing different species densities, it naturally regulates indoor climate, promoting energy efficiency. In essence, mass timber construction provides holistic benefits, encompassing environmental sustainability, structural integrity, aesthetic appeal, and physical and mental well-being.
PROBLEM STATEMENT | NEPAL’S CONTEXT
Like the global scenario, Nepal’s urbanization is rapidly increasing, According to the 2011 census, the total population of the country stood at 26.5 million, with only 17.1% residing in a total of 58 municipalities. However, recent data shows more than one-third of Nepal’s population, exceeding 33%, now resides in a total of 217 municipalities. However, this surge is concentrated in the capital, leading to unmanaged urbanization and pressure on large cities. National policies like the National Urban Policy and National Urban Development Strategy aim to direct growth towards secondary towns for balanced development. As urbanization rises, so does the demand for construction materials like cement, steel, and bricks, which currently form the backbone of infrastructure development. However, The production of construction materials in Nepal, particularly cement, is highly carbon-intensive. The country’s cement industry has an installed capacity of 20.5 million tons, with expectations of further growth driven by government emphasis on infrastructure development and increasing demand from the private sector. The global emissions intensity for cement production has remained stable, resulting in a total CO2 emission capacity of 12.3 million tons for Nepal’s cement industry.
GLOBAL FORESTS | NATURAL FORESTS VS. PLANTATIONS
The global forestry sector faces challenges of deforestation but aims to increase forest cover through initiatives like the Bonn Challenge. However, current commitments heavily rely on commercial monoculture plantations, raising concerns about long-term effectiveness. Analysis of government pledges shows 45% focus on monoculture, 21% on agroforestry, and only 34% on natural forests. This highlights the need for a balanced and sustainable approach to reforestation to preserve ecological diversity.
An in-depth analysis of this reforestation programs reveals that restoring natural forests across 350 million hectares could remove 42 billion tons of carbon by 2100. In contrast, the current distribution of pledges for plantations, natural forests, and agroforestry initiatives would only sequester 16 billion tons, with commercial monocultures exhibiting a significantly lower carbon sequestration capacity, estimated at just one billion tons. As we aim to reduce the carbon footprint of building materials with alternatives such as mass timber, balancing sustainable forest management with roundwood production is crucial. This research focuses on using multispecies cross-laminated timber (CLT) panels sourced from sustainably harvested wood within natural forests to achieve this balance.
RESEARCH QUESTION
How can the sustainable harvesting of various wood species from forests be leveraged to develop multispecies Cross-Laminated Timber (CLT) panels and subsequently a mass timber value chain in Nepal?
This question will be tackled through topics of:
Utilization of diverse local species: Studying the forest cover of Nepal and the diverse species distribution there and utilize multispecies for prototyping & testing.
Reinterpretation of Vernacular architecture: Developing a re-interpretation of the Vernacular architecture- its tangible and intangible values into a modern innovative approach.
Introduction of new perception of timber: Introduction of new perception of timber through engineered timber elements, focusing on a loadbearing Cross laminated wall panel
NEPAL’S FORESTS | DO WE HAVE ENOUGH WOOD?
In the 1970s, Nepal faced forest degradation due to grazing and fuelwood harvesting, leading to environmental issues. In 1993, the government empowered forest rangers to transfer national forests to community groups, nearly doubling the forest cover by 2016. Research shows community forest management helped regenerate forests, especially in middle elevations. It involves collaboration between rangers and communities, allowing sustainable resource use while restricting harmful activities. Currently, 34% of state-owned forests are managed by community groups, representing a significant shift towards community-led conservation efforts in Nepal.
Nepal’s diverse landscape hosts a rich variety of tree species, offering valuable resources for sustainable timber production. Leveraging data on species distribution and wood quantity is crucial for informed decision-making. Researching each species’ properties and exploring innovative mass timber technologies can maximize benefits while promoting ecological sustainability. This study focuses on eight commonly used timber species in Nepal, analyzing their distribution across altitudes and available growing stock. Conducted remotely at Valldaura Labs in Barcelona, the research provides valuable insights despite limited data availability. It lays the groundwork for future fieldwork and prototyping to explore the properties and applications of each species. This approach promises to enhance our understanding of Nepal’s timber resources and inform more innovative utilization practices.
