Bathrooms are the most expensive rooms per square foot in a house, and the reason is that a small room contains more trades than any other.
The trades in one small room
Demolition. Plumbing rough and finish. Electrical. Framing. Insulation. Waterproofing. Tiling. Drywall. Painting. Cabinetry. Glass. Flooring. Ventilation.
Each one arrives, works for a day or two, and leaves. The scheduling overhead is a real cost and it does not scale down with the room.
Why area matters less than expected
Doubling the floor area of a bathroom adds tile, some drywall and a little more of everything. It does not add a second toilet, a second rough-in, or a second set of trade visits.
Fixture count is the driver. Going from one sink to two adds a rough-in, a drain, a vent consideration, a second faucet, and cabinetry. That costs far more than the extra square footage the double vanity occupies.
The five decisions that set the number
Does anything move? Keeping the layout is the single largest saving available. See the plumbing article — the toilet is the expensive one.
Tub, shower, or both? A tiled shower with a bench, a niche and glass is several times a fibreglass surround. A freestanding tub adds a filler and floor structure.
How much tile, and what kind? Floor only, or floor plus a full-height shower, or floor plus every wall. Large-format tile needs a flatter substrate and more skilled labour.
Fixture tier. The spread between builder-grade and premium fittings is enormous and it is entirely a choice. A faucet can cost the same as a whole vanity.
What is behind the walls? An old house frequently reveals galvanised supply, no venting, rotten subfloor under the toilet, or knob-and-tube wiring. None of it is optional to fix and none of it is visible at quoting.
The contingency is not optional
A bathroom is the room most likely to produce surprises, because it is the room where water has been leaking quietly for decades.
Set aside a meaningful contingency — commonly cited around 15 to 20% — specifically for what appears when the walls open. On an older house, the higher end.
The most common findings are rot at the toilet flange, rot in the shower pan area, undersized or corroded supply, missing or improvised venting, and wiring that does not meet current requirements.
Where the money is well spent
Waterproofing, which is invisible and is the thing that decides whether the room lasts fifteen years or five.
Ventilation, sized correctly and vented outside, which prevents the moisture problems that destroy bathrooms.
Labour quality on tile, because tile is most of what you see and bad tiling is visible forever.
Valves and rough plumbing, which are behind the wall and expensive to reach later.
Where it is easily wasted
Fixture upgrades beyond a solid mid-tier, which have diminishing returns.
Heated floors in a room used for ten minutes a day, unless it is the primary bathroom.
Moving the toilet for a marginal layout improvement.
A tub that will not be used, which occupies the space and the budget that a larger shower wanted.
Getting comparable quotes
Give every contractor the same specification: same layout, same fixture list, same tile area, same waterproofing system. Then the differences are labour and margin rather than scope.
Without that, three bathroom quotes are three different bathrooms and the totals mean nothing next to each other.
Powder room, hall bath, primary bath
Three rough tiers, and the jump between them is fixture count rather than area.
A powder room has a toilet and a sink. No waterproofing, no tile beyond the floor, no glass, no ventilation requirement in some jurisdictions. It is the cheapest room in the house to renovate.
A hall or family bath adds a tub or shower, which brings waterproofing, tile, a valve, a fan and glass or a curtain. That single addition roughly doubles the trades involved.
A primary bath adds a second sink, frequently a separate tub and shower, more tile, better glass and often a separate toilet compartment. Each of those is another rough-in or another trade day.
Timeline, and why it costs money
A bathroom is typically three to six weeks, and much of that is waiting rather than working — waterproofing curing, tile setting, grout curing, paint drying, and gaps between trades.
Where it is the only bathroom, that timeline is the real cost of the project and it is worth asking about before the price.