What base does a garden sauna need?

A garden sauna needs a base that is flat, firm and sheds water, finished before the cabin arrives. How much base is enough depends on who made the sauna: Harvia's instructions for its barrels name a concrete slab or strip foundation with the cabin anchored to it, while Almost Heaven accepts compacted gravel, paving or a deck under its barrels. The base also counts for planning, because height is measured from the ground, not from the top of a raised frame.

What does your sauna's maker actually ask for?

Start here, because the manufacturers do not agree, and the instructions for the model you buy are the ones your base has to meet.

Maker, from their own documents or the live product page	Base	Anchoring
Harvia, assembly instructions for the Kaski 180 and Kuusi 180 Panorama	A foundation slab or a strip foundation, which Harvia says must be "absolutely flat and load-bearing"	"The outdoor sauna must be firmly anchored on the base plate or the strip foundation", and anchoring "is the responsibility of the customer"
Almost Heaven, site guidance and FAQ for its barrels	"Firm and flat (a slight taper for run-off is fine)": deck, concrete, paved stones or pressed gravel, but "not the bare earth"	Not stated in the guidance read for this article
Holl's and France Sauna, from Tarnfell's live product pages	The Gaïa Urban page says the cabin "stands on a flat, hard base you lay first"; the Hestia 160 page says preparing the base is the buyer's to arrange	Not stated on the pages

The Harvia point has a warranty consequence. The warranty terms on the Harvia Kuusi 180 Panorama page state that anchoring the cabin against wind is the buyer's responsibility and that damage to a cabin that was not anchored is not covered. So a Harvia barrel set down without anchoring is outside the warranty if the wind moves it, whatever it is standing on.

Almost Heaven's reason for insisting on level ground is worth knowing whichever barrel you buy. Its guidance says a site that is not level can leave the staves "difficult or impossible to line up correctly" and the door not latching. The practical advice: get the assembly instructions for your exact model before anyone quotes you for groundwork, and give them to whoever builds the base.

Slab, paving, gravel or frame: which suits your garden?

Each base type below is matched against the two sets of manufacturer instructions on file. This describes what each one asks of your garden; what it costs depends on your site and is a question for a groundworker's quote.

Base	Named by Harvia	Named by Almost Heaven	What it asks of the garden
Concrete slab	Yes	Yes	Excavation and a pour; gives a continuous surface to fix anchors into; permanent
Strip foundation	Yes	No	Concrete only where the cabin bears, so less digging than a slab; still permanent
Paving on a prepared bed	No	Yes	A level bed and slabs laid true; can be lifted later
Compacted gravel	No	Yes	A compacted, level layer that drains freely; the lightest groundwork on this list
Timber deck or frame	No	Yes	A structure rated for the load; raises the cabin, which matters for planning (see below)
Ground screws with a frame	No	No	Not named in either manufacturer's guidance on file; ask the maker before using one

Two readings of that table. First, the concrete slab is the only base both makers name, so it is the choice that keeps every model in the range open to you. Second, the two makers disagree on what flat means: Almost Heaven allows "a slight taper for run-off", Harvia asks for "absolutely flat". If you pour a slab with a fall for drainage, check it against your heater and cabin maker's wording first.

How much weight is the base carrying, and where?

Two outdoor saunas in the range publish a weight. The Holl's Hestia 160 is 649kg on a footprint of 205 by 160cm. The Harvia Kaski 180 Panorama is 510kg.

The arithmetic for the Hestia: 2.05m × 1.60m is 3.28m², and 649kg over 3.28m² is roughly 198kg per square metre, before anyone sits in it. That is an average across a flat cabin floor.

A barrel does not spread its weight that way. The Kuusi 180 page describes the cabin standing on four impregnated feet, and Harvia's instructions have them placed on the foundation parallel to one another. Almost Heaven's barrels sit on cradles, which its guidance gives as 53 by 6 inches for its six foot diameter barrels. On those figures it follows that a barrel's weight, and its bathers', goes through a few narrow strips rather than across the whole footprint. That is the reason a strip foundation suits a barrel, and it is the thing to check if you lay paving: every slab under a foot or cradle is carrying the cabin.

Whether your particular ground will take that load without settling is a judgement for whoever builds the base, on site. Nothing on this page replaces it.

Can the base push your sauna over a planning limit?

It can, and this is the part most buyers do not expect. In England, an outbuilding within two metres of a boundary must stay under 2.5 metres overall to be permitted development, per the Planning Portal. The government's technical guidance defines ground level as "the surface of the ground immediately adjacent to the building", which "would not include any addition laid on top of the ground such as decking". Where ground slopes, it is "the highest part of the surface of the ground next to the building".

