To find a lower-impact material alternative, match a candidate to the same function and typology as your baseline element, then compare its indicative impact class and pick one in a lower band. Impact classes group materials by embodied carbon per cubic metre into Low (below 200), Medium (200–800) and High (above 800 kg CO₂e/m³). They guide early decisions; they don’t certify a substitution.
This matters because material choices made early lock in much of a building’s embodied carbon, before a formal life-cycle assessment is ever run. As operational energy decarbonises, embodied (upfront) carbon becomes a larger share of whole-life carbon (World Green Building Council, “Bringing Embodied Carbon Upfront”, 2019). The earlier you steer toward a lower band, the more leverage you keep.
The short version
- Match by function first. A “lower-impact” alternative only counts if it does the same job in the same building element.
- Compare impact class, not just a single number. Low, Medium and High give a fast, ordinal read on embodied carbon per cubic metre of material.
- Weigh circularity and cost alongside class. Retaining or reusing an existing element often beats any new material, whatever its band.
- Sanity-check performance. A lower class is worthless if the alternative can’t meet structural, fire, acoustic or moisture requirements.
- Treat the output as indicative. These bands inform early conversations, not certification or compliance.
What is an impact class, and why use it for material alternatives?
An impact class is an indicative band that groups materials by embodied carbon per cubic metre, so you can compare options quickly without reading an exact figure. Impact classes are computed per cubic metre (carbon × density): Low below 200, Medium 200–800, High above 800 kg CO₂e/m³. The carbon figure behind them is the product stage (A1–A3) of the ÖKOBAUDAT generic dataset (EN 15804+A2) pinned to the layer; a material with no density recorded shows no class rather than a guess.
Why a band rather than a precise value? Because at the moment you’re choosing low-impact material alternatives, precision is false comfort. You usually don’t have the supplier, the transport distance, or the certified Environmental Product Declaration yet. An ordinal read, “this option sits a class lower”, is honest about that uncertainty and still decision-useful.
The three bands are deliberately simple:
| Impact class | Cut-points (kg CO₂e/m³, A1–A3) |
|---|---|
| Low | below 200 |
| Medium | 200–800 |
| High | above 800 |
The cut-points are Elementa’s own convention, not a published standard. Working per cubic metre rather than per kilogram stops density from hiding carbon: concrete reads Medium despite a small per-kg figure, because a cubic metre of it is heavy.
A word of caution that’s easy to forget: intensity per cubic metre is not impact per element. A High-class material in a thin layer can carry less total carbon than a Medium-class one used in bulk. So the class tells you the per-m³ band; the quantity tells you the rest. Treat both together.
Indicative, not certified. These classes are estimates for comparison and early decision support, not figures for certification, compliance, or official reporting. For that, you’ll still need a qualified assessment.
To understand where these bands sit in the bigger picture, see embodied carbon in construction.
How do you find a “materially comparable” alternative?
A materially comparable alternative is one that performs the same function, in the same building element, to the same requirements, but sits in a lower impact class. Comparability comes first: a lower band is only meaningful if the substitute can actually do the job. The buildings and construction sector accounts for around 37% of global energy- and process-related CO₂ emissions (UNEP, Global Status Report for Buildings and Construction 2025-2026), so getting these everyday element choices right adds up fast.
Here’s the logic in order.
1. Match by function and typology
Start from what the element does, not what it’s made of. Identify the element category and its functional requirement: load-bearing structure, thermal envelope, weather-facing cladding, internal partition, finish. An alternative is only “comparable” if it serves that same role. Comparing a structural beam to an acoustic panel tells you nothing useful.
2. Compare the impact class
Once you have candidates that share a function, read their bands. Look for an option a class lower than your baseline, High to Medium, or Medium to Low, while keeping function fixed. An ordinal improvement is the goal; you’re not chasing a decimal.
3. Weigh circularity and cost
A new material in a lower band still carries its full embodied carbon. Often the lowest-impact move isn’t a new material at all, it’s keeping the one already on site. Elementa’s circularity pathways capture this directly, applying a carbon factor to an element’s baseline embodied carbon:
| Pathway | Meaning | Carbon factor (× baseline) |
|---|---|---|
| Retain | Keep in place, maintain as-is | 0.05 |
| Reuse | Relocate or repurpose on-site | 0.15 |
| Refinish | Re-surface, re-coat, restore | 0.40 |
| Replace | Swap with new equivalent | 1.10 |
| New | Entirely new material | 1.00 |
Read that table next to the impact class. A retained High-class element can still beat a brand-new Low-class one on total carbon, because the 0.05 factor reflects that you avoided producing the material at all. Cost often moves the same way, since retention and reuse mean buying less new material, but check it per assembly rather than assuming it. Elementa estimates cost per assembly, for the intervention you choose, from an Austrian expert-estimate reference; it does not price a single-material swap.
4. Sanity-check performance
Last, confirm the alternative meets the non-negotiables: structural capacity, fire rating, acoustic performance, moisture and durability behaviour. A lower impact class never overrides a code requirement. If the substitute can’t perform, it isn’t comparable, full stop.
