A “70% circular” building is 70% of something, and the something is almost never stated. Measured by mass, by cost, or by number of elements, the same project can land anywhere from a modest share to a headline figure, because heavy structure, expensive fit-out, and countless small components each pull the ratio in a different direction. Until a claim names its denominator, lists the elements counted, and says which pathway each one took (retained, reused, recycled, or new), it is a description, not a result.
This is not a complaint about any one project. It is a reading guide. Circular percentages are appearing on case studies, awards, and tender responses, and most of them cannot be checked. This article explains what a defensible one looks like, and what to ask when you meet one that isn’t.
The short version
- The same conversion can score roughly 90% circular by mass and 14% by cost (illustrative example below). The denominator, not the design, decides the headline.
- A circularity percentage needs three things to be checkable: a denominator (mass, cost, or element count), the list of elements counted, and a pathway per element.
- Every “70%” with a legal definition in EU construction is a waste-recovery threshold by weight (Waste Framework Directive Art. 11(2)(b); Taxonomy Delegated Regulations 2021/2139 and 2023/2486). None of them measures the share of reused material in the finished building.
- The closest thing to a legal circular-material share is the Taxonomy’s per-material cap on primary raw material (2023/2486, activity 3.1), and it is set per material group by mass, not as one whole-building number.
- “Recycled” and “sustainably sourced” are different pathways with different carbon consequences. Adding them into one figure hides which is which.
- Ask for the denominator before you compare two projects. Different denominators are not comparable.
- All figures here are indicative, for early comparison, not for certification or compliance.
Why does the denominator change the answer?
Because buildings are lopsided. Structure and envelope hold most of the mass. Services and finishes hold much of the cost. Fixtures, fittings, and small components hold most of the count. A strategy that reclaims windows, gratings, and timber offcuts while pouring a new slab scores very differently depending on which of those three you divide by.
Take a simplified conversion of an existing industrial hall into offices. The shell is retained. Some windows and steel gratings are reclaimed from other sites. Internal walls are new hemp-lime, ceilings get new felt acoustic panels, and a new timber gallery is inserted into the volume. Now score it three ways:
| Denominator | What dominates | Where the “circular” share comes from | Tendency |
|---|---|---|---|
| Mass (kg) | Retained shell, slabs, foundations | Retention of the existing structure | High, driven almost entirely by what was already there |
| Cost (€) | New fit-out, services, timber insert | Reclaimed windows and gratings offset a little | Lower, because new work is where the money goes |
| Element count | Panels, fixtures, small components | Every reclaimed item counts once, same as a slab | Anywhere, depending on how finely you itemise |
To make that concrete, here is a deliberately simplified, illustrative element list for such a conversion. The quantities are round numbers chosen to show the mechanism, not survey data from any real project.
| Element | Pathway | Mass (t) | Cost (k€) |
|---|---|---|---|
| Existing masonry shell and slabs | Retained | 1,800 | 150 (repairs) |
| Reclaimed windows | Reused | 6 | 60 |
| Reclaimed steel gratings | Reused | 4 | 20 |
| New hemp-lime internal walls | New | 90 | 220 |
| New timber gallery | New | 60 | 380 |
| New felt acoustic panels | New | 3 | 90 |
| New services and finishes | New | 40 | 700 |
| Total | 2,003 | 1,620 |
Circular share (retained + reused) by mass: 1,810 / 2,003 ≈ 90%. By cost: 230 / 1,620 ≈ 14%. By element count: 3 of 7 ≈ 43%. Same building, same decisions, three defensible percentages spanning 14% to 90%. Whichever one a case study reports, it is the denominator doing most of the talking.
None of these is wrong. Each answers a different question. Mass tells you about material flows and roughly tracks embodied carbon. Cost tells you about procurement decisions. Count tells you about design effort. The problem is only that a bare percentage doesn’t say which question it answered, and readers assume the flattering one.
