Outdoor Sauna Roofs Compared: Metal Roofing, Bitumen Felt, Asphalt Shingles, Covers and Shelters

When comparing outdoor saunas, the roof is probably not the first thing most people look at. The design, size, windows, benches and heater naturally receive more attention. In some sauna models, you may not even see the roof properly when viewing the sauna at a showroom or online, and the actual roofing material may receive very little thought until it requires maintenance or attention.

Yet an outdoor sauna is also a small building and, in our view, one that should be designed to last for decades. During that time, it can face very different conditions depending on where it is located, from rain, snow and significant temperature changes to hot and dry climates, high humidity, strong winds and coastal environments with salt-laden air. How it is protected from above can therefore have a significant impact on its durability, maintenance requirements and the way the entire structure ages.

There are several different approaches to roofing an outdoor sauna. The right solution can also depend on where and how the sauna is used, from a private garden to a larger wellness or hospitality setting. Permanent metal roofing and bitumen-based roofing are common solutions. Some sauna manufacturers use flexible roofing membranes or PVC and fabric-based roofing and covers, including solutions that function almost like a “rain jacket” for the sauna. For saunas without their own permanent external roofing, weather protection can also be provided by placing the sauna underneath a separate roof or shelter. Some outdoor saunas may have no separate roofing material at all, leaving the wooden exterior directly exposed to the weather.

Each of these approaches can be appropriate depending on the type of sauna, climate, budget, intended use and expectations regarding maintenance and lifespan. In this comparison, we look at how they differ and what is worth considering when choosing an outdoor sauna.

A good outdoor sauna roof is more than the material you see

Before comparing the alternatives, it is important to distinguish between the roofing material and the complete roof construction. The material visible from the outside is only one part of the solution.

The primary purpose of an outdoor roof is to protect the structure from rain, snow and melting water and direct water away from the building. With a wooden building, the construction also needs to manage moisture and allow materials to dry. Roof shape, slope and detailing all play a role, as do the structures underneath the visible roofing material.

The construction of the sauna itself also influences what kind of external roofing is needed. Depending on the sauna design, the roof construction may include insulation, moisture-control layers, ventilation or an air gap and the structural components supporting the roof. These layers need to be protected from the weather, making the external roofing part of a complete roof assembly rather than simply a covering placed on top of the sauna. This is particularly relevant for a sauna, where the temperature and moisture conditions inside can be very different from those outside.

Not every outdoor sauna is built this way. In some designs, the wooden structure itself forms the upper exterior surface, with no separate insulated roof assembly above it. In that case, the wood itself becomes the weather-exposed outer layer. This is one reason why different types of outdoor saunas can use very different roofing solutions.

Snow is another important consideration, especially in northern and alpine climates.

Heavy, wet snow can create a considerable load, so the supporting structure needs to be designed for the snow conditions expected at the sauna’s location. Wind loads and the secure attachment of the roofing system can also become important in exposed locations. The roofing surface can influence how snow behaves, but no roofing material should be considered a substitute for adequate structural design. For these reasons, when comparing outdoor saunas it is worth looking beyond whether the visible surface is metal, bitumen or something else. The complete roof construction, and the sauna construction underneath it, matter.

1. Permanent metal roofing for an outdoor sauna

Metal roofing is a well-established solution for houses, cabins and other permanent outdoor buildings and can also be very suitable for an outdoor sauna. A properly designed metal roof provides a permanent external layer that protects the wooden structure and roof assembly underneath from direct precipitation and directs rain and melting water away from the building. Metal roofing is available in many different forms and qualities, so its durability depends on the material, surface treatment, detailing, installation and environmental conditions.

One practical advantage of many metal roofing surfaces is that they are relatively smooth. Leaves, conifer needles and other organic material can generally be removed relatively easily, which can be useful when an outdoor sauna is located close to trees. The smooth surface can also allow snow to move or slide from a sloped roof under suitable conditions, although this depends on the roof pitch, temperature and characteristics of the snow and should not be taken for granted.

Metal roofing can be incorporated into a complete permanent roof construction, allowing the external roofing, insulation, moisture management, ventilation and supporting structures to be designed as one system. As with any roof, correct detailing and moisture management underneath the visible surface remain important.

Coastal environments require additional consideration. Salt-laden air can accelerate corrosion, and the suitability of the metal, coating, fasteners and other components should therefore be checked for the particular environment. Different metals and coating systems can perform very differently in marine conditions, making the manufacturer’s specifications and warranty conditions particularly relevant when a sauna is located close to the sea.

