What is Module D and how do I use it?

What is Module D and how do I use it?

European (CEN) Standards relating to the sustainability assessment of construction works adopt a modular approach to assess and report the impacts over the life cycle of a building. These include (Module A) from the production of the construction products and their assembly into buildings, (Module B) the use of the building over its design life and (Module C) the end-of-life of the building including demolition and disposal of the demolition waste.

Module D is a supplementary module that reflects benefits and loads beyond the defined system boundary, i.e. the building lifetime, and includes reuse and recycling potentials of materials and products recovered from the end-of-life of buildings. BS EN 15804 now mandates the reporting of Module D.

Module D is calculated based on the avoided impacts of primary production. For example, if a product is recycled, the Module D benefit is the avoided impact, i.e. the impact avoided by not producing the product via the primary production route. Where there is a loss of quality, for example crushing concrete into rubble, then a value-correction factor is applied to reflect the lower value of this type of recycling.

While BS EN 15804 and BS EN 15978 make clear recommendations about how the environmental impact data should be calculated and reported, how they are used to make decisions is outside the scope of these standards.

Guidance is therefore needed to help designers and specifiers use separate values, e.g. Module A and Module D, to make decisions. Whereas reducing Module A impacts may be a current priority for many, ignoring Module D effectively equates a material that is landfilled following demolition with one that is reused or recycled. To transition to a more circular economy, we have to start incentivising design for deconstruction and reuse and set Module D targets alongside those currently being proposed for Module A.

European (CEN) Standards relating to the sustainability assessment of construction works adopt a modular approach to assess and report the impacts over the life cycle of a building project. The different life cycle stages are defined as separate information modules (A to D) to promote transparency of assessment and reporting.

The assessment boundary of a building is defined as its full life cycle, i.e. from the production of the construction products and their assembly into buildings (Module A), the use of the building over its design life (Module B) and the end-of-life of the building including demolition and disposal of the demolition waste (Module C).

Module D is a supplementary module that reflects benefits and loads beyond the defined system boundary, i.e. the building lifetime, and includes reuse and recycling potentials of materials and products recovered from the end-of-life of buildings.

It is important to note that these are ‘potentials’ that are based on things/scenarios that might happen at some point in the future, not actual impacts as is the case for Module A.

Module D is intended to be a measure of the benefits of reusable and recyclable products/materials and to encourage measures to deliver a future circular economy, for example through design for deconstruction and reuse.

Note that BS EN 15804:2019, now mandates the reporting of Modules A1-A3, C1-C4 and D for almost all construction products.

Module D is calculated based on the avoided impacts of primary production. For example, if a product is recycled, the Module D benefit is the avoided impact, i.e. the impact avoided by not producing the product via the primary production route. Where there is a loss of quality, for example crushing or downcycling concrete into rubble, then a value correction factor is applied to reflect the lower value of this type of recycling.

How is Module D calculated?
Calculation of Module D is complex and is related to some fundamental Life Cycle Assessment (LCA) concepts, including the goal and scope of assessment, etc. It is not intended to cover this complexity here.

In the context of steel however, the Module D approach can be explained relatively simply, using the following equation:

The first bracket is a measure of ‘net flow’ of the product through the building system. For example, for BF-BOF steel production with 15% scrap input and an end-of-life recovery and recycling rate of 90%, the net flow over the product life cycle is 90% - 15% = 75%.

The second bracket reflects the ‘potential saving’ achieved through recycling (or reuse) relative to primary (BF-BOF) production. For example, if we recycle a steel section we emit typically 0.5 tCO2e per tonne (by recycling) but we ‘save’ typically 2.5 tCO2e per tonne, i.e. by avoiding primary (BF-BOF) production.

For this scenario therefore Module D = (0.9 − 0.15) x (0.5 – 2.5) = -1.5 tCO2e per tonne

Note that a negative value indicates a ‘saving’ whereas a positive value indicates an additional ‘burden’.

Annex D of BS EN 15804:2019 provides end-of-life formulae for the assessment of the environmental impact of different information modules of construction products including Module D.

How to use Module D?
CEN standards, BS EN 15804 and BS EN 15978, and embodied carbon assessment guidance based on these standards, for example from RICS and the IStuctE, do not allow aggregation of any of the information Modules A to D and require Module D to be reported and communicated separately.

Despite the above, there is no definitive guidance in standards about what can and cannot be done in terms using Modules A and D to make decisions regarding building design and product selection. While BS EN 15804 and BS EN 15978 make clear recommendations about how the environmental impact data should be reported, how they are used to make decisions is outside the scope of these standards.

Guidance is therefore needed to help designers and specifiers use separate values, e.g. Module A and Module D, to make decisions. Whereas addressing or reducing Module A impacts may be a current priority for many, ignoring Module D effectively equates a material that we landfill following demolition with one that we reuse or recycle. To transition to a more circular economy, we have to start incentivising design for deconstruction and reuse and quantifying Module D benefits and setting Module D targets. Although there is uncertainty about future scenarios for reuse and recycling, particularly for long-lived products like buildings, we should not let this hinder taking action today to facilitate better utilisation of our buildings and our building products in the future.

It is recommended therefore that targets are set for Module D alongside those currently being proposed for Module A.

It is noted that some EU member states have developed national rules, assessment methods and databases of environmental impact data in which a proportion of the Module D saving can be taking into account, i.e. aggregating a proportion (typically 30-50%) of the potential Module D benefit with today’s Module A impact to derive a single value. This can help to set targets and make decision-making easier.