Cross-laminated timber (CLT), today a mainstream structural material told in the chapter on wood, has its own dedicated harmonised European standard — EN 16351 — in force since 2015, just over twenty years after the original 1994 Austrian patent. That's a relatively fast regulatory maturation time for a new structural material. None of the materials told in this chapter are, as of 2026, in a position even remotely comparable: mycelium, self-healing concrete, bacterially grown bio-bricks, chitosan biocomposites have no equivalent harmonised EN standard, and most won't for several more years. Understanding why helps clarify a real limitation of these materials, distinct from — and often more significant than — their technical limits.
How CE marking works for a building material
In the European system, a construction product can obtain CE marking — required for regular sale and use on site across the Union — through two distinct routes. The first, simpler for the manufacturer, is conformity with an existing harmonised standard (hEN): if a product falls within the category covered by a standard such as EN 206 for concrete or EN 338 for structural timber, the manufacturer applies the test methods set out in that standard and declares performance in a standard format, automatically recognised in every member state. The second route, reserved for products that don't fall under any existing harmonised standard — almost all the materials in this chapter — is the European Technical Assessment (ETA), issued by a Technical Assessment Body based on a European Assessment Document (EAD) drawn up specifically for that particular product, if a similar one doesn't already exist.
The practical difference between the two routes is enormous. A harmonised standard is public, free to consult, applicable by any manufacturer who meets the requirements, and its test methods are already validated and recognised by every control body. An ETA, by contrast, is a case-by-case process negotiated between the individual manufacturer and the assessment body, often requiring months or years of ad hoc testing, carrying a significant direct cost borne by the manufacturer, and — crucially for the material's spread — the resulting document is technically specific to that product and that manufacturer, not a general reference anyone else can apply to their own similar product. Every new manufacturer of self-healing concrete, for example, must in theory go through their own technical assessment process, even if the underlying chemistry is the same one already validated by a competitor.
The specific case of self-healing concrete
Self-healing concrete illustrates the problem well, because it's technically a hybrid: the basic cementitious matrix is already covered by EN 206, but no standard exists defining how to measure, in a standard and recognised way, "self-healing efficiency" — that is, how much and how quickly a crack of a given width closes, under defined exposure conditions. RILEM, the leading international association for construction materials research, set up a technical committee dedicated specifically to self-healing concrete as early as 2008 (RILEM TC 221-SHC), which published a first collective state-of-the-art report on available test methods from the scientific literature in 2013 — a necessary preparatory step, but still far from a proper harmonised standard, which typically requires much broader consensus among CEN (European Committee for Standardization) technical committees and a validation path at industrial, not just academic, scale.
Mycelium, bio-bricks and biocomposites: no starting baseline
For mycelium, bacterially grown bio-bricks and biocomposites like Aguahoja's (told in the dedicated piece on Neri Oxman in this section), the regulatory situation is even further behind, because even the starting technical baseline is missing: there isn't yet a consolidated standard test method, even at the level of shared academic research, for measuring — comparably across different labs — properties such as the compressive strength of dried mycelium as substrate and fungal strain vary. Some international standards bodies, such as ASTM International, have opened working groups in recent years dedicated specifically to bio-based composites, but the results so far are draft test methods still under discussion, not published and binding standards.
A partially different case is hempcrete, the hemp-lime biocomposite already discussed in this chapter's main guide: in France, where its use is more widespread than elsewhere in Europe, a document called "Règles professionnelles de construction en chanvre" has existed since 2007 (revised in 2012), drawn up by a consortium of trade associations and recognised by the Agence Qualité Construction (AQC) as a technical reference for good practice. It isn't a harmonised European standard or a Document Technique Unifié (DTU) in the strict sense, but it partially fills the regulatory gap with a document of professional consensus that French insurers and site managers accept as a reference — an intermediate model other countries haven't yet replicated for other materials in this chapter.
Why it matters more than the science itself
The regulatory gap isn't a marginal bureaucratic detail: it's often the most significant practical obstacle to adopting a material that has already cleared its basic scientific challenges in the lab. A site manager specifying a material covered by a harmonised standard can rely on clearly defined professional liability, an insurer who knows exactly what they're insuring, and testing that follows a recognised procedure. With a material certified only through an ETA — or, worse, not certified at all and used only on the strength of an ad hoc technical opinion — each of these three parties faces a less well-defined risk, and tends to pass it on through price, through timelines, or simply by avoiding the material altogether on any project that isn't explicitly experimental or research-funded. It's the technical reason, more than the cultural one, why most real-world uses of these materials, described in this chapter's main guide, remain concentrated today in exhibition pavilions, academic prototypes and pilot public infrastructure — the only contexts where the residual regulatory risk is explicitly accepted in exchange for an innovation benefit declared from the outset.