The single most expensive mistake in bathroom renovation is changing your mind after tiling has started. Repositioning a toilet, moving the shower to the opposite wall, or adding a bath that wasn't in the original plan can easily cost £1,000–£3,000 in abortive work — tiles removed, floors relaid, drainage rerouted. Good layout planning before a single fitting is ordered prevents all of it.
Start With Drainage
Drainage constraints define what's possible more than any other factor. Before considering any layout, establish where your existing soil stack is, where the floor waste positions are, and whether you're on a suspended timber floor or a concrete slab.
Moving a toilet is the most significant drainage change. The pan connector must run to the soil stack with adequate fall (minimum 18mm per metre for a 100mm waste pipe). On a timber floor above a void, there's usually some flexibility to reroute. On a ground-floor concrete slab, repositioning a toilet means breaking out concrete — add £500–£1,500 to the budget for that alone.
A shower waste on a concrete floor is less problematic — a 40mm waste pipe can be chased into the screed and pumped if gravity fall isn't possible. But if you want a low-profile shower tray or wet room with a linear drain, you need at least 100mm of floor depth for the trap and waste run.
Minimum Space Clearances
Building Regulations don't specify minimum bathroom dimensions, but good practice guidance gives workable minimums:
- In front of a WC pan: 600mm clear space (measured from the pan front to the wall or obstacle opposite)
- Beside a WC: 200mm either side
- In front of a basin: 700mm clear (for comfortable use)
- Shower enclosure minimum: 700 x 700mm (800 x 800mm is much more comfortable)
- Bath length: standard 1700mm, short bath 1500mm, but both need clear access on at least one long side
A bathroom that meets the minimums on paper often feels cramped in practice. If the room is genuinely small, a wet room (shower over drain in a fully tiled, tanked floor) is often better than a shower tray with a screen, as it removes the enclosure step and visual boundary.
Bath vs Shower-Only
Removing the bath entirely in a family bathroom has a negative impact on property value in most UK markets — buyers with children specifically look for at least one bath in a family home. In an en-suite or a second bathroom, shower-only is often the better use of space. The right answer depends on the role of the room in the property.
If you want both and space is tight, a shower-bath combination (a full-width 1700mm bath with a shower over it and a fold-flat or pivot screen) is a legitimate solution. It's a compromise in both directions — not as good a shower, not as comfortable a bath — but it works in small rooms.
Ventilation
Part F of Building Regulations requires mechanical ventilation in bathrooms without openable windows, and recommends it even where windows exist. An intermittent extract fan running at minimum 15 litres per second for a bathroom is the standard. Humidity-sensing fans that run until the moisture is cleared are significantly better than timer-only fans.
The fan must vent to outside — not into the loft void. This is a common shortcut that saturates loft insulation and causes condensation damage. The ducting run should be as short and direct as possible; long or kinked runs reduce extract performance significantly.
Tile Layout Planning
Decide on your tile size before finalising the layout. Large-format tiles (600x600mm or larger) look better in bigger spaces but create more waste and require a flatter substrate. In a small bathroom, a 600mm tile that lands with a 50mm cut strip at every edge looks poor and signals poor planning.
Draw the tile layout to scale before ordering. Work out where full tiles land relative to the room's focal points — the shower wall, the wall opposite the door, the floor centre. Adjust the layout or the starting point to avoid narrow cuts at visible edges. Add 10–15% to the tile order for waste, cuts, and future repairs.