Loft Insulation - existing bathrooms condensation

[frank999]

I am installing a loft, the existing bathrooms ceiling does not have a vapour barrier - it simply has one 12.5mm plaster boards thickness for the ceiling, with 100mm rockwall on top.

I am concerned condensation will build up in the void above the ceiling and the new loft floor - 250mm above, which itself will be a bathroom.

Whilst stripping tiles off we placed a tarp over the bathroom area, when we removed it a day later the rockwall was soaked and the tarp very wet - so a a lot of moisture is either condensing above the ceiling - or moisture is escaping - which could be a result of using ordinary down lighters (ie not IP65's - which I assume have a rubber seal to stop this moisture escaping into the fitting and beyond.

 

[Chri5]

Having swiss cheese holes in a bathroom doesnt help.

Correct venting via a humistat controlled fan will help, as for the spots then a sealed unit will help but in terms of reg is only required if the floor to ceiling height is less than 2.25m

Since there is now an occupied room above the existing unit I'm pretty sure the regs require fire rated fittings.

Id change them over for some LED units, down from 50w to 6-7w offsets the cost after a year or two.

 

[frank999]

Your correct, fire rated fittings are required, down lighters create a break in the fire proofing provided by the plasterboard ceiling.

So no need to create any type of vapour barrier in the existing bathroom ceiling? this will mean moisture rising up into the void between the new loft floor and the existing bathroom ceiling.

I would have thought it better to try trap the moisture and keep it in the bathroom - venting that out with a powerful fan, 150mm 250 m2, these little 90 m2 dont seem to clear the air quick enough.

With this in mind, I can see us putting any form of vapour barrier above the existing ceiling - ie between the rafters, and on top of the plaster board in the loft.
Could we not simply sandwich a vapour barrier on the underside (in the bathroom) and put plaster board over that ? - or should the existing plasterboard be stripped down vapour layer pinned up and plaster board then over that. Is there not a product for such an application available ?