Building a Hot Tub In: Costs and Preparation

By the Fonteyn UK team · Outdoor living advisers at Fonteyn

Building a hot tub in means setting the spa into decking or the ground so the rim sits flush with the surface. UK groundwork typically adds £2,000 to £8,000 to the project.

A built-in spa turns a corner of the garden into a finished wellness space, and a little planning up front keeps the whole job smooth.

What does building a hot tub in actually mean?

There are three main ways to set a spa into a garden, and each suits a different space and budget. A free-standing spa with a timber or composite surround is the quickest to fit and the easiest to live with, because every panel stays in plain sight. A partly recessed spa drops the cabinet halfway into a raised deck, so the seating sits at a comfortable step-in height. A fully in-ground spa finishes level with a patio or lawn for the most seamless, designer result.

The most common question Fonteyn hears is which layout looks best, and the honest answer is that all three can look superb when the surround is planned around the spa. A partly recessed deck tends to be the sweet spot for many UK gardens. It gives that built-in feel, keeps the step-in low, and still leaves the cabinet panels within easy reach for the day a service engineer calls. Pairing the spa with a veranda or patio cover extends the season further, turning the area into a sheltered spot for autumn and winter soaks.

What does it cost to build a hot tub in?

The spa is one figure and the build around it is another, so it helps to plan both together from the start. Three items make up most of the groundwork budget: the base, the electrical supply and the surround. A reinforced concrete slab and a hardwired connection by an electrician are fixed costs that hold their value, because they stay in the ground for the life of the spa. Decking or a paved surround then sets the finished look.

Running the spa afterwards is reassuringly steady. A well-insulated hot tub kept at 38°C uses roughly 3 to 6 kWh a day depending on size and weather, which works out at around £25 to £45 a month at about 25p per kWh, based on the unit rate published by Ofgem (2026). The Ofgem price cap for the period from April to June 2026 was set at £1,641 for a typical household, a useful benchmark when budgeting the year ahead. Good insulation and a snug cover do most of the work here, keeping the heat in so the spa stays ready whenever the mood strikes.

After 30+ years in spas and outdoor living, what Fonteyn finds is that a partly recessed deck delivers the built-in look most people picture while keeping the groundwork sensible. It is a smart way to get a premium finish and great value at the same time. The advisers at the Leicester showroom walk through the figures for each layout so the whole project is costed before any digging begins.

What base does a built-in hot tub need?

Weight is the headline here. A mid-size spa full of water and people can reach around 1,500 to 2,000 kg, so the surface underneath has to spread that load evenly and stay perfectly level. A reinforced concrete slab of at least 100mm is the benchmark that suits almost every garden, and it gives the spa a stable, true platform for decades. Where a raised deck is the plan, the frame is built to a structural specification so the joists and posts comfortably carry the full filled weight.

Level matters as much as strength. A spa shell is designed to sit flat, and an even base keeps the water line true and the cabinet square. For a fully in-ground layout, the slab sits at the base of the excavation with room around the shell, and the same load-bearing thinking applies to a well-compacted paved base. Planning the base early also lines up neatly with getting the spot outdoors ready, from levelling the ground to protecting the surround.

How are the electrics planned for a built-in spa?

The electrical supply is the part to settle first, because the cable route is easiest to lay before any decking or paving covers it. Performance spas, with their fuller jet systems and heaters, are typically hardwired on a 32A supply. That work is carried out by a qualified electrician and notified under Part P of the Building Regulations, which keeps the installation safe and properly certified. Smaller plug-and-play models keep things simpler still, running from a standard 13A domestic socket on an RCD-protected circuit.

Planning the cable run alongside the base means the supply arrives exactly where the spa pack sits, with a tidy isolator within reach. For a built-in spa it pays to think about water as well: a fixed drain to a soakaway or surface drain, plus a clear fall away from the shell, keeps the bay around the spa dry and pleasant to work in. The advisers at Fonteyn coordinate the spa specification with the electrician's requirements so the supply and the model match from day one, and the delivery and installation team sequences the visit around the groundwork.

