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Hot tub base and placement: what your garden needs

The ground under a hot tub matters more than the tub. A full tub is heavy, it concentrates that weight on a small footprint, and a poor surface leads to a tilted, strained or damaged tub. Placement matters too: the clearances, the drain and the route for the power all need deciding before the tub arrives.

This guide uses published manufacturer, retailer and trade guidance, checked on 12 November 2026. We show the weight sum for a typical inflatable so you can do the same for your tub. We are not structural engineers, and where the stakes are high (decks, raised patios) we say to get one.

The short answer

For an inflatable, the safest surfaces are a level, well-drained concrete pad or flat concrete patio, with an insulating mat underneath. The Lay-Z-Spa manual also lists grass as acceptable but not decks, gravel, sand or driveways. For a hard shell, one UK retailer recommends a concrete pad of at least 10 cm. Decking can work only if it is built to carry the load; check with a specialist decking installer or a structural engineer before you put a full tub on one.

Step 1: Work out how much it weighs

Water weighs about 1 kg per litre. Take the tub's published water volume, add the tub's own weight and add the bathers. Hydropool, a hot tub maker, suggests planning with an average of 185 lb (about 84 kg) per person.

Worked example: Lay-Z-Spa Miami AirJet (inflatable)

  • Water: 669 litres = 669 kg (Bestway's published water capacity)
  • Tub: about 31 kg
  • Four adults at 84 kg: 336 kg
  • Total: about 1,036 kg, just over a tonne

The tub is 180 cm across, so a round footprint of 1.8 m diameter is π x 0.9 x 0.9 = 2.54 m². Spread evenly, that is roughly 407 kg per square metre. This is an approximation (the weight is not perfectly even, and the pump unit sits outside the circle), but it gives you an order of magnitude.

Hard shells are heavier

Happy Hot Tubs gives dry weights of roughly 250 kg to 750 kg, a small tub at about 710 kg full, an average five-seater at 1,500 to 2,000 kg, and one large model at about 3,085 kg. Always use the manufacturer's filled weight for your model.

Step 2: Choose the surface

Concrete pad

The most recommended option. Happy Hot Tubs recommends a pad of at least 10 cm thick, sloped about 1.5 cm over 3.5 m so water runs away rather than pooling. If you plan decking around the tub, Ecodek's installation guide for its hot tub decking specifies a concrete base reinforced with re-bar, at least 5 inches (about 127 mm) for standard concrete or 4 inches (about 100 mm) for fibre-filled concrete.

Existing patio or block paving

Happy Hot Tubs says most patios and paved areas are already reinforced and can usually take a hot tub's weight, but you should check that the stones are level and drainage is adequate so water does not collect underneath, and consult a specialist if unsure. Look for rocking slabs, voids underneath or a patio laid over soft fill, because loading these can cause settlement. Ecodek, by contrast, does not recommend patio slabs as a support for its decking system, so the answer depends on what you are building.

Grass and soil

The Lay-Z-Spa Miami manual recommends grass and concrete but not dirt, sand, gravel or soft soil, and says to use an insulating mat. Check the manual for your specific model. A lawn that is soft, sloping or waterlogged is the wrong surface, however the manual is worded.

Gravel, driveways and sand

Not recommended by the Lay-Z-Spa manual for an inflatable. Finnmark's sauna guidance (a different product but a similar weight problem) uses compacted gravel 100 to 150 mm deep as a base, so gravel can work for some structures when properly prepared, but follow your own tub's manual.

Decking

This is where mistakes are expensive. The facts we can state:

  • The Lay-Z-Spa manual does not recommend decks, balconies or platforms.
  • Happy Hot Tubs says a hot tub needs more joists than a normal deck, and the foundations must be adequate, whether concrete or another hard base. It advises consulting a specialist decking installer.
  • Hydropool suggests placing the tub on a concrete slab and building a deck around it, and says a structural engineer can confirm a deck or pad will withstand the load.
  • Ecodek says decking must not be installed on soil or hardcore for its hot tub system, and gives 450 mm as a maximum support spacing.
  • Deckorum, a composite decking vendor, says composite joists are not suitable as a load-bearing support for a hot tub and recommends treated timber or plastic lumber. (Vendor claim; their load figure on the page appears to contain an error, so we do not rely on it.)

We could not find a published standard load rating for ordinary garden decking, so do not assume yours can carry 400 kg per square metre. Decking attached to a house can also amplify pump noise and vibration, according to Happy Hot Tubs, which suggests EVA floor matting or a quieter circulation model.

Step 3: Choose the position

From the Lay-Z-Spa Miami manual:

  • Install near a drain.
  • Keep at least 1 metre from surrounding objects and at least 2 metres from metal surfaces.
  • Keep away from overhead power lines, trees, underground utilities and house entrances.
  • Keep the socket at least 4 metres from the tub, with the plug directly in the socket (no extension lead or multi-plug adapter), and keep other electrical appliances at least 2 metres away.

Lay-Z-Spa also advises against crowding the tub, because water and air temperature changes can make the liner expand and contract. For the layout of a small garden, see our small garden guide.

Step 4: Plan the power before the base

If the supply runs underground, plan the route before any paving or base is laid. A UK retailer's guidance says to use protected cable buried at least 500 mm below the lowest local ground level, lay marker tape about 150 mm below the surface, record the route, and agree it before the base and paving go in. The IET's guidance says the supply to a hot tub should be protected by a 30 mA RCD, that there are no specific hot tub requirements in BS 7671 but that its swimming pool section (702) should be applied to outdoor hot tubs, and that in England new circuits are notifiable under Part P.

Plug-in (13 amp) tubs and 32 amp tubs need different supplies; see our inflatable vs hard-shell guide. One retailer estimates £150 to £450 for an outdoor socket and up to £750 for a 32 amp supply with an isolator.

Step 5: Planning and permissions

The Planning Portal says you typically will not need planning permission to install a hot tub in your garden, but you may need it if you live in a listed building or conservation area. If the tub is housed inside a large shed-style structure, that structure has its own planning and building control limits. Electrics must be safe and adequate and carried out by a registered competent person.

Base and placement checklist

  1. Get the tub's filled weight (or work it out as above).
  2. Choose the surface: reinforced concrete is the safe default; get specialist advice for decks.
  3. Check the surface is flat, level and drains away from the tub.
  4. Measure the clearances: 1 metre from objects, 2 metres from metal.
  5. Locate the drain, so you can empty the tub.
  6. Plan the socket position and cable route before laying anything.
  7. Check planning status if the property is listed or in a conservation area.
  8. Lay an insulating mat before you inflate.

Frequently asked questions

Can I put a hot tub on decking?

Only if the deck is designed for the weight. For an inflatable, the Lay-Z-Spa manual does not recommend decks. Ask a decking specialist or structural engineer.

Do I need a concrete base for an inflatable hot tub?

The manual we checked recommends grass or concrete, so a concrete base is not compulsory, but the surface must be flat, level and strong enough. A UK retailer recommends a concrete pad at least 10 cm thick for hard-shell tubs.

Can I put a hot tub on patio slabs?

Often, if they are level, well supported and drain properly. One UK retailer says most patios can take the weight but advises a specialist check if you are unsure.

How heavy is a full inflatable hot tub?

A 669 litre tub with four adults is roughly 1,036 kg, or about a tonne, on our calculation above.

Do I need planning permission?

Typically not, according to the Planning Portal, unless the property is listed or in a conservation area.

Sources (checked 12 November 2026)

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