Apartment bathroom standards: why the area is capped

Every bathroom in every apartment generator on this site is constrained between 3 m² (floor) and 7 m² (ceiling for shared baths) or 8 m² (ceiling for ensuites). At first glance these look like arbitrary numbers. They are not: they reflect what bathrooms actually do in real construction, what materials and fixtures cost, and how plumbing is run. Knowing the reasoning helps when you read a generated plan, and it helps when you decide whether to push your real apartment's bathroom outside the typical range.

The 3 m² floor

A 3 m² bathroom is the minimum that supports a shower, a WC, and a basin in a workable arrangement. The shower needs at least 0.8 × 0.8 m of footprint for the cubicle plus a swing zone for the door. The WC needs 0.4 m of space on each side and 0.6 m in front. The basin needs 0.5 × 0.5 m of footprint plus 0.7 m of standing space. Add the wall thicknesses and door swing and you cannot fit all three below 3 m² without compromising one of them. Below this, you have a half-bath (just WC and basin) — an entirely different room category.

Most building codes set a similar floor: ANSI A117.1 in the US implies it through dimensional minimums; UK Approved Document M sets the bathroom minimum around 3.7 m² for accessibility; Australia's NCC has a similar lower bound. The 3 m² figure used here is approximately the smallest a non-accessible standard bathroom legally and practically can be.

The 4 m² shower-and-tub threshold

Adding a tub (or a tub-shower combo, which is the most common Western fixture) requires another 0.7–0.8 m² beyond the basic shower-WC-basin layout. So a bathroom with a tub starts at 4 m² and is more typical at 4.5–5 m². The generator templates produce baths in the 4–6 m² range for shared bathrooms in 1BR and 2BR apartments — comfortable enough for a tub if you want one, small enough to not waste plumbing area.

Why we cap shared baths at 7 m²

In real construction, a shared bathroom past 7 m² is unusual. Once you have the WC, basin, and shower-plus-tub, a 7 m² envelope is comfortable. Beyond that, the additional area starts being wasted on circulation that no one needs in a bathroom (you don't pace around in there) or on a second basin that duplicates fixtures. The generator caps shared baths at 7 m² because beyond that the m² is better spent on a slightly larger bedroom or a real second bathroom.

Ensuite bathrooms (only accessible from the master bedroom) get a slightly higher cap of 8 m² because they often include a double basin or a separate WC alcove — features that justify the extra m² in master suite logic.

The aspect ratio rule

Every bathroom generated here has its aspect ratio capped at 2.35. That means a 5 m² bathroom can be 1.5 m × 3.3 m at the most extreme, but never 1.0 m × 5.0 m. Below 1.0 m clear width a bathroom is unusable; the 2.35 cap prevents the generator from producing pencil-shaped baths even when the surrounding template's geometry would otherwise allow it. The aspect ratio rule is enforced by the post-processing pipeline (the clampRooms step) — every bathroom in every generated plan satisfies it.

Plumbing wall logic

All bathrooms (and the kitchen) need access to plumbing risers — vertical pipes that run between floors. In real apartment buildings, plumbing risers are placed in shared walls between units to consolidate plumbing, and bathrooms in adjacent apartments are typically arranged back-to-back so they share a riser. The generator does not model the building's overall plumbing layout, but in 2BR/2BA plans the stacked template specifically arranges the two bathrooms back-to-back to share a plumbing wall — that's the generator's nod to plumbing-cost reality.

The reason this matters for you: if you are using a generated plan to think about a renovation, moving a bathroom across the apartment is expensive precisely because the plumbing wall has to be moved. Within the same wet wall is cheap; across the apartment is a major change.

When to break the rules

Real apartments occasionally have larger bathrooms. Master suites in luxury apartments above 150 m² sometimes have 10–12 m² master bathrooms with separate tub and shower areas, double basins, and a separate WC compartment. The generator does not produce these because they're outliers — common at high price points but rare in the apartment-floor-plan distribution overall. If you want one in your plan, generate a smaller one and edit the SVG manually, or consider that an architect-drawn plan is the right tool for the job at that price point.