Whole-building life cycle assessment in LEED v4 and v4.1
Achieving building life-cycle impact reduction credits (MR) in LEED v4 and v4.1
Conducting a whole-building life-cycle assessment to reduce impact helps you earn credits in LEED Building Design and Construction (BD+C), v4. The latest version, LEED v4.1, encourages wider adoption of LCA by offering a credit for completing a whole building LCA, even if no improvements are demonstrated. This article offers practical guidance on how to achieve building life-cycle impact reduction credits in both LEED v4 and LEED v4.1.
Comparing LEED v4 and LEED v4.1
LEED v4.1 is described as an evolution of LEED v4. Its changes reflect a focus on improving performance while widening access so that more project teams can commit to sustainability. The LEED MR Building Life-cycle Impact Reduction credit requirements and options for each version are summarised below. LEED v4 BD+C MRc1 Building Life-cycle Impact Reduction
- A completed LCA of the project’s structure and enclosure must demonstrate a minimum 10% reduction compared with a baseline building.
- Three base credits are available, and an exemplary performance credit is available for improvements over the required credit thresholds in all six impact categories. In some countries, including Canada and Sweden, this is also a regional priority credit.
|Credit option||Requirements||Credits available||Impact category requirements|
|LEED v4 MRc1 Option 4||Complete a whole building LCA and demonstrate 10% reduction in core impact categories||3 base credits & optional exemplary performance / regional priority credits.||Reductions must be achieved in at least 3 out of 6 impact categories, including GWP. Impacts should not increase in the remaining categories by more than 5%.|
|LEED v4.1 MR Path 1||Complete a whole building LCA only – no requirement to demonstrate impact reduction.||1 credit|
|LEED v4.1 MR Path 2||Complete a whole building LCA and demonstrate 5% reduction in core impact categories||2 credits||Reductions must be achieved in at least 3 out of 6 impact categories, including GWP. Impacts should not increase in the remaining categories by more than 5%.|
|LEED v4.1 MR Path 3||Complete a whole building LCA and demonstrate 10% reduction in core impact categories||3 credits||Reductions must be achieved in at least 3 out of 6 impact categories, including GWP. Impacts should not increase in the remaining categories by more than 5%.|
|LEED v4.1 MR Path 4||Complete a whole building LCA and demonstrate 20% reduction of GWP and incorporate building reuse and/or salvage materials.||4 credits||As well as a 20% reduction for GWP, also need to demonstrate a 10% reduction in two additional impact categories.|
How is a baseline building defined in LEED?
LEED states that the baseline and proposed buildings must be of comparable size, function, orientation, and operating energy performance. But what does this mean in practice? It may help to think of the baseline building as a building meeting the same function and size but without all of the clever design choices that make it more efficient. Baseline buildings are defined differently in the U.S. and internationally.
- U.S. projects: Define the wall, roof, and floor assemblies following the performance requirements of the building envelope in ASHRAE 90.1–2010 for the project’s climate zone (Appendix G, Opaque Assemblies, Vertical Fenestration, Skylights, Roof Solar Reflectance, and Thermal Emittance sections).
- International projects: Projects outside the U.S. are expected to develop a baseline building representing typical construction for their region, meeting local applicable building performance requirements. Consider ASHRAE 90.1 – 2010 for a minimum set of guidelines for the building.
To make sure that the baseline and proposed models can be accurately compared, some aspects must be kept the same in both the baseline and the proposed building. Here is a summary of what changes are and are not allowed.
|You are allowed to||You are not allowed to|
|Optimize and reduce the mass of your actual building (from any studied part of the building)||Increase wall mass or insulation unnecessarily for the baseline building to show dematerialization|
|Change the structures and design of the building, including stud spacing, floor-to-ceiling heights, changes in the use of beams and pillars||Use a different area for the baseline building and actual design (specified as gross area)|
|Identify opportunities to make design changes to use lower -emissions materials or specify the use of specific products with quantified life-cycle impacts||Omit required parts of the envelope and structure: footings and foundations, structural wall assembly (from cladding to interior finishes), structural floors and ceilings (not including finishes), roof assemblies|
|Include additional elements, such as interior nonstructural walls or finishes (no extra credit)||Include excavation, site development, parking lots or building technologies and systems|