Designing and building a traditional sauna is a rewarding project combining craftsmanship and cultural appreciation. This comprehensive guide will take you through each step, providing detailed insights and addressing frequently asked questions to ensure your sauna is functional, durable and authentic.
Part 1: Sauna Pre-Build Considerations. This section covers the planning stages, space requirements, planning permissions, mechanical and electrical considerations, materials, and important steps to consider before starting your sauna build.
Part 2: How to Build a Sauna (A Step-by-Step Guide). A general guide on how to build a traditional sauna with instructional images as a visual aid.
Part 3: Sauna Cleaning, Care & Maintenance
Part 4: Sauna Use & Well-Being
Contents Table
Part 1: Sauna Pre-Build Considerations
1. Planning Your Sauna, Mechanical & Electrical Considerations
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Choosing the Location: Indoor vs. Outdoor
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Space Requirements For a Traditional Sauna
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Regulatory, Mechanical & Electrical Considerations
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Planning Permission
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Building Regulations
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Electrical Considerations
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Cable Routing
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Ventilation
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Drainage
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FAQ
2. The Sauna Interior
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Wall Build-Up
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Fireboard
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Specialist Insulation Boards
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Vapour Sealing
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Sauna Battens
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Sauna Cladding
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FAQ
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Layout & Ergonomics
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Bench Configuration
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Door Location & Opening
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Windows/Glazing
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Heater Placement
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Material Choices
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Cladding
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Benches
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Door
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Sauna Heater & Extras
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Lighting
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Other Components (Tiling, Feature Walls, Heat Shielding)
3. Heating Options
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Types of Sauna Heaters & Installation Considerations
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Wood-Burning Sauna Heaters
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Electric Sauna Heaters
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Heater Sizing
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FAQ
4. Cladding Installation - The Sauna Walls & Ceiling
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Preparation
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Ceiling Cladding
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Wall Cladding
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Finishing Touches
Part 2: How to Build a Sauna (A Step-by-Step Guide)
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Pre-Installation Checklist
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Equipment You’ll Need
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Step-By-Step Installation Guide
Part 3: Sauna Cleaning, Care & Maintenance
Part 4: Sauna Use & Well-Being
1. Planning Your Sauna
Choosing the Location: Indoor vs. Outdoor
Decide whether your sauna will be inside an existing building or a standalone outdoor structure. While indoor saunas offer added convenience, finding a large enough space can sometimes be challenging. Outdoor saunas provide a more natural ambience and beautifully integrate into the garden, but could entail additional costs if you are also building the exterior structure. Consider what works best for you. If you build your sauna outside, plan the cable routes from the sauna to a consumer unit to power any electrical components, such as an electric sauna heater. If you intend to install a wood-burning sauna heater, it is strongly advised to consult a HETAS engineer and think about suitable flue connections at the early stages of planning.
Important points to consider when planning your sauna are the design, timelines, materials and budgeting, whether you have an existing, large enough space that can be converted into a sauna, or if additional work is required to create a dedicated sauna area. It is also advised to check planning permissions with your local authority.

Space Requirements for a Traditional Sauna
Ensure a sufficient area for the sauna. You may also wish to consider dedicating space to a changing area or an adjacent wet room. As a rule of thumb, a suitable internal height for a sauna is 2.1m from the finished floor level so that you can have two tiers of benching with a step. In a standard home sauna, we recommend the upper bench to be 1050mm from floor level, the lower bench 600mm, and the bench step at 300mm. As an example, a standard, comfortable 3-person sauna measures around 2m x 2m. However, sauna sizes vary, and you can have a smaller or a larger space than this. There is no minimum size requirement, but make sure there’s enough room for the bench system and the sauna heater with minimum required safety distances accounted for. All sauna heaters have specified minimum required safety distances to combustible materials. These are always outlined in the heater manual. You also want to make sure that access to and safe movement around the sauna are well-planned.
The wall build-up (covered in section 2) adds approximately 70-80 mm to each wall, so the original size of the space will be slightly reduced.
At this stage, you should check what power supply is available on site. Most UK homes have a single-phase 240-volt supply. Some homes and large commercial settings may have a three-phase 400V power supply. The type of power supply available will determine the maximum power (kW) of the electric sauna heater you can install.
Once the power supply to the property has been established, the next areas to check are your distribution board (consumer unit) and service head. The distribution board contains the fuses for the property, and a qualified electrician should be consulted prior to installation to confirm that the sauna's power requirements can be met. A qualified electrician can identify the maximum load capacity of your property and review existing circuits and their loadings to understand what spare capacity you have for your sauna.
The heater power requirements depend on the total computational volume of the space, which includes uninsulated areas, such as glass. Most sauna heaters up to 9 kW are suitable for single-phase installations and will draw up to 40 amps of power. However, some models may require a three-phase supply, so it’s important to check the specifications of each unit.
If you have a large sauna space and plan to include features like a glass wall, you will need a heater that requires a three-phase supply. In the case that a three-phase supply is not available, it may be worth considering a wood-burning sauna heater instead.
We have outlined important electrical considerations in the following section in more detail.

Regulatory, Mechanical & Electrical Considerations
Planning Permission
In the UK, small detached saunas usually fall under permitted development. However, always check with your local planning authority. If you intend to have a wood-burning sauna heater, check whether you are in a smoke-free zone.
Building Regulations
Ensure compliance with building and electrical regulations to guarantee safety and efficiency. Always review and refer to the instruction manuals for all products that you choose for the sauna. This includes the fireboard, insulation, lights, electric or wood-burning sauna heater, adhesives and accessories. Choose products that are suitable for the hot and humid sauna environment and specifically designed for saunas.
Electrical Considerations
All electrical components in the sauna should be discussed with and installed by a qualified electrician.
Check whether the available power supply is single-phase or 3-phase. This is a key consideration early in the planning process, especially if you’re installing an electric sauna heater. The type of power supply directly affects which heater models are suitable, and thus the recommended minimum and maximum sauna volume for each power rating (kW). Choosing the right-sized heater ensures your sauna is energy-efficient, safe and enjoyable.
