To give reliable results, building LCA must capture the interactions that occur across an entire design (the system). A design decision in one part of the design will, in many cases, cause knock-on effects to other parts of the design. If only part of a building being designed is included in the building LCA the designer may choose a design option that optimises environmental impacts for the limited part analysed, but will be unaware of potential detrimental effects to the overall environmental impact of the building.
In addition, if a building LCA only includes the construction products that form the BREEAM assessment area, inconsistencies arise with regards to construction products that serve all areas of the building in common. For example, an assessment on a central floor that excludes the roof, compared with an assessment on the (otherwise identical) top floor that does include the roof. This approach would be unfair.
Therefore, the building LCA scope must include the whole building design (as defined in Mat 01, ‘Scope of assessment’) even if the area covered by BREEAM assessment is only part of the design.