More New Zealanders are building their own outdoor saunas than ever before. The health benefits are well documented, sections are getting bigger, and there's real satisfaction in building something yourself. This guide covers everything you need to plan and build a solid outdoor sauna from scratch.
A full build series is coming soon to our YouTube channel. This guide covers the key decisions and process in the meantime.
Do You Need Building Consent?
This is the first question to answer, not the last.
In New Zealand, single-storey detached outbuildings up to 30m² are generally exempt from building consent, provided the work is carried out or supervised by a LBP and certain conditions are met around materials, height, and boundary setbacks. This threshold applies to general outbuildings like sheds, sleepouts, and saunas.
Even if your build is exempt, all work must still comply with the New Zealand Building Code. And if you're adding a wood-burning heater, the flue installation may trigger separate consent requirements depending on your region.
Check with your local council before you start. Rules vary by district and it's a quick conversation that could save you a costly rebuild.
Choosing the Right Location
Close enough to your home to be convenient, far enough to feel like its own space.
Access to power matters. The shorter the cable run from your switchboard, the simpler and cheaper the electrical install. Even if you go wood-burning, you'll want power for lighting.
Drainage matters too. The area around the sauna gets wet from rinsing off, and rain. Avoid low lying spots that hold water.
Orientation is worth a moment's thought. A view of the garden or bush adds to the experience. Neither is essential but both are easy to factor in at the planning stage.
Choose Your Heater Before You Finalise the Size
Your heater choice drives several other decisions, room dimensions, ventilation placement, electrical requirements, and whether you need a flue. Sort this out early.
For most NZ builds, electric is the practical choice. No flue, no complications, and you can set it on a timer. Wood-burning delivers a more traditional experience but requires council checks.
Not sure which is right for you? Read our electric vs wood-burning sauna heater guide.
Once you've chosen what type of heater, use our sauna heater sizing calculator to match it to your room volume before you lock in dimensions. Browse our full heater range here. We can also order anything from Narvi.
Size and Design
A common family sized sauna is around 2m x 2m internally. That comfortably seats two-four people and heats quickly.
Ceiling height of 2.1 to 2.2 metres is the sweet spot. Lower than 2.1m and the upper bench gets very hot. Higher than 2.2m and you're heating dead air that doesn't benefit the experience if you are only using two benches. You can go to 2.4h but this would require a third tier on your bench.
A small covered porch or deck off the door is worth building in from the start if space allows. Somewhere to cool down between rounds, and it protects the door from the weather.
Materials
Framing
All framing should must be structural must comply with the NZ building code. I have added a link to a free copy.
For a typical sauna build, 100x50mm framing for walls and 150x50mm ceiling joists for spans up to 3m are common starting points. Your specific sizing, spacing, and connections need to be appropriate for your wind zone and ground conditions. If you're not sure, talk to a builder, designer or one of the team here at Kauri Point Sauna.
Insulation
Use mineral wool. It handles the heat and moisture of a sauna better than glass wool, polyester or polystyrene insulation. Pack it tight with no gaps, and go as thick as your framing depth allows. Don't skimp on the ceiling, that's where most of the heat goes.
Vapour Barrier
A foil-faced vapour barrier goes on the warm side of the insulation, between the insulation and the internal lining. This is non-negotiable. Without it, moisture migrates into the wall over time and causes rot. Lap and tape every join properly with aluminium foil tape.
Internal Cavity
After the vapour barrier, fix cavity battens before your interior cladding. Cedar castellated battens or untreated pine both work well. This creates a crucial air gap that lets the wall breathe and keeps fixings out of the vapour barrier.
Sauna Timber
For internal lining and benches, use timber specifically suited to sauna conditions. Western Red Cedar and Thermo Pine are the two most popular options in New Zealand.
Not sure which to choose? Read our cedar vs thermo pine guide.
Whatever you choose, avoid any treated, painted, or sealed timber inside the hot room. Your sauna needs to breathe, and so do you.
Door
An insulated glass door is worth the investment. It lets light in, makes the space feel less enclosed. A solid timber panel door is also a good option provided the panel inside is lined in the same material as the walls. The door must open outwards for safety.
