Yes, I do agree with you that a free standing wall would be dangerous. However in my case I was going to tie it in to right angled walls either end of the wall and as it goes through to the first floor I was going to fasten joists to either side for my flooring.
But going back to my question was is the maximum height and length I can build an internal wall without supporting blocks?
It has been normal practice to build single leaf internal walls to roof level as dividing walls between rooms as long as they are built into a property as you propose.
If this proposal is a new wall? Then you need to give serious consideration to its finished weight and how you can provide adaquate foundations for it and what effect it may have on the existing property.
I would suggest that you consult your local council before starting work.
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