From a VAT perspective its VAT exempt - so you can claim back all your VAT for both materials and labour (but not professional fees).
From a building control perspective its pretty much treated as a new build although clearly there are pre-existing features, limitations etc that have to be taken into account. Like a new build it normally requires certification throughout the build and upon completion (an architect can do this and its a bit like an NHBC stamp).
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local