I have just purchased 50% of shared freehold. I have the first floor flat and my neighbour has the ground floor flat. I would like to convert the bigger of the two loft spaces, my neighbour does not have access to them. Would I need her permission to

[teresalyons]

convert/alter the space and would I need to buy her out of the loft I wanted to convert. I I am presuming she owns half the space?

[Count-A-Strong]

How come there are two loft spaces if hers is the ground floor flat. Presumably one of the spaces is over your first floor, so where's the other?
Are you aware that there are some quite strict building regulations which have to be met to convert a loft into living accommodation concerning fire protected routes, means of access etc?

[cassa333]

What does it say on your deeds about the loft?

I cannot see how the downstairs have rights over the loft space if they cannot access it. If there were a basement do you think you would have rights over this if you had no access?

If you own it then you do not need their permission but wuld probably need planning permission.