Small bathroom design in NZ: layouts, showers and keeping moisture out

Plenty of New Zealand bathrooms are small. Older villas and bungalows often got a bathroom squeezed into a back porch or a converted bedroom corner. Ex-state houses usually have a compact room with a separate toilet next door. Many townhouses and apartments built since the 2000s have ensuites under three square metres. A small room isn't a problem in itself. What goes wrong is a layout that fights the space, and moisture that has nowhere to go.

This guide covers the layout decisions, shower options and ventilation basics that make a compact bathroom pleasant to use and durable over the long term.

Start with the plumbing you already have

In a small bathroom the biggest cost and disruption usually comes from moving the waste pipes, not from the finishes. The toilet waste in particular is large and needs a steady fall to the drain. Moving it across a timber floor can mean cutting joists. On a concrete slab it can mean cutting the slab.

Before sketching anything, note where the existing toilet, shower and basin wastes sit. A layout that keeps the toilet roughly where it is and moves lighter fixtures around it is usually the economical one. If the plan only works with the toilet moved, budget for it early. Set aside a contingency of 10-20% for what turns up once the floor is open.

Three layouts that suit small rooms

Most compact bathrooms fall into one of a few patterns.

The single wall. Toilet, vanity and shower all line up along one wall, with the door opposite. Plumbing stays in one wall cavity, which keeps the work simple. It suits long, narrow rooms around 1.5 m wide.

The corner shower. The shower takes one corner and the toilet and vanity share the remaining walls. This suits squarer rooms. It lets the shower be generous without crowding the door swing.

The wet room. The whole floor is waterproofed and falls to a single waste, and the shower is open or screened by a single fixed glass panel. Without a hob or tray edge the room reads as one larger space. It also makes the bathroom easier to use for anyone with limited mobility. The trade-off is that everything in the room will get wet at times, so storage and toilet-roll holders need thought.

Getting the dimensions comfortable

A few working rules of thumb help a small plan feel usable rather than cramped:

• Shower size. Around 900 x 900 mm is about the smallest shower that feels workable. Going to 1,000 mm or more in one direction makes a noticeable difference to elbow room.
• Space in front of the toilet and basin. Aim for a clear zone of roughly 700-800 mm in front of each fixture, so you can stand, bend and dry off without hitting a door handle.
• Door swing. An inward-opening door eats floor space. A cavity slider or an outward-opening door can free up enough room to fit a bigger shower or a wider vanity.
• Wall-hung fixtures. A wall-hung vanity and toilet show more floor, which makes the room look larger and easier to clean. Both need solid framing or a proprietary frame in the wall behind.

In a small bathroom, moisture is the real design brief. Everything else is arrangement.

Shower options for tight spaces

Tiled shower with a hob or step-down. Familiar and robust. A low hob keeps water in the shower area but adds a trip edge.

Level-entry (wet room) shower. The floor falls continuously to a channel or point waste, and the whole bathroom floor is waterproofed. It looks clean and is easier for ageing bodies. However, it needs careful detailing of the falls and the membrane. On timber floors this often means lowering part of the floor structure.

Prefabricated shower module or tray. Usually the quickest and most predictable choice, with fewer joints for water to find. Modules come in a range of compact sizes and suit rooms where the budget is tight.

Whichever you choose, the floor and walls around it must handle water properly. Building Code clause E3 Internal moisture sets the performance requirements. It covers preventing fungal growth from condensation, dealing with accidental overflow, and keeping water from splashing into concealed spaces such as wall framing. The current acceptable solution, E3/AS1 Amendment 7, treats washing machines and dishwashers as sanitary appliances. It also expects flooring within 1.5 m of sanitary fixtures and appliances to be impervious and easy to clean. In practice, that rules out carpet in all but the largest bathrooms.

Ventilation: the part people skimp on

A family's showers put a lot of water vapour into a small room every day. If it isn't removed, it condenses on the coldest surfaces: the window frame, the ceiling above the shower, the outside wall behind the towel rail. That is where mould starts.

A few principles:

• Extract to the outside. A fan that dumps damp air into the ceiling space just moves the problem somewhere you can't see it. Duct it through the roof, soffit or wall.
• Size it properly. For bathrooms in rentals, the healthy homes standards ask for a fan of at least 25 litres per second or a 120 mm diameter, vented outside. That is a sensible minimum for any home.
• Put it in the right place. Place it near the shower and away from the door, so replacement air is drawn across the room.
• Let air in. An extractor can only remove air if replacement air can enter, so leave a gap under the door or provide a small passive vent.
• Make it automatic. A fan wired to the light, with a run-on timer or humidity sensor, keeps running after you leave. Most damp happens in the ten or fifteen minutes after the shower stops.

Warmth helps too. A heated towel rail or small wall heater keeps surfaces above dew point. Insulated walls and ceilings reduce the cold spots where condensation forms. If the external wall is open during the renovation, that is the moment to add insulation.

Finishes that tolerate a small, steamy room

Smaller rooms get wetter, so choose finishes that cope. Large-format tiles mean fewer grout lines to clean. A bathroom-rated paint with a mould inhibitor suits the ceiling. Moisture-resistant cabinetry, with sealed edges on any board material, will outlast standard joinery. Light colours and a single continuous floor finish help the room feel larger, and so does a mirror cabinet that runs the full width of the vanity.

A quick checklist before you commit

• Is the toilet staying put? If not, is the cost of moving it in the budget?
• Does the door swing clash with any fixture?
• Is there a clear, ducted path for the extractor fan to the outside?
• Have you checked with your council whether your planned work needs consent? This is more likely if you're adding fixtures, moving drainage or changing the floor structure.
• Is the plumbing being done by an authorised plumber? In New Zealand, sanitary plumbing has to be done by one, consent or not.

Get these right and even a 3 square metre bathroom can be a calm, dry, easy room to live with.