---
name: epd-compare
description: Compare EPD products on normalized GWP and other impacts while checking declared units, system boundaries, and LEED eligibility. Use for side-by-side EPD comparison.
allowed-tools:
  - Read
  - Write
  - Edit
  - Bash
  - Glob
  - Grep
  - AskUserQuestion
---

# /as:epd-compare — EPD Comparator

Compare 2 or more products side-by-side on environmental impact metrics. Validates comparability (declared units, system boundaries, PCR alignment), generates comparison tables with percentage deltas, and checks LEED v4.1 MRc2 eligibility.

This skill reads EPD records but does not persist or modify them. Fields follow [`schema/epd-schema.md`](../../schema/epd-schema.md), which is distinct from the FF&E product schema. Output is a markdown comparison report.

## Input

The user provides EPD data in one of these ways:

1. **Inline data** — pasted product names with GWP values
2. **File path** — a canonical `epd-library.csv` or markdown file with EPD data
3. **From prior skills** — "compare the EPDs I just parsed/found" (uses structured data from the current conversation)
4. **Mixed** — combine pasted, prior, and canonical local CSV records

If the user doesn't specify a source, first use structured EPD data from the current conversation. Otherwise ask for pasted values or an EPD CSV path. When reading `epd-library.csv`, validate it with `python3 "${CLAUDE_PLUGIN_ROOT}/skills/master-schedule/scripts/csv-library.py" validate epd`; reject FF&E-shaped or malformed files. Validation is read-only; never invoke `init`, `import`, `append`, or `update`.

## Workflow

### Step 1: Collect data

Gather EPD data from the specified source. For each product, you need at minimum:

- Product name and manufacturer
- GWP (A1-A3) value
- Declared unit

Additional fields improve the comparison: ODP, AP, EP, POCP, energy use, water use, system boundary, PCR, validity dates, LEED eligibility.

### Step 2: Validate comparability

Before comparing, run these checks and report findings:

**Declared unit alignment:**
- Are all products using the same declared unit (e.g., all per m3, all per kg)?
- If units differ, attempt normalization where possible:
  - kg ↔ ton (multiply/divide by 1000)
  - m2 at different thicknesses (if thickness is known, normalize to same thickness)
- If normalization is impossible, warn: "Product A reports per m2, Product B reports per kg. Direct comparison requires density or thickness data. Provide conversion factors, or I'll compare only within matching units."
- **Never silently compare products with different declared units.**

**System boundary alignment:**
- Flag if some are cradle-to-gate (A1-A3) and others cradle-to-grave (A1-A3 + C1-C4 + D).
- Note: "A1-A3 comparison is still valid across both types. Full life cycle comparison is only valid for cradle-to-grave EPDs."

**PCR alignment:**
- Flag if products use different PCRs. Products under the same PCR are most directly comparable.
- Note the PCR names if they differ.

**EN 15804 version:**
- Flag if some use +A1 and others +A2. Impact indicator units may differ (AP in kg SO2e vs. mol H+ eq).
- GWP in kg CO2e is comparable across versions.

**Validity:**
- Flag any expired EPDs with their expiration date.

**EPD type:**
- Flag mix of product-specific and industry-average EPDs. Note that industry-average EPDs are less precise.

Report all findings before proceeding:

```
## Comparability Check

✓ Declared unit: All products use 1 m3
✓ System boundary: All cradle-to-gate (A1-A3)
⚠ PCR: Products 1-2 use NRMCA PCR, Product 3 uses NSF PCR — results are comparable but not identical methodology
⚠ Validity: Product 2 expired 2025-12-01
✓ EPD type: All product-specific
```

### Step 3: Generate comparison

Produce three outputs:

#### a. Side-by-side impact table

```
## Environmental Impact Comparison

| Metric | ECOPact (Holcim) | ProPaving (CEMEX) | ReadyMix (Buzzi) | Unit |
|--------|-----------------|-------------------|------------------|------|
| **GWP-total (A1-A3)** | **242** | 298 | 385 | kg CO2e/m3 |
| GWP-fossil (A1-A3) | 238 | 291 | — | kg CO2e/m3 |
| GWP-biogenic (A1-A3) | 4 | 7 | — | kg CO2e/m3 |
| ODP (A1-A3) | 1.2e-6 | 1.5e-6 | 1.8e-6 | kg CFC-11e/m3 |
| AP (A1-A3) | 0.45 | 0.52 | 0.61 | kg SO2e/m3 |
| EP (A1-A3) | 0.08 | 0.11 | 0.14 | kg PO4e/m3 |
| PERE (A1-A3) | 180 | 95 | 72 | MJ/m3 |
| PENRE (A1-A3) | 1,450 | 1,890 | 2,340 | MJ/m3 |
| FW (A1-A3) | 0.32 | 0.41 | 0.55 | m3/m3 |
| Recycled Content | 35% | 22% | 12% | % |
```

Bold the **best value** in each row (lowest for impacts, highest for recycled content/renewable energy).

Use `—` for missing data. Never fill in missing values.

