Aisle width is the rule most often quoted about laboratory layout, and the one most often quoted wrongly. The figure is easy to remember. The definition underneath it is where every real argument happens: what counts as an aisle, which pairs of units create one, and whether the number is a target or a floor.
The number, and what it is for
AISLE_MIN_CLEAR_WIDTH_MM defaults to 1200 mm, attributed to EN 14056 and carried in the rule set as a placeholder pending confirmation against a purchased copy. The plain statement of intent behind it is this: the clear space between two work positions must let one person work at a bench while another passes safely behind them. Two bodies, one working and one walking, back to back.
The band floor is 700 mm, which is a single body width — the space one person needs to get past. That is an egress figure, not a comfort figure, and it exists so a project working under a different authority can state its own number without being able to set the aisle to nothing. Across 26 issued layouts from ten real projects, nothing was drawn below 1200 mm anywhere, and the tightest facing aisle measured 1209 mm. 1200 mm is where professionals stop, not where they aim.
What counts as an aisle
The definition matters more than the number, and the first version of this rule got it wrong in an instructive way. It filtered to bench types, and it required both fronts to point at each other. The consequence: a write-up desk 300 mm from a bench reported a clean pass, because seating, sink cabinets and fume cupboards were not bench types, and because a front-to-back pair is not mutually facing.
The rule now says something much simpler. Any two work-facing units sharing a gap create an aisle when one of them works INTO that gap and their faces overlap laterally by at least 300 mm. Equipment type does not matter. Mutual facing does not matter. Somebody stands in the gap to use one of them, and that is the entire test.
What is not an aisle
Equally important, and the place where an over-strict rule does real damage. Side-by-side runs and back-to-back islands are not aisles and are exempt at any gap, including zero:
- A fume battery — several cupboards packed on one run, every sash facing the same way.
- A sink cabinet let into a bench line, sharing the worktop either side of it.
- A back-to-back island pair, whose working space is on the two outer faces and never between them.
All three sit at 0 mm in issued drawings and in this app’s own double-island template. Flagging them would have produced a rule that fires on every professional layout, and a rule that fires on every professional layout is a rule people switch off — taking the readings that mattered with it.
Seated positions need more
SEATED_AISLE_MIN_CLEAR_WIDTH_MM is 1500 mm. A chair pushed back from a desk occupies roughly 900 mm on its own, which is the band floor, and someone still has to be able to pass behind the person sitting in it. It is also the one position in a laboratory where a person sits still for hours without protective equipment, which is a reason to be generous rather than tight.
The check grades this in two steps: a gap below 1500 mm is a warning, and a gap below half the requirement is an error. A 700 mm slot behind an occupied chair is not a near miss.
Floors, comfort widths and end passages
Three different numbers do three different jobs here, and conflating them is how a layout ends up defensible on paper and unpleasant to work in.
- 1200 mm — the checked floor for a working aisle. Below it the checker reports an error.
- 1500 mm — the comfort width the generator actually spaces interior aisles at. Reference layouts run 1500 to 2400 mm and only approach 1200 mm under floor-space pressure.
- 1050 mm — the island END passage, a separate and deliberately tighter figure. The tightest issued end passage measured about 1115 mm and typical values run 1000 to 1580 mm. There is no checker rule for it: an end passage is a way round, not a place to work, and professionals go below 1200 mm here routinely.
When the room is too small
The corpus is unambiguous about what experienced designers do under pressure: they trim furniture, never aisles. Equipment footprint runs between 20 and 48 per cent of floor area in issued layouts, with 35 to 45 per cent typical and the low end belonging to instrument-heavy rooms. LabPlanner follows the same order — anything that cannot be placed legally is reported as a shortfall rather than squeezed in, and the generator drops a unit before it narrows a gap.
That is also the honest reading of a layout that only just passes. The checker measures what is drawn; it cannot see the trolley that will live in the aisle, the cylinder that arrives next year, or the door somebody props open. The margin between 1200 mm and the 1500 mm the drawings actually run at is where those things live.