Adding an en-suite or shower room on the Côte d'Azur

Waste water runs downhill. A new shower, basin and WC all have to drain into an existing soil pipe, and the pipe needs a steady fall over the whole distance. The further the new room sits from that pipe, the more floor or wall has to open up to carry it there.

The toilet is the hardest piece to place, because its pipe is the widest. A shower and basin take a smaller pipe and are easier to route. So the first question for the plumber is simple: where will the waste run, and how far is it to the soil pipe? That answer decides the layout. Bedrooms that back onto an existing bathroom, or sit above one, are usually the easiest to fit.

In a flat, the shared soil stack belongs to the copropriété (the building's co-ownership). Ask the syndic (the building's managing agent) before anything is connected to it. Cutting into the stack, or running a pipe through a shared floor, needs a vote at the AG (the owners' general meeting).

Taking a shower room out of the corner of a bedroom often leaves it with no window. The local health rules don't allow any change to a home that creates a badly ventilated room, and that covers converting existing space as well as new building.

A shower room with a window that opens needs an extract vent high on the wall. One without a window needs a fresh-air inlet, plus extraction at high level by a vertical duct or a mechanical fan. In practice most windowless en-suites get a fan. Ask whether it will join an existing VMC (mechanical ventilation) or run on its own, and where the damp air will leave the building.

That last answer can bring in other rules. A new vent grille or window in an outside wall changes the facade, which needs a déclaration préalable (planning declaration) at the town hall. In a flat it also needs a vote at the AG. A fan connected to an existing shared duct is a question for the syndic.

Don't let the fan drop off the devis (written quote) to bring the price down. Steam with nowhere to go ends up as mould on the bedroom side of the wall.

A shower room next to an existing bathroom can share its drains. One across the house means lifting floors, boxing in pipes or opening a ceiling below, and putting all of it back afterwards.

A missing window adds the fan and its duct, and sometimes a hole through a thick stone wall or the roof to get the air out. If that hole is in the facade, the planning declaration and, in a flat, the owners' vote come first.

Lifting an old floor can turn up rot or damp that has to be dealt with first. If the building's permit predates July 1997, old tiles or boards need an asbestos check before anyone breaks into them. The shower floor needs a waterproof layer under the tiles, which should be named on the devis as its own line. Add a bigger water heater if the old one can't keep up.

Get two written quotes for the same plan, each showing the drain route and the ventilation, so you can compare them line by line. What drives the price of any bathroom is on our bathroom renovation page.

Dividing a bedroom, or turning a box room into a shower room, creates no new floor area. That needs no planning declaration and triggers no taxe d'aménagement (one-off building tax). The paperwork starts when the outside changes: a new window or vent in an outside wall needs a declaration, and in a flat a vote too.

Converting a garage or a loft into the en-suite is a different case, because it can create floor area. The rules on declarations, the building tax and when an architect is compulsory are on our house extensions page.

For TVA (French VAT), fitted work inside a home over two years old is taxed at 10% when the firm supplies and fits it. A freestanding cabinet or mirror bought on its own stays at 20%. If the en-suite sits in an extension built onto the house, the extension's work is taxed at 20%. Ask for the rate on every line of the devis.