How to Build Your Own Sauna - Step by Step with Finnmark

Planning Considerations & Building Regulations

In the UK, small detached saunas typically fall under permitted development, but it’s important to confirm this with your local planning authority before proceeding. If you plan to install a wood-burning sauna heater type, check whether your area is designated a smoke-free zone, as this may affect your installation options.

Equally important is ensuring full compliance with building and electrical regulations to guarantee safety and optimal performance. Always carefully review the instruction manuals for every product you choose, whether it’s fireboard, insulation, lighting, electric or wood-burning sauna heaters, adhesives, or sauna accessories. 

Selecting materials specifically designed for the hot, humid sauna environment is essential to maintain durability and safety throughout your sauna’s lifespan.

Electrical Considerations

All electrical work for your sauna should be handled by a qualified electrician. It's important to check early in the planning process whether your power supply is single-phase or three-phase, as this directly affects which sauna heaters are suitable for your space. This is particularly important when it comes to Electric Heaters.

Heater Power Rating

The heater’s power rating (kW) is a key factor and should be specified upfront to ensure your sauna heats efficiently and safely. When calculating the sauna’s heating needs, consider the total computational volume, not just the physical space. This includes adjustments for uninsulated areas like glass surfaces, which increase heat source loss. 

For every square meter of single-glazed glass, add 1.5m³ to your sauna volume; for double-glazed glass, add 0.75m³. This ensures your heater type can compensate for heat loss and provide consistent warmth. Most electric sauna heaters up to 9kW can operate on single-phase power 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. Larger heaters require a three-phase supply. If you have a large sauna space and plan to include features like a glass wall, you will likely 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.

Sauna Computational Volume Calculation 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: 

• Single-glazed glass adds 1.5m³ per 1m² of glass

• Double-glazed glass adds 0.75m³ per 1m² of glass

 

Sauna With Single-Glazed Glass

Sauna With Double-Glazed Glass

Saunas as a “Special Location”

Saunas are identified as a “special location” under wiring regulations, meaning 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 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.

For further electrical considerations, it’s important to pair it with a compatible Control Panel to ensure proper operation. Lighting is another key factor, both for safety and ambience. Always choose vapour-proof, heat-resistant fixtures specifically designed for sauna use, and install them away from direct heat source exposure.

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.

Drainage

Having a drain in the sauna facilitates easy cleaning, enables users to pour as much water as they wish over the sauna stones (or sauna rocks) 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.  

The Sauna Interior - Pre-Build Considerations

When learning how to build a sauna at home, planning the sauna interior layout is just as important as the structure itself. Including inside home sauna building materials and components such as fireboard, insulation, cladding, bench boards, and doors, every detail plays a role in comfort, function, and authenticity, ensuring your DIY home sauna delivers the best possible experience from the inside out.

 

Sauna Battens

Sauna Battens play a vital role in allowing airflow between the insulation and interior cladding, helping manage moisture and prevent condensation. The 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 - The Sauna Walls & Ceiling

After the insulation and sauna battens have been installed, you can secure the Sauna Cladding onto the battens with stainless steel fixings that can be hidden within the grooves of the cladding. 

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

• 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

• Cutting for Fixtures: Drill holes for cables or ventilation before installation.

• 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

• Installation Order: Start with the ceiling, extending boards beyond the wall cladding plane.

• Attachment: Secure boards with nails through the tongue side, concealing fixings.

Wall Cladding

• Alignment: Install wall boards with a 10 mm gap at the bottom to prevent moisture absorption.

• Vent Covers: Secure sauna vent covers over ventilation openings.

Finishing Touches

• 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.

 

Sauna 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. 

 

The Sauna Interior - Layout & Ergonomics 

This section explores the layout and ergonomics of your sauna interior, covering everything from bench configurations, the entrance and windows to heater selection and placement. Thoughtful design choices can dramatically impact comfort, heat source distribution, and the overall experience.

Bench Configuration 

Planning how to build a sauna at home involves choosing your Bench Configuration; it can be as simple or sophisticated as you would like, ranging from classic two-tier layouts, opposing benches with raised floors, to L-shaped, U-shaped, or custom-designed body-form loungers.  Finnmark also offers Ready-Made Sauna 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

Since heat naturally rises, the warmest air in a sauna tends to gather toward the ceiling. Even with effective ventilation, some temperature difference between the floor and ceiling is inevitable, and a perfectly even temperature (an isotherm) is hard to achieve. For this reason, traditional sauna design focuses on generous upper bench space. Many cultures position benches so that bathers' feet sit above the heater, ensuring full-body warmth and more effective steam ("Löyly").