The power (kW) of the sauna heater is essential to specify in the early planning stages. This can affect the maximum amount of uninsulated areas, such as windows or glass walls, incorporated into the design. The more glass and other uninsulated areas in the sauna, the more powerful the heater needs to be. For every square meter of single-glazed glass, you should add 1.5 m3 to the volume of the sauna. Double-glazed glass has a volumetric factor of approximately 0.75. This will give you the actual computational volume of the sauna, which is the volume to adhere to when choosing a sauna heater. We have covered different heating options and guidance on how to choose a sauna heater in section 3.
Most heater suppliers’ models up to 9kW can be installed on a single-phase power supply. Anything above requires a 3-phase supply.
Sauna Computational Volume Example
In this example, we have a sauna with internal dimensions of 2 metres by 2 metres by 2 metres, giving a total volume of 8m³. The front wall of the sauna is made entirely of glass, measuring 2m wide by 2m high, which equals 4m² of glass.
To calculate the Computational Volume, which is used to determine the appropriate heater size, we must consider any glass surfaces. Glass loses heat more quickly than timber, so it increases the effective size of the sauna for heating purposes. The adjustments are:
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Single-glazed glass adds 1.5m³ per 1m² of glass
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Double-glazed glass adds 0.75m³ per 1m² of glass
Sauna With Single-Glazed Glass
Component |
Calculation |
Result (m³) |
Sauna Volume |
2m x 2m x 2m |
8m³ |
Single-Glazed Glass Area |
2m x 2m = 4m² |
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Glass Adjustment |
4m² x 1.5m³ |
6m³ |
Total Computational Volume |
8m³ + 6m³ |
14m³ |
Sauna With Double-Glazed Glass
Component |
Calculation |
Result (m³) |
Sauna Volume |
2m x 2m x 2m |
8m³ |
Double-Glazed Glass Area |
2m x 2m = 4m² |
|
Glass Adjustment |
4m² x 0.75m³ |
3m³ |
Total Computational Volume |
8m³ + 3m³ |
11m³ |

Saunas are identified as a “special location” in the wiring regulations, meaning that special measures must be taken due to the unique environment and challenging conditions. Firstly, a residual current device (RCD) must be provided as circuit protection on all circuits except for the sauna heater. Section 703 of the wiring regulations explains that “RCD protection need not be provided for the sauna heater unless such protection is recommended by the manufacturer.” This is because a small amount of latent and ambient moisture in the heater may cause nuisance tripping. Without RCD protection, additional protective measures should be taken to ensure the cables are routed and installed safely. It is recommended that the supply cable have some form of mechanical protection, like steel wire armour (SWA), along its route from the consumer unit to a local point of isolation at the sauna. Inside the sauna, the conditions influence the specification of the cables and equipment. Cables should match or exceed the specification stipulated in the installation manual. For electric sauna heaters, the power supply cable is usually specified as H07RN-F rubberised cable or SiHF silicone rubber cable. Ensure your electrician consults both the installation manual and section 703 of the wiring regulations so they are familiar with the requirements of a sauna.
Most electric sauna heaters have a digital thermostat and a control unit, the placement of which both need to be considered. It is important to check the heater instruction manual and adhere to the rules on where to place the thermostat and the control unit.
Sauna heaters are one of the exceptions in the electrical wiring regulations. Always adhere to manufacturer's guidelines, use suitable cables and work with a certified electrician.
Additional Electrical Considerations
Safety
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Professional Installation: Always hire a certified electrician familiar with sauna electrical installations.
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Wiring: Use heat-resistant wiring and comply with local electrical codes.
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Electric Sauna Heater & Controller: Choose a suitable sauna heater for the space that you have with a compatible sauna control panel. Always adhere to the heater manufacturer’s installation guidance regarding safety distances and the heater controller’s instructions for thermostat and controller placement. More about choosing an electric sauna heater in section 3.
Lighting
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Fixture Selection: Choose vapour-proof, heat-resistant lights designed for saunas.
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Placement: Install lights to provide adequate illumination without direct exposure to intense heat. More about sauna lighting in section 2.
Ventilation
A well-considered ventilation system ensures good air quality, helps to circulate hot air, reducing stratification, regulates humidity and prevents mould growth.
Ventilation is one of the most crucial aspects of a long-lasting sauna, and creating an experience that is authentic and pleasant. In most cases, it is recommended to have two points of air intake and two points of exhaust. The ventilation set-up will depend on the shape and location of the sauna, as well as whether you have an electric or a wood-burning sauna heater.
A common ventilation system for a sauna with an electric heater:
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Intake Vent: A vent often near the base of the heater, always left open to allow fresh air in. Introducing fresh air above the top of the heater can also be an option, but it may interfere with your thermostat. Consult your heater’s installation manual for the best practice.
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Door Gap: A standard sauna set-up typically includes an approximately 15mm gap under the door to ensure proper air circulation. However, recommended door gaps can vary depending on the type of ventilation system. Passive ventilation and installations with a wood-burning heater often require a larger gap. The ideal ventilation depends on the unique shape, size, type, layout and location of the sauna; it’s important to tailor the system to your specific installation.
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Exhaust Vent: A vent in the back wall, diagonally opposite the heater, just below bench level (usually level with bathers’ feet when sitting on the upper bench). Keep it open at all times to enable airflow.
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Drying Vent: Position a vent in the ceiling or near the ceiling, typically opened after use, to help dry out the sauna.
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In-line Fan: The exhaust benefits from a high-temperature in-line extraction fan, preferably with adjustable speed. Aim for six air changes per hour.
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Metal Components: Use only metal ducting and fan components, as plastic may melt or fail under high temperatures.
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Single Penetration: The dump and exhaust vents can be connected in front of the fan to share a single wall penetration for simplicity.
An example ventilation setup for an outdoor sauna with passive ventilation:
INTAKE
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50mm gap under the entrance door, even if it opens to the outdoors.
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125mm vent leading to the base of the heater, or as near as possible. The vent may be installed as adjustable if the quantity of incoming cool air is a concern.
EXHAUST
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125mm adjustable exhaust vent(s) between the upper and lower benches, positioned diagonally opposite the heater.
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125mm vent in the ceiling, positioned directly above the other exhaust. This is a dump vent and is kept closed during normal operation. It can be opened to quickly dump heat or to dry out the sauna after use.
