1 General LCA Prioritization

Early incorporation of environmental impact reduction strategies is vital. Decisions made during the concept phase often determine the bulk of a project’s environmental footprint. Fixed decisions made during the concept phase, such as the building’s form, structural system, layout, or material choices, can ‘lock in’ a project’s resource consumption and emissions early on, leaving limited opportunities for significant sustainability improvements later in the design process. A successful project is not merely the sum of each discipline’s individual contributions, it requires integrated, transdisciplinary collaboration and data-driven decision-making from the earliest design phases through the final tender. If the LCA is treated as an afterthought, aligning the project with meaningful environmental goals or KPIs becomes highly unlikely – same goes for other initiatives.

“Painting over the cracks won’t strengthen the wall"

No amount of late-stage refinement can correct a fundamentally flawed design. Therefore, strong collaboration and early consideration of LCA are essential to achieve a more sustainable outcome. Figure 1.1 depicts the Influence Curve, illustrating the relationship between one’s ability to influence a project’s success and the cost of making changes. As the project progresses, the ability to implement changes decreases, while the cost of it increases.

Figure 1.1 The Influence Curve. Illustration from Celoxis - A Quick Introduction to Project Planning.

Before exploring how each discipline can contribute to reducing the carbon footprint of their project, the following three subsections outline key focus areas that all project teams should address throughout the design phase to significantly reduce their project’s environmental footprint. These strategies, listed in order of highest potential influence, include building geometry, material selection, and specific product choices. Specific product choice can however wait for last as it has the lowest influence, but by addressing these critical elements early, designers can lay a strong foundation for more subject-focused optimization in the later stages.

1.1 Building Geometry

Building geometry refers to the overall shape, size, and spatial layout of a structure. It includes characteristics like the building’s footprint, height (total and f2f), volume arrangement and the complexity of its form. The building’s geometry has a profound influence on its LCA result. Decisions regarding geometry made during the concept stage can have a significant impact on material quantities, structural needs, and operational energy use. As a rule of thumb, simpler geometry translates to a lower environmental footprint, whereas unusual forms should be justified by other benefits to outweigh the extra environmental impacts.

An effective way to support informed geometric decisions is to conduct early variation studies. These studies provide the project team with valuable insight into how changes such as building/floor height, overall shape, or floor plan layout can influence material consumption, carbon footprint, and energy performance.

Example 1: Figure 1.2 and Figure 1.3 shows a student-made design proposal from a previous iteration of course 41936, focusing on Building 313. The project-case reimagined Building 313 as a 97.7 m tall high-rise office building with 22 above-ground floors and 3 basement levels, covering a footprint area of 1 404 m² and GFA of 23 621 m². While the design fulfilled the project KPIs and reached a carbon footprint of 8 kg CO₂e/m²/year, it was evident that sustainability was not the primary driver in the initial design iteration, particularly in terms of embodied carbon and early-stage variant study.

The massing, composed of three stacked boxes with decreasing floor areas toward the top, was intended to create a strong architectural statement. However, this form introduced significant structural challenges. As the project progressed, the height and fragmentation of the volumes demanded far more structural support than anticipated, leading to oversized beams and a reliance on large quantities of high-impact materials. In hindsight, this became a band-aid solution for a flawed geometric choice where aesthetics locked in excessive material use early on.

This example highlights the importance of conducting early LCA variant studies during the concept phase and not as a checklist item after the geometry is fixed.

Figure 1.2 3D illustration of the project from a Southwest and Northwest perspective.

Figure 1.3 Detail of the project’s load-bearing structure, illustrating where the main structural loads are concentrated. Seven castellated box beams, each measuring 2000x1500 mm and spanning 10.5 m, were estimated to be necessary to carry and transfer the loads in the most cricical area.

1.2 Material Selection

As a rule of thumb, the production phase (module A1-A3) typically represents the largest share of a building’s carbon footprint due to the carbon-intensive processes of material procurement, manufacturing and transportation. Therefore, making material selection one of the most effective focus areas for improvement of your project’s building LCA improvement. Module A1-A3 is also expected to play an even more significant role, as the building example shown in Figure 1.4 demonstrates how the production phase may become increasingly dominant starting July 1st, 2025.

Figure 1.4 LCA calculation of a case using BR18 (2023) and BR18 (2025) emission data and assumptions from BUILD Rapport 2023:21.

From a sustainability standpoint, the design team should ideally aim at choosing durable, adaptable, and low-carbon materials or even recycled materials (e.g. reused bricks and recycled steel). However, availability constraints and project-specific factors can complicate and impact the material selection. Like building geometry, an effective approach for making informed decisions on material selection is to conduct a simple variation study early in the design phase. By comparing different materials and systems, project teams can gain insights into which choices will yield the most substantial carbon reductions for their specific project.