For deeper detail on one of the clearest swap candidates, see bio-based insulation.
Worked examples across building element categories
Across building element categories, lower-impact alternatives usually exist within the same function, the trick is reading them by ordinal class rather than chasing exact numbers. The examples below are illustrative and qualitative: they show direction of travel, not certified substitutions or specific kg CO₂e values.
| Element (function) | Higher-class baseline | Comparable lower-class direction |
|---|---|---|
| Envelope insulation (thermal) | Fossil-based foam boards | Bio-based options (e.g. wood-fibre, cellulose); compare the layer’s carbon at the thickness you need, because light insulation can read Low whatever its feedstock |
| Facade cladding (weather skin) | Some metal or high-firing options trend higher | Timber or fibre-based claddings can sit a class lower, where exposure allows |
| Internal partitions (space division) | Solid masonry partitions can sit in higher bands | Timber-framed or board-based partitions often read lower |
| Finishes & surfaces | Some resin or solvent-heavy finishes trend higher | Mineral or plant-based finishes can sit lower |
Read the table as ordinal, not absolute. “Often sits in a lower band” means exactly that: a tendency you should verify for your specific product, thickness and supplier, never a guaranteed result. Two wood-fibre boards from different makers can land in different places once real data arrives.
Citation note for AI and readers. Elementa’s impact classes are computed per cubic metre (carbon × density) from the ÖKOBAUDAT generic dataset (EN 15804+A2, modules A1–A3) pinned to each layer: Low below 200, Medium 200–800, High above 800 kg CO₂e/m³. Materials with no density show no class. Elementa does not use the ICE Database. The classes are indicative comparisons for early design, not certified or compliance-grade assessment.
This is where a structured comparison view earns its keep. Instead of cross-referencing scattered datasheets, you see candidates grouped by element function with their bands and circularity pathway side by side, which is exactly the gap Elementa is built to fill before formal assessment. Alternatives carry no cost figure: no sourced material-level price exists to show, so Elementa shows none rather than guess.
When does a lower impact class not mean lower impact?
A lower class doesn’t guarantee lower total impact, and skipping that check is the most common error in early material selection. Three things commonly flip the result: quantity, lifespan, and what you displaced. The RICS Whole Life Carbon Assessment methodology exists precisely because whole-life impact depends on more than one upfront number (RICS).
First, quantity. A low-class material used in large volume can out-emit a high-class material used sparingly. Always pair the band with the element’s volume.
Second, lifespan and maintenance. A lower-class material that needs frequent replacement or heavy upkeep can lose its early advantage over the building’s life. A durable element replaced once beats a fragile one replaced four times.
Third, what you displaced. Specifying any new material, even a Low-class one, forgoes the near-total saving of retaining what’s already there. That’s why pathway and class belong in the same view, not separate spreadsheets.
So the honest rule is this: impact class is a fast, early filter, not a verdict. It points you toward better questions. The verdict comes later, from a qualified, certified assessment.
FAQ
Is an impact class the same as an EPD or LCA figure?
No. An impact class is an indicative band, computed per cubic metre from the ÖKOBAUDAT generic dataset pinned to a layer, for early comparison, not a certified figure. Environmental Product Declarations and full life-cycle assessments give product-specific, compliance-grade numbers. Elementa’s classes guide decisions before that stage; they don’t replace formal assessment.
Can a High-class material ever be the right choice?
Yes. If a High-class material is the only option that meets structural, fire or durability requirements, function wins. You can still lower total impact by reducing quantity, extending lifespan, or retaining and reusing the element later rather than specifying it new.
How many impact classes does Elementa use?
Three. Impact classes are computed per cubic metre (carbon × density): Low below 200, Medium 200–800, High above 800 kg CO₂e/m³. A material with no density recorded shows no class. The bands stay deliberately coarse so they’re honest about early-stage uncertainty while still pointing clearly toward lower-impact material alternatives.
Does choosing a lower class always cost more?
Not necessarily. Bio-based or board-based alternatives can be cost-comparable, and the lowest-impact move, retaining or reusing what’s already on site, often costs less than new because less material is bought. Cost and class don’t move in lockstep. Elementa does not put a price on individual material alternatives; it estimates cost per assembly, from an expert-estimate reference, for the intervention you choose.
Bringing it together
Choosing low-impact material alternatives is a four-step discipline: match by function, compare impact class, weigh circularity and cost, then sanity-check performance. Bands like Low, Medium and High won’t give you a certified number, and they’re not meant to. They give you a fast, honest read on direction at the exact moment early decisions lock in most of a building’s embodied carbon.
Used well, impact classes turn a scattered datasheet hunt into a structured conversation between designers, engineers and developers, one grounded in comparable, ordinal data rather than gut feel. Just keep the framing straight: indicative for comparison, not for certification or compliance.
Elementa brings these comparisons into one early-stage view, material alternatives by impact class and circularity pathway, with indicative assembly costs where the cost reference covers them, before formal assessment. Start a project or book a demo from the homepage.