Underfloor heat in wet room

[hairyben]

Wet room floor construction: combined waterproof membrane/insulating construction board, then adhesive and tiles.

Now, I'd have thought, given it's a wet room, zone 0 would extend to the membrane, and the element would go underneath, but given it's an insulating membrane this would be pointless.

I've spoken to a couple of different companies who supply element, with differing results- one said it's fine to go on top, right under the tile, the other say it should be beneath a membrane.

Thoughts? It looks like, given the situation I'm working to, I'm gonna go with the "right underneath the tile" option, although I can't say I'm happy- and may run it by the NIC tech line chaps.

 

[ericmark]

I looked at this for my Mother's wet room and it seems some elements have a earthed brade around the heating wires and these do not need a fine mesh metallic grid see 701.753 as they have a metal sheath.
I emailed the manufactures to be sure but when reading the spec I agree it is hard to certain as to which is and which is not provided with the required protection.
However main problem is where one foot is at one voltage and the other foot is at a different voltage but my mother only has one foot so this would be no problem!
Eric

 

[hairyben]

Yes, the earth braiding/grid is a different issue though.

Where does zone 0 extend to? The tiles or the waterproof membrane? Surely it must be the membrane - it's the main water barrier because tiles and grout are not considered reliable enough on their own to contain the water in a wet room situation?

And if I'm right, you can't put a 240v element in zone 0!

 

[ericmark]

701.32.2 Description of zone 0
Zone 0 is the interior of the bash tub or shower basin (see Figures 701.1 and 701 2).
For showers without a basin, the height of zone 0 is 0.10 m and its surface extent has the same horizontal extent as zone 1 (see Figure 701.2).
701.753 Electric floor heating systems
For electric floor heating systems, only heating cables according to relevant product standards or thin sheet flexible heating elements according to the relevant equipment standard shall be erected provided that they have either a metal sheath or a metal enclosure or a fine mesh metallic grid. The fine mesh metallic grid, metal sheath or metal enclosure shall be connected to the protective conductor of the supply circuit Compliance with the latter requirement is not required if the protective measure SELV is provided for the floor heating system.
For electric floor heating systems the protective measure "protection by electrical separation is not permitted.

Under a bath where removal of sides require a tool is outside the zones so I would class under tiles the same. But that is a personal view.
Eric