A hot tub garden room is one of those projects that sounds like pure luxury, but it is more practical than you might think. Whether you want to sit in a hot tub under cover on a rainy evening or build a fully enclosed spa room at the bottom of the garden, there are several ways to make it work. We have been building garden rooms across South East London, Kent, Surrey, and Sussex since 2004, and in recent years the number of customers asking about hot tub setups has grown steadily.
The key question is whether you want the hot tub inside the garden room, next to it under a covered canopy, or positioned on adjacent decking with its own shelter. Each approach has different implications for ventilation, structural loading, moisture management, and cost. Here is what you need to know before committing to a design.
Can You Put a Hot Tub Inside a Garden Room?
Yes, you can. But it is the most demanding option, and it needs to be planned carefully from the start. Retrofitting a hot tub into a garden room that was not designed for one is rarely a good idea. The three main challenges are weight, moisture, and ventilation.
Weight and Structural Loading
A standard four to six person hot tub weighs between 1,300 and 2,500 kg when filled with water and occupied. That is a serious load. A typical garden room floor built on timber joists and concrete pad foundations is not designed to carry that kind of weight in a concentrated area. If you want a hot tub inside the room, the base needs to be a reinforced concrete slab, poured to an appropriate depth and specification for the load. This has to be factored into the design before the garden room is built, not after.
You also need to allow enough space. The hot tub itself will need a footprint of at least 2.2m by 2.2m, with a minimum of 40cm clearance around all sides for access, maintenance, and safe entry and exit. The ceiling height should be at least 2.5m so you can stand upright when climbing in and out. In total, an enclosed hot tub room typically needs an internal floor area of at least 3m by 3m, though 3.5m by 3.5m is more comfortable.
Moisture and Condensation
This is where most indoor hot tub rooms run into trouble. A hot tub in an enclosed space can evaporate several litres of water per hour, pushing humidity levels to 80% or higher. Without proper management, that moisture will condense on walls, windows, and the ceiling. Over time it causes paint to blister, timber to warp, and mould to grow in any damp corners.
The walls and ceiling of an indoor hot tub garden room should be lined with moisture resistant materials. Standard plasterboard is not suitable. Cement board, marine grade plywood, or specialist moisture resistant panels are all better choices. The floor needs to be fully waterproof and include a drain with a minimum 100mm (4 inch) diameter to handle splashes and any overflow. Tiling or vinyl flooring with sealed edges works well.
A dehumidifier rated for the room size is strongly recommended. The target humidity level for a hot tub room is between 45% and 55% relative humidity. Above that, condensation becomes a persistent problem. Wall mounted dehumidifiers designed for pool and spa rooms are the most effective option for a dedicated hot tub garden room.
Ventilation Requirements
Ventilation is not optional. You need a way to move humid air out and bring fresh air in. There are several approaches that work well together.
- Louvre windows. These allow controlled natural airflow even when it is raining outside, and they are a good passive ventilation option for milder weather.
- Extractor fans. Wall mounted extractor fans controlled by a humidistat will kick in automatically when moisture levels rise. These are essential for any enclosed hot tub room.
- Roof vents. Hot, humid air rises, so a roof mounted vent or turbine ventilator helps draw moisture out from the highest point in the room.
In practice, most indoor hot tub garden rooms use a combination of all three. The extractor fan does the heavy lifting, the roof vent handles the rising steam, and the louvre windows provide background air exchange when the tub is not in use.
Covered and Adjacent Hot Tub Options
For many people, the best approach is to keep the hot tub outside the main garden room but under some form of cover. This avoids the ventilation and moisture challenges of a fully enclosed room, while still giving you weather protection and a sense of privacy. It is also typically less expensive because the structural requirements are simpler.
Garden Room with Side Canopy
This is the most popular layout we see. The main garden room serves as a changing area, lounge, or social space, and an attached canopy on one side shelters the hot tub. The canopy has a solid, waterproof roof but open or partially open sides. This gives you rain protection overhead while allowing steam and humidity to escape naturally, which removes the need for mechanical ventilation.
