D.G. Horswill & T.H. Nielsen
Søren Jensen Consulting Engineers, Copenhagen, Denmark

ABSTRACT: PC (precast concrete) construction has a long history in Denmark and has devel- oped into a dominant technology in response to client and contractor demands for a low cost, low risk structural system.
CLT (cross-laminated timber) construction is new to the construction industry in Denmark and has not had the benefits of time and financial investment to be able to compete commercially with PC construction.
In the absence of ambitions beyond low cost and risk, the situation is destined to remain un- changed.
In 2009, Copenhagen announced plans to be the world's first CO2 neutral city by 2025. To- gether with the City's plans to build 6.8 million sqm of new buildings by the same year, a new development trajectory now exists that couples development with sustainability.
While this new incentive may suit the environmental benefits of CLT construction, perceived increased risk and cost represent significant barriers to its adoption in Denmark.
The results of the research show that CLT construction would reduce the existing CO2 deficit of 70,000 tons by 22% - a contribution similar in magnitude to other CO2 reducing initiatives such as the use of solar cells or using new fuels for transport. However, it also shows that the cost of CLT construction is 26% higher than PC construction for the same building.
The paper concludes by suggesting a number of ways to increase the adoption of CLT con- struction in Denmark in light of its environmental advantages and commercial disadvantages.

1. INTRODUCTION
The Copenhagen Resource and Waste Management Plan 2018 states the following:
It is important to have focus on choice of materials and building methods in connection with new building or renovation in order to cause the least possible burden to the environment and mini- mize resource wastage when the buildings are to be demolished or renovated in the future. (WASTEMAN, 2014, p25).
It is clearly a priority of the City of Copenhagen to ensure that the design of new buildings con- siders the environment, both in terms of their initial construction, as well as in terms of their life after their final demolition. But how well does the current Danish construction market support this ambition?
PC (precast concrete) construction consists of pre-fabricated reinforced concrete floor and wall elements which are connected together to form a stable structure. This construction system has a long history in Denmark and has developed in response to client and contractor demands for de- creased risk, increased profits and cost certainty.
In the search for savings, organizations look to improve the cost efficiency of the way they work, often using familiar material and processes – so called incremental improvements (Slaugh- ter, 1998). Such path-dependent development of technologies can lead to the emergence of dom- inant technologies that have had the benefits of scale economies, learning & network effects and the adaption of actor expectations, each reducing cost or risk perceptions (Foxon, 2007). In the context of construction systems, PC construction can be considered a dominant technology in Denmark.
CLT (cross-laminated timber) construction has only been applied in Denmark to a few, very small private projects. Therefore, CLT construction can be considered a novel approach in Den- mark. CLT construction uses prefabricated timber floor and wall elements and is very similar in nature to PC construction in terms of transportation, erection and its underlying structural princi- ples.
By their nature, novel and unconventional approaches have not had the benefit of these path- dependent reductions in risk and cost and as a result are likely to be perceived as more expensive, risky, or both (Jones et al, 2015).
The need for resource efficiency has introduced a new improvement trajectory that threatens profit margins which have been achieved using cost and risk efficient technologies. As such, in the absence of regulation or client direction, a contractor seeking to minimize cost and risk would lack the motivation to adopt such an approach as it threatens the delivery of acceptable rates of return or the winning of projects in a lowest cost auction (Jones et al, 2015).
In 2009, Copenhagen announced plans to be the world's first CO2 neutral city by 2025. To- gether with the City's plans to build 6.8 million sqm of new buildings by the same year, a new development trajectory now exists that couples development with sustainability.
The purpose of this document is to question the dominance of PC construction in light of the City’s new sustainable demands by comparing it with CLT construction and to suggest ways in which to increase the adoption of CLT construction in the Danish construction market.