The trade-off is typically a higher initial cost and a more substantial construction than some simpler roofing solutions. For a sauna intended to remain outdoors year-round for a long time, that additional investment may be justified.

2. Bitumen felt and asphalt shingles for outdoor saunas

Bitumen-based roofing is widely used on cabins, garden buildings and garden saunas. Common forms include bitumen roofing felt and shingles, with the latter generally known as asphalt shingles in North America. They are established, relatively cost-effective roofing materials and, when correctly specified and installed, can provide reliable protection against rain and snow. Their versatility and relatively straightforward installation make them an understandable and practical choice for many smaller wooden buildings and outdoor saunas.

Compared with many metal roofing surfaces, bitumen felt and asphalt shingles typically have a rougher surface. Leaves, conifer needles and other organic material can therefore accumulate more readily, particularly in shaded or wooded environments, potentially contributing to moss growth and increasing the need for cleaning. The surface can also retain snow more readily than a smooth metal surface. This is not necessarily a problem when the roof structure is appropriately designed, but it means that accumulated snow may remain as a load on the roof. This can become particularly relevant when snow becomes wet and heavy during changing winter and spring conditions.

Sun exposure is another factor worth considering, particularly in hot and sunny climates. Heat and ultraviolet radiation contribute to the ageing of asphalt roofing, while the granules and other protective surface treatments used in modern roofing products are intended to protect the asphalt underneath from UV exposure. There can therefore be considerable differences between products, and product quality, ventilation, climate and correct installation all influence long-term performance.

If you are considering an outdoor sauna with bitumen felt or asphalt shingles, it is therefore worth asking the manufacturer or seller what roofing product is actually used, how it is designed to perform in your local climate and what maintenance and expected service life the manufacturer specifies. Choosing a high-quality roofing product appropriate for the conditions can make a significant difference over the lifetime of the sauna. None of this makes bitumen felt or asphalt shingles a poor roofing solution: the quality of the particular product, the complete roof construction, installation, climate and regular maintenance all have a significant influence on how the roof performs over time.

3. PVC, EPDM and other flexible roofing membranes and covers for outdoor saunas

Some outdoor saunas use PVC, EPDM rubber, coated fabric or other flexible waterproof materials as part of their weather protection. These materials can be used in different ways, from permanent roofing membranes and fitted roof covers to larger covers or hoods that extend over much of the sauna. The latter are sometimes described as a “rain jacket” for the sauna.

These solutions should not all be considered the same. A properly designed membrane or fabric roof can form part of a permanent roofing system, while a fitted cover or hood is a separate protective component placed over the sauna. The materials themselves can be highly weather-resistant, and these solutions can provide effective protection against rain, snow and sunlight when correctly designed for their intended use.

Compared with a rigid roof, flexible roofing and cover solutions place particular importance on support, fastening, drainage and the way water and moisture are managed. With covers that sit directly over or close to the wooden structure, ventilation and the ability of the underlying materials to dry are also important considerations. Secure fastening and the behaviour of the complete system under wind loads should also be considered, particularly in exposed locations.

Mechanical damage is another consideration with flexible roofing membranes and covers. Depending on the material and construction, sharp objects or falling branches can potentially puncture or tear the roofing surface. The risk depends on the particular material, its thickness and reinforcement, the supporting construction and the environment in which the sauna is located.

Material suitability is another point worth checking, particularly when a flexible cover is placed directly over a lightweight wooden sauna construction. In some sauna designs, the external covering may be separated from the interior by a complete insulated roof assembly, while in others the wooden structure itself forms much of the building envelope. If gaps can develop between the wooden components, the relationship between the external covering and the sauna interior can be quite different. For this reason, it is worth asking the manufacturer not only about weather resistance, but also whether the particular PVC, EPDM, coated fabric or other membrane material has been specified for the way it is used in the sauna construction. Where the material is not fully separated from the sauna interior, information about its suitability for the temperatures involved and the intended application is particularly relevant.

Snow loads need to be considered separately. Flexible materials can change shape under load, and areas where the material sags may allow snow, ice or melting water to accumulate if the complete system has not been designed to prevent this. Properly engineered membrane structures can also be designed for demanding conditions, so it is important to consider the complete construction rather than judging the solution simply by whether it is made from PVC, EPDM or fabric.

