Named after the Latin word for "strength," the ThermaSol Fortis Sauna Cabin is a study in how a single architectural decision changes the entire character of a structure. That decision is the eave. The modern eave-style roofline - with its deliberate overhang projecting beyond the front face and sides of the cabin - transforms what would otherwise be a standard rectangular outdoor sauna into something that reads as genuinely architectural. The eave creates a shadow line across the top of the glass front, frames the view from inside, and gives the Fortis a presence in any outdoor setting that is quiet, self-assured, and unmistakably designed. Combined with the contrast of natural Nordic spruce and pinewood exterior against the contemporary 8mm Parsol Dark Grey glass front - and the practical details of hidden hinges and interior coat hooks - the Fortis is a sauna that rewards attention to detail because it was built with the same attention.
The eave roofline - one design decision that changes everything
Most outdoor saunas have a flat roof cap that sits flush with or slightly above the cabin walls. The Fortis is different: its eave-style roofline extends beyond the front face of the cabin as a deliberate architectural overhang, covered in Firestone EPDM and projecting a clean horizontal shadow line across the top of the glass front. This overhang is not structural necessity - it is a design choice. It gives the Fortis a profile that is unmistakably modern when viewed from the side (the clean horizontal line of the eave reads from thirty feet away), while also providing practical overhead protection for the glass front against direct rain and accumulating snow. The Firestone EPDM covering the eave and roof is the same commercial-grade rubber membrane used in the Spectra - UV-stable, cold-flexible, and fully waterproof across decades of use without maintenance or resealing.
Nordic spruce and pinewood exterior - natural two-material character
Where the Spectra uses a single exterior material (Tyrol wood panels, applied uniformly), the Fortis uses a combination of thermally modified and brushed Nordic spruce and pinewood - two naturally related Nordic timber species whose grain and texture respond slightly differently to brushing, light, and weathering. The combination creates a subtle variation across the exterior surface that reads as rich and considered rather than repetitive. Both woods are thermally modified - a non-chemical heat and steam treatment that permanently improves moisture resistance, dimensional stability, and rot resistance - and both are brushed to enhance the grain texture and give the exterior surface the refined, tactile quality that is the trademark of the Fortis finish. Against this warm natural wood exterior, the 8mm Parsol Dark Grey glass front reads as a confident contemporary statement - the contrast between the materials is the core of the Fortis design.
Brushed thermo-spruce interior walls - a different warmth from Tyrol panels
Inside the Fortis, the interior walls are clad in brushed thermally modified spruce panels - different from the Tyrol panels used in the Spectra and other models. Spruce has a more open, linear grain than Tyrol wood, and the brushed finish on the Fortis interior accentuates that grain with a texture that catches light differently than smooth-planed panels. The interior spruce is lighter in tone than the darker exterior, creating a warm transition from the dark glass front to the naturally luminous interior. Thermo-aspen benches and backrests provide the seating - stable, moisture-resistant, and smooth to the touch at any temperature. RGB LED colour light therapy lighting is recessed throughout the interior and adjustable via remote to any point across the full colour spectrum, with warm amber and cool blue as the common session modes. Coat hooks are included inside the cabin - a small but genuinely useful detail that reflects the Fortis design philosophy: every element serves a function, and every function is considered.
8mm Parsol PSDG glass, aluminum framing with hidden hinges
The Fortis glass front uses 8mm Parsol Dark Grey Glass in aluminum framing - with hidden hinges on the door panel. This is a specific detail worth noting: hidden hinges are more complex to install than exposed hinges, but they eliminate the visible hardware that would interrupt the clean line of the door edge. From outside the Fortis, the glass door has no visible hinge protrusion - the door simply appears as a clean panel within the aluminum frame. The 8mm PSDG provides the same dark grey-green tint, solar protection, and diffuse privacy as the thicker Parsol glass used in the Spectra, at a specification appropriate to the Fortis cabin volume and design brief. The 8kW Harvia Virta heater with Wi-Fi is included, sized precisely for the Fortis's 3-4 person cabin volume, with the Harvia app enabling remote preheating from anywhere.
