LCA Climate Requirements in the Building Code: The CO2 Limit

With the climate requirements in the building code, the choice of materials is no longer just a question of cost, aesthetics and buildability. It has become a regulatory parameter. A building must now be able to document its CO2 footprint through a life-cycle assessment (LCA), and for most new construction that footprint has to stay below a fixed limit value per square metre per year. This means that a decision about the structural principle or the facade material, which used to be made late in the design process, can now determine whether the building can obtain a permit at all.

For consultants, engineers and architects, this moves LCA from a voluntary sustainability add-on to a design discipline on a par with the energy frame and the fire requirements. The point of this article is not to walk through each individual figure — they are adjusted on an ongoing basis and must always be verified against the current edition of the building code — but to give a professional overview of how the LCA climate requirement in the building code fits together, when it is triggered, and how it should be approached so that it does not turn into an expensive surprise at the end.

What the LCA climate requirement actually demands

The requirement rests on two elements that are inextricably linked:

• An LCA calculation. A life-cycle assessment must be prepared that quantifies the building’s total climate impact over a defined assessment period (typically calculated over a long service life for the building).
• A CO2 limit value. For the buildings covered, the result must stay below a limit value expressed as kg CO2 equivalents per square metre per year.

The LCA itself covers the building’s life cycle in phases — production of materials, transport, construction, operation (including energy consumption and replacement of building components) and finally disposal or recycling. It is this whole-life view that sets the climate requirement apart from the energy frame: the energy frame looks at operational energy, while the LCA also captures the embodied CO2 in the materials themselves. A building can therefore be energy-efficient in operation and still carry a heavy climate footprint if the structure is material-intensive.

The calculation is based on environmental data for the individual materials (typically drawn from recognised environmental product declarations) multiplied by the quantities used in the project. This makes the quality of the LCA directly dependent on how precisely the quantities are known — and hence on how far the project has matured.

When the requirement is triggered

The climate requirement follows the ordinary logic of the building code: it attaches to the construction of new buildings and is documented as part of the building case. The limit value is the strict part and is in principle aimed at the more resource-heavy new construction, while the documentation requirement itself — that an LCA exists — has a broader reach.

Because the specific thresholds (which building categories and which area limits trigger the limit value) have been tightened in several steps and continue to develop, they should always be confirmed against the current edition of the code and with the municipal building case officer for the specific project. The practically important thing is to establish early: Is this project subject to the limit value, or do we “only” need to document an LCA? The answer determines how hard the requirement binds the architectural and structural choices.

For the full picture of which requirements are otherwise activated by a new build, and when they apply, there is a complete overview in the article on the most important BR18 requirements for new construction and when they are triggered.

How LCA connects to the energy frame

It is tempting to see the climate requirement and the energy frame as two separate exercises, but they are two sides of the same building’s climate accounts — and they can pull in opposite directions.

A thick, heavy structure can improve the energy frame through thermal mass and low transmission, but it pushes the embodied CO2 up in the LCA. Conversely, a lightweight structure can lower the material footprint, but place greater demands on insulation and air-tightness in order to comply with the energy frame for new construction. The professional task is to optimise the two requirements simultaneously, not sequentially. If they are handled separately, you risk locking in a choice in one set of accounts that comes at a high cost in the other.

Rule of thumb: If a material choice markedly improves one set of climate accounts, check what it does to the other before the decision is locked in. The energy frame and the LCA should always be seen in the same movement.

What it means for early-stage design

The most important consequence of the climate requirement is one of timing: the LCA has to be built in early, not documented at the end.

The choice of materials becomes a regulatory decision

The choice between concrete, steel, brick and timber — or combinations — has always had economic and structural consequences. Now it also has a regulatory one, because the load-bearing structures and foundations typically weigh heavily in the climate accounts. The earlier the principal structural choice is qualified against a preliminary LCA, the cheaper it is to adjust.

Quantities drive the result

Because the LCA is quantities times environmental data, it is only as precise as the project’s quantity take-off. In the early phases you work with qualified estimates and benchmarks per square metre; later with concrete quantity lists from the design model. This means that an early LCA is a management tool, not final documentation — but that is precisely why it is valuable: it tells you whether the project is heading above or below the limit value while there is still room to act.

Practical moves that often shift the result

• Reduce the volume of material by optimising spans, storey heights and the structural principle, rather than choosing “green” materials on top of an over-dimensioned structure.
• Prioritise materials with well-documented, low environmental product declarations over industry averages.
• Keep an eye on the building components that have to be replaced several times during the assessment period — repeated replacements add up across the life cycle.
• Build in recycling and separability so that the end-of-life phase does not push the figure up unnecessarily.

LCA is not an isolated discipline

The climate requirement lives side by side with the code’s other requirements, and they have to add up to a single solution. A facade that is optimised for a low CO2 footprint still has to deliver on the requirements for daylight and indoor climate in dwellings and habitable rooms, and a structure that minimises material still has to comply with fire and load-bearing requirements. Skilful design finds the choices that lift several requirements at once — for example a structure that is both material-efficient and provides good daylight conditions — rather than optimising one requirement at the expense of the others.

This is also where the documentation for the building case comes together: the LCA, the energy-frame calculation and the rest of the project documentation must all point to the same building and hang together when the municipal building case officer reviews it.

How to take it further

The manual exercise of keeping track of exactly which requirements apply to your project, when the limit value is triggered, and how the LCA interacts with the energy frame and indoor climate, is time-consuming — not least because rates and thresholds keep changing. This is exactly the kind of question Rex in Arcili Chat is built for: an assistant with the building code as its domain, which can qualify whether a given new build is subject to the climate requirement and help you get an overview of how the requirements connect — so you move quickly from doubt to a qualified direction in the early phase.

It does not replace the professional LCA calculation or the consultant’s judgement. It removes the initial legwork of making sense of the requirements, so the hours can be spent on the design itself. If you want to see how it works on a concrete project, you can book a walkthrough.