Mobile sauna 6.5×2.5 m made of thermowood

Why the 6.5x2.5m Format is Becoming the Mobile Construction Standard in 2024–2026

The modular building market is undergoing a structural transformation. While mobile saunas were previously perceived as temporary or "summer cottage" solutions, today they are fully-fledged engineering structures, rivaling permanent structures in terms of commissioning time, energy efficiency, and durability. The 6.5 x 2.5 m format (building area 16.25 m², height 2.85 m) has become optimal in terms of transport logistics, structural load-bearing capacity, and functional zoning.

Why these particular dimensions?

• Transport compatibility : The 2.5 m width allows the finished structure to be transported on a standard lowboy without requiring special permits for oversized cargo. The 2.85 m height complies with standard road infrastructure restrictions (bridges, power lines, gas station arches).
• Structural rigidity : The aspect ratio ensures uniform load distribution. The frame requires no additional bracing or internal load-bearing walls, preserving usable space for the steam room, relaxation room, and bathroom.
• Functional flexibility : 16.25 m² is sufficient for a full-size steam room (6–8 m³), ​​a relaxation area, a shower/toilet, and a utility room. At the same time, the structure remains lightweight and can be installed on lightweight foundations.
• Investment efficiency : The cost per square meter of a mobile solution is 40–60% lower than a stationary equivalent of the same grade. The payback period for commercial use is reduced to 6–9 months.

In this expert guide, we'll take a detailed look at the Gartensauna-44 mobile sauna from Thermowood Production . The analysis will focus on engineering nuances: from a layer-by-layer breakdown of the structure and physics of materials to logistics solutions for delivery as a prefabricated or prefabricated house, as well as economic models for both private and commercial customers.

Technical specification of the design: Frame-panel technology

The frame-panel system used at Gartensauna-44 differs from traditional prefabricated construction in that it is highly precision-manufactured. Each wall, floor, and roof panel is manufactured in a workshop with geometric control of up to ±1.5 mm, after which it is assembled on a jig, tested for leaks, and finally packaged.

Basic design parameters:

The structure is designed in accordance with DBN B.1.2-14:2018 (Load and Impact) and European standards EN 1995-1-1 (Eurocode 5). All wooden elements are kiln-dried to a moisture content of 12±2%, after which they are treated with a water-based bioprotective coating. This eliminates the risk of shrinkage, insulation failure, or condensation within the wall structure during the first 2–3 years of use.

Detailed Specification of Materials: A Level-by-Level Analysis of the "Pie"

The energy efficiency, durability, and microclimate of a modular sauna are determined not only by the wall thickness but also by the sequence of layers and the physics of their interaction. Below is a detailed analysis of the materials used for the exterior walls, floor, and roof.

External wall "pie" (from street to room):

1. Exterior cladding (façade) : Heat-treated 35mm Belgian pine batten. Heat treatment at 215°C alters the chemical structure of the cellulose and lignin, removing resins and reducing hygroscopicity by 60–70%. The material does not require annual antiseptic treatment and is resistant to UV radiation and biological pests. Its wear resistance class complies with EN 350-2, class 1-2.
2. Ventilated gap : 20–30 mm, formed by a 20×40 mm counter batten. Provides natural air circulation, drains condensation that forms on the outer surface of the waterproofing, and extends the lifespan of the insulation by 30–40%.
3. Wind and water protection : A diffusion membrane with a density of 150 g/m² and vapor permeability of ≥1500 g/m²/24 hours. Protects the insulation from external moisture, allows vapor to escape from the structure, and prevents condensation from accumulating inside the wall.
4. Frame : Pine timber, 150x50 mm, 12–14% moisture content, treated with class B bioprotection (EN 13301). Provides load-bearing capacity and spatial rigidity.
5. Insulation : Mineral basalt wool, density 35–45 kg/m³, thickness 100 mm. Flammability class NG (non-combustible), thermal conductivity λ = 0.037 W/m K. Placed between the studs with an allowance of 10–15 mm for a tight fit without additional fastening.
6. Vapor barrier : Reinforced polyethylene film, 200 g/m². Joints are sealed with a special butyl rubber tape. This protects the insulation from internal vapor and prevents a reduction in the wall's thermal resistance.
7. Interior paneling : Extra-grade linden lining, 8-10% moisture content. It has the lowest thermal conductivity of any wood species (0.11 W/m K), does not emit resin when heated, is hypoallergenic, and feels pleasant to the touch. It is finished with a clear, natural-based varnish to preserve the texture and facilitate maintenance.

Floor structure (layer by layer):

1. Load-bearing joists : Pine beams 150×50 mm, 400 mm pitch. Provides rigidity under load of up to 300 kg/m².
2. Subfloor : 18mm OSB-3 or 12mm CSP (depending on the zone). Moisture-resistant and stable under temperature fluctuations.
3. Waterproofing : Coating or roll waterproofing in “wet” areas (bathroom, steam room).
4. Finishing (base) : 32 mm tongue-and-groove thermo-pine board. Moisture-resistant, non-slip, does not require chemical impregnation.
5. Optional finish : cement particle board + 600x600 mm porcelain tile with a 6 cm edge + drain. Ideal for bathrooms and steam rooms: easy to clean, durable, and compatible with underfloor heating.

Roofing "pie" (single-slope roof):

1. Coating : Corrugated sheet, galvanized + polymer coating (color according to RAL catalog). Durability of 25+ years, hail and UV resistance.
2. Lathing and counter-lathing : 25x100 mm board, 20x40 mm batten. They form a ventilation gap to remove moisture from under the roof.
3. Waterproofing : Diffusion membrane 150 g/m².
4. Insulation : Mineral wool 100 mm (optional for year-round use).
5. Vapor barrier and ceiling lining : Same as the walls. Linden paneling is used in the steam room.

Expert note : The layer sequence follows the principle of "vapor permeability increases from the inside out." This prevents moisture accumulation in the insulation, which is the main cause of deterioration of frame buildings within 5-7 years.

Turnkey assembly and additional options: Engineering analysis

The base price of the structure (UAH 428,399) includes the frame, insulation, exterior and interior cladding, roofing, and bio-protection. Additional options (UAH 482,915) create a fully functional structure ready for utility connections. Let's examine their technical necessity.

Total cost of the set : UAH 911,314 (~€17,869). With a 10% discount: €16,082 . Bonus: 2 linden headrests.

Important : The sauna is supplied "ready for connection" without a stove. This allows for the installation of a locally certified stove (wood-burning or electric) in accordance with the regulations of the country of use, simplifying customs clearance and warranty service.

Delivery formats: Ready-made sauna vs. house kit for on-site assembly

The choice of delivery format depends on the site's logistical conditions, the availability of a construction crew, and the budget. Both options use the same materials and meet the same quality standards.

Criterion	Ready-made bathhouse (factory assembly)	House kit (assembly on site)
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