Citation capsule: A building circularity percentage depends on its denominator. Measured by mass, retained structure dominates and the figure tends to be high; measured by cost, new fit-out dominates and the figure tends to be lower; measured by element count, the figure depends on how finely the project is itemised. Percentages calculated on different bases are not comparable.
What does “recycled or sustainably sourced” hide?
A common phrasing runs “around 70% of the materials are recycled or sustainably sourced”. Two different things sit inside that “or”.
Recycled or reused content means an element that already existed, either kept in place or recovered from another site. In Elementa’s circularity pathways a retained element carries an indicative carbon factor of 0.05 against a new baseline of 1.00, and a reused one 0.15. The saving is large because the manufacturing emissions were spent long ago.
Sustainably sourced usually means a new product with a lower-impact supply chain, such as certified timber, hemp-lime, or straw panels. These can be excellent choices, and bio-based materials often carry lower embodied carbon than mineral or foam equivalents (see bio-based insulation compared). But they are new manufacture. In pathway terms they sit at 1.00, or at best a lower-impact 1.00, not at 0.05.
Merging the two into one figure means a project could be, say, one-fifth reuse and four-fifths certified new products, or the reverse, and report the same headline. The carbon consequences of those two buildings are not remotely alike.
Citation capsule: “Recycled or sustainably sourced” combines two pathways with very different carbon outcomes. Reuse and retention avoid most of an element’s embodied carbon (Elementa’s indicative factors: Retain 0.05, Reuse 0.15 against New 1.00). Sustainably sourced material is new manufacture with a lower-impact supply chain and does not avoid upfront emissions in the same way. A single combined percentage hides the split.
Isn’t there an official 70%?
There are several, and they are all about waste, not materials. The original is the Waste Framework Directive, which required member states to reach at least 70% by weight of non-hazardous construction and demolition waste prepared for re-use, recycling, or other material recovery by 2020 (Directive 2008/98/EC, Art. 11(2)(b)). The EU Taxonomy then re-used the threshold. Under the EU Taxonomy’s technical screening criteria for constructing new buildings, the do-no-significant-harm condition for the circular economy requires that at least 70% by weight of the non-hazardous construction and demolition waste generated on site is prepared for re-use, recycling, or other material recovery, in line with the Waste Framework Directive (Commission Delegated Regulation (EU) 2021/2139, Annex I, section 7.1; a corresponding criterion applies to renovation under 7.2).
Three things to notice. It has a denominator (weight). It has a defined population (non-hazardous CDW generated on site). And it measures what leaves the project, not what goes into the finished building. A project can meet the Taxonomy’s 70% by sorting its skips well and still be built almost entirely from new material.
The later Taxonomy delegated act for the circular economy raises the bar and changes the population again: 90% by mass for new construction, 70% for renovation, both excluding backfilling, reported through the Level(s) indicator 2.2 (Delegated Regulation (EU) 2023/2486, Annex II, activities 3.1 and 3.2). Same headline number, different denominator, different scope.
The same act is also where the nearest thing to a legal material-input share lives. For a new building it caps the share of primary raw material in the three heaviest material categories by mass: 70% for concrete and stone, 70% for brick and ceramic, 80% for bio-based, 70% for glass and mineral insulation, 50% for non-bio-based plastic, 30% for metals, 65% for gypsum. Reused products count as zero primary material; a product with unknown recycled content counts as 100% primary (2023/2486, Annex II, 3.1, point 4). Note the design: per material group, by mass, with a stated rule for unknowns. There is no whole-building “X% circular” anywhere in the regulation.
So when a case study says “70% circular”, it is worth asking whether it means a waste-recovery threshold, a per-material primary-content cap, a material-input share of the finished building, or something else. Coincidence of the number does not mean coincidence of the method.