A fully assembled outdoor sauna for 3-4 people - 90"L x 87"W x 89"H, 2,161 lbs. Modern eave-style roofline with deliberate overhang - Firestone EPDM. 8mm Parsol Dark Grey Glass (PSDG) front with aluminum framing and hidden hinges. Thermally modified and brushed Nordic spruce + pinewood exterior. Brushed thermo-spruce interior walls. Thermo-aspen benches and backrests. Multi-layer wood fiber insulation. Interior coat hooks. 8kW Harvia Virta heater with Wi-Fi included. RGB LED colour light therapy with remote - recessed. Left or right entrance - select at order. Fully assembled via flatbed. Licensed electrician required. Designed and built in USA. 1-year warranty. 12-13 week lead time.
3-4 people Eave-style roofline with overhang Firestone EPDM roof 8mm Parsol Dark Grey Glass (PSDG) Aluminum framing + hidden hinges Nordic spruce + pinewood exterior Brushed thermo-spruce interior Thermo-aspen benches + backrest Multi-layer wood fiber insulation Interior coat hooks 8kW Harvia Virta Wi-Fi included RGB LED colour therapy + remote Left or right entrance Designed and built in USA 1-year warranty
Specifications
Dimensions and weight
| Exterior length (depth) |
90" (2,286 mm) |
| Exterior width (front face) |
87" (2,210 mm) |
| Exterior height |
89" (2,261 mm) |
| Capacity |
3-4 people |
| Assembled weight |
2,161 lbs |
| Shipping weight |
2,381 lbs |
Exterior and roofline
| Roofline |
Modern eave-style with deliberate overhang projection |
| Roof membrane |
Firestone EPDM - commercial-grade, fully waterproof |
| Exterior cladding |
Thermally modified and brushed Nordic spruce + Pinewood |
| Exterior texture |
Brushed - two-material natural grain variation |
| Insulation |
Multi-layer wood fiber insulation - year-round performance |
| Foundation |
Firm, level surface with slight drainage runoff |
| Origin |
Designed and built in USA |
Glass and door
| Glass type |
8mm Parsol Dark Grey Glass (PSDG) |
| Glass effect |
Dark grey tinted - solar protection, diffuse privacy |
| Framing |
Aluminum - clean, modern, UV resistant |
| Hinges |
Hidden - no visible hardware on door edge |
| Coat hooks |
Included - interior, near door |
| Entrance orientation |
Left or right - select at order |
Interior
| Interior walls |
Brushed thermally modified spruce panels |
| Benches |
Thermally modified aspen - upper and lower |
| Backrest |
Thermally modified aspen |
| Bench quality |
Moisture and warp-resistant |
Heating and lighting
| Heater |
8kW Harvia Virta - freestanding electric |
| Heater control |
Wi-Fi app - remote preheat, temperature, scheduling |
| Heater body |
Black stainless steel - front maintenance hatch |
| Sauna stones |
Included with heater |
| Loyly (steam) |
Yes - add water to stones for traditional steam |
| Lighting |
RGB LED colour light therapy - full spectrum, recessed |
| Light control |
Included remote controller |
| Heater circuit |
240V hardwired - licensed electrician required |
Delivery
| Delivery condition |
Fully assembled - turnkey-ready |
| Delivery method |
Flatbed trailer - curbside |
| Off-loading |
Forklift or crane required (customer responsibility) |
| Electrician required |
Yes - licensed electrician for 8kW heater connection |
| Site notification |
2 weeks prior to scheduled delivery |
| Lead time |
12-13 weeks (made to order) |
| Warranty |
1 year |
Fortis Sauna Cabin - Dimensions
What's included
Fully assembled Fortis Sauna Cabin
Eave-style roofline with Firestone EPDM membrane
8mm Parsol Dark Grey Glass front (PSDG)
Aluminum door and window framing
Glass door with hidden hinges
Interior coat hooks
Thermally modified brushed spruce + pinewood exterior
Brushed thermo-spruce interior wall panels
Thermo-aspen upper bench
Thermo-aspen lower bench
Thermo-aspen backrest
Multi-layer wood fiber insulation
8kW Harvia Virta electric heater
Sauna stones
Wi-Fi heater control + Harvia app compatibility
RGB LED colour light therapy system (recessed)
LED remote controller
Full electrical pre-wiring
Why the Fortis stands out
Eave roofline - the defining detail
The deliberate eave overhang transforms the Fortis profile from a rectangular box into a considered architectural form. The clean horizontal shadow line reads from across the garden, provides practical overhead protection for the glass front, and is covered in Firestone EPDM for decades of waterproof performance without maintenance.