Standard Home Sauna Bench Guidelines

For a standard home sauna, we recommend the following:

• Ceiling height: 2100 mm from finished floor level

• Upper bench: 1050 mm from floor level, and at least 600 mm wide

• Lower bench: 600 mm from floor level, approximately 400 - 500 mm wide

• 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.

 

Sauna Doors

For safety, Sauna Doors should open outward and be positioned near the heater to support air circulation. Sauna doors should be 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 tinted bronze, grey, frosted glass and darkened for additional privacy. 

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. 

Most sauna doors are timber-framed with around 8 mm toughened glass, which can be customised. A 15–50 mm gap at the bottom of the glass allows fresh air intake. The door opening should typically be 10 mm larger than the frame, e.g., a 690 x 1990 mm door requires a 700 x 2000 mm aperture. However, exact sizing may vary, so always check your specific door’s requirements.

 

Sauna 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 Type & Extras

Choosing between an Electric or Wood-Burning Sauna Heater should be based on your overall design, bench layout, and desired experience. Electric heaters offer precise temperature control, ease of use, and are well-suited for saunas both indoors and outdoors, especially when convenience and quick heating are priorities. 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. 

Electric saunas will need a compatible Controller and suitable Cables. Ensure all necessary electrical components are in place, including an isolator, rubberised cable, and armoured cable connected to the consumer unit. These details are best confirmed and planned in consultation with a qualified electrician.

Modern electric sauna heaters come with flexible control options, including Wi-Fi connectivity, allowing you to conveniently operate your heater from your smartphone.

 

Wood-burning heaters provide an authentic, traditional sauna atmosphere with the comforting aroma and crackling of burning wood, making them ideal for outdoor options or rustic settings. Wood-burning options need a specified Flue Kit and potentially some Heat Shielding. Also, it's important to check whether you're located in a smoke-free zone with the local authority when considering a wood-burning sauna heater

Sauna Stones or sauna rocks, used with both electric and wood-burning heaters, are often sold separately. Additional accessories may include heater safety railings, mounting collars, and decorative stones, each contributing to improved safety, functionality, or visual appeal within the sauna space

For further guidance, check out our How To Choose The Best Heater Controller For Your Sauna guide.

Wood-burning heaters guarantee a traditional experience. Image by HUUM.

Heater Size - Calculating Sauna Computational Volume

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. 

To choose the right sauna heater, it's essential to calculate your sauna’s computational volume, especially if your design includes glass elements, which lose heat faster than timber. Here’s an example:

Let’s say your sauna’s internal dimensions are 2m x 2m x 2m, giving a base volume of 8m³. The front wall is made entirely of glass and measures 2m wide x 2m high, equalling 4m². Depending on the glass type, here’s how it affects your heater size calculation:

If your sauna includes single-glazed glass, you’ll need to adjust the total volume accordingly. In this case, a 4m² glass area would require an additional 6m³ to be added (4m² x 1.5m³), resulting in a total computational volume of 14m³ (8m³ base volume + 6m³ adjustment).

If you’re using double-glazed glass, the adjustment is slightly less. A 4m² area of double-glazing would require an additional 3m³ (4m² x 0.75m³), giving you a total computational volume of 11m³ (8m³ + 3m³). This adjusted volume helps determine the correct sauna heater size to ensure consistent heat.

Consider the door location making sure it opens outwards, as well as the heater placement, size, safety rails or heat shielding, and windows when designing the optimal layout for the space. 

 

Timber Choices

Sauna environments are high in heat and humidity, so it's essential to use timber sauna materials that can withstand these conditions without warping, releasing resin, or becoming uncomfortable to the touch. At Finnmark, we offer both natural timber and thermally modified wood species, such as:

• Aspen

• Alder

• Western Red Cedar

• Spruce

• Thermo Aspen

• Thermo Pine

• Thermo Alder

• Thermo Spruce

• Thermo Radiata Pine

• Dark Thermo Alder

 

When selecting wood for Sauna Benches and cladding, it’s important to choose types that remain cool to the touch, resist warping, and don’t release resin or splinters when exposed to high heat and humidity. Among the top choices for benches and cladding are cedar, aspen, alder, and thermo-treated woods. These woods have smooth surfaces and excellent thermal properties, ensuring longevity and that they don’t become uncomfortably hot during use. 