As with other roofing alternatives, the quality and specification of the particular product matter. It is worth asking the sauna manufacturer or seller what material and construction are used, whether the solution is intended for year-round exposure in your climate, what snow, wind or other loads it has been designed for, and what maintenance or eventual replacement the manufacturer recommends.

4. Protecting an outdoor sauna with a separate roof or shelter

Not every outdoor sauna has its own permanent external roof or roofing layer. In these cases, weather protection can instead be provided by placing the sauna underneath a separate roof, canopy or shelter. A properly designed shelter can provide very effective protection from the elements and, depending on its size and design, protect not only the top of the sauna but also parts of the exterior walls from direct rain, snow and sunlight. In practice, however, the weather protection is then provided by an additional structure rather than by the sauna itself.

For a backyard sauna, this can also be an attractive architectural choice. The shelter can form part of a terrace, pool area or garden pavilion and provide a covered place for cooling down, changing or sitting between sauna sessions. In this case, the additional structure serves a wider purpose than simply protecting the sauna.

The distinction is worth making when comparing different outdoor saunas. A sauna that requires a separate shelter for weather protection is a different overall solution from one that has a permanent weather-protective roof incorporated into the sauna itself. The shelter requires additional space, materials, construction work and investment and, depending on its location and size, may also have implications for planning or permitting. There is nothing inherently better or worse about incorporating a shelter into the wider outdoor design. The important point is simply to understand where the necessary weather protection comes from and what is included with the sauna itself.

5. Outdoor saunas without separate external roofing

Some outdoor saunas are designed without a separate external roof covering, meaning that the wooden structure itself forms the weather-exposed upper surface. This approach is common in barrel saunas, where the curved wooden staves form both the walls and the upper exterior surface of the structure. Rainwater is intended to run down the curved sides without the need for a conventional roof.

In many such designs, there is no separate insulated roof assembly underneath these exterior wooden boards or staves. In other words, the wood is not simply a roofing material protecting insulation and other roof layers below it. The wood itself forms the building envelope between the sauna interior and the outside environment.

This has an important practical implication. Wood naturally responds to changes in temperature and moisture, and joints between boards or staves can change over time. If gaps develop, there may be no separate waterproof roofing layer underneath to provide a second line of protection. Depending on the construction and the size and location of the gaps, wind-driven rain or melting water may therefore be able to reach the sauna interior. This does not necessarily mean that the construction has failed. Rather, it reflects a different design principle and a different level of weather protection, in which movement of the wooden structure and its implications need to be taken into account.

The upper wooden surfaces are also directly exposed to sunlight, rain, snow, moisture and temperature changes. How the construction performs and ages therefore depends on factors such as the wood, detailing, surface treatment, maintenance, local climate and degree of weather exposure. Additional weather protection can be added in different ways and, depending on the sauna design, this may include bitumen felt or asphalt shingles, metal roofing, a waterproof cover or the separate shelter discussed above. An exposed wooden exterior can be a perfectly functional solution, but its construction principle, maintenance requirements and approach to weather protection are different from those of a sauna with a permanent external roof and a protected roof assembly underneath.

How to choose the right roof for a garden sauna

There is no universal answer to which outdoor sauna roof is best. A lightweight sauna intended primarily for seasonal use may have very different requirements from a permanent outdoor sauna expected to remain outside throughout the year in a demanding climate. Climate, location, intended use, budget, expected lifespan and willingness to perform regular maintenance should all be taken into account.

The appearance of the sauna matters too, as different roofing solutions can have a surprisingly large impact on the overall architecture and design. A permanent metal roof can be clean and discreetly integrated into a modern sauna, while shingles, fitted fabric or PVC covers, and separate shelters each create a very different visual character. This is worth considering particularly when the sauna is intended to become a permanent part of a carefully designed garden, terrace or architectural environment.

The sauna experience matters as well. The roof and ceiling construction, including insulation where used, affects how well heat is retained inside the sauna and how the sauna performs in different outdoor temperatures. The construction of the sauna itself therefore matters: an insulated roof containing several structural layers has different requirements for weather protection from a sauna where the wooden structure itself forms the exterior surface.

In areas with significant snowfall, the structural capacity of the roof is particularly important. Even a high-quality roofing material cannot compensate for a supporting structure that has not been designed for the conditions in which it will be used. Wind exposure should similarly be considered when specifying and fastening the roof or any separate covering.

