Can a bathroom have no window?
Yes — entirely legal and extremely common in London flats and new en-suites. Building regulations require ventilation, not daylight: a windowless bathroom needs mechanical extraction (15 l/s, ducted outside), and good ones add design compensations — layered lighting, large mirrors, and light finishes.
No regulation requires a bathroom window. What Part F requires is air movement, and a correctly ducted fan does that job better than a window a British January keeps shut anyway. Most en-suites we build are internal rooms; so are most central-Croydon and peninsula flat bathrooms.
What windowless rooms punish is bad lighting. The single centre downlight makes an internal bathroom feel like a lift. The fix is layers: downlights for task, an illuminated or backlit mirror at face height (the light that actually matters), and something warm and low — LED under a floating vanity transforms these rooms. On a renovation the wiring for all three costs little while walls are open.
The moisture story is the same as any bathroom, just less forgiving: a windowless room cannot be 'aired', so the extraction must genuinely work — which loops back to ducting and, increasingly, continuous-running fans with humidity sensing. Get that right and internal bathrooms stay as fresh as windowed ones.
More in regulations & practicalities, or browse all 38 questions on the FAQ index.
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