tiling on a flat roof?

[bluesky]

hi all ,
just been to price up some more victorian work and one of the floors is going to be on a flat roof which the client has now made into a proper room with glass roof etc so is completely watertight and is a part of the house .need to build the floor up 5-7 mm before tiling .i believe the flat roof is solid 22mm ext ply with the flat roof covering on top .my thoughts are to add 6mm cement boards (or ply)screwed and glued through to the ply which can be tiled on with flex adhesive .any thought /advice - this is not the norm i`m sure !!!
many thanks

[doug boardley]

you'll be talking extremes of weather on a substrate that is likely to move in the best of conditions, I'm gonna chicken out on this one

[bluesky]

thanks doug , the weather shouldn`t be a problem as there has been strengthening work done to enable the new 1st floor to be built above .concerns are that the builder!was going to lay levelling compound to build the levels up .and i would prefer to fix something more solid.
thanks for advice and your worries!

[doug boardley]

sorry bluesky, having re read your post ( I initially thought you were doing a terrace roof, it's been a long day), but you seem to have thought it through with the hardiebacker, that's how I'd be tempted to tackle it too

[Dave]

So all deflection issues have been sorted..?

[mikethetile]

is it a built up felt roof

if its felt the felt will slowly compress with the weight, also if its a warm roof construction there could be foam insulation boards between the felt and boarding

its best to have the roof covering off and then treat the floor as you would any other wood floor

its unlikely to be asphalt as that is laid over concrete

[bluesky]

no deflection - i will check tomorrow re relt roof materials and if they can be taken back to 22mm ply.thanks to all.

[lucius]

I definitely wouldnt go over the felt, it has been mentioned before that Shluter do a system specficly for flat roofs balconies etc.
Lucius.