Always refer to the recommended wastage allowance for each timber species, as the approximate materials loss during installation can vary between 5 and 15%. 

For sauna door frames, durability and stability are key, as the door undergoes frequent use and temperature fluctuations. The frames are made of popular sauna woods, such as alder, aspen, pine or their upgraded thermo-treated alternatives.

Sauna Lighting

Sauna lighting plays an important role in creating a relaxing and welcoming atmosphere, while also needing to withstand high heat and humidity. Many people prefer energy-efficient LED spotlights and strip lights. For placement of strip lights, they are often mounted onto the bench lips or backrests, while most spotlights can be installed in the ceiling and on the benches.

Just be sure to check their temperature limits and recommended mounting heights. For a more traditional sauna feel, wall or corner lights with wooden shades provide a soft, warm glow. If you’re looking to add a touch of luxury, fibre optic sauna lighting offers gentle, ambient illumination that enhances the overall sauna experience.

Sauna Accessories 

Incorporating sauna accessories like Sauna Speakers, Diffusers, and Headrests can elevate the atmosphere of any sauna space. Whether it's enjoying calming music, the scent of essential oils, or improved support during sessions, thoughtful accessories help transform the sauna into a tailored wellness retreat.

Other Components 

In addition to the main structure and essential materials, there are several optional components to consider when designing your sauna:

• Tiling & stone may be used on floors or wall sections for durability, safety, design features or splashbacks behind the heater.

• 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.

• 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.

  

Part 2

How to Build a Traditional Finnish Sauna - Pre-Checklists

Before starting your DIY sauna project, we recommend reading this full 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. 

Always consult with qualified professionals, 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 suited to your setup. 

 

Pre-Installation Checklist

• Check that you have all the necessary equipment and materials prepared before beginning, including tools, fixings, insulation, and any specialist items for your chosen design.
  

• Record all critical dimensions. This includes stud-to-stud measurements, door and window openings, ventilation cut-outs, and the spacing between sauna battens.

• Confirm the routes for all electrical cabling and the planned location of components such as the heater, lighting, thermostat, and control unit.
  

• Review your ventilation layout and mark the placement of intake and exhaust vents to ensure effective airflow and compliance with installation requirements.
  

• Identify all surfaces that will require fireboard installation, particularly areas surrounding the sauna heater or flue system if used.

• Make note of the wall and ceiling build-up layers, including insulation, vapour barriers, battens, and cladding, to ensure accurate spacing and fit.

• Check for any features that require additional preparation, such as timber feature walls, tiled splashbacks, or backlit panels.

• Ensure the orientation of sauna battens and cladding is correct. Battens must always run perpendicular to the cladding direction to maintain airflow and structural support.

• Mark the glazing lines and confirm any spacers or mounting channels needed for installing glass doors or panels.

Equipment Checklist

• Low-tack painters’ tape

• Tape measure

• Laser measure

• 3-axis laser level

• Spirit level

• Folding square

• Stainless steel nails

• Narrow crown stapler/Brad nailer

• Pencil

• Combi Drill

• Impact driver

• Multitool

• Saw

• Tape measure

• Hammer

• Quick clamps

 

How to Build a Traditional Finnish Sauna: Step-by-Step

 

Part 4

Sauna Use & Well-Being

To get the most from your sauna, both in terms of relaxation and well-being, it’s essential to use it mindfully and safely. A sauna should be an enjoyable and restorative experience. Only use the sauna when you're in good personal health, and always pay attention to how your body feels throughout each session. 

Temperature & Length of Sauna Sessions

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, but this can vary greatly depending on personal tolerance, experience, and how you’re feeling that day. Some people may prefer shorter sessions, while others enjoy a little longer; there’s no one-size-fits-all. 

The key is to always listen to your body and avoid pushing yourself beyond your comfort level. Throughout your session, water can be added to the sauna stones to increase steam and humidity, creating a more immersive and enjoyable environment, but moderation and self-awareness are essential for safe and effective use. 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. 