In summary, for both ventilation setups, the intake points can be a gap under the door and a vent in close proximity to the sauna heater. The two points of exhaust can be a vent at head height, which is sometimes considered the drying vent to allow the sauna to dry off after use. The second exhaust is often located lower down in the sauna, under the benches. This assists in bringing the heat and humidity down, preventing heat and humidity stratification. Multiple exhausts may be installed to account for larger saunas with multiple benches across different walls.

Drainage
Having a drain in the sauna facilitates easy cleaning, enables users to pour as much water as they wish over the sauna stones to create the soft steam, “löyly”/”leil”, and allows you to wash in the space if required. We recommend an anti-slip rated (R11 or higher at home settings, R12 or R13 in commercial saunas) tiled floor, but if you prefer a wooden floor, it is best to use a duckboard, as it allows for easy lifting and cleaning when necessary. The most suitable drainage solution will depend on the location of the waste outlet. A slot drain or a centrally positioned drain with equal falls towards the middle of the room may be optimal. Alternatively, the falls can be offset to keep the drain and trap less visible, positioning them discreetly beneath the benches.
FAQ
Do I need planning permission for an outdoor sauna?
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Generally, no, if it's a small, detached structure. However, always confirm with your local authority.
What is the ideal size for a home sauna?
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A standard, comfortable 2-3 person sauna measures around 2m x 2m, but sizes vary based on preference and available space, and they can be smaller or larger than this. We recommend a 2.1m finished internal height for the sauna. You may need to consider lowering the ceiling height if it is over 2.1m.
Why is ventilation crucial?
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It ensures a fresh air supply, enhances comfort, and prolongs the sauna's lifespan.
Can I use mechanical ventilation?
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Yes, but ensure the system is designed for sauna conditions.
How much air exchange is needed?
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Aim for around six air changes per hour for efficient airflow and temperature control.
Can the low-level exhaust and drying vent share the same duct?
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Yes, they can be connected to one wall outlet for a simpler, more efficient design.
2. The Sauna Interior
Wall Build-Up:
The interior wall build generally includes a fireboard, insulation, vapour barrier, sauna battens and the interior sauna cladding. This adds approximately 72-84 mm to each wall.
Fireboard
If the sauna room has timber or stud walls, it is worth considering covering them with a fireboard for safety reasons. A fireboard isn’t necessary, especially if the space has blockwork walls. Insulation is installed on top of this. The easiest and most effective way to insulate your sauna is by using specialist sauna-safe insulation boards, such as Finnfoam or Kingspan Sauna-Satu.
Specialist Insulation Boards
Standard PIR insulation boards are not heat-safe beyond +60- 80°C, whereas sauna-safe insulation boards, such as Kingspan Sauna- Satu and Finnfoam, are heat-safe up to +100°C for long periods, and up to +250°C for short periods. Standard PIR insulation can also begin to off-gas toxic hydrogen cyanide after being exposed to hot air. Sauna insulation boards also act as a vapour seal. The boards are foil-faced and backed, allowing easy sealing using aluminium tape and preventing thermal bridging from occurring in the interior structures. They stop condensation from accumulating and the risk of mildew, mould, and rot growth on the timber structures.
Insulation boards are easy to fix on the walls with stainless screws and insulation washers, and can be joined and sealed with expanding foam (i.e. Pinkgrip or Everbuild) and aluminium foil tape respectively. Another alternative is to use rock wool and aluminium foil vapour barrier.

Sauna Battens
To let air circulate between the insulation and the interior cladding, battens are secured onto the insulated and vapour-sealed layer, perpendicular to the sauna cladding. This creates a gap between the insulation boards and the back face of the interior cladding. For vertical cladding, install specialist-shaped rhombus sauna battens that allow any excess water and condensation to run down the vapour barrier, over the top of the chamfered edge of the batten and down the grooves on the back of the cladding. Alternatively, cross-battening may be done to maintain airflow and drainage behind vertical cladding. Sauna battens should be at least 20 mm thick and 45 mm wide. A suitable batten spacing is 400 mm. Thermo-treated pine battens provided additional stability to the substrate, reducing the risk of cladding moving due to battens warping or shrinking.
Sauna Cladding
After the insulation and sauna battens have been installed, you can secure the cladding onto the battens with stainless steel fixings that can be hidden within the grooves of the cladding. More about the installation of cladding in section 5.
Corner Mouldings
Sauna corner mouldings are an important finishing touch that enhances both the appearance and durability of your sauna. As an example for SI 25x25 mm mouldings, the mouldings are installed in the interior corners where the cladding panels meet, covering any gaps and creating a clean, polished look. These are screwed on with stainless steel “lost head” flooring screws.
The installation method depends largely on your chosen moulding. Some mouldings require installation during the cladding process, so may be pinned or screwed to the battens. Other mouldings are pinned and glued after the cladding is installed. Use stainless steel finishing nails or a wood-safe adhesive rated for high temperatures to secure them in place.
Sauna corner mouldings are often overlooked in a sauna build, but they provide a clean, finished look by neatly concealing any gaps or cut edges in the cladding.
FAQ
Is insulation necessary for a sauna?
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Yes, it ensures efficient heating and energy conservation.
Can I use standard household insulation?
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No, only use high-temperature-rated, sauna specialist insulation or rock wool and aluminium foil for safety and performance. Regular PIR insulation can off-gas harmful chemicals in high temperatures.
Are there specific woods recommended for saunas?
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Yes, we recommend thermally-treated timbers and wood types with natural qualities that make them suitable for higher humidity and heat environments, such as aspen, alder and Western red cedar. They resist warping and remain comfortable to the touch at high temperatures. More about wood types later in this section under Material Choices.
Layout & Ergonomics (Bench Design, Entrance, Windows & Heater Placement)
Bench Configuration
Sauna benching can be as simple or as sophisticated as you like. From the classic two-tier layout (upper and lower bench on one wall with a step) to L-shaped or U-shaped configurations, opposing benches with raised floors, or even custom-designed body-form loungers, the options are wide-ranging and flexible to suit both space and style.
As heat rises, in a sauna, this means the hottest air collects in the upper half of the room. Even with effective ventilation, there will always be some temperature differential between the upper and lower regions. No sauna will ever reach a perfectly even temperature (an isotherm), no matter how long it runs. That’s why traditional sauna design prioritises generous upper bench space. It’s where users will spend the majority of their time. Many sauna cultures tout the importance of bench heights that make sure the bathers’ feet are higher than the top of the heater when sitting on the upper bench. This helps to avoid disappointing cold feet and “Löyly”/steam that only warms the torso.