Citation capsule: EU “70%” construction thresholds are waste-recovery ratios by weight: Waste Framework Directive Art. 11(2)(b) and Taxonomy Delegated Regulation 2021/2139 (Annex I, 7.1 and 7.2) require at least 70% of non-hazardous construction and demolition waste prepared for re-use, recycling, or other recovery; Delegated Regulation 2023/2486 requires 90% for new build and 70% for renovation excluding backfilling. 2023/2486 separately caps primary raw material per material group by mass (for example metals 30%, concrete 70%). None defines a whole-building circular-material percentage.
What does a checkable circular claim look like?
It has an element list. Everything else follows from that. The minimum disclosure is:
| Field | Why it matters |
|---|---|
| Denominator | Mass, cost, or count, stated once, used throughout |
| Scope | Which building systems are in (structure, envelope, fit-out, services) and which are out |
| Element list | Each element with its quantity in the chosen unit |
| Pathway per element | Retained, reused, refinished, replaced, or new |
| Data source per element | Survey, EPD, generic dataset, or estimate |
| Range, not a point | Concept-stage quantities are uncertain; say so |
With that table, anyone can recompute the percentage, swap the denominator, or compare with another project on the same basis. Without it, the number is trust-me. For the table applied to a published claim, see a worked brewery-to-coworking example.
Carbon comparisons work the same way. A national benchmark set, such as the whole-life carbon benchmarks INDICATE LIFE is developing for Austria, is only a fair yardstick for projects assessed on a matching basis.
This is the structure Elementa is built around. You describe the existing building and the proposed one system by system, assign each element a pathway, and the tool reports indicative carbon per element and in total, with the basis visible, and indicative cost per assembly where its Austrian expert-estimate reference covers it. It is pre-assessment decision support, not a certified LCA, and it is designed so that the number you show a client comes with its own working.
Citation capsule: A checkable building circularity claim states its denominator, its scope, an element list with quantities, a pathway per element, the data source per element, and an uncertainty range. With these, the percentage can be recomputed and compared. Without them it cannot be verified.
Frequently asked questions
Which denominator should I use?
Mass, if your interest is carbon or material flow, because embodied carbon scales roughly with tonnage and mass is what waste and recovery regulation measures. Cost, if you are reporting to a client or funder on procurement. Count, rarely, and only for design-effort discussions. Whichever you pick, state it, and if you report more than one, keep them in separate columns.
Can a project be 70% circular by mass and 20% by cost at the same time?
Yes, and it is a normal pattern for conversions. Retaining a heavy shell delivers a large mass share at low cost, while the new fit-out is light but expensive. Neither figure is misleading on its own. Reporting one without saying which it is, is.
Does the EU Taxonomy 70% apply to materials in the building?
No. The 70% (and the later 90%) concern non-hazardous construction and demolition waste, measured by weight, and how much of it is prepared for re-use, recycling, or other recovery. The Taxonomy’s material-side rule is different: a cap on primary raw material per material group, by mass, for the three heaviest categories. Neither produces a whole-building circular percentage.
What targets do certification schemes use?
DGNB’s circularity criterion (TEC1.6, version 2023) sets target quotas by mass for “circular material origin”, meaning reuse, recycled content, and renewable material combined: 20% for a moderate contribution and 50% for a high one, with the method to be stated (DGNB TEC1.6 Neubau 2023). Note that even here the scheme asks for the basis and the method alongside the number.
Can Elementa certify a circularity percentage?
No. Elementa produces indicative, element-level pathway assignments and carbon figures, and expert-estimate assembly cost ranges, for early comparison. The pathway factors are Elementa’s own modelling conventions, not certified values. Formal circularity reporting, for example under the EU Level(s) framework or a certification scheme, needs a qualified assessor and a certified method.
The takeaway
A circular percentage is only as good as the three things behind it: the denominator, the element list, and the pathway per element. Every “70%” with a legal definition in EU construction is a waste-recovery threshold by weight, and the only regulated material-side figure is a per-material cap, not a whole-building share. When a claim gives you the number but not the basis, ask for the basis. When you publish one, give the basis first.
If you want to see your own project’s circular share by element, with the denominator stated and the pathway for each part visible before formal assessment, start a project.