Three categories, three sets of requirements
The scheme distinguishes buildings by height, in three categories: low, medium and high. Each category falls under a separate annex.
Each category has its own annex, addressing the same headings with graduated requirements. The requirements increase with the height of the building.
The headings covered are identical across categories, notably siting and access routes for emergency services, and compartmentation and evacuation. It is the levels of requirement that differ, and the gap between categories is substantial.
A fourth category exists for industrial buildings, covered in its own annex, with a different logic based on activity rather than height alone. Its scheme cannot be inferred from the others.
| Category | Classification criterion | Level of requirement |
|---|---|---|
| Low buildings | Conventional height, lowest category | Base of the scheme |
| Medium buildings | Conventional height, intermediate category | Tighter on compartmentation and evacuation |
| High buildings | Conventional height, highest category | Strictest, equipment included |
| Industrial buildings | Activity carried on, irrespective of height | Separate scheme, own annex |
The measured height is not the actual height
This is the most important technical point, and the greatest source of error. It concerns the measurement of the height of the building.
The height used is a conventional height, defined by the text, not the total height of the building measured from ground to ridge.
That convention has been the subject of an interpretative note from the administration, which testifies to the difficulties of application encountered. The note is consulted before the number of levels is fixed.
Two practical consequences.
A building may change category without changing silhouette, depending on how its conventional height is calculated.
The calculation must be made early and documented. Redoing it mid-project, with a different result, calls into question all the measures adopted.
What crossing a threshold triggers
It is a cliff effect, comparable to that of major renovation thresholds. Crossing a threshold changes the regime at once.
Moving from one category to the next does not make the project progressively dearer: it changes the applicable set of requirements, with consequences for compartmentation, escape routes, equipment and access for emergency services. The arbitration therefore happens at sketch stage, not at permit stage.
Those consequences translate into area and structure, not merely equipment. They therefore cannot be retrofitted late.
Hence a rule of judgment: where a project sits near a threshold, it is worth examining whether a change of brief allows it to stay within the lower category, and comparing the cost of that change with that of the additional requirements.
Why this question precedes all others
Three reasons.
It determines which annex to consult. Looking for a requirement in the wrong annex produces a wrong answer, and nothing signals it.
It governs structural design. Compartmentation and evacuation are questions of plan and structure before they are questions of equipment.
It frames the dialogue with emergency services. Their opinion, covered in the article on what the municipality adds, sits within the category adopted.
The structuring headings
Two headings deserve noting, because they govern the plan well beyond fire safety. They concern siting and compartments.
Siting and access routes. Emergency services must be able to reach the building and to stand there, which constrains the layout of the surroundings and sometimes siting itself.
Compartmentation and evacuation. They determine how the building is divided and the number, position and characteristics of escape routes, which structures the layout.
Those two headings must therefore be addressed at sketch stage, not after the plan is fixed.
What this means for a professional
Four rules.
Determine the category before any other analysis, and document the calculation of conventional height.
Check the applicable definition of height, rather than assuming it matches the measurable height.
Examine the thresholds where a project sits close to one, as the trade-off may be favourable.
Address emergency access and compartmentation at sketch stage, since they govern the plan.
This article reflects the position of the rules at the date of checking and serves professional orientation. It does not constitute legal advice and does not replace consulting the applicable texts.