In a typical home sauna, we recommend the following dimensional guidelines:
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Ceiling height: 2100 mm from finished floor level
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Upper bench: 1050 mm from floor level, and at least 600 mm wide
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Lower bench: 600 mm from floor level, approximately 400 - 500 mm wide
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Step: 300 mm from the floor level
There are multiple bench design options for saunas from a classic two-tier set-up to raised floors.
Door Location & Opening
The door should open outward for safety reasons and be placed near the heater for optimal air circulation. Sauna doors are often timber-framed with approximately 8 mm toughened glass. The glass can have additional features and treatments - the colour and finish may be customised from clear to tinted bronze or darkened for additional privacy. The door should have a 15 or 50 mm gap at the bottom of the glass for fresh intake to the sauna.
The door aperture is usually 10 mm larger than the frame. As an example, if your door measures 690 x 1990 mm, the opening should be 700 x 2000 mm. This will, however, depend on the door.
Windows
Incorporating windows into the sauna design is an excellent way to bring in natural light and create a more spacious and open feel. Bear in mind that windows and doors are uninsulated areas that should be accounted for when calculating the computational volume of the sauna. A sauna-safe double-glazing solution is argon-filled and silicone-sealed. The formula we tend to use in our bespoke installations is double-glazed 6-12-6, with silicone-sealed aluminium spacer.
Heater Placement
Where you place the sauna heater depends on the design, bench set-up, the heater model and whether the heater is wood-burning or electric. The heater should be positioned for easy access, allowing bathers to comfortably pour water over the hot stones to create the pleasant “löyly” - the gentle steam that rises from the heater. At the same time, it must be placed in a location that ensures a safe distance from anyone entering, sitting in or moving in the sauna. Make sure you check and maintain the manufacturer’s recommended clearances to combustible materials, such as wooden walls and benches, for safety and performance. Consider additional heat shielding and safety rails to install around the heater. Depending on the heater model, you may be able to mount it on the wall, into the sauna benching, or have it as a freestanding centrepiece. We have covered different sauna heater options and how to choose the best heater for your sauna in section 3.
Consider the door location making sure it opens outwards, heater placement and safety rails or heat shielding and windows when designing the optimal layout for the space.
Material Choices
Wood/Timber
Use wood types that are suitable for the sauna environment, resist high temperatures and don’t weep resin. The most common sauna wood types are:
Benches
You can choose the same wood type as the wall and ceiling cladding for a uniform look or mix different timber species to create contrast and unique design features. We recommend spruce or thermo spruce for the bench framing timber. Consider whether you require adjustable feet and additional boards for the backrests. You can build every component of your benching, or opt for cost-effective, ready-made bench elements.
Door
Choose a specialist sauna door built from durable and heat-safe materials. Glass sauna doors are most common in indoor saunas, but you can also opt for a wooden door. Glass finishes range from clear to bronze, grey and frosted glass. A high-quality sauna door is often made of tempered glass, and the handles are either a stainless steel and wood combination or wood on both sides. You want to avoid metal handles inside the sauna, as these will get too hot to touch. The frames are made of popular sauna woods, such as alder, aspen, pine or their upgraded thermo-treated alternatives.
Sauna Heater & Extras
The sauna heater is the heart of the sauna. If you opt for an electric sauna heater, you will need a compatible controller and suitable cables. For a wood-burning heater, a specified flue kit and potentially some heat shielding should be purchased together. Sauna stones for both electric and wood-burning sauna heaters are often purchased separately. Additional extras include heater safety railings, mounting collars and decorative stones. More about the heating options and choosing the right sauna heater is in section 3.
Lighting
Sauna lighting is another specialist field. Lighting in a sauna should create a calm, inviting atmosphere while withstanding the extreme heat and humidity. Popular sauna lighting options include:
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LED Sauna Spotlights and Strip Lights: Energy-efficient and specified for saunas, LED spots and lighting strips are ideal for most setups. Strip lights are often mounted onto the bench lips or backrests, while most spotlights can be installed in the ceiling and on the benches. Check the maximum installation heights and temperatures, as these will affect where in the sauna you can install the lights.
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Wall and Corner Lights with Wooden Shades: A classic look, typically placed in corners for a warm, diffuse glow.
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Fibre Optic Lighting: A premium choice that brings soft, ambient light.
Other Components (Tiling, Feature Walls, Heat Shielding)
In addition to the main structure and essential materials, there are several optional components to consider when designing your sauna:
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Tiling & stone may be used on floors or wall sections for durability, safety, design features or splashbacks behind the heater.
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Wooden feature walls can add visual warmth and character to your sauna design, often using contrasting timber or unique profiles to create a focal point.
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Heat shielding is essential when the heater is close to combustible materials. Proper shielding using stainless steel plates ensures safety and compliance with installation regulations.
Choose materials that are specified for saunas and create a design that aligns with your personal preferences while adhering to safety regulations.
3. Heating Options
Types of Sauna Heaters & Installation Considerations
Wood-Burning Heaters
A wood-burning sauna stove provides a traditional experience with a pleasant aroma. Ideal for outdoor saunas but requires a chimney and fire safety measures, as well as access to firewood.
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Flue Kit: A wood-burning heater requires a compatible chimney or a flue kit. It is always advisable to consult a HETAS engineer and have these components professionally installed. Always refer to the manufacturer’s instructions for safe installation.
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Heat Shielding: Depending on the placement of the heater, you may want to consider some heat shielding for the walls around the heater, around the flue and on the floor if it is made of wood.
Wood-burning heaters guarantee a traditional experience. Image by HUUM.
Electric Heaters
An electric heater offers precise temperature control and is suitable for both indoor and outdoor saunas.
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Power Supply: As mentioned in the earlier sections, check the site’s power supply and whether it is single-phase or three-phase and has a suitable capacity for the power of the required sauna heater.
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Cables & Isolator: Ensure you have all the correct electrical components, such as an isolator, a rubberised cable, as well as an armoured cable running to the consumer unit. These are best discussed with the electrician.
