Answer
Can a garden room have a bathroom?
Yes, but the drainage and water supply bring building regs in and can affect permitted development.
In short
Yes, but it changes things. Adding a bathroom or shower means drainage and a water supply, which brings building regulations into play, and it can affect whether the room counts as permitted development. It is doable, and we design it properly, but it is a more involved project than a plain room.
A note
General guidance, not advice. Rules vary by site, and Article 4 directions or conditions can change what applies. Check with your local authority and the Planning Portal.
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