Canopy extensions typically range from 1.5m to 4m in depth, going up in half metre increments. A canopy of 2.5m to 3m deep is usually enough to shelter a standard hot tub with some room to spare. Bi-fold or sliding doors between the main room and the covered area let you open up the space in summer or close it off in winter.
Garden Room with Pergola
A pergola provides a lighter, more open feel than a solid canopy. Traditional pergolas have an open slatted roof, which offers partial shade and some rain protection. For hot tub use, a louvred pergola with adjustable slats is a better choice. You can open the slats fully on clear evenings for stargazing, close them for rain protection, or angle them to control sunlight during the day.
Some pergola designs also accept sliding glass panels on the sides, which turns the structure into a semi-enclosed room when needed. This gives you flexibility across the seasons without the full commitment of an indoor hot tub room.
Hot Tub on Adjacent Decking
If you prefer a more open setup, positioning the hot tub on a dedicated decking area next to the garden room is a straightforward option. The decking needs to be built to support the full weight of the hot tub, water, and occupants. Standard domestic decking is not strong enough. You will need reinforced subframe joists, thicker deck boards (composite decking handles moisture better than softwood), and solid foundations underneath.
A decking area of at least 3m by 3m gives you space for the tub plus room to move around it safely. If the decking is raised, the substructure needs to be engineered to carry concentrated loads rather than just foot traffic.
Verandas and Glass Rooms
For year round use with maximum weather protection, a veranda or glass room extension attached to the garden room is worth considering. Modern flat roof verandas use aluminium frames and laminated glass roof panels to create a bright, sheltered space. You get full rain and wind protection with the open, airy feeling of being outdoors. Adding glazed side panels creates a glass room that keeps the warmth in during colder months while preventing the moisture issues that come with a fully insulated, sealed room.
Planning Permission and Building Regulations
Hot tubs themselves do not usually require planning permission in the UK. They are generally treated as portable, temporary structures and fall under your permitted development rights. However, the garden room or structure that houses or shelters the hot tub does need to comply with the usual outbuilding rules.
Under permitted development, a garden room must be single storey, must not cover more than 50% of the garden area, and must have a maximum eaves height of 2.5m (or 2.5m overall height if within 2m of a boundary). If your property is in a conservation area, an Area of Outstanding Natural Beauty, or is a listed building, additional restrictions may apply. For a full explanation of how these rules work, see our planning permission and building regulations guide.
Building regulations come into play if the garden room includes plumbing, drainage, or habitable space features. An indoor hot tub room with floor drainage will likely need building regulations approval for the drainage connection (Part H) and any electrical work (Part P). A hot tub under a simple canopy or on an open deck is far less likely to trigger building regulations requirements, which is another practical reason many people prefer the covered outdoor approach.
Electrical Requirements for a Hot Tub
Regardless of whether the hot tub sits inside or outside the garden room, the electrical installation must comply with Part P of the Building Regulations. This is not a job for a general handyman. You need a qualified, Part P registered electrician.
The hot tub must be hard wired on its own dedicated circuit back to the household consumer unit. It cannot share a supply with other appliances. The circuit requires a suitably rated MCB (miniature circuit breaker) sized at 25% above the maximum current draw of the tub. So a hot tub with a 20 amp draw needs a 25 amp MCB. The circuit must also include a 30mA RCD (residual current device) for protection against earth faults.
A waterproof IP65 rated isolator switch must be installed between 2 and 3 metres from the hot tub, positioned so that bathers cannot reach it from inside the water. The cable running from the house to the garden room should be 6mm three core SWA (steel wire armoured) cable, either buried in a trench or run through protective ducting. Once the installation is complete, your electrician will issue a Part P certificate, which you should keep on file.
Drainage Considerations
Hot tubs do not need a permanent water supply. You fill them with a garden hose and drain them every three to four months for a full water change. The drainage question is about where that water goes when you empty the tub, and how you handle day to day splashing and overflow.