Our reading of that guidance, and it is an inference rather than a quoted rule: a base that raises the cabin above the surrounding ground adds its height to the building's height. So the headroom that matters is the gap between the cabin's published height and 2.5 metres.

Model, published overall height	Headroom under 2.5m near a boundary
Holl's Cocoon 130, France Sauna Gaïa Urban: 2.0m	50cm
Holl's Orphée 180, Holl's Orphée Lounge 240: 2.15m	35cm
Holl's Hestia 160, Holl's Hestia Lounge 210, Holl's Onyxia Cube, France Sauna Gaïa Bella, Luna and Nova: 2.2m	30cm
Holl's Onyxia Barrel: 2.26m	24cm

A separate limit applies to the base itself: permitted development for outbuildings excludes a raised platform, which the guidance defines as more than 0.3 metres high, and garden decking is permitted up to that height. A frame built to level a sloping plot can reach it quickly at the low end.

Building regulations are simpler. The Planning Portal says a detached outbuilding under 15 square metres with no sleeping accommodation does not normally need building regulations approval, and the largest footprints in the live outdoor range, the Onyxia Barrel at 2.25 by 2.4 metres and the Orphée Lounge 240 at 2.05 by 2.4 metres including its terrace, are about 5.4 and 4.9 square metres. The electrical work is the exception: a room containing a sauna heater is a special location under Approved Document P, so the circuit is notifiable whatever the building is. Our planning permission guide covers the rest of the permitted development conditions.

What has to be finished before delivery day?

• The base, complete. The Hestia 160 page says the cabin arrives on a pallet, delivered kerbside, with moving it to the base the buyer's to arrange. A base still being built on that day leaves a 649kg pallet at the kerb.
• A route for the cable. Every live outdoor product page specifies its heater circuit in steel wire armoured cable. If the base is concrete, agree with your electrician where the cable comes up before it is poured; that is our advice rather than a maker's instruction, and it saves breaking into a finished slab.
• The fixings, for a Harvia. Agree how the cabin will be anchored with whoever builds the base, because Harvia makes anchoring the buyer's job.
• Somewhere for water to go. Harvia's instructions say two holes are pre-drilled in the lowest stave "to drain water from the floor", so a barrel empties onto its base by design. The base should carry that water away rather than hold it.
• Room to build. Almost Heaven says assembly needs space for a person on each side, though a finished barrel needs only a few inches. The Hestia 160 page puts assembly at three to four people.

How the pallet arrives, what comes off it and how many people it takes to carry to the base are covered in our guide to how a garden sauna is delivered.

What this means when choosing a sauna

The base is usually decided after the sauna. It is better decided alongside it, because it can change which model suits your garden.

If you want the lightest groundwork, or the plot is one where pouring concrete is awkward, look first at the Almost Heaven barrels, whose maker accepts compacted gravel or paving. The Almost Heaven Audra is the canopy version of the four person barrel, seating two to four, with a 6kW heater in the price.

If you are pouring a slab anyway, the whole range is open, including the two Harvia barrels, provided the slab is flat enough for Harvia's wording and the cabin is anchored to it.

If the only space is against a fence, choose the base and the cabin together. A 2 metre cabin such as the Cocoon 130 or Gaïa Urban leaves half a metre for a base; the 2.26 metre Onyxia Barrel leaves 24cm.

Every model in the outdoor sauna collection states its dimensions on its page, and most state their height. Plan your space asks about your base and access before recommending anything, and the outdoor sauna buying guide puts the base in order with the other four decisions.

Sources

• Harvia, assembly instructions for the Kaski 180 and Kuusi 180 Panorama, pages 3, 4 and 7. Assembly instructions (PDF)
• Almost Heaven, How to prepare your barrel sauna site, updated 14 March 2025. almostheaven.com
• Almost Heaven, frequently asked questions. almostheaven.com
• Permitted development limits for outbuildings: Planning Portal. planningportal.co.uk
• Ground level, raised platforms and decking: Permitted development rights for householders, technical guidance, updated 10 September 2019. gov.uk
• Building regulations for outbuildings: Planning Portal. planningportal.co.uk
• Notifiable electrical work and special locations: Approved Document P, 2013 edition. gov.uk
• Weights, dimensions, heights, heaters, circuits and warranty terms: Tarnfell's live product pages for each model named, read 21 and 24 September 2026.