In recent years, timber has been considered as an alternative source of building material because of its sustainability and design efficiency. However, the cost competitiveness of timber buildings is still under study due to the lack of available cost information. This paper presents a comprehensive cost comparative analysis of a mass timber building mainly developed with cross-laminated timber (CLT). The actual construction cost of the project is compared with the modeled cost of the same building designed as a concrete option. The result shows that the construction cost of timber building is 6.43% higher than the modeled concrete building. The study further investigated the change orders associated with the project and found that the total cost of change orders contributed 5.62% to the final construction cost of mass timber building. The study is helpful to provide insight into the construction cost of typical mass timber buildings. It also can be used as a guide for the project owners to make decisions regarding their initial investments on a mass timber project.
The research presents a Carbon Value Engineering framework. This is a quantitative value analysis method, which not only estimates cost but also considers the carbon impact of alternative design solutions. It is primarily concerned with reducing cost and carbon impacts of developed design projects; that is, projects where the design is already a completed to a stage where a Bill of Quantity (BoQ) is available, material quantities are known, and technical understanding of the building is developed.
This research demonstrates that adopting this integrated carbon and cost method was able to reduce embodied carbon emissions by 63-267 kgCO2-e/m2 (8-36%) when maintaining a concrete frame, and 72-427 kgCO2-e/m2 (10-57%) when switching to a more novel whole timber frame. With a GFA of 43,229 m2 these savings equate to an overall reduction of embodied carbon in the order of 2,723 – 18,459 tonnes of CO2-e. Costs savings for both alternatives were in the order of $127/m2 which equates to a 10% reduction in capital cost.
For comparison purposes the case study was also tested with a high-performance façade. This reduced lifecycle carbon emissions in the order of 255 kgCO2-e/m2, over 50 years, but at an additional capital cost, due to the extra materials. What this means is strategies to reduce embodied carbon even late in the design stage can provide carbon savings comparable, and even greater than, more traditional strategies to reduce operational emissions over a building’s effective life.
Michigan State University (MSU) will develop a construction time and cost estimating tool for the use of cross laminated timber (CLT) in commercial building construction. This responds to a significant barrier to adopting such buildings among the architecture, engineering, and construction (AEC) industry, which has been reported since 2014. Despite broad agreement that first costs (and by extension time) and life cycle costs are an important facet of CLT buildings, over one third of architects were uncertain about this topic. Nine out of ten architects also listed costs and cost information as a significant barrier. This project will expand wood products markets by addressing this significant AEC industry barrier, and as a result, encourage more designers and constructors to specify CLT in their buildings. The project includes the development of a web-based predictive cost and time tool; this is quite common during the conceptual design stage, and as such, these tools exist for steels and concrete buildings, yet very little information exists for CLT. The team will also develop up to 20 CLT building case studies, with a focus on as-built costs, life cycle costs (building maintenance, energy, and carbon), construction time, and green building certification. These cases will be used to develop continuing education training modules for designers and constructors. Finally, in an attempt to motivate current students to become more knowledgeable about CLT, MSU will sponsor a 4- and 2-year CLT construction management competition. We expect these efforts to reach over 300 designers and constructors, and up to 75 AEC students.
The Canterbury earthquakes in 2010 and 2011 caused significant damage to the Christchurch building stock. However, it is an opportunity to build more comfortable and energy efficient buildings. Previous research suggests a tendency to both under heat and spot heat, meaning that New Zealand dwellings are partly heated and winter indoor temperatures do not always meet the recommendations of the World Health Organization. Those issues are likely to be explained by design deficiency, poor thermal envelope, and limitations of heating systems.
In that context, the thesis investigates the feasibility of building an energy efficient and cost-competitive house in Christchurch. Although capital costs for an energy efficient house are inevitably higher, they are balanced with lower operating costs and improved thermal comfort. The work is supported by a residential building project using Cross Laminated Timber (CLT) panels. This atypical project is compared with a typical New Zealand house (reference building), regarding both energy efficiency and costs.
The current design of the CLT building is discussed according to passive design strategies, and a range of improvements for the building design is proposed. This final design proposal is determined by prioritizing investments in design options having the greatest effect on the building overall energy consumption. Building design features include windows efficiencies, insulation levels, optimized thermal mass, lighting fixture, as well as HVAC and domestic hot water systems options. The improved case for the CLT building is simulated having a total energy consumption of 4,860kWh/year, which corresponds to a remarkable 60% energy savings over the baseline.
The construction cost per floor area is slightly higher for the CLT building, about 2,900$/m² against
2,500$/m² for the timber framed house. But a life cycle cost analysis shows that decreased operating costs makes the CLT house cost-competitive over its lifetime. The thesis suggests that the life cycle cost of the CLT house is 14% less than that of the reference building, while the improved CLT design reaches about 22% costs savings.
Project contact is Mark Weaver at Karagozian & Case
Buildings for the U.S. Department of State (DOS) and U.S. Department of Defense (DOD) often have to meet blast as well as forced entry / ballistic resistance (FE/BR) design requirements to mitigate the hazardous effects associated with terrorism. Historically, DOS and DOD buildings exposed to these threats have been constructed using concrete and steel. However, the emergence of cross-laminated timber (CLT) presents an opportunity to provide a sustainable building material alternative to owners and architects developing such structures. Several wood characteristics (i.e., propensity to rupture in a brittle fashion upon being overstressed, relatively low penetration resistance) serve to limit CLT’s effectiveness in resisting blast and FE/BR threats. The proposed effort seeks to address these limitations by investigating the possibility of incorporating commercial off-the-shelf (COTS) building materials into CLT panel designs in order to meet DOS/DOD blast and FE/BR design requirements. Particular emphasis will be placed on ensuring the developed panel designs are cost competitive to facilitate their inclusion in actual buildings. The project team includes an American CLT manufacturer to quickly assess the cost impacts of incorporating COTS materials into CLT panel layups. Additionally, representatives from the DOS, DOD, and an architecture firm routinely involved with the design of DOS buildings will be consulted to ensure programmatic, aesthetic, and detailing issues are considered during candidate panel design development.
Project contact is Frank Lam at the University of British Columbia
A continuous CLT floor/roof system that has two way bending action across multiple CLT panels will create open floor space with long spans in both major and minor directions, making mass timber construction more competitive and cost-effective. A design guide on CLT two way floor/roof system, incorporating the results from the two phases of study, will be developed at the end.
The Task Group on Combustible Construction is in the process of evaluating a proposed code change request related to buildings of encapsulated mass timber construction (EMTC). As part of the analysis of the code change request, an impact analysis is required that includes a cost-benefit analysis.
Hanscomb was hired to provide a cost-benefit analysis and to compare the estimated value of the following:
1. The cost of constructing a building of mass timber (unprotected) versus a building constructed of encapsulated mass timber (e.g. mass timber protected with a double layer of Type X gypsum board) versus a traditional concrete and steel building.
2. The time to build a building of mass timber construction (unprotected) versus a building of encapsulated mass timber construction versus a traditional concrete and steel building.
3. The annual maintenance costs of building of mass timber construction versus a building of encapsulated mass timber construction versus a traditional concrete and steel building.
For the purposes of this study two sets of conceptual floor plans and elevations have been created:
1. A 12 storey building with a Group C major occupancy (residential) where each storey is 6,000 m2 in floor area.
2. A 12 storey building with a Group D major occupancy (office) where each storey is 7,200 m2 in floor area.