By The Sauna Company · Published 7 Nov 2026
Yes, an under stairs sauna can work. In Clapham we built one for up to two people in the space beneath a staircase, clad in Thermo Aspen laid vertically and at angles to follow the stairs, with floating benches and a HUUM CLIFF 10.5kW heater controlled over Wi-Fi.
The key is designing the heater, benches and ventilation around the shape you have, rather than forcing a standard box into it.
Key takeaways
- It fits. The void under a staircase can hold a fully working two-person traditional sauna.
- The slope becomes a feature. Angular cladding turns the stair's slope into part of the design instead of a compromise.
- Floating benches help. Benches with no legs keep a tight floor easy to clean and make the room feel larger.
- Slim heater, small clearances. A heater with small safety distances, such as the HUUM CLIFF, suits awkward geometry.
- Ventilation matters more in small rooms. CO2 builds up faster in a small air volume, so it needs careful calculation.
What was the brief?
The space under a staircase is usually a cupboard for coats and the vacuum cleaner. In this Clapham home it became a bespoke sauna for up to two users. Like every sauna we build, it is a one-off, designed to the exact shape of the space.
Which design decisions made it work?
Cladding that follows the stairs. We clad the sauna in Thermo Aspen, arranged vertically and at angles. Thermo Aspen, a thermally treated aspen, is the timber we use for premium builds. Laying it to follow the angles of the stair keeps the lines clean and makes the shape of the room part of the design.
Benches without legs. The layout uses two floating lower benches and one raised upper bench, none with support legs. Floating benches leave the floor clear, which makes cleaning simple and lets the eye run under the benches, so a small room reads as larger.
Lighting. LED strips run along the room to give soft, indirect light. In a compact sauna, hidden lighting avoids glare at close quarters.
Heater and controls. The heater is a HUUM CLIFF 10.5kW single-phase, paired with a HUUM UKU Glass Wi-Fi controller, so the sauna can be pre-heated from a phone.
Why does the HUUM CLIFF suit awkward spaces?
The CLIFF appears in more of our case studies than any other heater. It has a natural stone surface and a slim body with small safety distances, which matters when you are working around a stair soffit.
Its large stone capacity gives mild, long-lasting steam, and an internal air duct helps it heat up faster. The CLIFF won a Red Dot design award in 2021.
How do you plan your own under-stairs sauna?
This section is general guidance for anyone considering a similar space, not a description of the Clapham build.
- Measure the usable volume, not just the footprint. The lowest part of a stair void may only suit a bench end or storage, so the heater usually sits where headroom is greatest.
- Plan the ventilation early. Indoor saunas need more ventilation planning than outdoor ones. In a small room, two people's exhaled CO2 builds up quickly, so inlet and outlet positions need calculating before anything is built. Heater maker Harvia, for example, recommends six air changes per hour for a sauna with an electric heater.
- Check the electrical supply. A 10.5kW heater needs a dedicated supply, arranged by your electrician to our wiring schematics. If only a 13A socket is available, an infrared sauna (Aqua Spazio Radiata) is the usual alternative.
- Doors open outward. Sauna doors must open outwards, must not be lockable and must not be able to jam. In a hallway, check the swing will not block the route.
- Remember the stairs above. The stair structure needs to stay sound, and your builder handles any partitions or alterations to our drawings.
Our sauna design package covers air volume, heat loss and heater capacity calculations, plus ventilation and joinery drawings.
What might a similar build cost?
The Clapham case study does not publish a project price. As a guide, our premium Finnish saunas (Aqua Spazio Premio) start from £14,995 for a 1.2m sauna, fully installed, excluding VAT and builders' preparatory work such as partitions, flooring and electrical supply upgrades.
A standard Finnish sauna (Aqua Spazio Sana) starts at £9,995 on the same basis. Every under-stairs space is different, so we price after seeing photographs and dimensions.
Frequently asked questions
Can you put a sauna under the stairs?
Yes. We built a two-person sauna under a staircase in Clapham using angular Thermo Aspen cladding, floating benches and a HUUM CLIFF heater. Whether it works in your home depends on the usable height, electrical supply and ventilation route, which we assess from photographs and dimensions.
How many people fit in an under-stairs sauna?
It depends on the space. The Clapham sauna was designed for up to two users, with two floating lower benches and one raised upper bench.
What heater works in a small under-stairs sauna?
A slim heater with small safety distances is easiest to fit. In Clapham we used a HUUM CLIFF 10.5kW single-phase heater with a UKU Glass Wi-Fi controller. For very small rooms, compact heaters such as the HUUM DROP 4.5kW are another option.
Does a small sauna still need ventilation?
Yes, arguably more so. A small room has less air, so exhaled CO2 builds up faster, and that causes the stuffy, dizzy feeling of a poorly built sauna. Ventilation is the most important part of any sauna design.
Why use floating benches in a small sauna?
Benches with no legs keep a tight floor easy to clean and make the room feel larger.
Talk to a sauna designer
Got a stair void, spare WC or box room you think is too awkward? Book a free design consultation, or email photographs and dimensions to spaziodesignlondon@gmail.com for an initial assessment. See the full Clapham under-stairs project.
Planning one for your own home? See our bespoke home saunas page for options and recent projects, or book a free design consultation and we'll talk through your space.
Sources
- HUUM — Three Red Dot award winners. CLIFF heater, Red Dot award 2021.
- HUUM — CLIFF electric sauna heater. Large stone capacity for mild, long-lasting steam.
- Harvia — Ventilation in the sauna. Six air changes per hour for electric-heater saunas.
Planning a sauna of your own? See how our sauna installation service works, from free design consultation to handover.