How do you keep the pump easy to reach?

This is the detail that makes a built-in spa a joy to own for years. Every spa has a technical bay where the pump, heater, filtration and controls live, and that side wants to stay reachable. The simple solution is to design a lift-out deck panel or a removable hatch directly above it, so an engineer can open up, service the equipment and close it again in minutes. Leaving around 50cm of clearance to that side gives comfortable working room.

Build this access in from the very first sketch and the rest follows naturally. The hatch blends into the deck pattern, the spa keeps its seamless built-in look, and annual servicing stays a quick, tidy job. It also keeps routine water care and filters easy to top up between visits. After 30+ years in spas and outdoor living, what Fonteyn recommends is confirming the hatch position against the chosen model before the deck frame is built, because each spa places its pack slightly differently. The advisers at the Leicester showroom mark this on the layout so the panel lands in exactly the right spot.

The Spa Green Kodiak from Grizzly Spas is a favourite for a built-in deck. It offers generous seating with a lounger position and a strong hydrotherapy jet layout, and its solid cabinet construction sits beautifully when framed into timber or composite. The technical side stays neatly defined, which makes planning that access hatch refreshingly simple.

Grizzly Spas Spa Green Kodiak

Generous seating with a lounger · Full hydrotherapy jet layout · Solid cabinet, ideal for building in

Save £2,909

£9,590 £12,499

View the Spa Green Kodiak

For a more compact recessed deck, the Spa Corsica Luxury from Island Spas is a beautifully judged choice. Its lounger seating and refined jet setup deliver proper hydrotherapy in a footprint that drops neatly into a smaller garden. The advisers at the Leicester showroom often suggest it for a partly recessed layout where space is at a premium.

Island Spas Spa Corsica Luxury

Lounger seating · Refined hydrotherapy jets · Compact footprint, great for a recessed deck

Save £1,400

£5,690 £7,090

View the Spa Corsica Luxury

Do you need planning permission to build a hot tub in?

For most gardens the planning side is wonderfully straightforward. A hot tub is treated as everyday garden use rather than a structure, so the spa on its own generally needs no permission at all. The point worth a quick look is the surround. Raised decking, a platform or a screen around the spa is covered by permitted development limits, which set out heights and positions, and these are published by the Planning Portal on GOV.UK.

The usual rules of thumb apply to decking and platforms, with height and ground coverage being the main figures to check. Listed buildings and conservation areas can have their own arrangements, so a quick word with the local planning authority confirms everything before the deck goes in. It is a five-minute call that gives complete peace of mind. The advisers at Fonteyn point customers to the right starting point so the surround is planned within the guidance from the outset, and a little homework here keeps the whole project on a confident footing.

How long does building a hot tub in take?

Timing follows the layout. A spa framed into a deck is the quickest, often complete inside one to two weeks once the base is set. A partly recessed deck usually runs to two to four weeks, and a fully in-ground installation takes three to six weeks because of the excavation and the slab. The one fixed point in every timeline is curing time: a concrete base wants around seven days to reach strength before the spa sits on it.

Sequencing keeps everything moving smoothly. The electrical first fix and the drainage go in while the slab cures, the deck frame goes up next, and the spa is delivered and set once the base is ready. Booking the spa around the groundwork schedule means each trade arrives at the right moment. The most common question Fonteyn hears at this stage is when to place the order, and the advisers recommend confirming the model early so the base, the cable route and the access hatch are all sized to the exact spa before any work starts. Browsing the full hot tub and spa range is the natural first step.

Seeing the models in person makes the whole plan click into place. At Fonteyn's Leicester showroom, the largest outdoor living showroom in the UK, the advisers map the chosen spa against decking and in-ground layouts so every measurement is confirmed before the build begins. Pairing the project with a garden room or veranda is easy to plan in the same visit, found across the veranda and patio cover collection.

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