Garden Office with Bathroom: Cost & Planning Guide
Adding a bathroom to a garden office adds £4,000–£10,000 to the build, depending on whether you tap into existing drains or need a Saniflo / pumped system.
Cost breakdown
Plumbing & drainage: £2,000–£5,000. Sanitaryware (WC, basin, shower): £800–£3,000. Tiling & finish: £600–£2,000. Hot water (instant electric): £400–£800.
Planning & building regs
Bathrooms inside a permitted-development outbuilding don't trigger planning permission, but the plumbing must comply with Part G and Part H of building regulations. Foul drainage usually needs a notification to your water company.
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