Given the recent movements in the climate justice campaign, the release of UKGBC Net-Zero Carbon Framework in April this year has been very timely. Although we have seen various “net zero” definitions in the UK in the past (such as the scrapped zero-carbon homes targets under building regs over 10 years ago) it feels this time the general idea has more industry backing with 100s of architects, structural engineers and councils formally declaring a climate emergency.
The UKGBC definition is an interim step on the pathway to assessing full life cycle impacts. It introduces embodied carbon in materials (A1-A3), their impacts for transport (A4) and constriction (A5) alongside operational energy (both regulated and unregulated emissions).
Figure1: UKGBC Net Zero Carbon definition (April 2019)
Unfortunately, it does not go as far as full LCA yet with the idea that it simplifies the work and encourages uptake. However, module B1-B5 presents a large chunk of CO2e that will be missing from the calculations. Typically B1-B5 can be responsible 500-1000 kgCO2e/m2 over 60 years and ignoring these impacts will lead to good potential design opportunities being missed. Onsite renewables such as PV will be replaced over the life cycle and whilst the energy that they offset will be included in B6 the embodied impacts of their replacements are not. There are plans to increase the scope in future updates and it is encouraging to at least see some level of joined-up thinking between operational energy and construction embodied carbon. This will no doubt drive some improved design outcomes as design teams can assess the relative merits of strategies that impact on both energy and construction impacts such as thermal mass or triple glazing.
Modelling in eToolLCD
There are two choices of dataset groups in eTool currently. Either BRE IMPACT data or eToolLCD default data (regionalised data available for UK, EU, Aus, NZ and USA regions). Both can be used to model net-zero under the current definitions however if future expansions include modules C and D then eTool default data would be preferred.
|Module||UKGBC Net Zero Construction||UKGBC Net Zero Operational||UKGBC Net Zero Whole of Life (Yet to be Finalised)||BREEAM 2018 (IMPACT)||eTooLLCD|
|Construction||A1-3 Product Stage|
|A4 Transport of Equipment and Materials|
|Use Stage||B1 Products in Use|
|B6 Integrated Energy Use|
|B6+ Non-Integrated Energy Use (Plug Loads)|
|B7 Water Use & Treatment|
|End of Life||C1 Deconstruction & Demolition|
|C2 Transport of Waste Offsite|
|C3 Waste Processing|
|Benefits and Load Beyond the System Boundary||D1 Operational Energy Exports|
|D2 Closed Loop Recycling|
|D3 Open Loop Recycling|
|D4 Materials Energy Recovery|
|D5 Direct Re-use|
Figure 2: Scope of Carbon Assessments
Below are the impacts in kgCO2e/m2 for a typical medium density office building. (Note B6 energy impacts assume today’s grid (0.25kgCO2e/kWh) applied over the 60 year life cycle. Note the RICS Whole Life Carbon for the Built Environment Professional Statement is provided as a reporting reference, this level of reporting is simple to pull from eToolLCD using our All Impacts Report
Figure 3: Typical medium density low rise office building
Impacts associated with construction represent a third of the total. This is significantly higher now than in previous years when the UK grid was 0.6kgCO2e/kWh and usually made up 80-90% of life cycle impacts had that the grid has a lower. However, there is still a large chunk impacts missing from the guidance in the form of replacement and maintenance (B2-B5) which can be 500-1000 kgCO2e/m2.
Once quantified the design team can start to consider strategies, some examples are shown below. Without strategies, 1.755 tonnes/m2 of CO2e would need to be offset in a typical office. For net zero the cost of implementing these strategies will need to also be weighed up against the cost of purchasing offsets.
Offsets come with varying degrees of quality, cast and “additionality” arguments. The offset schemes referenced by UKGBC (Gold standard and Clean Development mechanism) carry a cost of between £0.6/tonne and £14/tonne. In an average office this could result in up to an extra £24/m2 or 1-2% of construction costs. However, the Greater London Authority recommends a price of £60/tonne. It will be interesting to see whether this gives the industry further incentive to implement low carbon strategies (in particular timber) early on in the design process. Furthermore, the onus will be on us LCA practitioners to improve the accuracy of our LCAs with the total kgCO2e figures resulting in a significant increase to net-zero development costs.