Avoid Sauna Use When Unwell

It’s important to avoid using the sauna if you’re feeling unwell or experiencing illness. Despite common misconceptions, sauna use during sickness, especially when paired with cold plunges or cryotherapy, can make symptoms worse and put added stress on your body. While regular sauna sessions may contribute to overall wellness and support immune health, they should only be enjoyed when you’re in good physical condition. Listening to your body and resting when needed is just as essential to your well-being as the sauna itself.

Avoid Substance Use

Saunas should not be used in conjunction with alcohol, narcotics, stimulants, or painkillers. These substances can impair your body’s natural ability to regulate heat, putting you at greater risk of overheating, dehydration, or even fainting. They may also dull your awareness of discomfort or warning signs, making it harder to listen to your body and respond appropriately.

Medical Conditions & Sauna Use

Sauna use is not recommended for individuals with cardiovascular conditions. If you have any other medical concerns or are taking medication, it's essential to consult your doctor before using a sauna. Even with medical approval, it’s important to ease into sauna use gently, starting with lower temperatures and shorter sessions. Gradually increase the heat, duration, and humidity over time, always monitoring how your body responds. Taking a cautious, step-by-step approach helps reduce the risk of aggravating existing health issues and ensures a safer, more enjoyable sauna experience.

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. 

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

Make sure you’re well hydrated before entering the sauna, and remember to replenish fluids afterwards. For a revitalising and balanced thermal cycle, consider pairing your sauna session with a cold plunge, cold shower, or another form of cryotherapy. 

However, it’s important to finish your session by warming up gradually. Resting on the lower bench allows your body to return to a comfortable temperature naturally. Avoid ending your session while still very hot or very cold, as this can leave you sweating or shivering long after you've stepped out of the sauna.

For further information on sauna use and wellbeing, explore our Sauna Etiquette and Sauna for Health frequently asked questions.

PART 5

Top 10 Mistakes When it Comes to How to Build Your Own Sauna

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- boards 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, like aluminium foil.

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 computational 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.

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.

 

How To Build Your Own Sauna: FAQs

Do I need planning permission for an outdoor sauna?

In most cases, you don’t need planning permission for a small, detached outdoor sauna, as it often falls under permitted development rights. However, it’s always best to double-check with your local planning authority, especially if you live in a conservation area or are planning to install a wood-burning sauna in a smoke control zone. Rules can vary depending on location and property type, so confirming in advance can save time and avoid complications later.

What is the ideal size for a DIY sauna project?

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. 

Which is better: A wood-burning or an electric sauna heater?

This is completely up to personal preference and your DIY project. Wood-Burning Heaters offer a traditional sauna experience but have higher upfront costs due to flue kits and heat shielding, with no ongoing electricity expenses, just firewood. Electric Heaters provide modern convenience, easy maintenance, and precise control, but require a suitable power supply, especially for most models over 9 kW that may require a 3-phase connection.

Read our Buyer’s Guide to Sauna Heaters to help you choose the best heater for your sauna. 

 

How To Build A Sauna At Home: Final Thoughts 

This comprehensive step-by-step guide has walked you through every stage of how to build a sauna at home – from early planning to long-term care. We've covered everything, including essential, pre-build considerations and detailed pre-checklists, to step-by-step construction instructions. You’ve also learned about key cleaning and maintenance routines, and how to get the most from your sauna in terms of wellbeing and regular use.

Whether you're asking how to build an outdoor sauna or how to build an indoor sauna, the insights here apply to both, offering clear and practical guidance to suit a wide range of spaces, styles, and user preferences. We hope this guide has provided everything you need to know about building your version of Finnish saunas. If you have any further questions or need more tailored advice, take a look at our FAQs following this guide or get in touch with the team at Finnmark. 

Not Into DIY? Finnmark Has You Covered

DIY project not for you? At Finnmark, we offer a Bespoke Sauna Installation Service for those who want the luxury of a professionally built sauna without managing the details. Get inspired by our sauna installations and explore endless possibilities from our expertly crafted designs including Barrel Saunas, which blend tradition and modern aesthetics.

Get In Touch today with one of our expert advisors and take the first step toward creating your dream sauna. 

If you prefer professional help from start to finish, why not consider a bespoke sauna installation service? Get inspired by our sauna installations.