Installing a Garden Hot Tub or Sauna: The Groundwork, Dig-Out, and Skip Hire Essentials

The brochure photograph always shows the same thing: steam lifting off the water at dusk, a glass of something in hand, the garden looking its best. What it never shows is the fortnight of graft that came first, the string lines, the wheelbarrows, the argument with a stubborn tree root. A hot tub or a garden sauna is, in the end, only as good as the few square metres of ground it sits on. Get that wrong, and you will spend years chasing a lean, a crack, or a puddle that should never have formed in the first place.

This is the part of the job homeowners tend to underestimate, and it rewards slowing down.

Start with the load, not the look

Before anyone picks a spot for its view of the borders, it helps to understand what that spot has to hold up. A mid-sized hot tub feels almost weightless while it is empty and being manoeuvred over the fence. Fill it, climb in with three friends, and the picture changes entirely: industry installation figures put a filled tub with bathers at roughly 1,500 to 2,000 kilogrammes, comparable to a small car left parked permanently on one patch of lawn. A sauna is lighter, but its timber frame is even less forgiving of a base that shifts or heaves over a winter.

All of that means excavation, and excavation means (spoil, turf, topsoil, old slabs, broken concrete) that has to leave the site somehow. For most domestic projects the answer is a skip, and it pays to arrange one early; skip hire firms such as easySkip.uk generally deliver within a few working days rather than on demand, so a Monday dig-out wants booking the week before. This is a bigger waste stream than most people picture, too. 

According to the Department for Environment, Food and Rural Affairs, construction, demolition and excavation together make up the single largest share of all waste produced in the UK — the majority of it precisely this sort of soil and rubble.

Being honest with yourself about how much you will dig out is what saves the classic error: a skip two sizes too small, filled and lidless, with half the spoil still in a heap by the shed.

The dig-out: level, layers, and drainage

A proper base is never simply a slab dropped onto grass. The dig-out strips away the soft, living top layer (grass, roots, organic matter that will rot and settle, down to firm subsoil). From there, most installers build up in deliberate layers: a compacted sub-base of hardcore or MOT Type 1, then either a reinforced concrete slab or a structurally rated deck.

For a hot tub, the received wisdom in the trade is a concrete slab of at least 100 millimetres, and often 150, laid over well-compacted hardcore and reinforced with steel mesh or rebar so it spreads the load rather than cracking under it. Saunas can sit on a lighter footing, but they still want a flat, free-draining pad that will not wick moisture up into the timber.

Two details separate a base that lasts from one that disappoints. The first is level, checked with a laser or a long spirit level across every axis, because a tub that looks fine by eye can still throw its waterline off by an inch across two metres. The second is drainage. Water finds the lowest point, and if that point sits against a sauna’s sole plates or beneath a tub’s cabinet, you will be replacing timber long before you should. A slight fall away from the structure, with somewhere for run-off to go, is cheap to design in and painfully expensive to retrofit.

Skips, spoil, and the paperwork nobody mentions

Here is where a garden project quietly becomes a waste-management exercise. Excavated soil is far heavier than people expect (a cubic metre of wet clay can exceed 1.5 tonnes), so the skip that looked generous on the website fills fast, and loading one above its marked line is both unsafe and, for the operator, unlawful.

There is a legal layer as well. If the skip stands on your own drive, you are largely free to get on with it. The moment it sits on a public road or the kerb, though, you need a permit from the local council: this is governed by the Highways Act 1980, and the licence carries conditions on lighting, reflective markings, and safe placement. In practice, the skip company usually arranges that permit on your behalf, which is one sound reason to use an established operator rather than the cheapest van answering a classified advert.

That legitimacy matters more than it first appears. Reputable firms must be registered with the Environment Agency as licensed waste carriers before they can lawfully move your spoil, and many councils will not grant a skip permit to a company that cannot prove such registration alongside adequate public liability cover. Waste fly-tipped after leaving your garden can, in certain circumstances, be traced back to the household it came from,  so knowing where your soil actually ends up is not merely good manners. Bodies such as the Federation of Master Builders make much the same argument about checking a contractor’s credentials before the work starts, not after it has gone wrong.

Sequencing the job so nothing waits on nothing

The commonest source of stress on these projects is not the digging; it is the order of operations. The base needs curing time before it takes any real weight (freshly poured concrete is not ready for a two-tonne tub the next morning) and the electrics almost always sit on the critical path, since a hot tub typically wants either a dedicated 13-amp supply or a hardwired 32-amp circuit installed by a qualified electrician.

A sensible sequence runs: mark out and dig; remove spoil; lay and compact the sub-base; pour and cure the slab; run the electrical supply while the concrete sets; then deliver and fill. Book the skip around the dig-out rather than the delivery day, and you avoid a full container squatting on your kerb, quietly collecting a neighbour’s bin bags, while you wait for the slab to cure.

None of this is glamorous. But it is the whole difference between a feature you enjoy for a decade and a standing repair job, and it all happens below the waterline, long before the steam ever rises.

This is a collaborative post.