THE WAY FORWARD | SUSTAINABLE FOREST MANAGEMENT
Sustainable forestry entails responsibly managing forests to preserve biodiversity, ecological services, and forest health, while addressing climate change by enhancing carbon sequestration. It involves regulating harvest cycles to ensure ongoing resource availability. Adaptation strategies include conserving existing forest structures, passive adaptation through natural processes, and active measures like species selection to mitigate climate change impacts.
Before 1933, Nepal’s forest management was minimal, relying on indigenous practices. In 1957, all forests were nationalized, and regulations for protection were introduced. Scientific forest management started in 2011, covering 121,852 hectares by 2020. The Forest Resource Assessment of 2015 identified over a million hectares suitable for scientific management, emphasizing the need for balanced practices. This timeline reflects Nepal’s commitment to sustainable forest stewardship and its potential for integrating with timber production. However, sustainable practices may yield lower timber production compared to commercial plantations, highlighting the need for hybrid strategies optimizing both biodiversity and timber production for long-term sustainability.
TRADITIONAL URBAN SETTLEMENT
The Kathmandu Valley is a region rich in history, comprising towns like Kathmandu, Patan, and Bhaktapur, each with unique significance influenced by ancient trade routes. Traditional urban settlements in the valley feature organic layouts with narrow roads leading to squares and courtyards filled with temples, palaces, and residences. The architecture showcases uniform pitched roofs, intricate woodwork, and bay windows, creating a vibrant urban environment deeply rooted in cultural heritage. Open spaces like streets, plazas, and courtyards play a crucial role in preserving local customs and traditions, hosting various festivals and rituals throughout the year. However, amidst rapid urbanization, these traditional areas face neglect, with open spaces being overtaken by parking. It’s important to research and document these old settlements to integrate their cultural essence into modern developments, maintaining a unique urban identity while incorporating innovative features.
TRADITIONAL TIMBER BUILDINGS
The traditional building systems of the Kathmandu Valley blend brick loadbearing walls with timber frame systems, featuring intricate wood-to-wood joineries. The iconic Kashthamandap exemplifies this craftsmanship with its wooden core supported by sturdy posts. Residential blocks in the valley typically feature sloped roofs around shared courtyards, accommodating urban expansion. Colonnaded porticos on the ground floor act as transitions between private and communal areas, often used as shops or workshops. Courtyards serve as versatile spaces for daily activities and celebrations. The first floor houses sleeping quarters, while the top floor serves as living space with large wooden bay windows offering privacy. The communal aspect of this architecture is valued but often absent in modern construction, suggesting a reinterpretation of traditional values in contemporary living.
TIMBER VALUE CHAIN | EXISTING
In Nepal’s construction industry, traditional materials like brick, concrete, and steel dominate, while timber remains underutilized despite abundant forest resources. Annual timber production is well below its potential, hindered by perceptions of timber as primitive compared to modern materials. Lack of education on structural wood technologies and a fragmented timber value chain contribute to high prices and limited use in construction. Overcoming these challenges is vital to harnessing timber’s sustainability and viability in Nepal’s evolving construction landscape. With an annual demand for 140,000 housing units, especially 25,000 in Kathmandu, there’s an urgent need to diversify construction materials beyond concrete and steel. Initiating a market for alternative materials like timber is crucial for leveraging resources, acknowledging its cultural significance, and embracing modern innovation to reshape Nepal’s construction landscape sustainably.
TIMBER VALUE CHAIN | PROPOSED
The aim of this research was to develop a framework for creating a circular mass timber value chain in suburban satellite towns, focusing on detailed design of worker housing clusters, individual residential units, and prototyping a multispecies Cross-Laminated Timber (CLT) panel. The primary focus is on designing individual units and testing the CLT panel prototype due to time and resource constraints, while providing a conceptual framework for future neighborhood and satellite town proposals. The project envisions a suburban satellite town demonstrating sustainable community forest management alongside a decentralized, low-scale mass timber production factory. It integrates forest conservation with local timber production to promote environmental sustainability and economic empowerment, aiming to optimize timber use, reduce environmental impact, foster community ownership of forest resources, and serve as a replicable model for sustainable development.
PILOT PROJECT | NEIGHBORHOOD DESIGN
The envisioned neighborhood design for a new suburban satellite town draws inspiration from sacred geometry, merging traditional symbolism with contemporary urban planning. The urban grid reflects a dynamic tapestry, intertwining diverse street types to accommodate various modes of mobility while maintaining Nepali urban landscapes’ compact-city essence. The central plaza, influenced by mandala symbolism, serves as a communal hub for gatherings and festivals, promoting sustainability with greenery and timber construction. The Arboreal City Module integrates urban living with nature, fostering a self-sufficient community that preserves ethnic heritage amidst globalization. Urban forests provide green public spaces while meeting timber demands through careful harvest cycles.
