Adding a Bathroom to Your Extension: Costs & Value Guide
How much does an extra bathroom add to your home's value? Costs, plumbing considerations, and design tips for London extensions.
Key Facts About Extension Bathrooms
- Value added: Extra bathroom typically adds 4-5% to property value
- Ensuite cost: £8,000-£15,000 within an extension
- Ideal ratio: One bathroom per 3 bedrooms minimum
- Get instant cost estimate for your extension (Free)
Adding a bathroom to your London extension is one of the smartest investments you can make. Whether it's an ensuite for the master bedroom, a family bathroom in a loft conversion, or a ground floor WC, extra bathroom facilities consistently add value and improve daily life.
How Much Value Does a Bathroom Add?
| Bathroom Type | Typical Cost | Value Added |
|---|---|---|
| Master ensuite | £10,000 - £20,000 | 4-5% |
| Family bathroom (loft) | £8,000 - £15,000 | 3-4% |
| Ground floor WC | £3,000 - £6,000 | 2-3% |
| Jack-and-jill bathroom | £12,000 - £18,000 | 3-4% |
Note: Value added depends on current bathroom count and local market expectations.
Bathroom Cost Breakdown
Typical Ensuite Costs (within extension)
Plumbing Considerations
Soil Stack Location
Bathrooms need connection to the soil stack (main drain). Closer is cheaper. Macerator pumps can help distant locations but add cost and noise.
Hot Water Capacity
Extra bathrooms increase hot water demand. May need boiler upgrade or unvented cylinder. Budget £1,500-£3,000 if upgrade needed.
Drainage Falls
Gravity drainage needs adequate fall. Ground floor extensions rarely have issues. Lofts may need pumped waste systems.
Ventilation (Part F)
All bathrooms need mechanical extract ventilation (minimum 15 l/s). Ideally ducted to outside, not just into loft space.
Space Requirements
WC/Cloakroom
1.5m²
Minimum size with toilet and basin
Shower Room
2.5m²
Toilet, basin, and shower
Full Bathroom
4-5m²
Bath, shower, toilet, basin
Design Tips for Small Bathrooms
- Wall-hung sanitaryware: Creates sense of space and easier cleaning
- Large format tiles: Fewer grout lines make space feel larger
- Frameless shower screens: Visual continuity without barriers
- Recessed storage: Niches for toiletries without protruding shelves
- Good lighting: Natural light via rooflight if possible, plus task lighting
Planning an Extension With Bathroom?
Get an instant cost estimate for your extension project, including bathroom additions.
Frequently Asked Questions
How many bathrooms should a house have?
Rule of thumb: one bathroom per 3 bedrooms minimum. Premium London properties often have one bathroom per bedroom. Every floor with a bedroom should have bathroom access.
Can I add a bathroom anywhere?
Technically yes, but proximity to existing drainage makes it cheaper. Building regs require adequate ventilation and drainage. Some locations may need pumped systems like macerators.
Bath vs shower - which adds more value?
A house should have at least one bath. Beyond that, showers are often preferred for convenience. Ensuites typically work best as shower rooms.
What's the best ROI bathroom addition?
A master bedroom ensuite typically offers the best return, adding 4-5% to property value. This is especially true for properties with only one existing bathroom.