The standard house has water in every wall. Kitchen sink on the north wall, bathroom on the east, washing machine on the south, outdoor tap on the west. Each runs its own pipe through its own hole in a different stud. Each is a potential leak point buried behind plasterboard. When a joint fails, you cut open the wall, fix the pipe, repair the plaster, repaint. The cost of the leak is not the pipe. It is the destruction.
A one-wall plumbing system does the opposite. Every wet fixture, kitchen sink, bathroom, washing machine, even the outdoor tap, connects to a single plumbing wall. The wall is framed at 150mm or 200mm deep to accept all pipes comfortably. Every joint is accessible from one side, either through a removable service panel or by unscrewing the OSB skin.
Why builders do not do this
Because it requires planning. The conventional approach is lazy: the plumber arrives after framing, walks through with a pencil, and drills holes wherever needed. A wet wall demands that the architect (or the self-builder with a pencil) decided in advance where every fixture goes. That planning is the work. The reward is a system with fewer failure points, faster install, and trivial maintenance.
The cost difference
| Item | Conventional distributed | Single wet wall |
|---|---|---|
| Pipe length (50m² house) | 35–45 metres | 18–22 metres |
| Fittings and joints | 40–60 | 20–30 |
| Framing labour | Standard | +1 day (deeper wall) |
| Leak risk points | 40–60 buried joints | 20–30, all accessible |
| Repair access | Demolition | Unscrew panel |
The pipe length reduction alone saves €200–€400 in materials for a small house. More importantly, it saves the hidden cost: the time a plumber spends threading pipe through multiple walls, drilling studs, and sealing penetrations. A competent plumber can rough-in a wet wall in four hours. Distributed plumbing takes two days.
How it works in practice
In the Hestia layout, the wet wall runs along the corridor between the bathroom and kitchen. The bathroom sink, shower, toilet cistern (if using a flush toilet), and washing machine all connect from one side. The kitchen sink and dishwasher connect from the other. The wall is framed with 50 × 150mm studs at 400mm centres, but the wet section uses 50 × 200mm studs to give 200mm of clear cavity. PEX pipe, in continuous lengths with no joints inside the wall, runs vertically from a manifold at the base.
The manifold is the other key detail. Instead of branching with tees inside the wall, each fixture gets a dedicated home-run line back to a central manifold. The manifold is mounted on the wet wall, accessible behind a service panel. If a fixture develops a fault, you shut its valve at the manifold. No other fixture loses pressure. If the manifold itself needs replacement, it is on the surface, not buried.
The real objection: convenience
"What if I want an outdoor tap on the opposite wall?" Run a single 16mm PEX line through the ceiling space, above the insulation, in a clip-on conduit. It is one pipe, one hole, one exterior wall penetration. The rest of the house has zero plumbing in its walls.
"What about a second bathroom?" If the floor plan demands it, add a second wet wall. Two wet walls are still vastly simpler than six partially wet walls. The principle is concentration, not absolute singularity. But for a two-bedroom family house, one wet wall serves all needs comfortably.
"It looks cheap." This is the objection that has nothing to do with function. A wet wall requires that the bathroom and kitchen are adjacent or back-to-back. In a small house, they should be anyway. The corridor between them is the wet wall. There is no aesthetic penalty because the wall is inside the corridor, not a living space. The living spaces have clean walls with no pipes, no penetrations, and no risk.
Water damage containment
The hidden advantage, and the one that matters most over a twenty-year ownership, is containment. A leak in a conventional wall can run inside the cavity, across the wall, down to the floor, and into the subfloor before anyone notices. The damage spreads. Mold grows. Floor joists rot.
A leak in a wet wall is immediately visible: the service panel shows moisture, or the OSB skin on the wet wall shows staining. The wall itself is designed to handle moisture: rockwool drains and dries, OSB is bonded with waterproof adhesive, and the pallet subfloor is elevated on ground screws with ventilation beneath. The damage is localised and repairable in an afternoon.
The bottom line
One wet wall is a design discipline, not a compromise. It demands that you think about where water goes before you build. It rewards that thinking with lower cost, faster install, accessible maintenance, and contained risk. The houses that suffer catastrophic water damage are almost never the ones with a single, well-planned wet wall. They are the ones where a plumber drilled holes everywhere and nobody remembers where.