Steps to Net Zero: Step 6 - Consider whole life carbon in conjunction with whole life costing

By Qian Li

Whole life cycle carbon is all upfront embodied carbon and operational carbon emissions, including maintenance, fit-outs, minor and major refurbishments, deconstruction and the reuse of building materials. In our previous series we explained our steps toward Net Zero Carbon Design including limiting operation carbon and upfront embodied carbon, in this blog we will explain our approach when considering whole life cycle carbon.

Whole Life Cycle stages

Once the building is built it will require constant maintenance (planned and unplanned maintenance) and certain building element will need to be replaced over life cycle (façade, internal fittings, MEP etc.).

If you consider Carbon as another type of currency, the life cycle carbon of the building could be considered as the running ‘carbon cost’ of a building. Schemes like Display Energy Certificates and Design for Performance (DfP) method will help people to better predict and disclose the real operational energy demand, but it is equally important to provide a clear picture about the embodied carbon of the building during its life cycle.

Whilst minimising running cost for buildings through design are norm nowadays, there are growing awareness to identify ways to reduce the life cycle carbon emissions. Decision made today to reduce upfront carbon at completion should not have negative impact over the life cycle of the building. For instance, a timber front door for a commercial building might be lower carbon at completion comparing to metal doors but it will require much more maintenance and might need to be replaced much more often so the life cycle carbon impact might be much higher.

Buildings should be built to last and we obviously want robust materials that is durable, but this need to be considered holistically. The buildings need to be inherently flexible and therefore less prone to commercial redundancy. The most carbon-efficient approach is to build a durable building that can be adapted and modified as necessary to be suitable for future requirement.

For example, building structure should be robust enough for long term use (i.e., 100+ life span) but certain building element should be designed to be modified and replaced easily i.e. could the facade be dissembled from inside of the building and could fit into the building lifts, so the façade can be replaced/repaired without the need to use BMU or external scaffolding.

The life cycle assessment tool Cundall uses is able to help the client and design team to select the most carbon efficient solutions over the building’s life cycle and the key principles one should look at during design stage are:

• Designing for durability and flexibility: Durability means that repair and replacement is reduced which in turn helps reduce life-time building costs. A building designed for flexibility can respond with minimum environmental impact to future changing requirements and a changing climate, thus avoiding obsolescence which also underwrites future building value.
• Disassembly and reuse: Designing for future disassembly ensures that products do not become future waste and maintain their environmental and economic value.
• Optimisation of the relationship between operational and embodied carbon: Optimising the operational/embodied carbon relationship contributes directly to resource efficiency and overall cost reduction.
• Building life expectancy: Defining building life expectancy gives guidance to project teams as to the most efficient choices for materials and products. This aids overall resource efficiency, including cost efficiency and helps future proof asset value.
• Minimising waste: Waste represents an unnecessary and avoidable carbon cost. Buildings should be designed to minimise fabrication and construction waste, and to ease repair and replacement with minimum waste, which helps reduce initial and in-use costs.
• Efficient fabrication: Efficient construction methods (e.g. modular systems, precision manufacturing and modern methods of construction) contribute to better build quality, reduce construction phase waste and reduce the need for repairs during post completion and the defects period (snagging).
• Circular economy: The circular economy principle focusses on a more efficient use of materials which in turn leads to carbon and financial efficiencies.

Case study: 6 Pancras Square

The client wishes to have flexible meeting rooms that could be moved every few years (or even months) to suit their constantly evolving and changing business processes. The cheapest way to build meeting rooms will be plasterboard drywalls however it will be hard to reuse or remove and re-build it every few years is certainly uneconomical nor sustainable.

@ Google and AHMM and Timothy Soar

A modular unit made from a series of modular timber cassettes was developed which would have the full functionality of a meeting room yet could be built or taken down and reassembled elsewhere in a matter of hours or days.

Life cycle assessment of different systems was carried out during design development to test the viability of the proposal (one construction and two movements over 15 year time), it was identified that despite higher initial cost (in both carbon and cost terms) the life cycle impact was 47% and 40% less comparing to other more standard solutions.

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