TM59: Design methodology for the assessment of overheating risk in homes describes a methodology to assess whether a home stays comfortable in hot weather. It uses a...
Embodied carbon has been nagging at the ‘net zero’ building ambition for a while but is often considered too complicated to consider in a useful way. The latest TM from CIBSE aims to simplify the process and stands to make the subject a real hot topic.
What is ‘embodied carbon’ anyway? In a nutshell, it is the carbon debt that a product or system is already in before even considering its function. So it’s the greenhouse gas emissions from the material extraction, manufacturing and transportation that have already happened to get the thing to point of use.
Why should we care? The quest for low impact or ‘net zero carbon’ buildings, has heavily focused on operation thus far: operational emissions are generally proportional to running cost which is a well established point of interest; given the long lifetime of buildings, it has historically been assumed (probably correctly) that the operational emissions dwarf those of other life stages; and operational emissions are easier to conceptualize and hence to estimate. But if operational emissions decline as intended then the embodied carbon emissions will represent an increasingly high proportion of a buildings whole life cycle carbon emissions, and may out-strip it. And, irrespective of that shift, the urgency of the climate crisis and our carbon reduction obligations demand that all carbon emissions be of concern.
Why is CIBSE doing this? Calculating the embodied carbon of building services has felt particularly onerous thus far - consider just listing all the materials in a house brick versus listing all the materials in a heat pump and perhaps it can be seen why. CIBSE have undertaken this project to provide a simplified and accessible method and, perhaps more importantly, they are encouraging analysts to send back their results to build up a building service specific database.
What are the problems? To my mind, there are two main risks when calculating embodied or ‘upstream’ impacts. 
Firstly, it doesn’t take much for different calculations to come up with quite different answers; how far upstream does one go for instance? And often, the more rigorous the inventory collation the more impactful the product appears to be. The purpose is to make comparisons and aid design decisions so the approach must be consistent or else risk drawing meaningless comparisons and enabling ill-informed decisions. The TM65 Toolkit does seem to have taken pains to mitigate this risk. The method is heavily formulated and includes significant scale up and buffer factors to smooth out deviations.
Secondly, focusing-in so much can risk losing perspective - imagine agonising over the lowest embodied carbon concrete to use on clients private airstrip as an extreme example! The suggestion is, however, that the potential future CIBSE database would be anonymised so that comparisons would be between different technologies rather than different brands of the same technology. Information presented in this way makes sense for maintaining context and better enabling sustainable design.
Holistic and system thinking are fundamental to the Atamate ethos and as such, we welcome the addition of embodied impact calculations to the sustainable design process.
