Whole Life Carbon Assessment: A Deep dive into the B Categories

6 min readApr 28, 2023


The Whole life Carbon Assessment predicts the total emissions of a building from its design, to construction, to operations, to end of life & possible second life.

It is broken up into modules, to help calculate each of these aspects from the best available data.

Here we explore Module ‘B’, or the in-use categories.

When does module B start?

Post handover, after the building is built, sold, and in the hands of the client. It wraps up after the end of the reference service period (RSP), when the house is being demolished or repurposed.

Does this include energy use?

Yes, energy use is addressed in module B6 and B8. Emissions from water use are addressed in module B7.

What are the rest of the categories in the module?

B1-B5 is known as the In-Use Embodied Carbon.

These are emissions generated from buying things or employing people to maintain the building. Carpets, windows, plaster, they all go through wear and tear. They have a ‘service life’, the amount of time the manufacturer expects them to last, which is generally shorter than the building’s life span. Therefore there will be peaks of carbon within the building’s life span when some construction will occur to keep the building looking and functioning well. We’ll go into detail about how these are calculated below.

Is it easy to estimate?

This piece of the carbon assessment is assumption heavy, as it is very difficult to predict what repairs and replacements a building will need within 60–100 years. However the emissions can be significant for certain designs, so it’s essential that an estimation is made in order to drive down this carbon.

The Modules

B1 — The In-Use Emissions

But wait, isn’t B1-B5 the ‘In Use Emissions?’. Ah well we’re talking about a different kind of emission altogether here! These are the volatile chemicals emitted by the materials and services we have installed in A1-A3.

We split these into 3 different types of emissions.

B1.1 carbonation and other removals

This is usually a negative number, and accounts for the re-absorption of CO2 into cementitious materials, as they contain lime compounds which react with the CO2 in the atmosphere. These are going to be big, flat areas of concrete with large surface areas for absorption.

This is not to be used as ‘pro’ for traditional cements, as the upfront carbon from manufacture far outweighs this benefit. Can be taken into account in appropriate cases, more info provided in section 3.14.2 of the RICS WLCA V2.

More information on carbonation of cement.

B.1.2 emissions from materials

Some materials, although inert within the building, will emit chemicals throughout their lifespan. This is mainly a health issue (google VOCs if you dare), but it is also an environmental issue when these chemicals have adverse environmental effects. For example, blowing agents within foam insulations emit over time, and these have a GWP.

B1.3 fugitive emissions of refrigerants

After construction, you may have installed some things with specific jobs, for example AirCon or a Heat Pump (we call these services, or MEP, Mechanical, Electrical and Plumbing). This kind of equipment may emit secretions over time called refrigerants, and these leakages have GWP.

Details of how to account for these emissions can be found in CIBSE TM65.

B1 emissions are pretty specific to particular edge cases and might not apply to all buildings, particularly when taking a natural building system approach. Any emissions within this category should really be handled in the EPD, however some EPDs try to skimp on these emissions by opting for ‘Module Not Declared’. After all, the only required module for an EPD is A1-A3. To do a thorough job on the whole life carbon assessment, it’s best to take on this module separately by looking at any leakages that might occur by what you have installed in the building.

B2 — Maintenance Emissions

This module accounts for the energy and water required to keep things clean and functional. Think water and cleaning products, electricity for any required tools. Properly maintained installations last longer, and therefore need to be replaced less. Therefore investing time and energy in this module may have environmental and economical savings down the line. For example, specialist claddings may require upkeep in order to validate their warranty.

The emissions from energy and water from these activities should be estimated in B2. However, when considering actuals, it won’t be possible to accurately distinguish the metered water and energy for maintenance activities specifically, it will all be rolled into B6, B7 & B8.

How do we estimate this?

It’s tricky! There’s no set industry coefficient for this. Depending on the case, say it were a multi-unit development, there may be an FM plan with estimated energy costs, for which we can extrapolate carbon. This should be properly estimated in these kinds of developments.

Foremost, the information for specific materials should come from the manufacturer, stated in the EPD.

CIBSE had some assumptions for building services in TM65, this is likely to be the bulk of it in residential.

B3 — Repair Emissions

Slightly different is B3, pertaining to non-predictable repairing above the maintenance regime.

As it is non-predictable it is again difficult to estimate. Where available, data from facilities management/maintenance strategy reports, facade access and maintenance strategy, life cycle cost reports, operations and maintenance manuals, and other professional guidance can be used to develop scenarios for repair.

This is however very tricky to access and a huge body of work. Most projects will not have, nor need, this information.

RICS have given us some assumptions to work off:

‘If none of these sources are available, repair emissions should be assumed as equivalent to 25% of B2 maintenance emissions for the relevant items, and 10% of A1-A3 emissions for MEP in accordance with the CIBSE TM65 methodology.’

B4 — Replacement Emissions

Most installations within a building will have a service life lower than the RSP. Therefore we need to account for the emissions of replacing them.

We always assume like-for-like, therefore the original A1-A3 data can be taken for this. As national energy grids decarbonise, more up-to-date A1-A3 data may be applied, but this should be in accordance with new public EPDs.

Specific data on service life, and perhaps a pre-calculated GWP, should be stated in the EPD.

In absence of specific data, we should refer to A1-A3 data and the suggested service lives stated in 4.2.4 of the RICS WLCA V2.

In infrastructure projects, B4 is further broken down into 2 categories.

B4.1 — Replacement of construction materials, and B4.2 — Replacement of Industrial equipment.

In residential buildings this is not considered necessary.

If EPDs miss Service life data, take the generic data from the table below.

B5 — Refurbishment Emissions (Optional)

This optional module leaves space for any retrofit or refurbishment planned into the service life of the building. This is a large design change, outside the scope of maintenance or repair.

Possible examples: retrofit to comply with new policy, planned extension, change in function (eg commercial -> resi).

Takes into account all emissions from the demolition, removal, and new construction to handover.

Any biogenic carbon that occurs in this module is to be reported separately and not net, as throughout the assessment.

OPERATIONAL MODULES — Mandatory for Whole Life Carbon Assessment, but not within Whole Life Embodied Carbon.

B6 — Operational Energy Use.

‘For buildings, operational emissions must include all operational energy used in the building, including heating, hot water, cooling, ventilation, lighting, cooking, equipment and lifts, broken down separately by fuel type and energy end use. The inclusion of any energy use related to external works (e.g. car park lighting) is optional.’

This is an essential part of the WLCA, and can be ⅔ of the total carbon. It’s important that this is calculated well.

There are great calculator available for this purpose, such as NABERS, ASHRAE and PHPP.

B7 — Operational Water Use.

Water use has a carbon footprint. This should be accounted for in B6. Data should be sourced from an M&E professional (or from PHPP, NABERS) and uploaded to Cercula for WLCA.

B8 — User Activities.

A new one for the WLCA V2. This comprises implied energy use of the users of the building, such as office-use related emissions, or cars driving on a road.

The information for this module constitutes additional information in the WLCA, and any requirements for inclusion would typically depend on the nature of the project and/or the specific brief.

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So there we go! Thanks for sticking with us if you made it this far. Hope this is a useful resource / explainer for the your WLCA projects.

By the way — we have drafted a set assumptions for this process and put it in fully automated code. All you need to do is upload a Bill of Materials.

To find out more visit our website: https://cercula.io/