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Controller: Unless you opt for an electric heater with manual dials, an electric heater requires a compatible sauna control unit. The options vary from wall-mounted external control panels to advanced Wi-Fi controllers that allow you to switch your sauna on from your phone. You can read our guide on how to choose the best heater controller for your sauna.
Modern electric sauna heaters come with flexible control options, including Wi-Fi connectivity, allowing you to conveniently operate your heater from your smartphone.
Heater Sizing
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Calculation: Match heater power to the computational volume of your sauna. The computational volume of the sauna takes into account any uninsulated areas, such as windows and glass doors in the sauna.
Read our Buyer’s Guide to Sauna Heaters to help you choose the best heater for your sauna.
FAQ
Which is better: A wood-burning or an electric sauna heater?
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This is up to personal preference and your sauna. Wood-burning sauna heaters provide authenticity and a traditional experience. The up-front cost is generally higher than that of an electric sauna heater, as you need to purchase a suitable flue kit and potentially additional heat shielding. However, there are no ongoing electric costs. You just need to ensure you have access to firewood to heat the sauna.
- Electric sauna heaters provide modern convenience and are easy to maintain and keep clean. You also need to consider controlling options and the available power supply. Most electric heaters above 9 kW require a 3-phase power supply, which may limit the size of an electric heater you can install in the sauna.
Read more about our sauna heaters and our brands.
How do I choose the right heater size?
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Calculate the sauna’s computational volume (see section 1. Planning Your Sauna - Electrical Considerations), accounting for all glass and uninsulated surfaces, and selecting a heater that fits within the recommended room volume outlined by the heater manufacturer. If you’re debating between two power ratings, we recommend opting for the higher-power heater. Choosing an underpowered heater might seem economical at first, but it can lead to disappointing performance and costly issues. You’ll struggle to reach and maintain hot sauna temperatures, reducing the overall experience. Additionally, the heater will be forced to work harder than intended, causing the heating elements to burn out faster and leading to higher maintenance and replacement costs over time. Always size your heater appropriately for the computational volume of your sauna.
4. Cladding Installation - The Sauna Walls & Ceiling
Pick a cladding profile of your choice. You can opt for a traditional STS4 or STP cladding profile, or add a feature wall using more specialist profiles, such as the STEP profile, wooden feature wall panels or even tiled finishes as splashbacks behind the sauna heater. Most sauna cladding panels have an easy-to-install tongue and groove design. It is important to install the sauna cladding with precision to ensure the longevity of your sauna. We recommend treating the wood sauna with paraffin oil to protect it from humidity and heat. It is best practice to repeat the paraffin oil treatment on a yearly basis.
Always refer to the recommended wastage allowance for each timber species, as the approximate materials loss during installation can vary between 5 and 15%.
The installation of the sauna cladding is perpendicular to the batten orientation. If you wish to install the wall panels horizontally, make sure that the battens have been installed vertically. For a vertical cladding installation, the battens should be installed horizontally.
You can use a narrow crown staple gun and stainless steel staples (type 90), or a brad nailer with stainless steel brad nails (18 gauge) for the cladding installation. Some cladding profiles work with tongue and groove cladding clips which are nailed or screwed to the battens.
Preparation
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Treating the Timber: Sauna timber can be protected further from moisture and dirt by sealing it with a light mineral oil, like paraffin oil or a water-based sauna wax. Apply the treatment to all faces and ends of the sauna cladding panels to protect the wood prior to installing the cladding
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Cutting for Fixtures: Drill holes for cables or ventilation before installation.
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Check the Batten Spacing: Make sure the battens have been installed straight and level before beginning the cladding installation. A suitable distance between the sauna battens is 400 mm.
Ceiling Cladding
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Installation Order: Start with the ceiling, extending boards beyond the wall cladding plane.
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Attachment: Secure boards with nails through the tongue side, concealing fixings.
Wall Cladding
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Alignment: Install wall boards with a 10 mm gap at the bottom to prevent moisture absorption.
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Vent Covers: Secure sauna vent covers over ventilation openings.
Finishing Touches
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Corner Mouldings: Attach around the ceiling perimeter and corners for a polished look. For most cases, install the ceiling corner mouldings first, then the ceiling cladding. After that, fit the vertical corner moulding and finally install the wall cladding.
The installation of the sauna cladding is perpendicular to the batten orientation.
5. Top 10 Mistakes New Sauna Builders Make
Building your own sauna is an exciting and rewarding project, but it comes with its fair share of challenges. Avoiding these common pitfalls can save you time, money, and frustration while ensuring a far better end result.
1. Skipping Ventilation
Proper airflow is essential for a comfortable and healthy sauna. Neglecting ventilation leads to stuffy heat, uneven temperature distribution, and potentially mould growth. A good ventilation plan ensures fresh air circulation, enhances “löyly” or the steam quality, and prolongs the life of your sauna.
2. Underpowering the Heater
Underestimating your sauna’s computational volume, which includes glass and uninsulated surfaces, often results in an underpowered heater. This means longer heat-up times, disappointing steam and a low temperature, and an overworked heater. The elements may burn out quickly, leading to frequent maintenance and higher long-term costs.
3. Using the Wrong Insulation
Not all insulation is suitable for sauna use. Materials like PIR board can off-gas toxic chemicals when exposed to high temperatures. Always use sauna-safe insulation, such as specialist sauna insulation boards like Finnfoam or Kingspan Sauna-Satu, or mineral wool, paired with a proper vapour barrier.
4. No Drainage Plan
Water spills are inevitable in any sauna, whether from steam, washing, or ladling water onto the stones. Without proper drainage, moisture can accumulate and cause long-term damage. Plan for floor drainage from the outset.
5. Poor Bench Placement
Bench height and positioning matter more than many realise. If your feet sit below the top of the heater, you’ll likely experience cold feet and poor steam circulation. A tiered bench layout, with the main bench above heater level, makes for a far more enjoyable sauna.
6. Improper Cable Choices
Standard household wiring isn’t built to handle sauna temperatures and can degrade or melt. Use only heat-rated rubber or silicone cables designed specifically for high-heat environments to ensure safety and reliability.
7. Forgetting the Fireboard
Omitting a non-combustible fireboard behind or near your heater is a serious safety oversight. Fireboard protects surrounding walls from excessive heat and significantly reduces fire risk—an essential part of safe sauna design.
