A Bathroom Specification Guide for Architects

Most bathroom problems on site are not product failures. They are coordination failures — a decision made too late, or made without the information that another trade needed six weeks earlier. This is the sequence that avoids most of them.

Fix the concealed specification first

Concealed shower valves, installation frames, cisterns, shower channels and drainage all have to be decided before first fix. They determine wall build-ups, service routes and structural support, and none of them can be revisited once the walls are closed.

This means the shower system has to be chosen — at least to the level of valve body and number of outlets — considerably earlier than most clients expect. Building that into the programme early avoids the most expensive category of change.

Coordinate the wall build-up

• Confirm the pre-wall depth required by the installation frame and concealed valve, and check it against the drawn wall.
• Verify the finished tile or slab thickness against the valve's escutcheon adjustment range.
• Set the fixing positions for wall-hung ceramics before the frame is ordered.
• Locate the electrical supply for a smart WC at first fix, positioned to stay concealed.

Design the falls and waterproofing properly

Level-access shower areas are the most common source of defects. The fall has to be designed rather than assumed, the channel or gully position has to be coordinated with both the tile setting-out and the structure below, and the tanking has to be detailed at every junction.

Manufacturers such as Viega and Geberit publish detailed technical documentation for these conditions. Using it is faster than resolving the details from first principles.

Set out the tiling before ordering

With large-format tiles and slabs, setting out is a design decision rather than a site decision. Where the joints fall relative to the niche, the channel, the WC centreline and the vanity determines whether the room reads as resolved.

Produce a tiling layout drawing. It takes an hour and it removes the single most common cause of a bathroom looking almost right.

Confirm the water supply against the specification

A shower system with an overhead, a hand shower and body jets needs a supply capable of serving them. Check available pressure and flow before the system is specified, not after the client is disappointed by the result.

Lock finishes across the whole room

Schedule every visible metal component together — mixers, shower components, accessories, flush plate, channel grate, waste. Order them at the same time so batches match, and allow for the longer lead times that special finishes carry.

Build a realistic procurement programme

• Concealed components: required at first fix — order earliest.
• Ceramics and furniture: typically the longest lead items, particularly in non-standard colours.
• Special and custom finishes: allow substantially longer than standard finishes.
• Tiles and slabs: confirm batch availability for the full quantity, including wastage, in one order.