Bathroom Design: Decisions That Cannot Be Changed Later

Bathrooms concentrate services, waterproofing and finishes in a small area. The errors that become permanent.

A bathroom is the most service-intensive room in a house per square metre, and almost every decision in it is buried behind tile within weeks. Changes after that point mean demolition, which is why bathroom planning deserves disproportionate attention.

Why these keep happening

These mistakes share a characteristic: they are invisible once finishing is complete and expensive to reach afterwards. Getting them right costs attention at design stage and almost nothing in construction.

1. Drainage positioned without falls planned

Drain position is marked on a plan and the falls are assumed to be a screeding matter.

• Avoid it by: Plan falls and drain positions together, with the fall direction shown on the drawing.
• Proof it is closed: A drawing showing drain positions with fall directions and gradients.

What it costs you: Water stands rather than drains, which eventually finds a way through the waterproofing.

2. Insufficient space around fixtures

Fixtures are placed on a plan where they fit rather than where they can be used comfortably.

• Avoid it by: Check clearances in front of and beside each fixture against realistic use.
• Proof it is closed: Clearances dimensioned on the drawing.

What it costs you: Doors that conflict with fixtures, inadequate space in front of the basin, and a shower that is awkward to enter.

3. No ventilation or inadequate extraction

A window is assumed to suffice, or extraction is treated as a fitting to be added later.

• Avoid it by: Design mechanical extraction with a proper route, regardless of whether a window exists.
• Proof it is closed: An extraction route shown on the services drawing with the duct size and outlet.

What it costs you: Persistent humidity damages finishes, encourages mould and makes the room unpleasant.

4. Access panels omitted

Panels interrupt the tiled surface and are left out for appearance.

• Avoid it by: Provide access to every concealed valve, trap and connection, positioned deliberately so it reads as part of the design.
• Proof it is closed: Access panel positions shown on the drawings before tiling.

What it costs you: Any future maintenance of concealed valves or connections requires breaking tiles.

5. Waterproofing treated as a product rather than a system

A membrane is specified and assumed to solve the problem.

• Avoid it by: Specify the details: upturn heights, junction treatment, penetration sealing, and require a flood test.
• Proof it is closed: Detail drawings for each junction plus a documented flood test.

What it costs you: Failures occur at upturns, junctions and penetrations rather than in the middle of a surface.

6. Lighting planned as a single ceiling point

Bathroom lighting is treated as functional rather than designed.

• Avoid it by: Plan lighting for the tasks: at the mirror, in the shower and general illumination, with appropriate protection ratings.
• Proof it is closed: A lighting layout showing positions and fitting types.

What it costs you: Shadows fall exactly where light is needed at the mirror, and the room feels harsh.

A short check before you sign

• Are falls and drain positions shown with directions?
• Are clearances around every fixture dimensioned and realistic?
• Is mechanical extraction designed with a proper route?
• Is there access to every concealed valve and connection?
• Are waterproofing junctions detailed and is a flood test required?

If it has already happened

If a bathroom is finished and a problem appears, diagnose before demolishing. Water appearing in one place frequently originates elsewhere, and opening the wrong surface adds damage without finding the cause. Where access panels were omitted, adding one is usually cheaper than the alternative and useful thereafter.

If you are starting a design, Domira can help you write the brief, review the drawings and keep the design aligned with the budget before it reaches a contractor.