8. Poor Heater Placement
The position of the heater plays a crucial role in how heat and steam circulate within the sauna. Incorrect placement can lead to uneven temperatures and weak "löyly." Ensure the heater is installed in a location that promotes effective air movement and steam distribution, always following the manufacturer’s clearance and positioning guidelines for optimal performance.
9. Overusing Glass
Glass looks elegant and modern, but it greatly increases the sauna’s heat volume, putting extra demand on your heater. If you’re incorporating glass, either double-glaze to improve insulation or size up the heater accordingly to maintain proper performance.
10. Ignoring Post-Sauna Drying
Failing to ventilate and dry the sauna after use can lead to long-term issues with damp, mould, and timber rot. Always open vents or doors after each session to allow moisture to escape and surfaces to dry completely.
Part 2: How to Build a Sauna (A Step-by-Step Guide)
Before starting your home sauna project, we strongly recommend reading through this entire step-by-step guide to gain a clear understanding of the process. This guide is intended as a general resource to help guide your build. Please note that there are multiple methods and approaches to constructing a sauna, and the best practice may vary depending on your specific space, requirements, and local regulations.
This guide provides general advice for informational purposes only and should not be considered as a definitive or exhaustive instruction manual. We always advise consulting with a qualified professional, such as a certified electrician for electrical installations or a HETAS-registered engineer for wood-burning sauna stoves and flue systems, to ensure your build is safe, compliant, and tailored to your setup.
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Pre-Installation checklist
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Equipment you’ll need
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Step-by-step guide
Pre-Installation Checklist:
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Check that you have all the necessary equipment ready
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Note down the critical dimensions, including stud-to-stud distance, openings for ventilation, the door and windows, and the distance between the sauna battens
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Check the cable routes and the location of all electrical components
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Check the ventilation routes and location of vents
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Note down the surfaces that require fireboard (if used)
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Note the wall build-up for each wall and the ceiling
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Check components that require additional preparation (i.e., feature walls or tiled splashbacks)
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Check the battens and cladding orientation (these must be perpendicular to each other)
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Note the glazing line and spacers required for mounting the channels
Equipment you’ll need:
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Low-tack painters’ tape
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Tape measure
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Laser measure
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3-axis laser level
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Spirit level
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Folding square
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Stainless steel nails
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Narrow crown stapler/Brad nailer
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Pencil
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Combi Drill
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Impact driver
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Multitool
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Saw
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Tape measure
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Hammer
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Quick clamps
Step-by-Step Guide
NOTES
- The images supplied in this piece are meant as a visual aid only and should not be used for scaling or dimensioning.
- In many of the following images, the ‘front’ walls and/or ceiling are hidden to aid visualisation. Processes required of the ‘back’ walls and/or ceiling are likely required of the ‘front’ walls also.
- Where the studwork walls have been hidden, their positions have been marked on the images for reference.
- If you are ever uncertain of any measurement or detail, please contact Finnmark Sauna.
1. Construct Any Required Studwork
Make sure the walls and ceiling are plumb, level and square.
2. Fix Electrical Cables
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Possible cables include the electric heater, controller, lighting and mechanical ventilation
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Check all cable routes and mark the location of each electrical component
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Fix the electrical cables
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You can also fix the extractor fan/fans at this stage
The electrical cables for the sauna heater and lighting should be fixed by a qualified electrician. This phase will only include fixing the lighting cables if your sauna has a wood-burning heater.
For an electric sauna heater, the cables usually include:
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The rubberised heater cable (i.e., H07RN-F): Runs from the isolator to the electric heater or from the isolator to the heater’s contactor box and another from the contactor box to the heater location.
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A cable to the ventilation fan: Rubberised 3 core 1 mm2 H07RN-F if the cable runs from the heater. 3 core 1 mm2 flex cable if it runs from a contactor box located outside the sauna. It may be helpful to fix the ventilation fan at this stage as a target for routing the cable.
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A controller cable: If the sauna has a control panel located externally to the sauna, this cable from the heater location or the heater’s contactor box should be routed to the desired control panel location.
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Thermostat cable: Refer to the sauna controller manual to determine the correct location for the thermostat within the sauna, and run the cable accordingly.
Ensure pre-installation specification has been met
3. Ventilation routes + Holes
The ventilation system usually consists of a passive air intake low down near the sauna heater and a mechanical extraction vent in the opposite corner of the sauna at a high and a low level. Make sure all the joints are air and vapour-tight, any bends must be gradual so they don’t restrict airflow, and the ducting routes must be constrained. Fit the exterior vent covers in place
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Ensure proper drainage gradient - Route ventilation ducts with a slight downward gradient to allow any condensation to either drain safely out through an external vent or return into the sauna where it can evaporate. This prevents moisture buildup inside the ducting.
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Use gentle bends in ducting - Avoid sharp turns. All bends should be gradual to maintain consistent airflow and prevent unnecessary restrictions within the ventilation system.
- Keep ducting neat - Plan your ducting layout carefully. Routes should be as short and direct as possible, with minimal crossings or clutter. Secure cleanly along walls or framing, keeping the installation tidy and unobtrusive.
4. Fire-Rated Plasterboard
Measure and cut the fireboards to size. Measure and cut the penetrations for the cables and ventilation. Begin with the ceiling with screws at 200 mm centres and 150 mm centres at the edges of the boards. Install the wall boards with screws at 300 mm centres and 200 mm centres at the edges of the boards. Seal all the joints, holes and around the penetrations using intumescent sealant. It is best practice to mark the joist locations onto the wall to make it easier to find them when installing the insulation. Finally, mark the stud locations on the floor. You can use masking tape.
5. Insulation & Vapour Barrier
Specialist sauna insulation boards, such as Kingspan Sauna-Satu or Finnfoam, are 30 mm thick and have tongue and groove edges. The boards are usually 1200 mm long. The insulation boards can be installed vertically or horizontally. Ensure that all of the joints are sealed according to the manufacturer’s instructions. Use low-expansion foam around the edges and joins, as well as aluminium foil tape on the face of the joins. All cable and ventilation penetrations should be sealed with foam and aluminium tape.
If the insulation boards are installed on masonry, use additional screws and insulation washers or use concrete screws to secure the boards.