#### b. Percentage comparison (relative to lowest)

```
## GWP Comparison (relative to lowest)

| Product | GWP (A1-A3) | vs. Lowest | vs. Industry Avg |
|---------|-------------|------------|-------------------|
| ECOPact (Holcim) | 242 kg CO2e/m3 | — baseline — | -40% |
| ProPaving (CEMEX) | 298 kg CO2e/m3 | +23% | -26% |
| ReadyMix (Buzzi) | 385 kg CO2e/m3 | +59% | -4% |
| *Industry average (NRMCA Industry-Wide Member EPD v3.2, 2022)* | *~400 kg CO2e/m3* | — | — |
```

Include an industry average baseline **only if it is citable** — either the user provides one (e.g., an industry-average EPD or a published baseline document) or you can attach a named source and publication year, per the GWP Baseline Policy below. Label the baseline row with its source and year.

If no citable baseline is at hand, ask: **"Do you have an industry-average EPD or published baseline for this material category? If so, share it and I'll include it in the comparison. We're working on EC3 API integration that will automate baseline lookups — for now, provide an EPD or use `/as:epd-research` to find one."**

If no citable baseline is available, omit the "vs. Industry Avg" column entirely rather than guessing.

#### c. LEED v4.1 MRc2 assessment

Include this section if the user mentions LEED, or if LEED eligibility data is available:

```
## LEED v4.1 MRc2 Assessment

### Option 1 — EPD Disclosure (1 point for 20+ products with EPDs)
| Product | Qualifying EPD? | Type | Notes |
|---------|----------------|------|-------|
| ECOPact | ✓ | Product-specific | Third-party verified, ISO 14025 conforming |
| ProPaving | ✓ | Product-specific | Third-party verified |
| ReadyMix | ✓ (half) | Industry-wide | Counts as 0.5 product — LEED v4.1 MRc2 Option 1 values industry-wide (generic) EPDs at half the product count of product-specific EPDs |

### Option 2 — Embodied Carbon Optimization (up to 2 points)
Products must demonstrate GWP below category baseline
(baseline: 400 kg CO2e/m3, NRMCA Industry-Wide Member EPD v3.2, 2022):
| Product | GWP | Baseline | Delta | Qualifies? |
|---------|-----|----------|-------|------------|
| ECOPact | 242 | 400 | -40% | ✓ Yes — significant reduction |
| ProPaving | 298 | 400 | -26% | ✓ Yes |
| ReadyMix | 385 | 400 | -4% | Marginal — minimal reduction |
```

### Step 4: Recommendation summary

End with a brief recommendation:

```
## Recommendation

**ECOPact by Holcim** is the clear winner on environmental performance — 40% below
industry average GWP and lowest across all impact categories. The South Plainfield
plant is closest to the project site.

**ProPaving by CEMEX** is a strong second option if Holcim can't meet schedule or
volume requirements — still 26% below average.

Both qualify for LEED MRc2 Option 1 and Option 2 credits.
```

Be direct and opinionated. The user wants a recommendation, not just data.

### Step 5: Save output

Save the comparison report as markdown:

- **Default path**: `./epd-comparison-YYYY-MM-DD.md`
- If the user says it's final: `./deliverables/epd-comparison-YYYY-MM-DD.md`
- If no client context: keep it in the working directory (the default path above)
- Ask the user if they want a different path

After saving:

```
Comparison saved to [path].

Next steps:
- /as:epd-to-spec — generate spec language using ECOPact's GWP (242) as the threshold
- /as:epd-research — find more options to compare
```

## Edge Cases

- **Single product**: Can't compare, but can still show the data card with industry average context. Suggest finding more EPDs to compare against.
- **Mixed material categories**: Warn that cross-material comparison (e.g., concrete vs. steel) is generally not meaningful because declared units and functional roles differ. Offer to group by category.
- **Incomplete data**: Compare on whatever fields are available. Use `—` for missing values. Note which products have more complete data.
- **All expired EPDs**: Proceed with comparison but add a prominent warning that results are based on expired declarations and should be verified with current EPDs.
- **Very large comparisons (10+ products)**: Show summary table first, then offer to drill into top 3-5 candidates.

## GWP Baseline Policy

This policy is shared by all four EPD skills (`epd-parser`, `epd-research`, `epd-compare`, `epd-to-spec`) and must read identically in each. Industry-average GWP baselines are allowed only when cited with a named source and publication year (e.g., "NRMCA Industry-Wide Member EPD v3.2, 2022" or "AISC Fabricated Hot-Rolled Structural Sections EPD, 2021"). Uncited baseline numbers recalled from memory or training data are banned. If no source-and-year citation is available, ask the user to provide a baseline EPD or find one with `/as:epd-research` — never guess a baseline.

## Notes

- **This skill reads, not writes.** It does not add records to `epd-library.csv`. It produces a comparison report as a markdown file.
- **Baselines follow the GWP Baseline Policy above.** Cited source + publication year required; uncited from-memory numbers banned. EC3 API integration is in progress and will automate baseline lookups.
- **GWP (A1-A3) is the primary metric** for most comparisons and LEED. Other indicators (ODP, AP, EP) provide a fuller picture but GWP drives most specification decisions.
- **Suggest next skills.** After comparison, the natural next steps are `/as:epd-to-spec` (to write spec language) or `/as:epd-research` (to find alternatives).