FDES sheets detail the environmental impacts of construction products, calculated using a single benchmark (standard NF P 01-010), the only unbiased means of comparison.
However, some precautions must be taken for relevant comparisons to be made: Construction products are components whose purpose is to contribute to building a structure. Their individual environmental performances are integrated into the structure as well as their technical, aesthetic, economic, etc., performances.
For this reason, comparing building products out of context is not always appropriate. However, it is still possible, provided that:
- a functional unit (including a lifetime and at least one key performance indicator) is defined.
- the FDES sheets are checked to ensure that the products being compared have the same parameters (do they include packaging and complementary products?).
- the comparison is not limited to the environmental profile, and that technical performance criteria not included in the functional unit are taken into account if they differ greatly.
Comparing construction products should be kept to a minimum for construction components with the same function.
As with product comparisons, it is appropriate to define a relevant unit of comparison (functional unit), specifying the performances being compared and the lifetime used for this comparison.
The example in the table below shows that the lifetime used for the comparison should not be chosen at random, as it influences the results of the comparison. It is advisable to choose a lifetime for each product included in the comparison (equal or not to the lifetime indicated in the FDES), as well as the period over which the comparison will be carried out.
Defining a relevant functional unit often requires combining several products to form a complete solution (for example, comparing insulation + plasterboard + metal frame versus complex insulation/plasterboard bonded to masonry).
Even in this case, sometimes comparisons can be biased for highly multifunctional solutions (mechanical strength, heat resistance, thermal inertia, acoustic protection, fire behaviour, etc.) when this multifunctionality results in differences in performance on the scale of the overall project. For example, a functional unit based solely on heat resistance is not enough to compare conventional insulation solutions with applied insulation solutions in view of their vastly different thermal inertia and acoustic protection properties.
Often the most appropriate course of action is to evaluate the building in its entirety.