It's a bit like car mods: most of the things you do add no value, and a fair number decrease the value. A very few increase the value, and never more than a proportion of what you are paying for the work. The best value increase comes from an extra bedroom provided by an extension, and that will add about half the cost in value. If you are lucky and it's done well. A garage (if there wasn't one before) will add about a third of its cost. Any changes which do not increase the overall square meterage of the property fall into categories a or b: no extra value, or even value decreased. A hot tub falls here. If the OP actually planned to sell then there's a slight chance it might make a buyer more interested. But many prospective buyers would less interested. It certainly would not add value.
I assume the bank of mummy and daddy has offered the OP some money to improve the house. If it absolutely has to be a concrete thing, and it can't extend the house, then just do what the hell you want, and understand it will NOT increase the value.
I assume the bank of mummy and daddy has offered the OP some money to improve the house. If it absolutely has to be a concrete thing, and it can't extend the house, then just do what the hell you want, and understand it will NOT increase the value.