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Total mass of option A.
As BUILT, not as delivered: include the fixings, the adhesives and any substrate or support system that exists only because this option was chosen. That is where comparisons quietly break — a cladding counted as its panels alone, set against an alternative counted with its rails and brackets, is not a comparison of two claddings. Count both options to the same boundary and say where that boundary is.
A1-A3 GWP per kilogram.
Typical published ranges: primary structural steel around 1.9-2.5; recycled EAF steel around 0.7-1.0; sawn softwood around 0.2-0.5 excluding biogenic storage; glulam around 0.5-0.7; concrete expressed per kg is around 0.10-0.13.
Total mass of option B.
A like-for-like structural comparison rarely uses equal masses — a timber frame weighs a fraction of a concrete one for the same span.
A1-A3 GWP per kilogram.
From an EPD for the ACTUAL product wherever one exists rather than a category average — the spread between products within one material category is frequently wider than the gap between categories, which is the whole reason specifying by EPD changes anything. And note what A1–A3 covers: cradle to factory gate, and nothing after it. No transport to site, no installation, no replacement, no end of life — so two options with different service lives cannot be separated on this figure alone.
Carbon difference
11,000 kgCO₂e
Emission factors here are typical published ranges for orientation, not product data. A reportable assessment uses the supplier's own Environmental Product Declaration — the spread between two suppliers of the same nominal product routinely exceeds 30%.
- Option A total
- 23,879.57 kgCO₂e
- Option B total
- 12,600.12 kgCO₂e
- Lower option
- 2 (B is lower)
- Difference in tonnes
- 11.28 tCO₂e
- B as a percentage of A
- 52.77 %
They open the calculator with your figures already in it
Structural Material Carbon Comparison Calculator: 11,279 kgCO₂e — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- EN 15804 A1-A3 cradle-to-gate boundary applied consistently to both options
- Biogenic carbon in timber is reported separately under EN 15804+A2 and is not netted off the fossil figure here
Inputs used
- Option A — mass
- 26455 lb
- Option A — factor (kgCO₂e/kg)
- 1.99
- Option B — mass
- 61730 lb
- Option B — factor (kgCO₂e/kg)
- 0.45
Intermediate steps
- Option A total
- 23,879.57 kgCO₂e
- Option B total
- 12,600.12 kgCO₂e
- Lower option
- 2 (B is lower)
- Difference in tonnes
- 11.28 tCO₂e
- B as a percentage of A
- 52.77 %
Confidence note: Emission factors here are typical published ranges for orientation, not product data. A reportable assessment uses the supplier's own Environmental Product Declaration — the spread between two suppliers of the same nominal product routinely exceeds 30%.
What this calculation does not cover
- A fair comparison requires that both options actually do the same job — same span, same loading, same fire rating, same durability. Comparing masses that are not structurally equivalent produces a meaningless answer.
- Biogenic carbon stored in timber is excluded here. Whether it may be counted depends on the assessment method and on end-of-life assumptions, and netting it off silently is one of the more common ways these comparisons mislead.
- Cradle-to-gate only. Transport, erection, maintenance, service life and end-of-life all differ between materials and can reverse a close result.
Add the equipment this sizes
This result is a specification — 11,000 kgCO₂e — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-08-27 · in the site-wide review of 2026-09-06 · v1.1.0
Regulatory standards & verification citations2
- EN 15804 A1-A3 cradle-to-gate boundary applied consistently to both options
- Biogenic carbon in timber is reported separately under EN 15804+A2 and is not netted off the fossil figure here
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