Example 2: Figure 1.5 and Figure 1.6 covers a student-made variation study for a case study regarding the transformation of Building 308. The study compared two structural systems and three facade cladding options to assess their environmental impacts. Figure 1.5 compares a concrete element system with a timber deck supported by glulam columns and beams, highlighting that the timber option generates less than half the emissions of the concrete system. Figure 1.6 then examines three facade cladding materials, showing slate as the highest-impact choice and cement-fiber as having a slight edge over wood in terms of having the lowest environmental impact. These comparisons highlight the importance of evaluating multiple material options, particularly for major building elements. By incorporating simple variation studies for materials early in the design phase, project teams can make data-driven decisions that align with the project’s sustainability goals and improve the result of the LCA.

Figure 1.5 Variation study of two options for a structural system for a student-made transformation project of B308 at DTU. The study compares the environmental impacts of a concrete element system with a wood system, featuring a timber deck supported by glulam columns and beams. Both systems were designed by the group’s structural team to have similar load-bearing capabilities for a fair comparison. Results are expressed in kg CO₂e/m²/yr, as the variation study compares two systems with different material components and quantities. Generic data was used.

Figure 1.6 Variation study of three façade cladding options for a student-made transformation project of B308 at DTU. The study compares the environmental impacts of 1 m² wood cladding, slate cladding, and cement-fiber cladding, with results expressed in kg CO₂e /m². Generic data was used for the analysis.

1.3 Product Choice and EPD’s

An EPD is a standardized document (following EN15804 and third-party verified according to ISO14025) that quantifies the environmental impacts associated with a product across its life cycle. EPDs provide transparent and comparable information about a product’s environmental performance, enabling more informed decision-making when selecting specific products for your project. However, choosing specific products with EPDs should be considered as the final steps in optimizing your building LCA. The previously covered focus areas should be prioritized first before the project team begins comparing EPDs for environmental impact reduction. Once those strategies have been implemented, EPDs can further refine and optimize your choices. For an LCA, environmental data typically falls into four main categories, each varying in precision.

Generic data: A broad estimate of a material’s average impacts, typically based on industry averages or large-scale studies. While sufficient in the early stages of an LCA for estimating potential impacts, generic data lacks detail on the specific manufacturing processes or best practices of individual companies.

Industry-Wide / Average EPD: Represents the average impacts of a product type across multiple manufacturers (often developed by a trade association). Industry-wide EPDs are more reliable than generic data but typically worse than product specific EPDs.

Product-Specific EPD: A detailed declaration from an individual manufacturer quantifying the exact environmental impacts of a particular product or product line. Because it is tailored to one company’s processes and materials, a product-specific EPD offers greater accuracy than a generic or industry-wide EPD and tends to perform better.

Project-Specific EPD: An EPD developed for a specific project, considering the unique details and context of that project. While it offers the highest precision, it also requires significantly more data collection and coordination, making it more resource intensive.

Many LCA tools, such as LCAbyg, include built-in databases (e.g. GenDK or Ökobaudat) containing generic data for common building materials and components. Generic data is mostly useful in early design iterations or for components deemed not to be a hotspot in the building LCA. However, as the project progresses, using specific products supported by EPDs provides more accurate environmental impact data and often yields better results. Therefore, once geometry and general materials and systems have been selected, it is advantageous to seek out product-specific EPDs and conduct product comparisons to identify the best option for your project.

Example 3: Imagine a scenario where the project team opted for in-situ concrete slabs, and the structural team has estimated that the concrete should meet a strength class of approximately C20/25 to C25/30 MPa and an exposure class of X0 or XC1. Up until now, generic or average EPD data has been used in the LCA. However, to improve the accuracy of the assessment, it’s time to select a specific product that meets these requirements. This example compares four specific in-situ concrete mixes from two local manufacturers. All products satisfy the required strength and exposure classes, but they differ in their environmental performance. By evaluating these options, the project team can select the mix with the lowest carbon footprint without compromising on structural performance. Figure 1.7 compares environmental impact per m² of concrete slab for each product. The results show that the IBF C20/25 concrete mix has the lowest environmental impact among the options compared, making it the most suitable choice for minimizing the project’s carbon footprint.

Figure 1.7 Product comparison of four Ready-mixed (Passive) concrete products from two different manufacturers with approximately the same strengths and exposure class.

References

• Celoxis – A Quick Introduction to Project Planning. (n.d). https://www.celoxis.com/project-management/chapter/project-planning

• One Click LCA – Analyzing Life Cycle Carbon Footprint of Buildings. (2024, June 26th). https://oneclicklca.com/en/resources/articles/analysing-life-cycle-carbon-footprint-of-buildings#:~:text=building%20site%20will%20define%20the,emissions%20when%20purchased%20from%20less