This series highlights five whole building life cycle assessments (WBLCAs) of buildings incorporating the building material known as cross-laminated timber (CLT) into some or all of their structure, using a primary cradle-to-grave system boundary. This case study series will serve as an educational resource for academics, professionals, and CLT project stakeholders. While there is some uncertainty about the best way to reduce greenhouse gas emissions from architecture and construction, using CLT and other wood building materials is one possible means to reduce the emissions associated with a building’s materials. When forests are managed sustainably, wood construction materials can contribute to climate change mitigation goals as an indefinite carbon store and as a replacement of other fossil-fuel intensive materials. WBLCA is an assessment method to estimate the environmental impacts of buildings; this series offers insight into the current possibilities and limitations of WBLCA for CLT buildings. The series begins with background information on WBLCA methods and CLT, a review of previously published CLT building WBLCAs, and a life cycle assessment of an individual CLT wall element using the WBLCA softwares Tally® and Athena Impact Estimator for Buildings (Athena IE).
The study investigates the environmental benefits of reusing Cross Laminated Timber (CLT) panels. The Global Warming Potential (GWP) of a single-stored Coffee shop built in 2016 in Kobe city was calculated, considering different CLT reuse ratios, forest land-use and material substitution possibilities. The results showed that as the rate of reused CLT panel increases the total GWP decreases. Moreover, in all cases, the option with smallest GWP is when the surplus wood is used for carbon storage in the forest, revealing the importance of a growing forest for increasing the environmental benefits of timber utilisation. The results suggest the systematic reuse of CLT panels offers a possibility to increase the carbon stock of Japanese Cedar plantation forests and further mitigate the environmental impact of construction.
Many strategies have been investigated seeking for efficiency in construction sector, since it has been pointed out as the largest consumer of raw materials worldwide and responsible of about 1/3 of the global CO2 emissions. While operational carbon has been strongly reduced due to building regulations, embodied carbon is becoming dominating. Resources and processes involved from material extraction to building erection should be carefully optimized aiming to reduce the emissions from the cradle to service. New advancements in timber engineering have shown the capabilities of this renewable and CO2 neutral material in multi-storey buildings. Since their erection is based on prefabrication, an accurate construction management is eased where variations and waste are sensible to be minimized. Through this paper, the factors constraining the use of wood as main material for multi-storey buildings will be explored and the potential benefits of using Lean Construction principles in the timber industry are highlighted aiming to achieve a standardized workflow from design to execution. Hence, a holistic approach towards industrialization is proposed from an integrated BIM model, through an optimized supply chain of off-site production, and to a precise aligned scheduled on-site assembly.
The primary outcome of this work is to provide integrated analysis of the environmental, financial, and social benefits and costs of using CLT in tall wood buildings. Secondary outcomes will be (1) information, including a design team checkoff that can be used to inform the building community as they make decisions on specific, new building projects, and (2) an informational foundation for these stakeholders and others to begin to evaluate the complex tradeoffs between, and optimization of, environmental, financial, and social benefits and costs.
This report presents an overview into cross laminated timber (CLT) as a construction material and how it compares to traditional methods of construction. CLT is also examined in the context of a move to off-site manufacturing (OSM) and a greater emphasis on sustainability in the construction sector. In this context it is found to perform well with mass timber products such as CLT being the only carbon negative building materials capable of building mid and high-rise buildings.
The barriers and opportunities for CLT are explored looking at literature, industry reports and case studies. The main barriers to wider use of CLT still come from uncertainties around the material. Although they have been proven to not be a problem, worries over issues such as how it performs during fires and the lifetime of buildings persist. A lack of standardisation may be the primary cause for this as a range of products and specifications across different manufactures and countries creates confusion and means that each building needs to be individually specified. The opportunities identified for CLT include its carbon saving properties which could benefit governments wanting to reach their carbon reduction targets. In addition, the ability to use CLT on a wider range of sites such as unstable brownfield land and over service tunnels lends to its strength in aiding with urban densification.
In terms of costs, these are found to be comparable to those of traditional construction methods with high material costs being offset by reduced foundations and construction time. CLT buildings do, however, face a premium in insurance costs. Transport costs, resulting from a concentrated production base in central Europe, also add a considerable amount to the overall cost of the finished product. This in turn encourages domestic production in countries outside of Europe.
The possibilities for CLT in the UK residential construction market are investigated with a focus on mid-rise and high-rise flat construction as that is what the economics and material properties of CLT most lend itself to. Although CLT currently has a low market share of less than 0.1% of homes in this sector there is the potential for this to increase to 20-60% over time. The lower range of this estimate is not predicted to be reached before 2035 and this is also dependant on rising CLT production levels. The volume of timber that is needed to manufacture enough CLT to reach these increased construction volumes can be sourced sustainably from existing forests production in Europe and North America. In addition, the UK has enough excess timber harvesting capacity to provide for the entirety of CLT buildings in the UK, however, large scale domestic CLT production is required to make this a reality.
April 3-5, 2014, Boston, Massachusetts, United States
Tall buildings pose a challenge to the sustainability movement because they offer both positive and negative environmental impacts. Positive impacts include reducing urban sprawl, promoting alternative transportation, and allowing efficient energy use on...