The Build Process
Step 1: Foundation
A solid, level base is everything. A concrete slab is the most durable option. A timber deck on concrete piles works well too. Avoid setting a sauna directly on bare ground.
Get it level before you frame. Everything downstream depends on it.
Step 2: Framing
Frame walls plumb and square. Include rough openings for the door and any windows at this stage. If you're going electric, think about where the heater will sit on the wall and where your cables will run.
Step 3: Insulation and Vapour Barrier
Pack mineral wool tightly between studs with no gaps. Install the foil vapour barrier across the entire internal surface, walls and ceiling, lapping joins by at least 100mm and taping every seam. Fix your cavity battens over the top.
Step 4: Interior Cladding and Benches
Install sauna timber cladding on walls and ceiling. Pre-drill near the ends to avoid splitting, particularly with Thermo-Pine which is more brittle than Western Red Cedar.
Build benches from the same timber. The upper bench at around 900 to 1000mm from the floor puts you in the hottest part of the room. A lower bench at around 450mm gives a cooler option and works well as a foot rest. Make bench tops removable if you can, it makes cleaning much easier.
Use stainless steel fixings throughout for all internal timber and bench work. Standard steel corrodes in a sauna and leaves rust stains on the timber. Make sure you fix the bench seats from underneath.
Step 5: Heater Installation
Position your heater according to the manufacturer's minimum clearances from walls, benches, and combustible materials. These are safety requirements, not suggestions.
Electric heaters must be installed by a registered electrician on a dedicated circuit. Wood-burning heaters must be installed by a registered and certified fireplace installer.
Browse our range of heaters here Not sure what size you need? Use our sauna heater sizing calculator .
Step 6: Ventilation
Ventilation is what makes a sauna feel clean and breathable rather than stale. How you set it up depends on your heater type. The positions below are based on research by Äikäs and Holmberg at VTT Technical Research Centre of Finland, which tested different vent configurations to find what actually works.
For an electric sauna, the intake vent goes on the heater wall at approximately 890mm above the floor, roughly level with the top of the heater. Fresh air entering here hits the hot stones immediately, heats up and rises naturally. The exhaust vent goes on the opposite wall at approximately 690mm from the floor, below the upper bench. This pulls air down across the room and out before it goes stale, and makes sure löyly reaches the lower half of the sauna. Both vents should be adjustable. A small inline exhaust fan can help in larger rooms.
For a wood-burning sauna, the fire and flue do most of the ventilation work. The intake vent goes low on the heater wall, near the firebox base, to supply combustion air. The flue handles the primary exhaust, with a secondary vent high on the opposite wall near the ceiling. If you plan to add mechanical ventilation alongside a wood-burning stove, get professional advice first. Done wrong it creates negative pressure and draws combustion gases back into the room.
Step 7: Finishing
Fit the door, add soft lighting, LED strips rated for high humidity work well, and install a thermometer and hygrometer. A bucket and ladle for löyly, a sand timer, and a backrest are the finishing touches that make a sauna feel complete. Browse our sauna accessories to get kitted out.
Maintenance
Check for moisture around the door frame and floor junction seasonally. Sand bench surfaces lightly once a year if they start to look dry. Clean benches with a mild solution after heavy use, white vinegar and water works well. Remove and replace sauna stones annually.
Ventilate the sauna after every session by leaving the door ajar for 20 to 30 minutes. It's the single most important maintenance habit and costs nothing.
Final Thoughts
Building your own outdoor sauna is one of the better projects you can take on. The build is straightforward for anyone comfortable with residential framing, and the end result adds something genuinely useful to your property and daily life.
The key decisions, heater type, room size, ventilation, timber selection and bench heights are all worth getting right at the start. Everything else is just good building practice.
If you want to talk through heater sizing, room configuration, or materials before you start, get in touch with us at Kauri Point Sauna. We're happy to help you get it right.
Reference
Äikäs E, Holmberg R. Saunan lämpötilat ja ilmanvaihto (Temperature and ventilation of the Finnish sauna). VTT Technical Research Centre of Finland. VTT Tiedotteita — Research Notes No. 1431. Espoo, 1992. publications.vtt.fi/pdf/tiedotteet/1992/T1431.pdf