PILOT PROJECT | INDIVIDUAL UNIT DESIGN
The conceptual development of the worker’s housing unit design seamlessly blends Nepal’s rich architectural heritage with contemporary functionality, creating a distinctive living space. Inspired by traditional pagoda roofs and intricate lattice windows, the housing unit stands as a cultural landmark, reflecting pride and identity. Central to the design is the communal spirit of Nepali culture, embodied through the incorporation of a porch that extends into the public realm, fostering community interaction. The use of circumambulatory projections on the top floors provides both visual interest and functional benefits, such as privacy and sunshading. As a pilot project, the housing unit showcases the balance between innovative technologies, like engineered timber elements, and traditional craftsmanship passed down through generations.
The worker’s housing unit prioritizes communal living with an open ground floor layout encompassing a living room, bathroom, kitchen, and dining area, inspired by Nepali common courtyards. Private bedrooms on the first floor feature balconies with greenery, connecting residents with nature and surrounding activities. The second floor hosts a flexible space with a greenhouse and terrace, adaptable for different activities, from recreation to daily chores, promoting holistic urban living. Innovative features such as integrating solar panels into the greenhouse demonstrate a modern twist on traditional living methods, promoting sustainability in food and energy production. The design ethos of the worker’s housing unit represents a fresh interpretation of Nepali culture, blending nature, heritage, and modern amenities, with potential future developments including varied unit sizes and mixed-use programs to enrich community life. Structurally, the unit relies on a core cross-laminated timber (CLT) loadbearing wall system, supplemented by a separate framework for the facade and roof, echoing traditional Nepali wood joinery techniques for durability and flexibility. This commitment to design for disassembly ensures future adaptability with minimal environmental impact, although current efforts prioritize prototyping and evaluating the loadbearing CLT wall using two wood species—Cedrus Deodara and Pinus Halepensis—to determine their structural performance and compatibility within the envisioned framework.
PROTOTYPE PANELS | DESIGN & PRODUCTION
Sustainable material sourcing is a key focus of this research, especially regarding the mass timber value chain. While prior chapters extensively cover the theoretical examination of Nepal’s forest species, the current study, conducted at Valldaura labs in Barcelona, prioritizes locally available materials. Although the data may not directly apply to Nepalese species, it highlights the need for further exploration, prototyping, and testing to understand the unique properties of specific species for sustainable timber production. This underscores a shift in architectural design towards considering material aspects beyond space creation, advocating for the strategic use of multispecies timber elements to optimize structural integrity, durability, and sustainability in construction projects. Cedrus Deodara and Pinus Halepensis were chosen for prototyping and testing due to their availability, sourced from nearby urban plots and Collserola Park, respectively.
PROTOTYPE PANELS | SUBMERSION TEST
Individual lamellas of Pinus Halepensis and Cedrus Deodara, sized at 30 cm x 10 cm x 2 cm, underwent a water absorption test where they were submerged in water for 24 hours. Pinus Halepensis showed a water absorption rate of 20.9%, with slight thickness variation noted toward the lamella’s center. Conversely, Cedrus Deodara exhibited a lower absorption rate of 17%, with no change in dimensions. After soaking, Pinus Halepensis retained 14.6% water content while Cedrus Deodara had 11.5%. These results highlight Cedrus Deodara’s superior water resistance compared to Pinus Halepensis.
PROTOTYPE PANELS | DESIGN & PRODUCTION
In the prototyping and testing phase of this research, three panels of cross-laminated timber (CLT) were created using Pinus Halepensis and Cedrus Deodara. Timber harvested and processed at Valldaura labs was cut to size, and a frame jig was built for assembly and gluing. Soudal Pro 40P Wood Glue, a polyurethane adhesive, was applied to bond the layers, with a strict 15-minute open time. The assembled frame was pressed under the CLT press for 3 hours to ensure proper adhesion and structural integrity. While commercial factory settings may offer more efficiency and precision, the procedure for these scale panels is straightforward and can be executed with minimal manpower. Two sets of three prototypes with different layup distributions were produced, one majorly for weather testing and the second for structural testing.
