Planning permission

The first point you should consider (seeing where you give as your location) is that everything is totally legal and authorised as it is.

If so, start with an informal discussion with your local councillor, then with the planning department at your ayuntamiento. Given that there is not a shortage of property on the market it may well make better sense to buy whay you want, rather than get involved in what will at the very least be a complex and expensive procedure?

Gill52 - It is my understanding that the Town Hall will not give any official planning permissions for extensions to property on Camposol  at all, until they have finished their long drawn-out re-assessments on extensions etc.( for increased IBI purposes) that they don't know about.  I say official permissions, because I can see un-official extensions going up around where I live all the time; and if you can hide one for 4 years without being detected it will become official. But you will have an increase in IBI to pay when you are eventually re-assessed.I have just been given an increase in my IBI double what I paid last year, just because I have an underbuild.