Life cycle assessment (LCA): turning building data into design choices

Rather than producing a single headline figure, a building LCA considers defined stages, data and assumptions to show where impacts arise. This can help developers, architects, specifiers and sustainability teams compare options, identify significant impacts and make better-informed decisions as a project develops.

What Is a Building Life Cycle Assessment?

A building Life Cycle Assessment evaluates environmental impacts associated with a building across defined stages of its life cycle.

Depending on the scope, this can include the production and transport of materials, construction, use, maintenance, replacement and end of life. LCA can consider several environmental impact categories rather than focusing only on greenhouse gas emissions.

For building projects, the assessment needs a clearly defined scope and consistent basis for comparison. EN 15978 provides a framework for assessing the environmental performance of buildings, while ISO 14040 and ISO 14044 set out the broader principles and requirements for Life Cycle Assessment.

What Does a Building LCA Assess?

The life-cycle stages included depend on the assessment scope, project requirements and methodology being used.

Product and Construction Stages

The assessment can consider impacts associated with materials and products, including their manufacture, transport and incorporation into the building.

This can help a project team understand how different structural systems, façade specifications, insulation or other materials may affect the overall environmental profile of a design.

Use, Maintenance and Replacement

A building’s impacts do not necessarily stop when construction is complete. Maintenance, replacement and operational requirements can affect results over the assessment period.

The assumptions used for service life, replacement and building performance therefore need to be documented and applied consistently.

End of Life and Beyond the System Boundary

An assessment can also consider processes associated with demolition, transport, waste processing and disposal.

Some methodologies separately report potential benefits or loads beyond the building’s system boundary, such as those associated with reuse or recycling. These should not be treated as automatically offsetting impacts elsewhere in the assessment.

How Does LCA Support Building Design Decisions?

The value of building LCA is often greatest when the results can still influence project decisions.

Comparing Materials and Specifications

An LCA can provide evidence when a team is considering different materials or specifications. Comparisons need to use an appropriate and consistent basis, including relevant quantities, functional requirements, assessment period and life-cycle scope.

A lower impact in one stage does not necessarily mean a lower impact across the whole assessment.

Testing Different Design Options

LCA can be used to test realistic alternatives during design. For example, a team might compare different structural, façade or material options and examine how the change affects the assessment.

The aim is not simply to select the option with the lowest figure. Cost, performance, durability, fire safety, acoustic requirements, programme and other project considerations may also affect the final decision.

Identifying Environmental Impact Hotspots

The results can highlight which materials, systems or life-cycle stages contribute most to the assessed impacts.

This gives the project team a clearer starting point for investigating alternatives rather than making broad sustainability changes without evidence.

When Should a Building LCA Be Carried Out?

An LCA can be undertaken at different stages, but carrying out an assessment while important design decisions can still be changed gives the results greater opportunity to inform the project.

At early design stages, some quantities, products and specifications may be based on assumptions. As the design develops, these inputs can be replaced or refined with more project-specific information.

Current BREEAM UK New Construction V7 guidance recognises the use of LCA at different assessment stages and states that interim design-stage benchmark results are intended to support design decision-making.

An assessment should therefore be treated as something that can develop with the project, rather than a fixed calculation that is produced once and never revisited.

What Information Is Needed for an LCA?

The information required will depend on the scope of the assessment, but may include:

• ✓drawings and building quantities;
• ✓material and product specifications;
• ✓structural and architectural information;
• ✓Environmental Product Declarations (EPDs);
• ✓assumptions about building lifespan, maintenance and replacement;
• ✓construction and transport information;
• ✓operational information where relevant; and
• ✓project-specific requirements for the assessment.

The quality of the result depends on the quality and suitability of the underlying information. UKGBC guidance highlights the importance of transparency around assumptions, data and how embodied carbon assessments develop across RIBA stages.

LCA, Embodied Carbon and Whole Life Carbon: What’s the Difference?

These terms are related but they are not interchangeable.

The appropriate approach therefore depends on what the project needs the assessment to demonstrate or inform.

How Do EPDs Support Life Cycle Assessment?

Environmental Product Declarations provide standardised environmental information about specific products and can provide useful data for building assessments.

However, an EPD is not automatically evidence that a product is the lowest-impact option. The product covered, declared or functional unit, geographical scope, life-cycle modules and other assumptions need to be suitable for the comparison being made.

Enevo’s guide to Environmental Product Declarations in construction explains these checks in more detail.

Building Life Cycle Assessment Support from Enevo

A useful LCA should give a project team more than a set of figures. It should provide evidence that can be understood in the context of the design, the information available and the decisions still to be made.