Common bathroom renovation mistakes

In short

The most common bathroom renovation mistakes are:

Why do so many mistakes happen in bathrooms?

A bathroom is one of the most technical rooms in a home. Many trades have to work together in a very small space:

If one tradesperson changes a solution, it can affect the work of several others.

The plumber may move the floor drain. The tiler discovers that the large tiles are hard to combine with the slope. The electrician finds there is no room for the socket you wanted. The furniture collides with the door.

A good bathroom renovation is therefore not just about each tradesperson doing their own job. The whole project has to be planned and coordinated.

Overview of common mistakes

1. Starting without a detailed plan

A common mistake is to start demolition before the whole bathroom has been planned.

It is not enough to know which tiles and which washbasin you want. Before the work starts, you should also have decided:

If the planning happens after the work has started, the result is often improvised solutions and costly changes.

How to avoid this mistake

Make a dimensioned drawing and a complete product list before starting.

Check that:

2. The contract does not describe what is to be delivered

"A complete new bathroom" can mean different things to the customer and the tradesperson.

Is demolition included? Who hauls away the waste? Are the walls to be straightened? Are the furniture, the electrician and painting the ceiling included in the price? Who supplies the tiles?

An unclear agreement increases the risk of extra costs and disputes.

The contract should describe

• What is to be demolished
• What is to be built
• Which products are to be used
• Who buys the materials
• Which trades are included
• Price or method of calculation
• How additional work is approved
• Start and completion
• Payment schedule
• Division of responsibility
• Documentation requirements
• Whether the bathroom is to be built to the Wet Room Standard (Byggebransjens våtromsnorm)
• How defects and delays are handled

All changes should be agreed in writing, with their price and time consequences, before the work is carried out.

3. The customer chooses on the lowest price alone

A very low quote can be tempting. The problem arises when the quotes do not cover the same work.

One quote may include the plumber, electrician, membrane and documentation. Another covers only demolition, tiling and installing the furniture.

So compare:

The lowest total price is not necessarily the cheapest project once all the extras come in.

4. The old bathroom is not examined well enough

A price given before demolition will often contain uncertainty. Nobody necessarily knows what is behind the tiles or under the floor.

Common surprises include:

Ask the tradesperson to explain which assumptions the quote is based on and how hidden conditions will be handled.

In older homes it may be sensible to investigate the risk of asbestos before demolition starts.

5. The floor has too little slope

Slope means that the floor inclines towards the floor drain so that the water runs the right way.

Too little slope can lead to:

Even worse is a reverse slope, where the water runs away from the floor drain.

The building regulations (TEK17) require wet rooms to have a floor drain and sufficient slope. Leaking water must be made visible and led to a floor drain.

What do slopes of 1:100 and 1:50 mean?

• A slope of 1:100 corresponds to roughly one centimetre of height difference per metre.
• A slope of 1:50 corresponds to roughly two centimetres per metre.

TEK17 describes several pre-accepted solutions. One option is a slope of at least 1:50 in an area extending at least 0.8 metres from the floor drain when the shower is placed over the drain. Another option is a slope of at least 1:100 across the whole floor.

Which solution is suitable depends on the layout of the bathroom.

How to avoid slope mistakes

• Plan the floor drain and shower together
• Choose a tile format that can be adapted to the slope
• Measure the slope before and after tiling
• Check that the door and threshold work with the heights
• Carry out a practical water test before handover
• Document the measurements

The fact that the water eventually drains away does not necessarily mean the slope is good enough. Nor should large puddles be left standing elsewhere on the floor.

6. The height difference at the door is too small

The bathroom must be able to handle leaking water without it immediately running out into the hallway or into adjoining rooms.

The wrong height at the threshold or door can occur because:

TEK17 describes pre-accepted solutions for a watertight upstand and the height at the outer edges and the door opening. This has to be planned together with the requirements for accessibility and a step-free solution.

The problem can be hard to correct once the tiles have been laid.

7. The membrane is installed incorrectly

Tiles and grout are not the waterproof layer in a typical tiled bathroom. The water is handled by the membrane behind or beneath the surface.

Typical membrane faults include:

Membrane faults can be invisible until water has penetrated the structure.

How to reduce the risk

• Use a documented membrane system
• Follow the manufacturer's installation instructions
• Avoid random mixing of products
• Use an installer with relevant wet room expertise
• Take photos of the membrane before tiling
• Document the floor drain, corners, threshold and penetrations
• Do not let other trades damage the membrane afterwards

It should be clear who is responsible for the membrane and who checks it before the next trade starts.

