As the industry looks for continuous improvement, LEED has undergone an overhaul which aims to enhance sustainability codes and practices. But what do the changes mean for structural engineers?
The United States Green Building Council (USGBC) released the original Leadership in Energy and Environmental Design (LEED) system in 2000, which rated the sustainability levels of buildings across five primary categories, with 69 points available.
Version four (V4) now has six primary categories and 110 points available with buildings conferred with ratings ranging from "certified" (a minimum score of 40 points) to ‘platinum’ (for buildings scoring 80 points or more).
There are now more market sector categories, which addresses the fact that different types of buildings may have more or less intensive energy usage and material requirements. Although the basic premises under each of these categories are similar, each has been tailored to meet the specific requirements of the market sector area.
LEED V4 is also more technically demanding. This increased technical rigour means architects and developers will have to rely more on engineers and other professional with expertise outside their traditional roles.
The biggest changes for most structural engineers are in the section on Materials and Resources (MR).
There has been some controversy with the new focus on environmental life cycle assessment (LCA), which measures and gauges the impact of all the stages in the production of a product or building, from creation and installation to usage and disposal.
The new system considers LCA on two levels: the whole building and individual products. The whole-building LCA credit encourages the use of LCA tools in the design of a building's structure and shell to minimise the impact of the chosen materials. This process aims to give the structural engineer greater involvement in design decisions, in a manner similar to the way energy modelling now engages mechanical engineers in decisions about a building's thermal characteristics.
Speaking to Architectural Record, Frances Yang at Arup expressed his preference for the way this credit brings more parties to the design table early in the process, but raised the concern that “the rules aren't really clearly defined.”
The emphasis on adaptive reuse remains in the LCA credit, meaning structural engineers may be asked to evaluate existing structures and materials for new applications and loading.
“This creates some interesting structural challenges when buildings that have performed well for decades must be evaluated and upgraded to meet current codes, or when structural degradation must be evaluated as existing materials are adapted to new uses,” said Don Allen from DSi Engineering.
Environmental product declarations (EPDs), product category rules (PCRs), and eutrophication are some of the concepts and terms included in the new credits system which may be alien to structural engineers and the rest of the design team.
EPDs are detailed reports which outline a product's effect on the environment over the course of its life. Critics have highlighted that even EPDs for materials that have a poor environmental performance can count toward this credit. Nevertheless, this option should still bring about better and more transparent information on construction products and materials, allowing the design team to make more informed choices.
As with the energy optimisation credit, the LCA credits also require designers to model a base building and then model the intended design to show reduced life cycle impacts. Only the building's structure and enclosure are included, with site work and interior finishes excluded. This means material choices by structural engineers will have a greater impact in this area.
Despite the update, the LEED system certainly isn’t yet perfect.
Thanks to fears that V4 is too big a change, V3 will remain available until June 2015. One of the biggest criticisms levelled at LEED is that it is too easy to game the system. By offering two completely different systems for developers to choose between, critics argue that this is a retrograde step.
And perhaps even more damning, critics also still say that LEED V4 has nothing which encourages true green building innovation, instead emphasising cut-and-paste rules for achieving green credentials.
LEED V4 is still a progressive step but there are opportunities for further improvements in the next iteration.