Durability figures are the easiest numbers in roofing to print and the hardest to interrogate. Where a figure comes from a European Technical Assessment, there is a specific test behind it and a specific scope attached to it, and both are checkable. This is what sits behind a W3 classification and a 25-year assessed working life, and what to do with them when you are specifying or inspecting a roof.
A durability category is an outcome, not a statement
A European Technical Assessment is issued by a designated assessment body after the product has been tested against a published assessment document. The durability section is not copy the manufacturer supplies: the body ages the system, applies the test regime the assessment document prescribes, and records a working life category according to the result.
The category is therefore the outcome of a procedure rather than an input to it, which is the whole reason an assessed figure carries weight that a marketing figure does not. The assessment also names the body that issued it and the version it is on, so both can be checked rather than assumed.
What the W3 test is actually measuring
Working life categories are not awarded on a general impression of robustness. They rest on specific tests, and knowing which test produced a category tells you what the figure is good for.
The relevant one here is resistance to fatigue movement after thermal ageing. Read it in two halves, because the order is the point.
Substrate movement is continuous and concentrates at joints, laps and details. Thermal ageing is the second variable: heat gradually stiffens many materials, so a layer that was flexible on the day it was applied may not be flexible in a decade.
Either condition alone is usually survivable. The combination is what splits many roofs. A system that is still elastic will bridge a moving joint without complaint; the same system, once embrittled, splits at precisely that joint. Testing flexibility on fresh material therefore says very little about year fifteen.
The test behind a W3 classification puts the two in that order. The system is thermally aged first, and only then cycled through fatigue movement, so the question being answered is whether it still accommodates movement after ageing rather than while new. For the system described here, that test is recorded at clause 2.2.10.1 of the assessment, in class W3, with a result of Pass.
Why this is not a guarantee, in the document’s own words
The assessment is explicit on this, and the wording is worth carrying into any specification you write. It states that the assessed working life is not a guarantee given by the manufacturer. It is a basis for selecting a product, to be weighed against the service life expected of the building the product is going on.
That framing is precise, and it is worth noting which party issues each figure. The assessment body records the durability category; the manufacturer issues any commercial undertaking. The two are not interchangeable in either direction, and a longer category does not extend an undertaking.
Reading two competing assessments
The useful question is not only whether a durability figure was assessed or claimed. It is what it was assessed on.
Two assessments can both record 25 years while covering different ground. One may award the category across every substrate the product is sold for; another may award it on a narrower range while the product is marketed more widely. The regime behind the category can differ too, and a summary in a quotation will show you neither.
So read past the number to the scope: which category, awarded under which clause, across which substrates. Those are the three answers to look for, and they are where two apparently equal figures separate.
What to ask for
For a specifier, a surveyor or a managing agent comparing systems, the paperwork to request is short and specific:
- The assessment itself, by number and version, not a summary of it. Versions are reissued, and an older edition may carry a different category.
- The Declaration of Performance, which is the manufacturer’s formal statement of the declared characteristics and should agree with the assessment.
- The durability category and the clause it sits under, so the test behind the figure is identifiable rather than implied.
- The substrate scope attached to that category, checked against the substrate actually on the building.
If a supplier cannot produce the first two on request, the rest of the conversation is guesswork.
The figures for this system
HYDRONYLON® is a liquid-applied waterproofing system assessed under European Technical Assessment ETA-23/0735, version 2, issued on 17 July 2026 by Łukasiewicz, Warszawski Instytut Technologiczny. Table 2 of that assessment records an assessed working life of 25 years across all four substrates it covers: bituminous, metal, mineral and PVC membrane. The fatigue test behind the category is recorded at clause 2.2.10.1, class W3, result Pass. Separately, and on its own terms, the commercial undertaking is a 10-year product guarantee issued to the installing Approved Contractor.
The assessment and the Declaration of Performance are both published in full on the downloads page, so the clauses above can be checked rather than taken on trust. If you want the condition of a specific roof documented before any of this is applied to it, HYDRONYLON Roof Care is a free inspection with a written report.