8. The joint between the membrane and the floor drain is not watertight

The floor drain is one of the bathroom's most critical risk points.

The membrane must be connected correctly to the floor drain. The drain, collar, clamping ring and membrane system must work together.

Common mistakes include:

The fault can cause water to disappear into the floor structure instead of through the drain.

Ask for photos that clearly show the joint before it is built in.

9. There are too many holes in the wet zone

Every penetration of the membrane is a potential leak point.

Typical penetrations include:

Common mistakes are missing collars, incorrect sealing or screws driven through the membrane without a documented solution.

So plan the fixing points and timber backing before the wall is closed up. Choose glued or alternative fixing solutions where appropriate.

Do not drill into a finished bathroom wall without knowing where the membrane, pipes and electrical cables are.

10. Concealed pipe connections are not leak-protected

A small water leak can go on for a long time before it is discovered.

Water installations must be designed so that leaks are detected and do not cause unnecessary damage.

Common problems include:

Ask for photos of the pipes before the walls and floor are closed up. The documentation should show where the stop valves, manifold cabinet and pipe runs are.

11. The concealed cistern has no leak protection

A wall-hung toilet can give a clean look, but the cistern and several connections end up hidden behind the wall.

Any leak from a concealed cistern must be able to show itself. The water must not be left standing hidden inside the structure.

Check:

Ask for photos before the enclosure is closed up.

12. Electrical work is done by the wrong person

A bathroom has stricter requirements for the placement and installation of electrical equipment than ordinary dry rooms.

Fixed electrical work must be carried out and documented by a registered electrical contractor.

This includes, among other things:

A common mistake is that other tradespeople lay the heating cables and ask an electrician to connect them afterwards. Unqualified people are not allowed to lay, install or connect fixed heating cables.

After the work you should receive

• A declaration of conformity (samsvarserklæring)
• A final inspection report
• An updated circuit list where relevant
• Product documentation
• Measurement results for the heating cables
• Photos or a drawing showing the position of the heating cables

Check the company in the Electrical Contractor Register (Elvirksomhetsregisteret) before the work starts.

13. Ventilation is forgotten

A bathroom produces large amounts of moisture. Without sufficient extraction, the moisture can linger long after the shower.

Signs of poor ventilation can include:

TEK17 requires wet rooms to have extraction with satisfactory efficiency. The ventilation must also have access to replacement air. A powerful fan is of little help if no air can get into the room.

Do not casually connect a fan to a shared ventilation duct in a housing cooperative (borettslag). Changes to the shared system can affect other homes and require approval from the board.

14. The wrong materials are used in the wrong place

A product that works in a living room does not necessarily work in a bathroom.

Common material mistakes include:

CE marking does not automatically mean the product suits every construction or can be combined with other products.

Follow the installation instructions and the documentation for the whole system.

15. Drying and curing times are not followed

When the schedule slips, it can be tempting to make up time by working faster.

But levelling compound, membrane, adhesive, grout and sealants need time to dry or cure.

If the next stage starts too early, the result can be:

Drying time is affected by temperature, humidity, layer thickness and product. The schedule must therefore be adapted to the products - not the other way round.

Document which products were used and when the different layers were applied.

16. The tile format does not suit the floor drain and the slope

Large tiles can give a luxurious look, but they can be hard to combine with a slope in several directions.

Around a traditional floor drain, the floor often has to slope from several sides. Very large tiles may then need to be cut or split to follow the slope.

If this is not planned, the result can be:

Clarify how the tiles, floor drain and slope work together before the products are ordered.

17. The bathroom ends up with an impractical layout

A bathroom can be technically correct and still be impractical.

Common planning mistakes include:

Test the layout on a dimensioned drawing. Also mark how doors, drawers and shower screens move.

Think a few years ahead. A bathroom can be hard to change once the pipes and floor drain are in place.

18. The fire separation in a flat is damaged

In an apartment block or multi-family house, the floors and walls between the homes can be part of the fire and sound separation.

The work may require an application to the municipality if the renovation affects more than one unit or breaches a fire compartment. New pipe runs or replacing a floor drain in the floor structure between dwelling units can be such interventions.

Common mistakes include:

Contact the board and the municipality before the work starts if structures or shared installations may be affected.

19. Assuming no bathroom work needs a building application

Renovating surfaces and replacing furniture does not normally require an application.

