A sauna in a shed or garden room

Short answer: you can turn a shed or garden room into a sauna, but what you’re really doing is building a sauna room inside it: insulation, a foil vapour barrier, timber panelling, ventilation, a heater with its safety distances kept, and its own electrical supply. Compare that with a sauna cabin that’s designed for the job: the cheapest cabin with a heater in our data is £1,999.

What a shed conversion involves

Heater makers’ installation manuals describe the room a sauna heater needs. From Harvia’s, HUUM’s and Narvi’s manuals:

1. Insulation: 50 mm to 100 mm in the walls and ceiling, so the heater can stay a sensible size.
2. A vapour barrier: moisture protection such as aluminium paper behind the panelling, with the seams taped.
3. Panelling: 12 mm to 16 mm timber boards, with sturdy timber behind them to carry a wall-mounted heater and the benches.
4. Ventilation: the air should change three to six times an hour, with vents placed as the heater’s manual says.
5. A heat-proof floor under the heater.
6. The heater’s safety distances to walls, ceiling and benches, which differ for every model and are given in its manual and on its rating plate.
7. A qualified electrician to connect an electric heater.

That’s the same build-up as a sauna cabin, done inside a building that wasn’t designed for heat and moisture. Our guide to how to build a sauna takes each step in turn. A shed’s frame, roof and floor also need to cope with a room heated to sauna temperatures and the weight of benches and people.

Sources: Harvia: Cilindro Pro HPCE2642 EN - Instructions for installation and use of electric sauna heater (PDF hosted by Zöchling Holz); HUUM: DROP electric sauna heater user manual (EU, 2025); Narvi: Installation and instruction manual, Narvi Velvet Electric 9.0 kW / 10.5 kW; Harvia Support: I am about to start panelling my sauna – what do I need to take into account?; Harvia Support: How much space does the heater require around it?. Checked 30 September 2026.

Is your shed suitable?

• Headroom: Harvia says a sauna is usually 2.1 m to 2.3 m high inside, and HUUM and Narvi give 1.9 m as the minimum for some of their heaters. Many sheds are lower, especially at the eaves.
• Size: the benches and the heater’s safety distances all take floor space. Check the heater’s manual for its distances before you decide the room is big enough.
• Construction: a solid floor and frame, and walls you can insulate and panel without losing too much space.
• Where it is: a wood stove needs a flue to the maker’s clearances and, in a smoke control area, an exempt appliance. Check yours with our smoke control area checker.

The heater and the electrics

The cheapest electric sauna heater in our data is the Harvia Vega E Sauna Heater 4.5kW - BC45E at £355, and many need a separate controller and stones on top. Size it to the insulated room with the heater size calculator, and compare models on sauna heaters.

An electric heater needs its own circuit. In England, Part P covers outbuildings such as sheds, and a new circuit is notifiable work, so use a registered electrician who can certify it. Steam & Oak’s estimates for a garden supply run from £400 to £1,500. Our electrical supply calculator shows what a heater will draw.

Sources: GOV.UK: Approved Document P - Electrical safety, dwellings (2013 edition); legislation.gov.uk: The Building Regulations 2010, regulation 9 (Exempt buildings and work). Checked 30 September 2026.

Building regulations and planning

For a detached garden building in England with no sleeping accommodation, building regulations don’t normally apply under 15 m². For a single-storey building from 15 m² to 30 m², they don’t normally apply if it’s at least 1 m from every boundary or built substantially of non-combustible materials. Part P still applies to the electrics whatever the size, if the power comes from the house. We haven’t found official guidance on whether adding a sauna heater or insulation changes those exemptions, so if you’re unsure, ask your council’s building control team.

Planning is the same as for any outbuilding: height, position and coverage limits for permitted development. Run your shed through the planning permission checker.

Sources: legislation.gov.uk: The Building Regulations 2010, Schedule 2 (Classes of exempt buildings and work); legislation.gov.uk: The Building Regulations 2010, regulation 9 (Exempt buildings and work). Checked 30 September 2026.

What it costs compared with a sauna cabin

A conversion can make sense if you already have a sound, roomy outbuilding and the skills or a builder to do it properly. If you’re starting from scratch, compare the cost of a new shed plus the work with cabin saunas and small garden saunas.

Garden rooms with a sauna inside

If you want a garden room as well as a sauna, some cabins combine them: a sauna room with a changing area, relaxation room or veranda. 7 saunas in our data have a separate changing area and a heater included, from £10,400:

Buildings over 15 m² can bring building regulations into play, so check the limits above. See every model on cabin saunas.