Five square metres is not the scope of the work
The floor area tells you little about the condition of walls, pipe routes or a proposed shower. Replacing a basin in the same position differs from removing a bath, moving drainage and rebuilding the floor. Define the layout and what must stay before asking for a price.
Record the existing leaks or damp marks, ventilation, hot-water supply and usable access. If this is the only bathroom, plan how occupants will wash and use a toilet while it is unavailable. Keep that temporary arrangement outside the contractor’s works total so it is still funded.
Resolve the hidden decisions first
| Subject | Question for the relevant professional |
|---|---|
| Drainage | Can the intended route and available height provide a feasible discharge? |
| Floor and walls | What support condition and load constraints must be checked? |
| Waterproofing | Which system is suitable for the substrate, shower and junctions? |
| Ventilation | How will moist air be extracted and replacement air enter? |
| Electricity | How will the proposed equipment and positions comply with the applicable requirements? |
| Building interfaces | Does the work affect common pipes, the structure or collective ventilation? |
QUALITEL’s bathroom guidance identifies the services and constraints that must be considered together. Do not order an apparently flush shower until the contractor has confirmed the necessary floor build-up and drainage. A low tray can be the more feasible choice; style alone cannot determine the detail.
Waterproofing must describe a system, not just a finish
Ask for a written description of the preparation and water-protection solution appropriate to each area. A tile finish and visible silicone joints do not, by themselves, establish that the assembly below is waterproof. Record who treats corners, penetrations, the tray connection and any adjacent floor.
The AQC guidance on shower water damage explains why these junctions matter. Ask the contractor to document concealed stages before tiling and to follow the selected system’s instructions. Do not accept a generic product label as a substitute for a design suitable for your supports. Photographs help trace what was done; they do not replace the installer’s technical checks.
A worked budget with explicit boundaries
| Category | EUR |
|---|---|
| Strip-out, protection and waste | 900 |
| Preparation and repair of supports | 1 100 |
| Specified water-protection system | 850 |
| Plumbing and fixture connections | 1 800 |
| Electrical work and ventilation adaptation | 900 |
| Tiles, adhesive and tiling labour | 1 600 |
| Equipment supply and fixing, excluding connections above | 2 100 |
| Final checks and cleaning | 350 |
| Subtotal | 9 600 |
| Illustrative contingency, 10% | 960 |
| Total | 10 560 |
Do not add a second line for tile preparation if the tiler’s offer already includes it. Conversely, ask whether protection of the route through the flat, carrying waste downstairs and disposal charges are covered. If opening the floor identifies damage, record and price the required repair before proceeding with the affected work.
Compare alternatives by their consequences
Compare a retained layout with a relocated shower using separate prices for changed plumbing, substrate work, waterproofing and making good. A more expensive fixture may have little effect on labour; a different location can change several trades. Request the complete variation rather than looking only at the product-price difference.
If you supply products yourself, confirm who checks compatibility, delivery condition and missing components before installation. Direct purchases normally remain at 20% VAT in metropolitan France; qualifying installation may have a different rate. Compare final TTC costs, including extra visits if an unsuitable product has to be replaced.
For an apartment, check the co-ownership rules before affecting a common stack, structure or ventilation. An ordinary bathroom renewal and an intervention in common building services do not have the same approval implications.
Set inspection points before covering the work
- Confirm supports and drainage after safe strip-out.
- Have the relevant trades check services and specified water protection before concealment.
- Approve any necessary written variation, including its time impact.
- Complete finishes and equipment, then have the contractor perform the planned tests.
- Inspect together at acceptance and list any visible defects precisely.
Ask for checks of leaks under operating conditions, drainage, fitting stability, doors and screens, ventilation and controls. Electrical testing belongs to a qualified professional. Avoid commissioning equipment yourself in a way that conceals a defect or creates a hazard.
Keep evidence useful for the next owner and future repairs
Collect the accepted quotation, changes, invoices, product references, instructions, relevant test records and dated photographs of concealed areas. At acceptance, write “water escapes at the lower screen junction during the agreed test” instead of “finish unsatisfactory”. Identify the location and expected correction.
The post-acceptance guarantees depend on the nature of the work and defect. Do not treat a silicone maintenance issue, a non-functioning item and serious water damage as automatically covered by the same guarantee. Start by notifying the responsible company in writing with the facts and documents.
Sources and method
- QUALITEL — Rénover une salle de bain
- Agence Qualité Construction — Reprises d’humidité dans les coins douche
- Service Public Entreprendre — Taux réduits et achats directs de matériaux
- Service Public — Travaux dans l’appartement en copropriété
- Service Public — Garanties après la réception des travaux
Sources consulted on 18 October 2026. Worked cost tables are editorial examples, not average market prices or contractors’ offers. Tax explanations concern metropolitan France.