A full refurbishment of a bathroom within the same unit or fire compartment is usually also exempt from the application requirement, but the relevant requirements in TEK17 may still apply.

The work may require an application if it:

Ask the municipality before starting if you are unsure. In housing cooperatives and co-owned properties (borettslag and sameier) you must also follow the bylaws and obtain the necessary approvals.

20. It is unclear who has overall responsibility

A bathroom often involves several companies. The customer has an agreement with one tiler, one plumber and one electrician, but nobody is responsible for the whole.

Problems can then arise at the handovers between them:

Clarify whether you have:

If you coordinate yourself, you must make sure everyone uses the same drawing and schedule.

21. The customer pays too much up front

Large advance payments give the customer little security if the work stops or a dispute arises.

A better solution is to tie payment to clear milestones, for example:

Payment should reflect the value of the work actually done.

Do not pay the final settlement until you have checked the bathroom and received the agreed documentation.

22. No proper handover is carried out

By the end of the project the customer is often tired of dust and tradespeople. It is then easy to approve the bathroom without a systematic check.

During the handover you should check:

Record every deviation in a handover report. Take photos and agree a deadline for corrections.

23. The final documentation is missing

A finished bathroom should have documentation showing what has been done and how the hidden solutions were carried out.

The documentation should include, among other things:

A photo of the finished tiles does not document the membrane behind them.

Agree the documentation in the contract and require it to be delivered before the final payment.

Signs that something may be wrong

Not every deviation means the bathroom has a serious structural fault. The following signs should nevertheless be investigated:

A crack in a cement-based grout joint does not automatically mean the membrane is leaking. It can still be a sign of movement or another problem that should be assessed.

What should you do if you discover a fault?

1. Limit the damage

Shut off the water if there is an active leak. Stop using the shower if water can get into the structure. If there is an electrical hazard, contact an electrician.

2. Document the problem

Take photos and video. Note the date and how the fault develops.

3. Complain in writing

Notify the tradesperson as soon as possible. Describe specifically what is wrong, and ask for an inspection and a proposal for putting it right.

4. Give the tradesperson a chance to investigate

The tradesperson normally has both the right and the duty to remedy a defect. Do not tear out the bathroom or order a full repair from another company before the original tradesperson has had a reasonable opportunity to investigate the matter.

5. Use an independent expert

In a technical disagreement, a surveyor or wet room specialist can examine:

6. Notify your insurance company

Contact your insurance company early if there is water damage or a risk of consequential damage.

7. Withhold only what is necessary

In the event of a defect, you may, depending on the circumstances, withhold as much of the payment as is necessary to secure your claim. Pay the part of the invoice that is not in dispute.

How Fikso reduces the risk

When a bathroom job is carried out through Fikso, the whole delivery should be described in writing before the work starts.

Among other things, you can agree on:

The customer secures the payment before the work starts. Payout can be tied to agreed milestones and approval of the delivery in accordance with Fikso's current terms.

If a documented disagreement arises, the disputed amount can be held back in the payment solution while both parties are given the opportunity to submit documentation.

Fikso does not replace a technical inspection or public approval. The platform can nevertheless make the agreement, communication, payment and documentation easier to keep track of.

Checklist before the bathroom renovation starts

• I have a detailed description of the work.
• I have a dimensioned drawing.
• All products have been chosen and their measurements checked.
• Floor drain, tiles and slope have been planned together.
• I know who is responsible for the membrane.
• I know who is coordinating the trades.
• The electrician is registered in the Electrical Contractor Register (Elvirksomhetsregisteret).
• The plumber has relevant experience.
• The documentation requirement is in the contract.
• Additional work must be approved in writing.
• Payment is divided into milestones.
• Drying and curing times are included in the schedule.
• I have clarified whether an application is required.
• I have obtained approval from the board.
• I have set money aside for unforeseen conditions.
• A documented handover will be carried out.

Frequently asked questions

A good bathroom is built behind the tiles

It is easy to spend most of your time on tiles, colours, taps and furniture. But the quality of the bathroom is decided above all by what you cannot see.

A good bathroom has:

The best bathroom is not necessarily the one with the most expensive tiles. It is the bathroom that works every day - without leaks, bad odours or unpleasant surprises.

Method and sources

This article is based on Norwegian rules and professional recommendations available in August 2026. The requirements must be assessed according to the type of home, the scope of the work, the contract and the existing structure.

Sources:

This article provides general information and does not replace a specific assessment by a wet room specialist, electrician, plumber, municipality or insurance company.