A loft extension is potentially a great way of adding living space and value to a property, but beware of how it’s done. Not just on the building side, but on the legal side too.
Ensure the space you’re extending in to is yours. It’s in your lease and It’s part of your property. Regardless of how nice your freeholder is, ensure you have technical ownership, not just a “yeah, that’s not a problem” from them, or even a letter of consent to use it. DO NOT LEAVE THE LOFT SPACE IN OWNERSHIP OF THE FREEHOLDER. It just isn’t worth the risk.
When you come to sell, that freeholder may not be the same person. Any buyers solicitor will almost certainly demand that access and technical ownership is in the lease of the flat. This means you’ll have to buy the loft that you’ve already extended in to from the freeholder.
Doing this after the work has been done is incredibly dangerous. People often change their tune when they smell money. They’ll probably forget that they gave you consent to use the loft and can demand you jump through their hoops in order for your sale to go through.
They could choose to keep hold of their loft and not sell it to you and your sale will inevitably fall through. Some people are simply idiots.
If you’re lucky, you’ll have the greatest freeholder in the world that is entirely reasonable, kind and do anything to help you out. If you’re unlucky, you’ll have a freeholder that has you by the balls and wants to go on a very nice holiday.
You may think this is an unlikely scenario, but it does happen.
ALWAYS GET LEGAL ADVICE. ALWAYS. NO EXCEPTIONS.