To make sustainable product choices for construction projects, it’s necessary to compare environmental product declarations (EPDs). When different manufacturers make EPDs available for their products, it’s important to look for similarities and differences in the reporting so that appropriate judgements can be made.
On its own, an EPD is not a statement of whether a product is ‘sustainable’ or not. It is a tool for reporting the environmental impact of that product over its life cycle. Only through comparing the EPDs of different materials and products can an assessment can be made as to whether one will help to meet the project’s sustainability goals better than another.
Generic EPDs and manufacturer-specific EPDs
A first step in understanding commonality between EPDs is having an awareness of whether a product is being represented by a generic EPD or a manufacturer-specific EPD.
Generic EPDs use average data for similar products produced by a range of manufacturers, and report environmental impact accordingly. They might be offered by a trade association who has gathered data from its member companies, for example.
You could, therefore, find yourself requesting an EPD from two different manufacturers, and being provided with identical documents.
A generic EPD could be broadly representative of the environmental impact your product specification will have. However, there will always be a question as to how accurate it is, especially if a project is unique in a way that is unlikely to have been captured by ‘average’ data. More preferable is to obtain a manufacturer-specific EPD or, even better, a product-specific EPD.
A manufacturer-specific EPD can apply to more than one product (within a specific category of products) produced by a single manufacturer. A product-specific EPD applies to a single product from a single manufacturer.
In seeking to be transparent about the environmental impact of construction projects, the more specific the data the better.
What is functional equivalence in an EPD?
The environmental impact of a construction product is reported for a ‘unit size’ of that product. The EPDs that Polyfoam XPS makes available, for example, are based on one cubic metre of our extruded polystyrene. In the EPD document, this unit size is called the ‘functional equivalence’.
When comparing two EPDs from different sources, it’s important to check whether the functional equivalence is the same or different. For example, while our EPD uses one cubic metre as the basis for its reporting, there are EPDs for other types of lightweight rigid foam insulation that use one square metre of a specific product thickness.
One square metre of a 100mm thick insulation board has one-tenth the volume of one cubic metre of another insulation type. Even if the two insulation products had a broadly similar environmental impact, there would be a substantial difference in the figures reported by the EPD.
Manufacturers select the unit based on their production processes, so none of this is to say that one way is correct and another is wrong. It is simply something that specifiers have to check for when taking the EPD reporting at face value.
The scope of life cycle reporting in EPDs
In a previous blog post we described how EPDs report environmental impact across a series of stages and modules. The structure of these stages is designed to reflect the distinct stages of how a construction product is manufactured, delivered to site, used on site, and dealt with at the end of the building’s useful life.
‘Cradle to gate’ refers to the processes involved with manufacturing a product and it leaving the factory, and is covered by modules A1 to A3 of life cycle assessment. ‘Cradle to practical completion’ also deals with the installation of the product on site, being covered by modules A1 to A5.
‘Cradle to grave’ spans the complete life cycle of a product, including its use and what happens to it at the end of life – covered by modules A, B and C of life cycle assessment. Module D can also be factored in.
EPDs can be either a ‘cradle to gate’ type or a ‘cradle to grave’ type. There is a third option of ‘cradle to gate with options’, which means that relevant parts of module C can be accounted for alongside modules A1 to A3. This is useful for a product like insulation, which incurs minimal use stage (module B) impacts, but where the manufacturer wants to report a fuller scope than just ‘cradle to gate’.
Again, this is not necessarily a judgement on what is the ‘correct’ way to report impacts. As EPDs continue to mature then it will be desirable that reporting is done consistently across all modules to give the fullest possible picture of environmental impact.
For the purposes of this blog post, the important message is that the scope of reporting for similar types of products might be different. That difference should be taken into account when making an assessment of the reported impacts.
Polyfoam XPS has ‘cradle to gate with options’ EPDs that report on the environmental impact of its flooring and roofing products. The EPDs are independently verified and produced by BRE Global. For more information about EPDs, subscribe to our newsletter, The Build-Up. You can also download our EPDs from our technical support page, or contact us to discuss your current project.