Nordic spruce + pinewood exterior
Two thermally modified Nordic timber species - brushed to accentuate their natural grain variation and texture. The subtle two-material variation across the exterior reads as rich and handcrafted compared to a single uniform material, and develops a beautiful natural patina as it weathers.
8mm PSDG + aluminum, hidden hinges
Parsol Dark Grey tinted glass in clean aluminum framing with hidden hinges on the door panel - no visible hinge protrusion on the door edge. The result is a glass door that reads as a pure, uninterrupted panel within the aluminum frame - the sleekest door detail in the ThermaSol outdoor range.
Brushed thermo-spruce interior
A different interior character from the Tyrol panels used in the Spectra and other models. Spruce has a more open, linear grain that the brushed finish accentuates, producing a warmer, more organic texture. Thermo-aspen benches provide stable, moisture-resistant, smooth seating at any temperature.
Interior coat hooks
A small but genuinely useful detail that reflects the Fortis design philosophy: function is considered alongside aesthetics. Coat hooks inside the cabin near the door provide a place for towels, robes, and clothing - making the practical rituals of sauna use more comfortable and organised.
8kW Harvia Virta with Wi-Fi
Harvia Virta electric heater at 8kW - sized precisely for the 3-4 person Fortis cabin volume. Wi-Fi remote preheat via the Harvia app. Black stainless-steel body with front maintenance hatch and separated heating elements and stones for extended lifespan. Loyly-compatible: add water to the stones for traditional steam.
About ThermaSol
65+ years of steam and sauna expertise
Strength in design. The Fortis is what happens when every detail is deliberate.
ThermaSol has been engineering premium steam and sauna systems since 1958. The Fortis - named for the Latin word for strength - is an expression of that heritage applied to a specific design conviction: that a well-designed outdoor sauna should earn its place in any garden setting by being as considered in its architecture as any other structure on the property. The eave. The hidden hinges. The two-material exterior. The brushed interior. Each one is a decision made in service of an overall object that rewards attention rather than demanding it.
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Modern eave-style roofline - deliberate overhang, Firestone EPDM, clean architectural shadow line
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8mm Parsol PSDG + aluminum + hidden hinges - the sleekest door detail in the range
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Nordic spruce + pinewood exterior - thermally modified, brushed, two-material natural variation
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Brushed thermo-spruce interior + thermo-aspen benches - warm textural contrast throughout
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8kW Harvia Virta with Wi-Fi - precise, efficient, remote-controllable
About ThermaSol
Designed and built in the USA - where architectural intention meets sauna performance
ThermaSol designs every product with a specific intention. The Fortis's intention is the balance of contemporary architecture and natural materials - the contrast between the dark glass front and the warm spruce and pine exterior, between the modern eave and the natural timber texture, between the clean aluminum frame and the organic wood grain. This is not a sauna where the natural materials are painted or covered - they are thermally modified, brushed, and allowed to develop their own character over time. The Fortis gets better looking as it weathers.
The Fortis arrives via flatbed trailer fully assembled. ThermaSol notifies customers two weeks before the scheduled delivery date. A forklift or crane is required for off-loading at 2,161 lbs. The placement site must be firm and level with slight drainage runoff. A licensed electrician must connect the 8kW Harvia Virta heater before first use. Entrance orientation (left or right) is factory-set at order.
Manuals and Documents
Everything you need before and after installation
Download the ThermaSol Fortis installation manual below. It covers site preparation, foundation and drainage requirements, placement and clearance specifications, eave clearance from overhead structures, electrical connection for the 8kW Harvia Virta heater, RGB LED setup, and ongoing maintenance for the Nordic spruce and pinewood exterior, brushed thermo-spruce interior, and Firestone EPDM eave and roof membrane. Review it before your delivery appointment and ensure your licensed electrician is briefed on the 8kW circuit requirements.
Installation Guide
Warranty
1-year ThermaSol warranty
The ThermaSol Fortis Sauna Cabin is covered by ThermaSol's 1-year limited warranty, covering defects in materials and workmanship under normal residential use for one year from the date of delivery to the original purchaser. ThermaSol will, at its discretion, repair or replace any covered defective component at no cost. The warranty does not cover damage from improper installation, misuse, abnormal weather events, inadequate foundation or drainage, or failure to follow ThermaSol's published installation guidelines. The 8kW Harvia Virta heater is covered under Harvia's separate manufacturer warranty. Proof of purchase from an authorized dealer is required. We are an authorized ThermaSol dealer.
