Last updated: September 2026
Short answer: apartments with sauna are limited by 3 numbers that have nothing to do with the cabin — the spare current at the consumer unit, the floor’s imposed load allowance, and the free area of the air path in and out of the room. A 6 kW heater needs about 26 A on a single phase, a 4 m² cabin adds roughly 1.5 kN/m² to the slab, and the cabin needs an inlet and an outlet of about 125 cm² each. Everything else is joinery.
Most enquiries about apartments with sauna arrive as a plan with a rectangle drawn on it. The rectangle is almost always fine. What decides the job is the riser, the slab and the neighbour, and those 3 are settled by the building rather than by the cabin. This guide sets out the 15 checks we run before a cabin is priced for a flat, in the order the answers arrive.
What do apartments with sauna need from the building?
Usually yes, and the limit is rarely the space. A cabin for 2 people fits in 1.2 by 1.5 m, about 1.8 m², and a 4-person cabin needs roughly 2.0 by 2.0 m. The obstacles are the 3 supplies the flat has to give it: current, air and structural capacity.
We have fitted cabins into flats with as little as 1.6 m² of floor area, and we have turned down flats with 12 m² of spare room because the incoming supply had 4 A of headroom. The rectangle on the plan is the easiest part of the problem and the last thing worth arguing about.
In apartments with sauna the right sequence is to settle the electrics first, then the air path, then the load, and only then draw the cabin. Doing it the other way round produces a drawing everyone likes and a quotation that cannot be built, which is the single most common way these projects stall.
How much electrical supply does a sauna need?
Roughly 1 kW of heater for every 1.0 to 1.5 m³ of cabin, so a 2.0 by 2.0 by 2.1 m cabin of 8.4 m³ wants 6 to 8 kW. At 400 V across 3 phases a 6 kW heater draws about 8.7 A per phase; on a single 230 V phase the same heater draws 26 A.
That difference is the whole project. In apartments with sauna a 3-phase supply makes the heater a minor addition to the board. A single-phase supply puts a 26 A continuous load next to an oven, a hob and a water heater, on a main fuse that in many flats is 25, 32 or 40 A in total.
The heater circuit is also a dedicated circuit with its own protective device, and in a wet-adjacent room it sits behind a 30 mA residual current device. None of that is unusual, but all of it needs spare ways in the consumer unit, and older flats frequently have none. We set out the sizing arithmetic in full in our note on sauna heater sizing.
What if the flat has only a single phase?
Then the practical ceiling for apartments with sauna is a 4.5 kW heater, which draws about 19.6 A at 230 V and fits a 25 A circuit. That heats a cabin of roughly 4.5 to 6.5 m³, which in plan is about 1.5 by 1.5 m at 2.1 m high — a genuine 2-person cabin rather than a compromise.
The second option is an infrared cabin, where emitters of 1.5 to 2.4 kW run on a normal 16 A circuit. It is a different product with a different experience, not a smaller sauna, and it should be presented that way rather than as a downgrade. The types of sauna heater differ in what they heat, not only in how much.
The third option is an upgrade to the supply, which is a building conversation rather than a flat conversation. Adding a second or third phase means work in the riser and in the meter position, and in most managed buildings it needs the freeholder’s consent before an electrician will quote it.
How much does a sauna actually weigh?
A 4 m² cabin in 15 mm panelling with benches weighs roughly 250 to 350 kg empty. The heater adds 20 to 45 kg and its stones another 20 to 60 kg. With 4 occupants at 80 kg the total reaches about 620 kg, which over 4 m² is about 1.55 kN/m².
That number is the one a structural engineer will ask for in apartments with sauna, and it is worth calculating rather than estimating, because the stone charge is the part people leave out. A heater specified for 60 kg of stones is carrying the equivalent of an extra adult, permanently, in one corner of the cabin.
Soapstone and cast-iron heaters change the answer again. A soapstone-clad heater can weigh 150 kg before stones, which concentrates about 200 kg into a footprint of under 0.25 m², or more than 8 kN/m² locally. That is a point load, and point loads are checked separately from the area load.
Does an apartment slab take that load?
Almost always, for the area load, which is why apartments with sauna are possible at all. Residential floors in the Eurocode category A are designed for an imposed load of 1.5 to 2.0 kN/m², and a loaded 4 m² cabin at about 1.55 kN/m² sits inside that band. The check that matters is the local one under the heater.
