Rooms
A garden room with a hot tub: bases, power and privacy
In short
A hot tub is best placed beside a garden room on its own reinforced base, under a canopy, rather than inside the room. A filled tub weighs two to three tonnes, it needs its own 32 amp electrical circuit fitted by a registered electrician, and the steam from it will cause condensation in any enclosed room without strong ventilation.
A garden room and a hot tub make an obvious pair: somewhere warm to change, a bar or a sofa, and the tub a few steps away. Getting them to work together is mostly about weight, electricity and steam. Here is how to plan it.
Inside the room, or beside it?
Most of the time, beside it is the better answer.
Beside the room, under a canopy or overhang. The tub sits on its own base next to the room, often under a roof that extends from the garden room or a separate pergola. The steam goes straight into the open air, the room stays dry, and the tub can be serviced from all sides. This is how most combined builds are laid out.
Inside the room. Possible, but the room then has to be designed as a wet space: a floor that takes two to three tonnes on a small area, a drain, moisture-resistant linings throughout, and mechanical ventilation strong enough to remove the steam. Without that, condensation runs down the glass and soaks into the insulation. The cost of doing it properly usually exceeds the cost of a canopy outside.
The base
A typical four to six seat hot tub weighs 300 to 500 kg empty and two to three tonnes once filled with water and people. That load sits on a footprint of around 2 × 2 m.
- A reinforced concrete slab at least 100 mm thick on compacted hardcore is the standard base, laid level and a little larger than the tub on every side.
- Ground screws with a steel frame can work if they are designed for the load; ask the builder to confirm the screw spacing and capacity in writing.
- A timber deck only works if it was engineered for the tub from the start. An ordinary deck or garden room floor will deflect and may fail.
Keep the tub base separate from the garden room base unless the two were designed together. They move differently.
Power
Most hot tubs need a dedicated 32 amp circuit from the consumer unit, run through armoured cable, with an isolator switch within sight of the tub but out of reach from the water, and RCD protection. Some smaller plug-in tubs run on a 13 amp supply but heat slowly.
All of this is notifiable electrical work under the building regulations. It must be done by an electrician registered with a competent person scheme, who issues a certificate. If the garden room is being built at the same time, the tub supply can go in the same trench as the room’s power and data, which saves digging twice.
A hot tub uses a lot of electricity to heat, especially in winter. A well-insulated cover and a tub with good cabinet insulation make a large difference to running costs.
Water and hygiene
Hot tubs are a known source of legionella if they are not kept clean. The Health and Safety Executive publishes guidance on keeping water treated and the filters clean. For a domestic tub that means regular testing, the right chemical balance, and draining and refilling every few months. Make sure there is a garden tap close by and a sensible route for draining water away from the room’s base.
Planning and the rules
A hot tub on its own normally needs no planning permission. A canopy or roof over it is treated as part of the outbuilding or as its own small structure, so the usual permitted development limits apply: behind the house, single storey, 2.5 m high within 2 m of a boundary.
Watch two details:
- Raised platforms. Permitted development does not allow a veranda, balcony or raised platform over 0.3 m high. A deck built up around a tub can cross that line.
- Privacy and noise. A tub used late in the evening, close to a neighbour’s bedroom window, is the kind of thing that leads to complaints. A screen on the boundary side and sensible hours help.
Typical costs
These are rough guides for a combined build, on top of the garden room itself:
- Reinforced slab for the tub: usually £800 to £2,000 depending on size and access.
- Electrical supply and isolator: commonly £600 to £1,500, more for a long cable run.
- Canopy or roof extension over the tub: from about £2,000 for a simple timber canopy to £6,000 or more for an integrated roof with lighting.
- The tub: from a few thousand pounds to well over £10,000.
A garden bar next to a tub is a popular layout: bifolds onto a deck, the bar facing out, the tub to one side under the canopy. Our price calculator prices the room and the bar fit-out together.