Can You Fit a Wetroom Upstairs in a Glasgow Tenement Flat?

The floor is the main question

Most Glasgow tenements, whether in Dennistoun, Shawlands, Partick or Govanhill, have timber joists spanning between the walls, with floorboards on top and a layer of ash deafening sitting on boards between the joists. That floor moves slightly underfoot, and movement is what cracks tiles and breaks waterproofing.

Before anything else, the old boards need to come up so the joists can be checked. After a century or more it is common to find joist ends softened by old leaks around the bath or WC, or deep notches cut by past plumbers. Any of that has to be repaired or strengthened first. The floor is then stiffened, usually with extra noggins between the joists and a new deck of 18mm to 22mm plywood or a purpose-made wetroom board, screwed at close centres.

Getting the fall and the drain to work

A wetroom floor has to slope towards the drain, typically at around 1 in 40 to 1 in 80 across the shower area. On a timber floor this is normally done with a preformed shower tray former that sits flush with the surrounding deck, so the fall is built in and you keep a level threshold.

The trickier part is the waste. The trap and pipe have to fit within the joist depth and run with a fall to the soil stack, which in a tenement is usually on the back wall or in a corner of the bathroom. Things that affect the layout:

• Which way the joists run. A waste pipe running between joists is simple. Crossing them is restricted, because joists cannot be notched freely without weakening them.
• Distance to the stack. The further the shower is from it, the more height the pipe run needs, and a shallow floor void may not have it.
• Joist depth. Tenement joists are often 200mm to 250mm deep, which generally gives enough room for a low profile trap, but it needs to be measured, not assumed.
• Shared stacks. The soil pipe is usually common property, so new connections should be made carefully and existing cast iron checked for condition.

Waterproofing with a neighbour below

In an upper flat, the tanking is what protects the ceiling underneath you. Tiles and grout are not waterproof on their own. The whole floor should be covered with a tanking membrane, lapped up the walls, with the full shower area walls tanked as well, and with reinforced tape at every junction and corner and a proper seal around the drain.

On timber floors a flexible or decoupling membrane is worth having, as it tolerates the small seasonal movement an old building has. It is also sensible to flood test the floor before tiling, by plugging the drain and leaving water standing for some hours. A leak found then costs very little to fix. One found after tiling costs a great deal, and may involve someone else's cornicing.

Permissions, neighbours and factors

Like for like bathroom work inside your own flat does not usually need planning permission. A building warrant from Glasgow City Council may be needed if you are altering drainage, making a new connection to the stack or doing structural work to the floor, so it is worth checking with Building Standards before work starts. Listed buildings and some conservation area properties, which are common in the West End and parts of the Southside, can carry extra restrictions.

It is also good practice to check your title deeds, tell your factor if you have one, and let the neighbour below know. Water will probably need to be turned off briefly, and work over their ceiling goes more smoothly when they know about it in advance.

What it tends to cost and how long it takes

For a typical tenement bathroom of around 3 to 5 square metres, a fully tanked and tiled wetroom in Glasgow commonly falls somewhere between £6,000 and £12,000. Where it lands depends on the state of the joists, how far the drain has to run, your choice of tiles and fittings, and whether you add underfloor heating or move the WC.

Allow roughly two to three weeks on site. Joist repairs or a building warrant will add time. If the floor void turns out to be too shallow for a flush floor, a low profile tray of 25mm to 40mm gives a very similar look with less risk, and an honest fitter should tell you when that is the better option.