Raising Bathroom Floor


I have a room that I'm converting into a bathroom. The height of the floor will not give enough of a drop for the toilet waste pipe. I have been advised that I should raise the height of the floor by laying some joists and floorboards. The floor underneath I guess is concrete with ceramic tiles on top.
How should I fix the joists and should I lay any type of insulation under the floorboards?
cheers
Dan
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This probably doesn't answer your question but in my mother's ground floor flat the previous occupants converted a room so it's now got a shower, toilet and wash basin. The shower and toilet are on a raised wooden platform, about 3" tall, going across the width of the room, but the rest is at standard level and it looks OK.
The alternative would have been some serious digging up of concrete floors to reach an outside drain at a lower level.
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