For an outdoor or covered hot tub, a simple soakaway in the garden is often sufficient for draining. The water should be allowed to cool and the chemical levels to drop before emptying onto grass or into a soakaway. Some people run a waste pipe to a nearby drain or inspection chamber for convenience.
For an indoor hot tub room, you need proper floor drainage. A floor drain connected to an appropriate waste outlet handles splashes and overflow during use. When draining the full tub, a submersible pump is the quickest method, discharging via a hose to a drain or soakaway outside. The floor of the room should be laid with a slight fall towards the drain so that any standing water runs off naturally.
How Much Does a Hot Tub Garden Room Cost?
The cost varies widely depending on the approach you choose. Here is a rough guide based on current UK pricing.
| Setup | Typical Cost Range |
|---|---|
| Garden room with attached canopy for hot tub | £20,000 to £35,000 |
| Garden room with pergola shelter for hot tub | £22,000 to £38,000 |
| Fully enclosed indoor hot tub garden room | £30,000 to £50,000+ |
| Garden room plus separate decking area for hot tub | £18,000 to £30,000 |
These figures include the garden room and the shelter or structural work for the hot tub area, but not the hot tub itself. A decent quality hard shell hot tub in the UK costs between £3,000 and £10,000 depending on size, features, and brand. Electrical installation adds £500 to £1,500 on top.
The enclosed indoor option is the most expensive because of the reinforced base, moisture resistant finishes, ventilation system, and drainage work required. The canopy or pergola approach typically adds £3,000 to £8,000 to the cost of a standard garden room, making it the most cost effective way to combine a garden room with a hot tub.
For detailed pricing on our garden room range, visit our buildings and prices page.
Design Tips from Over 1,000 Builds
After more than two decades of building garden rooms, here are a few practical things we have learned about hot tub setups.
- Face the hot tub away from neighbours. Privacy matters more when you are in a hot tub than when you are sitting in a garden room. Position the open side of a canopy or pergola towards your own garden, not towards neighbouring windows. Slatted screens, planting, or frosted glass panels can add screening where needed.
- Think about access from the house. On a cold winter evening, the walk from the back door to the hot tub matters. A paved or decked path with low level lighting makes the journey comfortable and safe in the dark.
- Plan for maintenance access. Hot tubs need periodic servicing, and the pump and control equipment need to be accessible. Do not box the tub in so tightly that a technician cannot reach the service panel.
- Consider a changing area. If you go with an outdoor or covered hot tub, the garden room itself makes a natural changing room. Include hooks, a bench, and towel storage. If the budget allows, adding a simple shower to the garden room means you can rinse off before and after using the tub.
- Lighting sets the mood. Warm, dimmable lighting around the hot tub area makes a huge difference to the atmosphere. Recessed LED downlights in a canopy soffit, low level deck lights, or festoon lights across a pergola all work well.
Which Option Is Right for You?
If you want a true all weather spa experience and are happy to invest in the ventilation, drainage, and structural work, an enclosed indoor hot tub garden room is the most self contained option. It works well as a dedicated spa room, especially if you add mood lighting, waterproof speakers, and quality finishes.
If you prefer the feeling of being outdoors but with overhead protection from rain, a garden room with an attached canopy or pergola is the sweet spot. You get a proper garden room for year round use, plus a sheltered hot tub area that does not need the same level of moisture management. This is the option most of our customers choose.
If budget is the priority, a garden room with a separate decking area for the hot tub keeps costs down while still giving you a dedicated outdoor space.
Whatever approach suits you best, it is worth designing the garden room and hot tub area together from the start. Bolt on solutions are always more expensive and less satisfying than a layout that was planned as one project. We design and build bespoke garden rooms to suit exactly this kind of brief.
Save £5,000 with Our Ambassador Programme
If you are planning a hot tub garden room, our Ambassador Programme could save you £5,000 on the total cost. In return, you allow us to photograph the completed build and host a small number of viewing visits for prospective customers. It is a straightforward arrangement that has helped hundreds of our customers get more garden room for their money. Get in touch to find out if your project qualifies.