There’s a moment in most luxury new build projects when the brief expands. The kitchen is agreed. The master suite is settled. The cinema room is on the plan. And then someone mentions a sauna. Or a steam room. Or a cold plunge. Or all three. What looks like a straightforward wellness addition turns out to require some of the most technically demanding infrastructure in the entire build.
Searches for home saunas, steam rooms and cold plunge pools have risen sharply since 2022 and show no signs of levelling off. Infrared saunas alone are one of the most rapidly growing home feature searches in the UK. What was once the preserve of high-end hotel spas now appears regularly on the briefs of clients building or refurbishing at the £500,000-plus level.
Wellness routines have moved from occasional treat to daily practice for a significant proportion of high-net-worth households. When you’re building a forever home from the ground up, the question isn’t whether a wellness space adds value to your life. It’s whether you’ve planned for it properly.
This is the part most people discover too late. A home spa room is not a space you can decide on at second-fix stage and hand to a specialist to sort out. Several critical elements need to be in the fabric of the build long before any tiles or joinery appear.
Every functional wellness space needs drainage — and drainage needs to be considered at groundworks stage. A cold plunge requires a substantial drain and ideally a dedicated run back to the drainage stack. A steam room requires a floor drain with a proper fall to it. A sauna requires at least a drain adjacent to the room for post-session rinsing. These are not pipes you can thread through a finished floor slab.
This is the element that causes the most problems when it's missed. Steam rooms operate at 100% humidity. Traditional saunas generate significant moisture through perspiration and steam. Without a properly designed, mechanically-controlled ventilation system, you will get moisture migration into adjacent walls and ceilings — and over time, that means mould, structural damage, and a remediation bill that dwarfs the cost of getting the ventilation right in the first place.
A steam room is essentially a sealed, fully waterproofed box held at high humidity. The waterproofing system has to be specified correctly and applied before any finish materials go on. It cannot be added afterwards. This is specialist work — and it needs to be done by someone who understands what they're building, not applied as an afterthought by the tiling subcontractor.
A traditional Finnish sauna heater typically draws between 4.5 and 9 kilowatts. A steam generator requires a dedicated circuit and isolation switch. A cold plunge with a chiller unit adds further electrical demand. All of this needs to be calculated and incorporated into the M&E electrical design at first-fix stage. It's straightforward to plan for. It's a significant and messy thing to add retrospectively.
The most robust and satisfying experience for regular use. Requires a dedicated electrical circuit, proper ventilation with fresh air intake and exhaust, and insulation behind the internal lining boards. Cedar, alder and aspen are the most common lining choices. The room itself can be fairly compact — four square metres is workable for two people — but the infrastructure requirements need to be designed in.
The most technically demanding of the four. Requires full waterproofing on all surfaces, a floor drain with adequate falls, a steam generator with water supply and drainage, and a high-capacity mechanical ventilation system. Non-negotiable: the ceiling must be pitched so condensation runs to the walls rather than dripping on bathers.
The most straightforward from an infrastructure standpoint. Infrared cabins operate at lower temperatures, require less ventilation, produce less moisture, and draw less electrical power — typically 1.2 to 2 kilowatts. They can in some circumstances be added after the fact, but allowing for a dedicated circuit and the right room dimensions in the original drawings costs almost nothing at build stage and removes compromise later.
The installation that surprises people most. A built-in cold plunge requires excavation or a structural upstand, a waterproof shell, a drainage run, a recirculation system, and a chiller unit with its own electrical supply. For an in-ground installation, excavation and drainage work must happen at the same stage as any other groundworks.
Not everything needs to be resolved at planning stage. The specific sauna heater model, the steam generator brand, the finish materials, the bench configuration, the lighting design — all of these can be developed as the project progresses, often in collaboration with your interior designer.
Planning a luxury new build in Hertfordshire? Talk to Marshall about specification from the ground up.
At Marshall Construction, we include a dedicated conversation about wellness spaces at the beginning of every luxury new build. Not because every client wants a spa room — but because for those who do, or who think they might, the decision needs to happen before the groundworks go in.
A client who raises this at the design stage gets exactly the space they want, built properly, at a fraction of the cost of retrofitting. A client who raises it after practical completion gets a disruptive, expensive project that inevitably compromises either the finish or the function.
The wellness home is not a trend that is going to pass. For anyone building at this level, the question is simply whether you plan for it properly — or wish, two years later, that you had. Marshall Construction builds bespoke luxury homes across Hertfordshire, working with architects, interior designers and discerning private clients. If you’re planning a new build and want to discuss wellness spaces and specification from the ground up, we’d be glad to talk.