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Measure and cut the insulation boards
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Apply low-expansion foam into the groove sides of the insulation boards
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Fix the boards to the walls and ceiling using stainless steel screws and insulation washers
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Cut holes for the ventilation
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Pull the ventilation through the insulation boards
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Cut off the excess foam when it has set
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Apply aluminium foil tape to the joins
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Seal the corners of the room
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Seal around cable penetrations
You can find full installation instructions for sauna insulation boards under the downloadable files on the Kingspan Sauna-Satu product page.
Fix insulation to interior surfaces of sauna (front walls and ceiling hidden)
6. Battens
Battens leave a gap between the insulation boards and the interior cladding, allowing condensation to drain off the vapour barrier onto the floor. They also provide a foundation to fix the cladding to. The battens are installed perpendicular to the orientation of the cladding.
If the battens are fixed into masonry, we recommend using concrete screws or wall plugs with wooden screws.
The battens should be kept clear of the room corners by a minimum of the thickness of the batten.
Fix battens to walls to support the benches
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Measure and cut the battens to the required length, keeping them short of the corners by the thickness of the batten
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Pilot drill the holes at 400 mm spacings
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Fix the battens to the ceiling and the walls using 100 mm screws. Be mindful not to overtighten the screws
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Add battens to areas that require a strong fixing substrate behind the cladding. As an example, if you intend to fix a wall-mounted electric sauna heater
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Level the ceiling battens
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Plumb and square the wall battens

Fix battens to walls and ceiling
7. Second Fix of Electrical Cables
This step often includes routing heat-resistant cables, such as the lighting cables, thermostat cable, electric heater controller cable and the door switch cable, along the vapour barrier and into position before installing the ceiling and the wall cladding. Please note that all electrical connection work in the sauna should be carried out by a qualified electrician.
8. Decorative Wall Panels (If Included in the Design)
If you’re including decorative wall panel features, such as a splashback behind the sauna heater or a feature wall made of log stacks or decorative wooden panels, they should be installed before the rest of the wall cladding. Decorative, wooden feature wall panels are usually applied to a plywood backing. They can be dimensioned, sawn and fixed to the battens by hiding screws between the decorative feature wall elements on the boards.
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Begin by measuring the required size of the decorative piece, accounting for required mouldings and a 15 mm gap to the floor.
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Fix the dimensioned panels in place, keeping the fixing centres no greater than 300 mm apart.
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If you’re intending to use decorative wall panels on multiple walls, or if you’re using multiple wall panel pieces, pay close attention to the order of installation and whether any additional mouldings are required. This will depend on the design of your sauna.
9. Corner Mouldings (Only Specific Corner Moulding Profiles)
Only specific corner mouldings, including the SI Moulding 25 x 25 mm and Internal Corner Moulding 27 x 27 mm for 15 mm cladding, require the installation of the moulding to occur before the cladding installation. If you’re not using either of these, you can move on to step 10.
SI Moulding 25x25 mm and Internal Corner Moulding 27x27 mm Installation:
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Treat the mouldings with paraffin oil
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Measure and cut the mouldings to length with mitres at the corner joints
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Keep the vertical corner beads at least 15 mm from the floor
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Ensure any breaks are gently sanded for a smooth finish
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Dry fit the mouldings until they are the correct length and keep tight joints in the corners. Fix the mouldings to the battens
10. Glazing Channels, windows and frames
With most installations, it is good practice to install the glazing channels, window and door frames before the cladding. This allows the cladding to be finished tightly to the glazing elements in the sauna.
Glazing Channels:
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Begin by measuring the head of the glazing aperture and cut an aluminium channel to length. A chop saw is recommended for a clean cut.
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Pilot drill and countersink the fixing holes in the channel at a hole spacing of approximately 200 mm - 300 mm.
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Align and fix the channel in place.
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Measure the lower channels, ensuring the opening between the channels and the wall is equal to the width of the door and its required gaps. Cut the channels to length.
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Insert the wall plugs and screw the channels in place.
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Do the same with the vertical channels.
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Once all of the channels are in place, remove the floor channels until the glazing stage of the sauna installation (step 16).
Exterior Glazing
External glazing should be installed before sauna construction begins to ensure a proper seal with the sauna’s vapour barrier. As glazing requirements can vary depending on the sauna’s location and design, they should be planned carefully. uPVC windows are not suitable for use inside the sauna and must be protected with an internal timber or aluminium-framed window to withstand high heat and humidity.
Timber Door Frame
The timber door frame should be installed before cladding begins, ensuring it is square, level, and securely fixed. This allows the wall cladding to be neatly fitted up to the frame for a clean finish. As with all timber elements in the sauna, the frame should be made from suitable heat- and moisture-resistant wood.
11. Cladding
The cladding stage involves the installation of tongue and groove sauna cladding, mouldings and trims. Make sure that the cladding orientation is correct and perpendicular to the batten orientation.
Make sure to note the centre points of penetrations, such as ventilation holes from adjacent battens or cladding.
Begin with the ceiling cladding and move on to the wall cladding afterwards.
Clad the walls and install the vent covers
12. Ventilation Covers
Ventilation covers, louvres, grilles, and valves are the final stage of installing the ventilation in the sauna. Check whether they require additional sealing between the ducting and the duct covers.
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Seal the inside of the ducting to the cladding using a male coupler cut to length by using aluminium foil tape
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Wooden disc valves may require a metric thread glued into a captive nut on the wooden disc
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Screw the back plate to the cladding for any disc valves
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Screw the disc valve into the backplate until it’s approximately 15-20 cm from the backplate
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Aluminium louvre grille vents should be installed into the cladding with the grilles level and the sloped fins pointing down
13. Benches & Heater Guards
The sauna bench system may take as little as 2 hours to complete if you have a simple, two-tiered bench set-up along one wall. Allow for a full day for more complex bench designs.
Floating benches are often installed onto bearers that are secured to the walls, or it can be installed onto frames and bench legs.
The benches should fit in the sauna with an even 5 mm gap between the bench boards and the wall cladding. Make sure to install all bench elements level and plumb. If you’re using sauna strip lighting, they can be installed together with the benches at this stage.
Install the benches
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Begin by installing the upper bench
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Armrests (if any)
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Backrest
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Lower bench
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Bench skirting (if any)
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Step or raised floor if the design incorporates one
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Heater Guard
14. Lighting
Fix the lights and drivers in place, adhering to the manufacturer’s installation manual.
