Bathroom in the loft — is it possible?

Drainage — the biggest obstacle

A new bathroom stands or falls with the drainage. The following applies:

• A slope of 1–2 cm per metre is necessary for proper drainage of the shower/sink.
• A toilet requires more clearance (110 mm pipe) and slope.
• The existing soil stack (vertical drainage pipe through the house) is the preferred place to connect. Check with the contractor and plumber to see where it runs.
• Too far from the soil stack? Then use a macerator (Saniflo or similar): pumps wastewater away under pressure. Works, but involves noise and is prone to blockages (no wet wipes!).
• You must never use the rainwater drainage for wastewater — a separate pipe is mandatory.

Request a preliminary inspection from the plumber — costs € 100 – € 300, often saves thousands in miscalculations.

Ventilation and moisture

A bathroom produces 1–2 litres of water vapour per shower. Without proper extraction, this enters walls and insulation:

• Mechanical extraction with a pipe directly outside through the roof or facade — minimum capacity of 50 m³/h.
• Humidity-controlled extractor fan (hygrostat) — turns on automatically at high humidity levels.
• MVHR system (heat recovery): makes sense to install during a major renovation.
• Avoid relying solely on natural draught ventilation or an open skylight — this is insufficient.
• Air supply: grille under the door or ventilation channel to the hallway.

A poorly ventilated loft bathroom will develop mould within 2–3 years — repairing this is expensive and harmful to your health.

Hot water — will it reach the top?

Before you invest: can your current system handle it?

• HR-combi boiler standard 24–28 kW: can properly supply one shower at a time. Two simultaneous showers is often not possible.
• For two showers: upgrade to a 35 kW+ boiler or install a heat pump boiler specifically for the loft.
• Distance: the longer the pipe, the more heat loss. Insulate pipes or install a local instantaneous water heater (electric).
• For underfloor heating: connect an additional return group to the central heating — an installer must calculate this.
• An average renovation: € 800 – € 2,500 for extra pipework and a potential boiler.

Waterproof construction

Not an option, a must:

• Floor: edge and corner sealing with sealing tape + waterproof powder bed.
• Walls up to 2 m high require waterproof pre-treatment.
• Sealing joints with sanitary silicone, not standard sealant.
• Shower enclosure or walk-in shower with a proper seal to the floor.
• With a wooden floor underneath: additional waterproofing layer. Lofts rarely have concrete floors — a leak will eat through to the floor below.

For an average loft bathroom, this means € 1,500 – € 3,000 in extra work and materials.

Space and layout

Minimum dimensions for various setups:

• Shower + sink + toilet: from 3.5 m².
• Shower + sink + toilet + bathtub: from 6 m².
• Walk-in shower XL: at least 2.5 m² just for the shower.

In a loft, headroom is critical. Above the shower and toilet, you want ≥ 2.1 m, otherwise you will hit your head. A bathtub under a sloping roof is possible, provided you do not need to sit upright with your head.

Place sanitary ware under the highest parts: in the middle or near a dormer. Sink and cupboards in the lower parts.

Lighting: a minimum of 2 spotlights per zone (shower, mirror, ceiling). Mirror lighting > 4,000 lumens for makeup/shaving.

Frequently Asked Questions

Short, honest answers to frequently asked questions.

Do I need planning permission?

No environmental planning permit (omgevingsvergunning) is needed for the bathroom itself. However, you do need to submit a construction activity notification for drainage and potentially gas. Dormer or skylight: see the relevant planning permission page.

What is cheaper: a macerator or connecting to the soil stack?

Connecting to the soil stack is structurally more expensive (cutting chases, insulation) but low-maintenance. A macerator is cheaper (€ 600–1,000 plus installation) but requires lifelong maintenance.

Can I fit a bathtub in the loft?

Structurally, yes — a full bathtub weighs ~250 kg. Ask a structural engineer if your floor joists can support it. Reinforcement is often necessary (€ 600 – € 1,500).

Which floor underneath the bathroom?

Wooden joists → 22 mm plywood + cement screed + tiles. Or a GRP shower floor as a prefab solution. With proper waterproofing, both work.

How do I arrange underfloor heating?

Electric (foil or mat) is common in lofts — easy to lay, € 60–100/m². Water-based underfloor heating is possible, but requires a connection to the central heating return.

How much does macerator servicing cost per year?

Proper maintenance and an annual inspection cost € 80–150. Costs are higher in the event of a blockage (often caused by wipes or grease). Avoid this by exclusively flushing toilet paper + bodily fluids.

Is a Saniflo reliable?

Perfectly fine for toilet use — millions of households use it. Discipline regarding what you flush is everything. With multiple people in the household, there is a higher chance of malfunctions.

How long does construction take?

Plumbing 3–5 days, tiling 4–7 days, installing sanitary ware 1–2 days. Total of 2–3 weeks including the drying time for the screed.

Summary

A second bathroom in the loft is technically highly feasible, provided you properly arrange the drainage (soil stack or macerator), ventilation (mechanical with a hygrostat), hot water (check central heating capacity), and waterproofing. Calculate on € 10,000 – € 18,000, all-inclusive. Ask a plumber in advance about the soil stack route — this determines whether the project is structurally viable and affordable.