An indoor home sauna is the more convenient version of the experience. Five paces from the shower to the heat, no walking across a wet garden in January, no concrete pad to lay. The trade-off is up-front complexity: indoor saunas need proper ventilation, the right floor, and (for most installs) a Part P-certified electrician. Done well, they’re a permanent and high-value addition to the house. Done badly, they create moisture problems that show up two years later.
This guide is for UK homeowners considering an indoor sauna in a bathroom, basement, loft, garage conversion, or dedicated room.
Where to put it
The four common locations:
- Bathroom (en-suite or family). Closest to the existing plumbing and ventilation. Best for retrofits — but most bathrooms are too small to drop in a 2m×2m sauna without losing the bath or shower.
- Basement / cellar. Excellent for sound and heat insulation, often the right footprint. Watch for damp — UK basements need careful waterproofing before adding a sauna.
- Garage conversion. Good footprint, often easier to run a 32A circuit from the consumer unit, and a sauna makes the garage useful again. The most popular new-build location in our reader survey.
- Loft / spare room. Works if the floor loading is adequate and you can get the unit up the stairs. Pre-built units rarely come apart again, so check the route in advance.
Indoor sauna types
- Pre-built freestanding cabin. A drop-in unit, typically 1.5m × 1.5m up to 2m × 2m. You move it into the room and connect the electrics. Easiest install. £2,500–£8,000.
- Custom-built room sauna. A sauna built into the room with wall-to-wall benches and integrated heating. More work but a much better use of awkward spaces. £4,000–£15,000 depending on size and finish. A UK builder can quote.
- Infrared cabin. A lower-temperature option that doesn’t need ventilation and runs on a standard 13A socket. £1,500–£5,000. See infrared saunas.
Ventilation
The single most important thing about an indoor sauna. Air must be able to enter the cabin (low intake, near the heater) and exit (high outlet, on the opposite wall) so the heat circulates and so moisture doesn’t build up in the surrounding room.
For a freestanding unit in a well-ventilated existing room, the cabin’s own vents are usually enough. For a built-in sauna in a bathroom or basement, plan an extractor that vents to outside — not just into the loft or roof space, which moves the moisture problem rather than solving it. Building regulations Part F applies to ventilation in habitable rooms.
Flooring
Sauna floors get wet. The acceptable options:
- Tile on a tanked screed with a drain. Most common in bathrooms and dedicated rooms. Slip-resistant porcelain is the safe choice.
- Sealed concrete in a basement or garage conversion. Cheap and indestructible.
- Treated hardwood in upstairs/dry installs. Less ideal — needs annual sealing.
Carpet under a sauna is a no. Standard laminate is a no. Engineered wood is a maybe, with a vapour-proof underlay.
Electrical work
A 6kW indoor sauna heater needs a dedicated 32A radial circuit. Larger heaters (8–9kW) need 40A. The work is notifiable under Part P of UK building regulations and must be done by a competent person. Budget £350–£900 for the electrical work in a typical UK home where the consumer unit isn’t on the other side of the house. Our installation hub has the detailed checklist.
Drainage and damp
Indoor saunas put moisture into the surrounding room. Three things to plan for:
- A floor drain if you’re going to wet down the rocks or rinse the cabin. Otherwise, a tray or duckboard handles the small amount of run-off.
- Adequate ventilation (see above) so moisture doesn’t sit in the wall void.
- Vapour barrier behind the wall lining — a foil-faced membrane between the cabin walls and the structural wall behind. Crucial. Most pre-built cabins include this; custom builds need it specified.
Realistic UK budgets
- Pre-built freestanding cabin in an existing room with sockets: £3,000–£7,500 all-in (unit + electrics + minor floor work).
- Built-in sauna as part of a bathroom refit: £6,000–£15,000.
- Garage conversion including the sauna: £15,000–£35,000 (most of that being the garage conversion itself).
- Basement sauna in an existing waterproofed basement: £5,000–£12,000.
Recommended home saunas
Our 2026 picks are in the buying guides hub. Until our affiliate partnerships are confirmed, links route to the parent guides.
Frequently asked questions
Will an indoor sauna damage my house?
Not if it’s installed properly. The risk is moisture, not heat. Get the ventilation and vapour barrier right and there’s no issue. Get them wrong and you’ve got a damp problem in 2–3 years.
Do I need planning permission for an indoor sauna?
No — internal alterations don’t typically need planning permission. You may need building control sign-off for the electrical work (Part P) and any structural changes.
Does an indoor sauna add value to my house?
A well-installed home sauna is broadly positive for resale value in the right kind of house. A badly installed one is negative — buyers can see moisture damage or worry about it. The honest answer: it adds the most value when the install is high-quality and the location makes sense in the floorplan.
Indoor or outdoor — which is better?
Indoor wins on convenience. Outdoor wins on experience (the cold-air contrast is half the point) and on installation cost. Our comparisons hub has a dedicated article.
Related categories
Want a UK installer for a built-in home sauna? Browse our directory — most of our listed builders take on indoor installations.