Given the superior water resistance of Cedrus deodara in previous tests, it is inferred that it would function effectively as the exposed layer in an external wall Cross-Laminated Timber (CLT) panel. However, a notable challenge for multispecies CLT panels is the heightened risk of delamination during weathering. To evaluate panel performance and establish a comparative analysis, three panels with different species layups were constructed.
- P-P-P-P-P (All Pinus Halepensis): Pinus Halepensis, is utilized as the sole material in this panel. This configuration serves as a benchmark to understand the baseline properties of the CLT panel.
- C-P-P-P-P (Cedrus External Layer): In this panel, Cedar is placed on the external layer exposed to water and weathering conditions, with a Pinus Halepensis core and interior surface. This setup aims to assess the impact of Cedrus as the external layer.
- C-P-P-P-C (Cedrus on Both Sides): Designed for external walls with internal sides facing moist areas like bathrooms and kitchens, these panels feature Cedrus on both external and internal surfaces, with a Pinus Halepensis core.
PROTOTYPE PANELS | WEATHER TESTING
To assess the performance of Multispecies 5 layered CLT panels as load-bearing external walls, a low-tech weathering test was conducted at Valldaura labs in Barcelona in March 2024, with average temperatures ranging from 7°C to 20°C. One face of the panels was exposed to natural weathering conditions, while daily water spraying was implemented to simulate humidity, correlating with Nepal’s average annual rainfall. Waterproof membranes were wrapped around the five sides of the panels to ensure only one face was exposed, and observations were made after 7 days. However, due to setup errors, water leaked inside the membrane, causing extreme dampness and initial fungal growth in panels with pine as the internal layer. Despite this, all panels showed similar humidity levels on their external layers, with no warping or delamination observed. After another 7 days of exposure, slight delamination was noted between the first and second layers in two panels. These findings emphasize the importance of further refinement in testing setups to accurately assess panel performance under weathering conditions.
PROTOTYPE PANELS | STRUCTURAL TESTING
While the choice to use cedar in the external layer and pine in the internal layer was primarily based on their qualitative performance regarding water and pest resistance, maintaining robust structural integrity remains paramount. To ensure this, compressive strength tests were carried out for each panelas part of a wall system evaluation. To accommodate the limitations of the testing equipment, the panels were cut into smaller pieces, yielding two samples for each panel configuration. Each sample comprised either two layers with fibers aligned parallel to the applied load or three layers with fibers similarly oriented. Notably, the latter configuration proved superior, consistent with the principles governing cross-laminated timber (CLT) panels, where vertical layers play a crucial role in distributing loads effectively. The testing setup and their corresponding performance graphs are shown in the diagram. Among the configurations tested, the panel featuring cedar on both external sides [C-P-P-P-C] demonstrated the most favorable performance.
PROTOTYPE PANELS | CONCLUSION
Based on the findings from the weathering test and structural assessments, the comparative analysis presented in the table above facilitated the grading of the panels. While all three layups exhibited similar discoloration effects due to weathering, panel C [C-P-P-P-C] demonstrated superior performance in terms of water resistance and structural integrity. This makes it a viable candidate for external load-bearing walls, given its resilience even when both sides are exposed to humidity. Prototype A [P-P-P-P-P] could serve effectively as a partition wall in areas shielded from rain and moisture. Meanwhile, prototype B [C-P-P-P-P] could be utilized for internal partitions, especially with Cedar on one side, suitable for moderately humid spaces. Further investigation into enhancing structural integrity by adjusting lamella thickness or introducing alternative species warrants exploration. However, to obtain more precise results, future testing endeavors should strive for a more scientific and controlled environment.
RESEARCH CONCLUSION
In conclusion, as we embrace the new timber era, it’s crucial to prioritize sustainable timber sourcing and local production to avoid repeating environmental mistakes seen with materials like concrete and steel. This entails shifting from centralized mass production and monospecies plantation towards sustainable forest management, local production, and extensive research on diverse forest species and their unique properties. Through collaborative efforts and responsible stewardship, we can ensure a sustainable and harmonious journey into the timber era. While Cedrus Deodara and Pinus Halepensis were used in this research phase, the aim isn’t to promote specific species but to advocate for localized research on diverse species globally. This approach emphasizes the importance of understanding forest outputs and incorporating unique species properties into design processes. Rather than pushing for a single ‘perfect’ species, this research highlights the significance of biodiversity and tailoring approaches to local ecosystems, fostering sustainable forestry practices. Furthermore, exploring woodworking traditions worldwide can infuse timber architecture with cultural identity, celebrating the rich heritage and ingenuity of wood use throughout history.