The honest caveat is that “almost always” is not a structural calculation. Balconies, terraces and converted roof spaces have different allowances, and a flat over an undercroft or a car park deck can have a slab designed for a completely different régime. The engineer needs the layout and the 3 weights, not a reassurance.
Where a point load is a concern, the fix is cheap if it is early: a spreader plate under the heater, or a bench-mounted heater that hangs the mass on the cabin frame. Both are decided before the cabin is manufactured, and neither is possible after it is delivered.
How much ceiling height does the cabin take?
The cabin wants 2.0 to 2.1 m of internal height, and it needs roughly 100 to 150 mm above that for the roof panel and the service void. A flat with a 2.55 m slab-to-slab ceiling therefore has around 300 mm to spare, which is enough for a cabin and nothing else.
Going taller is not a courtesy to the guest; it is a penalty. Every extra 100 mm of height on a 4 m² cabin adds 0.4 m³ that the heater has to bring to 80 °C and then keep there, and the heat that matters sits at head level anyway. A 2.4 m cabin runs a cool bench and a hot ceiling.
The other way this bites is the door. A standard sauna door leaf is about 1,890 to 1,900 mm high in a 2,000 mm frame, and where a flat has a 2,050 mm structural opening between rooms the cabin cannot simply sit under it. The door position is a coordination item, not a selection item.
Where does the air come from, and where does it go?
From a low inlet near the heater and out through a high-level outlet on the far side, each with about 125 cm² of free area for a 4 m² cabin. That is 3 to 6 complete air changes an hour, and it is what stops the top bench from going stale after 20 minutes.
The inlet is normally a slot or duct at floor level under or beside the heater, so incoming air is drawn across the stones. The outlet sits diagonally opposite, high, and it does not discharge into the room next door — it goes to a duct or to a genuinely ventilated void.
Apartments make both of these harder than houses do, because there is rarely an external wall to hand and the flat’s own extract system is already balanced. The full logic of the 2 openings is set out in our guide to sauna ventilation, and it applies unchanged inside a flat.
Can the cabin share the bathroom extract?
Rarely, and never without checking the fan, because apartments with sauna sit on a commissioned extract system. A sauna outlet delivers air at 60 to 80 °C into a duct sized for 22 °C bathroom air, and most domestic bathroom fans are rated for continuous running up to 40 °C. The fan is the item that fails, usually in the second year.
The other problem is balance. A flat’s extract system is commissioned as a set, and adding a branch changes the flow at every other terminal. In a building with a central extract riser, one flat’s alteration can move air in flats above and below it, which is exactly the kind of change a managing agent will refuse retrospectively.
Where a dedicated route is impossible, the workable answer is a passive outlet into the flat’s own bathroom or utility space, sized generously, with the flat’s normal extract dealing with it. That is a legitimate design, but it has to be drawn and agreed, not improvised behind the panelling.
What does the neighbour actually hear?
Three things, and in apartments with sauna they all travel through the frame: the heater contactor, the fan, and the bench. The contactor in a sauna control gear clicks each time it cycles, which on a 6 kW heater at temperature is typically every 2 to 4 minutes, and structure-borne clicks travel a long way through a concrete frame.
The fix is to mount the control gear on resilient pads, off the party wall, and to specify a solid-state relay rather than a mechanical contactor where the layout puts the controls near a bedroom. Both cost little at first fix and are unreachable after the cabin is clad.
The cabin itself should not touch the party wall. We build apartment cabins with a 20 to 30 mm cavity on any separating construction and resilient feet under the frame, so the structure-borne path is broken. A cabin screwed hard to a party wall turns the whole wall into a soundboard.
Does the floor under a sauna need waterproofing?
A domestic cabin used dry does not need a tanked floor, but it does need a floor that tolerates water. We build on a tiled or stone floor with a sealed junction, and where a shower sits within 1.5 m of the cabin door the tanking from the shower area is carried under the cabin footprint.
The load case people forget is the bucket. A 5 litre bucket tipped on a timber floor does no damage on the day and considerable damage over 10 years, because the water goes into the joint and stays there. A tiled base with a 10 to 15 mm upstand behind the skirting removes that risk entirely.
Where a floor drain is present, it needs a trap that will not dry out. A sauna floor gully that is used twice a month loses its seal to evaporation, and the first symptom is a smell in a room that is otherwise dry. A trap with a membrane insert or a regular top-up solves it.
