1. Drainage before layout
In every wet build, the drain position is the least movable thing in a wellness room and it should therefore be decided first. A wet wellness room wants a linear channel or a central gully with the finished floor falling toward it at roughly 1.5–2 %. That fall has to be built into the screed, which means the structural slab either has a recess or the finished floor rises above the corridor and you now own a threshold detail and a level change.
In Gulf residential towers this is the single most common blocker. The slab is post-tensioned, coring is restricted to surveyed zones, and the nearest stack is on the other side of a demising wall. Any honest contractor tells you this in week one. We would rather move the room than pump a wet room uphill, and where the room truly cannot move, a sealed tray with a shallow pumped waste is a solution — but it is a compromise, it needs maintenance access, and it needs to be written into the O&M documentation rather than discovered by the facilities team two years later.
2. Ceiling void and structural height
The internal clear height of a usable thermal room sits around 2,100–2,300 mm. Above that ceiling you need a services zone for supply and extract ductwork, luminaire drivers, and — in a steam room — the vapour-tight ceiling build-up and its fall. Below the slab soffit you also need the corridor’s own services crossing.
The arithmetic gets tight quickly. When a residential floor-to-soffit is modest, the room either loses its top bench or the ductwork loses its route. We have walked into more than one project where the sauna was delivered, the benches were installed, and the top bench was unusable because a fire main crossed at head height. Get the wellness room drawn in section, not just in plan. Our note on sauna ventilation covers what the void actually has to carry.
3. Ventilation as a designed system, not a grille
A wellness room is ventilated for three separate reasons and they pull in different directions: occupant fresh air, moisture removal, and drying the fabric between sessions.
For a commercial dry sauna we design toward roughly six to eight air changes per hour, with the supply low and near the heater so incoming air is drawn across it, and the extract high on the opposite side, ducted to outside rather than dumped into a ceiling void. For a wet room the extract has to keep running after the last session, on an overrun timer, or the room never dries and the grout, the silicone and the ceiling junctions start to fail in sequence.
The mistake we see most often in the region is a wet room extracted into a common ceiling plenum that also serves bedrooms. That plenum then becomes a condensation surface. This is a specification error, not an installation error, and it is caught by reading the MEP drawing rather than the sauna drawing. For the space outside the cabin the same discipline applies as in any other occupied room, and the ventilation reference most consultants in the region design to is the set of ASHRAE standards and guidelines.
4. Electrical supply, protection and cable rating
Thermal rooms carry unusual electrical requirements that a general fit-out package will not anticipate.
- Dedicated circuits. A commercial sauna heater is a fixed appliance on its own protected circuit, sized to the heater and not to a socket ring.
- Cable temperature rating. Wiring inside the hot zone must be rated for it — silicone-insulated cable rather than standard PVC, terminated in a junction outside the heater’s radiant field.
- Ingress protection. Fittings inside a wet room need the appropriate IP rating for their zone; a luminaire suitable for the ceiling of a dry sauna is not automatically suitable above a steam bench.
- Isolation and lock-off. Commercial rooms need a local means of isolation for service, plus a lockable enable for operations so the room cannot be switched on outside opening hours.
- Earthing and bonding. Every metallic element inside the room — heater guard, door hardware, drain body, bench frame — belongs in the bonding schedule.
Which of these you actually get depends on whether the wellness room was tendered as an electrical scope or as a joinery scope. When it is joinery, the electrical detail tends to be assumed. Our commercial sauna specification guide sets out the clause language that closes that gap in a tender document.
5. Substrate and tanking
Under the visible finish, a wet wellness room is a waterproof box. Cement-based boards or foam-cored tile backer boards, taped and sealed at every joint and corner, with a bonded liquid or sheet membrane, then adhesive, then finish. In a steam room the ceiling is part of the tanked envelope and is built with a fall so condensate runs to the walls rather than dripping onto a seated occupant. In a hammam the heated bench and the heated floor sit inside that same envelope with their pipework or elements laid before the membrane closes.
For dry saunas the requirement is different but not absent: a tanked and drained floor build-up under the cabin, because feet arrive wet and the floor beneath a timber cabin is the part nobody ever inspects. Our steam room build guide walks the layer sequence for wet rooms in more detail.