I have been advised to consider taking down a chimney stack which is no longer in use and have the resulting gap tiled over. as that would cost about the same as re-rendering, repointing and replacing flashings. I am receiving conflicting advice as to whether or not it is necesary to provide ventilation if its taken down to just below roof level. Can ayone give me a definitive answer please, and also, do I have to get Building Regs Approval?
I doubt you will get an answer with any guarantee of success from anybody. Suggest you try without ventilation and if this causes damp problems then ventilate the chimney at a later date.
You should not require building regulation approval for the removal of the top part.