What are the clearances around the heater?
They come from the heater’s own documentation, not from a general rule, and they are normally between 50 and 200 mm to the side walls and 1,000 to 1,300 mm above the stones. Those figures are set by the heater manufacturer and tested against IEC 60335-2-53, which belongs to the manufacturer rather than to us.
The guard rail is a separate item. Its purpose is to stop a bather falling onto the stones, and it is dimensioned so that no part of the body reaches the heater casing. On a floor-standing heater we build it as part of the cabin joinery rather than buying it loose, because a loose rail moves.
The ceiling above the heater is the surface that runs hottest and the one most often clad in something it should not be. It stays as timber board with an air gap behind, and it carries no light fitting, no speaker and no extract grille within the manufacturer’s stated clearance.
What does the building manager need to approve?
For apartments with sauna in most managed buildings, 4 things: any alteration to the electrical riser, any new penetration of a separating wall or floor, any change to the ventilation system, and any works that affect the building’s fire strategy. A cabin that touches none of those is usually treated as a fit-out item.
The paperwork is easier if it is asked for early and in the building’s own language. A single-page schedule listing the heater rating in kW, the circuit rating in amperes, the added floor load in kN/m², the ventilation openings in cm² and the working hours will normally get an answer in a week.
Retrofitting consent is the expensive path. We have seen cabins built and then required to be isolated because the supply upgrade was never authorised, and the cost of that is not the cabin — it is the 3 months the flat spends with a decommissioned room in it.
How does a shared residents’ sauna differ?
It becomes a commercial installation with domestic neighbours. A shared cabin needs an emergency call point wired to a manned position, a heater guard, a run-limiting timer, a lockable isolator and a duty cycle that assumes 6 to 10 hours a day rather than 3 hours a week.
The materials change with the duty. Bench slats that last 15 years in a private flat need replacing in 4 or 5 in a residents’ cabin, so we move to thicker sections and to a species chosen for wear rather than for appearance. The heater moves up a class for the same reason.
Cleaning access changes too. A shared cabin needs benches that lift out without tools, a floor that can be washed down, and a gap under the lowest bench that a mop head actually fits into — about 120 mm. None of that is visible in a photograph and all of it decides how the room looks in year 3.
How is the cabin carried in?
In pieces, through the lift, which in apartments with sauna is the dimension that decides the joinery. The controlling dimension is usually the lift car’s internal depth and its door width, commonly 900 to 1,100 mm and 800 to 900 mm respectively, and every wall panel is made to pass through both. A 2.0 m wall arrives as 2 or 3 elements rather than 1.
Where the lift will not take it, the next option is the stair, which sets a limit on panel length through the half-landing turn. We measure the tightest turn rather than the widest, and on a tight stair the cabin is made in 600 mm modules, which costs joinery time and saves a crane.
The heater is normally the single heaviest item that has to be carried, at 20 to 150 kg depending on type, and the stones arrive separately in 20 kg sacks so that nothing over about 30 kg has to be lifted by hand. That is a delivery note item, and it is worth stating on the order.
What has to be on the drawing before anyone orders
Eight items, and they fit on 1 sheet: the heater rating and its circuit, the available spare current at the board, the cabin’s loaded weight per square metre and its worst point load, the inlet and outlet free areas and routes, the party-wall cavity, the door swing, the lift or stair dimension, and the call point destination.
Every one of those is a number, and every one of them is cheap to change on paper. The reason they belong on a drawing rather than in an email is that the electrician, the joiner and the managing agent each need a different subset, and a drawing is the only document all 3 will read.
We settle all 8 before a cabin is manufactured, which is the same discipline we apply to a hotel thermal suite. Where a flat is part of a wider fit-out, the schedule goes into the main package rather than being treated as a late addition. Our spa design and installation services cover the cabin, the interfaces and the commissioning as 1 scope.
What this guide does not settle
The species and the section of the timber, which is a separate decision driven by how the cabin will be used rather than by the building. A residents’ cabin and a private one can sit in identical 4 m² shells and need different benches, and we treat that as its own exercise rather than a finish selection.
It also does not settle the kit-against-joinery question for a private flat. A factory cabin can be the right answer where the opening is regular and the supply is generous, and we set out what a boxed cabin does and does not include in our note on what an outdoor sauna kit contains. The same list applies indoors, minus the weather.
