How Detailed Should Your BOM Be for EPDs?
If your BOM feels like a 10,000‑cell whack‑a‑mole, you are not alone. The trick is choosing where precision pays off and where smart generalization speeds you up without risking verifier pushback. Here is the practical line to walk so data flows cleanly into an LCA and returns a reliable, spec‑winning EPD.
Start with the rulebook, not the spreadsheet
A PCR is the rulebook of Monopoly: ignore it and the game falls apart. Many construction PCRs follow EN 15804, which requires models to cover at least 95 percent of total mass, energy, and environmental relevance, so perfection is not the target, coverage is (EN 15804+A2, 2019). That single number is your north star when deciding what to model in detail and what to group.
A right‑sized BOM structure
Use three layers that mirror how factories and LCAs work. Level 1 is the finished product. Level 2 is subassemblies that ship or are built as units. Level 3 is parts and materials with purchasing units, suppliers, and the LCI dataset you plan to map.
That structure keeps ownership clear for data collection, and it slots neatly into background databases during modeling. It also makes changes easy to version and reuse across product families.
Set practical cutoffs that match the science
Adopt a working policy that aligns with the 95 percent rule. Model exact if a component drives more than a few percent of mass, cost, or energy, or if it is chemically sensitive like resins and alloys. Generalize when items are small, homogeneous, and consistent across SKUs like screws, clips, or minor shims.
Write the rule down so teams stop debating every washer. The policy should cover mass thresholds, toxicity flags, and any customer‑critical attributes such as recycled content claims.
Shared parts across families deserve a component library
Create a reusable component list with unique IDs, parametric fields, and an LCI mapping baked in. When a hinge, extrusion, or insulation batt repeats across ten SKUs, the library pays for itself on day one. Version components when suppliers, recipes, or energy mixes change so past EPDs remain auditable while new ones stay current.
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The small stuff without the small talk
Fasteners, labels, protective films, and minor fittings can be grouped into sensible buckets such as Hardware mix, Packaging mix, and Adhesives mix. Track the total mass, typical material split, and a single dataset link for each bucket. If any bucket creeps above your cutoff or contains a hazardous substance, break it out.
Map once to background datasets, then reuse
Choose representative LCI datasets upfront, document the rationale, and stick with them for the library components. When electricity is a key driver, align the dataset with the factory’s grid region and the reference year so results do not drift across product lines. If the power mix updates, create a new component version instead of quietly swapping the dataset.
Verifier‑friendly checkpoints
- A clear mass balance that shows included, grouped, and excluded items, tied to the 95 percent coverage rule (EN 15804+A2, 2019).
- A single reference year for utilities and volumes, stated plainly in the model notes.
- Transport distances and modes that match purchasing records, not guesses.
- Consistent units between purchasing, BOM, and LCI datasets.
- Rationale for any grouped buckets and the dataset chosen for them.
These five signals lower review friction and speed approval. They also make internal audits less painful later.
When detail should increase
Crank up granularity when a component is carbon heavy like primary aluminum, when it is chemistry sensitive like isocyanate‑based foams, or when a customer claim depends on it such as recycled content. Increase detail for in‑use replacements or consumables that recur in later life cycle modules because small parts can add up over time.
Plan for renewal and PCR updates without rework
Most program operators set EPD validity at up to five years, which means a solid component library amortizes quickly across renewals and product refreshes (EPD International GPI, 2023). When a PCR version changes, the library lets you remap only the affected components and carry forward everything else. That is how teams avoid the dreaded rebuild from scratch.
A quick sanity test before sending to LCA
Open the BOM library and ask three questions. Do the top five mass contributors have exact datasets and supplier ties. Do grouped buckets stay under your cutoff and include a written rationale. Does the reference year match the utility bills attached to the model. If yes on all three, you are definately ready.
The payoff for getting detail right
Right‑sized detail accelerates modeling, reduces verifier comments, and keeps numbers stable across SKUs so sales can speak with confidence. It also flips future EPDs from month‑long slogs into short cycles because most of the heavy lifting already lives in your component library. That is real speed with real quality, not spreadsheet heroics.
Frequently Asked Questions
What is the minimum coverage my LCA model should achieve to be compliant with EN 15804 based PCRs?
Aim for at least 95% coverage of total mass, energy, and environmental relevance across included flows. This threshold is widely required in EN 15804‑based rulesets and is the practical benchmark many verifiers use to assess completeness (EN 15804+A2, 2019).
Should we model every fastener and label individually?
No. Group small, homogeneous items into buckets like Hardware mix or Packaging mix and assign a representative dataset. Break items out only when they cross your internal cutoff, affect toxicity or safety flags, or materially change results.
How do we handle shared components across product lines?
Build a component library with unique IDs, supplier info, and dataset mappings. Version items when recipes, suppliers, or electricity mixes change. This approach lets you reuse validated data across multiple EPDs efficiently.
Do we need a new EPD if the PCR updates?
You can continue using a current EPD until its validity ends, then renew against the updated PCR. A structured BOM library reduces rework because only datasets or rules impacted by the new PCR need remapping (EPD International GPI, 2023).
What reference year should we use for data collection?
Pick a single, recent 12‑month period and apply it across utilities, production volumes, and waste. State it clearly in the model to keep verification smooth. For new products with limited data, a shorter prospective window can be used and updated later if the PCR allows.
About the Author
With a passion for sustainability and a love for complex data, Toby helps manufacturers efficiently collect data from across their organization and get their EPDs done right. He’s especially interested in how AI can support human expertise, helping R&D and factory teams work faster, smarter, and with less friction.
