The space you actually need
A workable shower room needs about 1.6 to 2.0 m2. That accommodates a 800 mm shower, a compact basin and a WC.
A comfortable shower room is 2.5 to 3.5 m2, which allows a 900 or 1000 mm shower and a proper basin with some worktop.
A cloakroom with just a WC and basin needs as little as 0.9 m2, though 1.2 m2 is far more pleasant.
Door swing eats space. An outward-opening or sliding door frequently makes an otherwise impossible space work.
Ceiling height needs 1,900 mm minimum over the shower and around 1,200 mm over a WC, which is what makes loft and understairs conversions viable.
Where a second bathroom usually goes
Realistic locations with the space and cost implications of each.
| Location | Typical cost | Space needed | Drainage difficulty | Time |
|---|---|---|---|---|
| Steal space from a large bedroom | £5,500-£9,000 | 2-3 m2 | Usually easy | 2 weeks |
| Convert a box room | £5,000-£8,500 | Whole room | Usually easy | 2 weeks |
| Split an oversized bathroom | £7,000-£12,000 | Existing room | Easy | 2-3 weeks |
| Loft ensuite | £6,500-£12,000 | 2.5-4 m2 | Moderate to hard | 2-3 weeks |
| Understairs cloakroom | £2,500-£5,000 | 1-1.5 m2 | Moderate | 3-5 days |
| Utility room corner | £3,000-£5,500 | 1.5-2 m2 | Easy | 1 week |
| Garage conversion shower room | £6,000-£10,000 | 2.5-4 m2 | Moderate | 2-3 weeks |
| Over-stack ensuite (above existing bathroom) | £5,500-£9,000 | 2-3 m2 | Easiest of all | 2 weeks |
Drainage decides the price
Stacking the new bathroom directly above, below or beside an existing one is the cheapest option by a wide margin, because the soil connection is metres away rather than across the house.
A WC waste needs a fall of roughly 1 in 40 and a 100 mm pipe. That is what limits how far from the stack a new WC can go on gravity.
Where gravity cannot be achieved, a macerator or pumped system works, adds a few hundred pounds and introduces an appliance that will need servicing.
Shower and basin wastes are 40 mm and much easier to route, so the WC position is almost always the constraint.
A new external soil stack is possible and is a planning consideration on the front elevation of some properties.
The hidden costs to budget for
Making good the room the space came from: new plasterboard, skirting, decoration and often a repositioned radiator.
Structural work where a partition is removed or an opening is formed, including any lintel required.
Heating: a new radiator or underfloor heating, plus the pipework to reach it.
Electrics: lighting, shaver point, extractor fan and possibly a new circuit, all notifiable and all certified by our own electrician.
Flooring in the corridor or bedroom where the new doorway lands, which is frequently forgotten at budgeting stage.
Is it worth it?
For a family of four sharing one bathroom, the daily benefit is immediate and considerable.
For resale, adding a bathroom where there was not one is the strongest return available in the bathroom category, particularly an ensuite to a main bedroom in family housing.
The exception is losing a bedroom entirely to gain a bathroom. Going from four bedrooms to three usually costs more value than the bathroom adds, whereas taking two square metres off a large bedroom does not.
We have fitted over 200 bathrooms since 2015 and hold a 4.9 out of 5 rating from 47 reviews, and the free survey will tell you honestly whether the space you have in mind will work before you commit to anything.
Frequently asked questions
How much space do I need for a second bathroom?
About 1.6 to 2.0 m2 for a workable shower room with a WC and compact basin, and 2.5 to 3.5 m2 for something comfortable.
Where is the cheapest place to add a bathroom?
Directly above, below or adjacent to an existing bathroom, because the soil connection is short and the drainage is straightforward.
Will I need a macerator?
Only where gravity drainage cannot achieve the required fall. We always design for gravity first because it is silent and needs no servicing.
Does adding a bathroom need building regulations?
Yes. The drainage, ventilation, electrics and any structural work are all covered, and we handle the notification and certificates.
Is it worth losing bedroom space?
Taking two square metres off a large bedroom is almost always worth it. Losing an entire bedroom usually is not, because bedroom count drives valuation.