Puddle flanges. What AS 3740 requires.

Water that gets under the tiles runs along the membrane to the waste. The puddle flange is the part that lets it into the pipe. Get it wrong and that water goes into the slab instead.

The five rules for the flange

1. Recessed. The flange is set into the floor so it finishes flush. It never sits proud of the surface.
2. Sealed to the pipe. The join between the flange and the riser is watertight.
3. Fixed. The flange cannot move once it is set.
4. Same size as the riser. A 100 mm pipe takes a 100 mm flange.
5. Filleted. A bead of sealant is tooled where the flange meets the floor.

The membrane on the flange

The membrane is bonded onto the flat of the flange, or onto the flat and down the leg. The standard gives no lap length, so follow the membrane's data sheet and the detail drawing. Keep the flange clear of bond breakers and of the wall and floor junction, so the two do not clash.

Where the membrane sits under a screed or tile bed, the flange has to drain the bed at membrane level, and the floor under the membrane falls to it at 1:100 or more.

Linear drains

With a channel drain, the membrane runs into the outlet without a break. If the channel has no built-in flange or upstand of 50 mm for the membrane to bond to, the membrane goes under the channel to a recessed flange below.

Who sets it?

The standards do not say which trade installs the flange. The plumbing standard covers the waste, the trap and the grate; it does not mention the flange at all.

FORSPEC's advice: the plumber sets the flange, and the waterproofer checks it is flush, fixed and sealed before the primer goes on. If it is not, stop and have it fixed.