Finally, it does not settle the wider wet area. A cabin next to a shower, a steam room or a plunge area is a different brief from a cabin alone in a spare room, and if the flat is large enough to hold a circuit, the circuit should be designed as a circuit. Our sauna manufacturing scope starts at the cabin and our wet-area product range covers what sits around it.
Who is writing this
Sauna Dekor has designed and built wellness and thermal facilities since 1987 and is now in its 40th year, manufacturing in its own Istanbul facility with 19 employees, working under TS EN ISO 9001:2015, with projects delivered in more than 35 countries. In apartment buildings we work turnkey: the survey, the cabin, the electrical and ventilation interfaces, the acoustic separation and the commissioning.
What we do not make is equally clear. Sauna heaters, control panels, extract fans and residual current devices are not our products; they come from the equipment manufacturers we buy from, and any CE marking or IEC 60335-2-53 conformity on that equipment belongs to its manufacturer rather than to us. The TS EN ISO 9001:2015 certificate is ours; the rest are theirs. If you want the 8-item schedule filled in for a specific flat, talk to us with the board photograph and the floor plan.
Frequently asked questions about apartments with sauna
Can a sauna be installed in any apartment?
Not in any. Apartments with sauna need spare current — about 26 A for a 6 kW heater on a single phase — an air inlet and outlet of roughly 125 cm² each, and a slab that takes about 1.55 kN/m² over the cabin footprint.
How much electricity does an apartment sauna use?
A 6 kW heater draws 6 kW while heating and cycles at temperature, so a 1 hour session typically consumes 3 to 4 kWh. The load matters more than the consumption: 26 A on a single phase against a 32 A main fuse leaves very little for anything else.
What size sauna fits in a flat?
A 2 person cabin needs about 1.2 by 1.5 m and a 4 person cabin about 2.0 by 2.0 m. Internal height is 2.0 to 2.1 m, with 100 to 150 mm more for the roof panel above it.
How heavy is a sauna in an apartment?
A 4 m² cabin is 250 to 350 kg empty, plus 20 to 45 kg of heater and 20 to 60 kg of stones. Loaded with 4 people it reaches about 620 kg, roughly 1.55 kN/m² over the footprint.
Will the neighbours hear an apartment sauna?
They can hear the control gear rather than the room. A contactor cycling every 2 to 4 minutes transmits through a concrete frame, so the controls go on resilient mounts and the cabin keeps a 20 to 30 mm cavity off any party wall.
Does an apartment sauna need planning or landlord consent?
Usually landlord or managing-agent consent rather than planning permission. Approval is normally needed for 4 things: riser alterations, new penetrations through separating construction, ventilation changes, and anything touching the building fire strategy.
Can a sauna share the bathroom extract fan in a flat?
Rarely. Sauna outlet air arrives at 60 to 80 °C and most domestic bathroom fans are rated for continuous duty to 40 °C. A shared branch also unbalances a commissioned system, which managing agents in buildings with central risers normally refuse.
Sources
- Eurocode 1: Actions on structures, EN 1991-1-1 — European Commission Joint Research Centre. Source for the residential category A imposed floor load band of 1.5 to 2.0 kN/m² used in the loading check above. The standard belongs to CEN rather than to us.
- BS 7671, Requirements for Electrical Installations (IET Wiring Regulations) — Institution of Engineering and Technology. Reference for dedicated circuits, 30 mA residual current protection and the zone classification applied to wet-adjacent rooms. The standard belongs to the IET and BSI.
- IEC 60335-2-53, Household and similar electrical appliances. Safety. Particular requirements for sauna heating appliances — International Electrotechnical Commission. The clearance and run-limiting requirements cited here are tested by the heater manufacturers and the conformity belongs to them.
- EOS Saunatechnik technical documentation — EOS-Werke Günther GmbH. Manufacturer data for heater output bands, stone charges between 20 and 60 kg and the stated clearances to walls and ceiling. The product data and its conformity marks belong to EOS as manufacturer.
- Approved Document F, Ventilation — HM Government, England. Reference for the treatment of dwelling extract systems as commissioned, balanced sets, and for the principle that added branches change the flow at other terminals.
- Approved Document E, Resistance to the passage of sound — HM Government, England. Reference for separating-construction performance in flats and for the treatment of structure-borne transmission through a shared frame.
- Thermal conductivity of common materials, The Engineering ToolBox — the conductivity and density values behind the cabin weight and heat-up figures used above.
