Waterproofing a balcony above living space

I have been researching different ways to waterproof an exterior deck/balcony over living space and it appears that using the Schluter system with the membrane (or a similar product) and on top of that the Ditra Drain plus a good tile is a good way to go for my 16 x 7 1/2 foot deck. That way you have a waterproof seal and the Ditra Drain isolates the tile from movement in the substrate and also allows moisture to “drain” away from the mortar in which the tile is set (as I understand it).

But wow that Ditra Drain is expensive, especially on top of the cost of the waterproof membrane. If I wasn’t concerned with expansion/contraction in the plywood and floor rafters would I need the Ditra Drain? Or: I don’t suppose there is some way to minimize the amount of water that would seep through the tiles and grout into the mortar and get by without the ditra drain?

Would it be possible to just put down the membrane and top it with mortar and perhaps some other type of material until a later time when i can afford to add the ditra drain and install the tile? Of course I still need the waterproof membrane, but is there a way to put off the cost of using ditra drain and then tiling on top of that?

Any other alternatives that you would recommend? Everything else that I have looked at , like liquid rubber, can sound good but when it is all said and done (sealing tape, primer, etc.) the cost isn’t really that much less per square foot that using a waterproof membrane system, especially without the ditra drain.

Just to recap my situation: right now I have an exterior deck over living space that is rafters and plywood and temporarily covered with ice and water shield. The space is about 16×7 foot and has 6×6 posts and cable rail around the outside edge. The roof is slightly pitched, certainly more than the 1/4 inch per foot that is usually seen as a minimum slope I believe. Would like to have a tile surface when it is all done, but wouldn’t have to do that if there are better alternatives that are a lot cheaper.



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