15. Heater
Electric sauna heaters must be installed by a qualified electrician. It is advised to consult and work with a HETAS engineer when installing a wood-burning sauna heater.

Fix the heater and heater guard in position
16. Glazing
The glazing may include windows and a sauna door with wooden frames or aluminium channels. uPVC is not suitable inside a sauna.
Make sure you handle the glass with care and protect your hands and eyes.
Glazing panels inside the sauna should be sealed with glazing silicone.

Install the glazing, including the door
17. Clean Up the Sauna
Clean the sauna thoroughly and inspect all components.
Equipment recommended:
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Vacuum cleaner
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Wonder wipes
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Microfibre cloth
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Glass cleaner
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Steam iron
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Sander
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Paraffin oil
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Fillers/wax
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Wood repair pens
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Mitre bond glue
Recommended Steps
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Fill pinholes in the cladding, trims and window beads using an appropriate colour matched wax or filler
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Sand any dents and scratches
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Wipe over any sanded areas with a cloth
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Oil the timber after filling dents and sanding
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Vacuum the sauna
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Clean glass surfaces
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Check that the lights are working properly
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Turn on the heater to check that it works properly
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Check that the fan is working
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Ensure the lower vent is open
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Once the heater is up to temperature, pour a little bit of water over the hot stones to clean any remaining dust or residue.
Additional Steps
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Heat Shielding
This step is only applicable for installations where the sauna heater’s minimum required safety distances to combustible materials, such as wood, cannot be observed. This could be the case if the heater is positioned close to the wall or where the ceiling is too low above the heater. The heat shielding should be made of non-combustible finishes, such as tiling or specialist metals or stainless steel heat shields.
Part 3: Sauna Cleaning, Care & Maintenance
After your sauna session, you should ensure that the sauna is allowed to dry off thoroughly. If the space is not properly dried off, you will get issues with mildew or damp. There should be no standing water, all squeegeed into a floor drain or mopped dry.
You can run the heater for longer than the intended session to allow the space to dry further and for the ventilation to continue running. Once the sauna heater cycle has finished, you can also open windows and, in some cases, open the sauna door to help the space dry off further. However, do not do this if you have an anteroom, shower room or room adjacent where heat or steam exposure could cause damage.
Any duckboard present should be lifted, cleaned and placed safely to dry. The floor should be mopped with water and a suitable floor cleaning detergent for the surface. The leftover detergent mopping water can be poured down the sauna drain, if present, to ensure the waste trap remains full and sterile.
Carefully wipe down any dirty or wet sauna bench boards using a mixture of sauna cleaner and water. See the bottle for instructions. Ensure rubber gloves and personal protective equipment are worn when using detergents in line with the guidance on the bottle. Use a soft, non-terry cloth or sponge to prevent the wood catching on the fibres and ripping splinters from the wood. Particular caution should be taken when wiping down cladding, as catching and ripping splinters from the wood is of greatest risk on cladding.
Residues can build up from the steam on glass windows, doors and glass walls. You should periodically wipe these down with a glass cleaning fluid to remove any oily water marks.
Do not attempt to touch or clean the heater until at least a day after the sauna session. You should not need to clean the heater after each session unless you have hard water causing limescale marks, but if you have hard water, you should only pour this on the stove once it has been descaled to prevent limescale from damaging the heater. Do not attempt to dry any sauna items, equipment or textiles above the heater, near the heater or on the heater guard. This is a significant fire risk, even when the sauna is cooling.
Read our Complete Guide to Cleaning Your Sauna for more information.

Part 4: Sauna Use & Well-Being
A sauna should be enjoyed, not merely tolerated. For a positive experience, it’s important to use the sauna when in good personal health and to listen to your body throughout each session. Sauna temperatures should be set with consideration for all users, ensuring a comfortable and relaxing environment. Most users should be able to relax comfortably for 15-30 minutes, with water regularly added to the stones for steam and humidity.
You should not use the sauna when feeling unwell or ill. Contrary to popular belief, sauna use during illness, especially when combined with a cold plunge or other cryotherapy, can actually worsen your condition. While regular sauna use may help support your overall health and immunity, sessions should only be enjoyed when you’re in good personal health.
Avoiding Substances
Saunas should not be used in conjunction with alcohol, narcotics, stimulants or pain killers, as these substances impair your body’s ability to regulate heat and can increase health risks.
Listening to Your Body
You should never force yourself to stay in the sauna beyond your comfort level. A safe and enjoyable sauna experience depends on listening to your body and exiting the sauna when you feel the need to cool down or rest.
Sauna Use & Children
In Finland, it’s common for children as young as six months to be introduced to the sauna at lower temperatures and under close supervision. While Finnmark Sauna does not provide an official minimum age, we strongly recommend that anyone under 18 is always supervised by a responsible adult. Parents choose to bring children into the sauna at their own risk.
Medical Conditions and Sauna Use
We do not recommend sauna use for individuals with cardiovascular conditions. If you have any other medical conditions or are taking medication, sauna use should only proceed with the approval of your doctor. Even then, usage should begin gently and gradually, with increases in temperature, duration, and humidity introduced in small, careful stages to avoid exacerbating any health issues.
Pre- and Post-Sauna Hygiene
Always shower before and after sauna use. Avoid using heavily perfumed or harsh soaps, shampoos, or shower gels, as your skin and pores will be more sensitive after exposure to heat.
Hydration and Cooling Down
Ensure you are well hydrated before entering the sauna and replenish fluids afterwards. We recommend pairing sauna use with a cold plunge, cold shower, or other cryotherapy treatment for an invigorating and balanced thermal cycle. However, it’s best to end your session by warming gently. Rest on the lower bench of the sauna and allow your body to reach a natural, comfortable temperature. Avoid finishing while still very hot or very cold, as this can leave you sweating or shivering long after your session ends.
Read about Sauna Etiquette and explore utilising Sauna for Health to learn more.

Building a sauna requires careful planning, high-quality materials, and adherence to safety regulations. Whether you choose an indoor or outdoor sauna, following these steps will ensure a durable, efficient, and relaxing space. By considering insulation, ventilation, and the right heating system, you can create the perfect sauna retreat for years to come.
If you prefer professional help from start to finish, why not consider a bespoke sauna installation service? Get inspired by our sauna installations.