The type of sauna heater also affects the roof design. An electrically heated sauna does not require a chimney, while a wood-heated sauna requires particular attention to the chimney and its connection to the roof. The chimney passes through or close to the roof construction, so the roofing material, required safety distances, fire protection, flashing and waterproofing all need to be considered as part of the complete design. The installation should always follow the chimney and heater manufacturers’ instructions as well as applicable local fire and building regulations, and the roof penetration should be carried out professionally.

It is also worth considering the complete life cycle rather than only the initial purchase price. When comparing sauna prices, it is worth checking what kind of weather protection is actually included. A metal roof or bitumen/asphalt roofing may be included as part of the sauna, supplied as components for installation, or offered as an additional option. Likewise, separate covers or “rain jackets” may be sold as accessories rather than being included in the base price.

The cost difference between these solutions can be significant. Even on a relatively small garden sauna, a high-quality permanent roof can represent a meaningful part of the total construction cost, while a simple fitted cover may cost considerably less. The initial price should therefore be considered together with what is included, the expected lifespan of the roofing solution, possible replacement costs and the level of maintenance required. A simpler and less expensive roofing solution may be entirely appropriate for one sauna, while another owner may prefer to invest more initially in a permanent construction designed for long-term use and relatively straightforward maintenance.

Why we chose a permanent metal roof for Hetki saunas

At Hetki, our starting point has always been to build outdoor saunas for long-term, year-round use. We want their expected lifetime to be measured in decades rather than just years, and this inevitably influences our choices of materials and construction methods. A high-quality solution can sometimes mean a somewhat larger initial investment, but from the beginning we have preferred not to compromise on structural solutions where we believe durability, long-term performance and ease of ownership justify the additional cost.

The roof is one example of this approach. Every Hetki sauna has a permanent, sloped metal roof as an integral part of the building. Underneath it is a complete roof construction including an insulated ceiling, moisture management, ventilation and supporting structures. For us, protecting this construction with a permanent external roof was a natural choice.

Snow conditions were also taken into account in the structural design. Hetki has a 5-degree mono-pitch roof, and the permitted snow load on the roof is 240 kg/m². The roof capacity has been assessed using the design principles, guidance and calculation methods of the relevant Eurocodes, including EN 1990, EN 1991 and EN 1995. We do not rely on snow sliding off the metal surface: snow can remain on the roof, and the structure is designed accordingly.

Our choice of a metal roof is ultimately about quality, durability and the experience we want our customers to have throughout the lifetime of their sauna. Weather protection is already incorporated into the building, without requiring the owner to add a separate cover or build another roof simply to protect the sauna from normal outdoor conditions. No outdoor roof is completely maintenance-free, but our aim is that the owner should need to give the roof relatively little attention over the years. Like many other details in a Hetki sauna, the roof may not receive much attention when everything is working as it should, but we believe these less visible structural choices matter when building a sauna intended to last for decades.

The choice is also architectural. Hetki is built on the principles of a genuine Finnish log sauna, with a clean and contemporary exterior. We wanted the roof to follow the same design language, so the metal roofing is discreetly integrated into the solid log construction. The result is a sauna designed to feel equally at home surrounded by nature or in a modern urban backyard.

Details matter when choosing an outdoor sauna

The quality and longevity of an outdoor sauna are the result of many individual decisions. Wall and roof construction, materials, insulation, ventilation, drainage, windows, doors and the way water and moisture are managed throughout the building all contribute to how the sauna performs, how much maintenance it requires and how it ages.

The roof is a good example of a detail that can easily receive less attention than the more visible parts of a sauna. There is no single roofing solution that is right for every outdoor sauna, and metal, bitumen or asphalt roofing, flexible membranes and covers, separate shelters and exposed wooden structures can all have their place. What matters is understanding what you are buying, how the complete construction works and whether it is suitable for your intended use, local climate and expectations for the lifetime of the sauna.

When comparing a garden sauna or backyard sauna, look beyond the appearance and the headline price. Ask what the roof is made of, what is underneath it, whether it is insulated, how moisture and water are managed, what snow and wind loads the structure is designed for where relevant, what maintenance is required and what is actually included in the price. If the sauna is wood-heated, ask about the chimney installation and fire safety as well. If something about the construction is unclear, ask questions and challenge the answers rather than assuming that all outdoor saunas are built in essentially the same way.

A good sauna manufacturer or experienced professional should be able to explain why a particular construction has been chosen, where its strengths and limitations lie and whether it is suitable for your location and intended use. If you would like to know more about how we have approached these questions at Hetki, we are always happy to explain our choices and provide further information.