Sorry if this is long. I know the standard (sensible!) advice around lofts is don't touch it with a barge pole if unofficial conversion and always do the job properly, but hear me out & then I'd be glad of advice as we've been going in circles.
Bought our house as a 3 bed (priced as a 3 bed) although it had an unofficial loft conversion which we were shown as a potential study or storage space- not included in price, but not discounted for either. It does need some obvious work such as a replacement skylight and decorating but it's actually in pretty good shape. Biggest visible issue = space saver stairs BUT they aren't the dodgy cheap ones, they're full width and custom made for the house. In fact, surveyor when we bought the property commented that for the £ they must have paid getting those done it's bizarre they didn't just do a formal staircase.
Surveyor when we bought said the loft was perfectly sound for its sold use but would require further inspection if to be used as a bedroom and may need bringing up to regs or may be ok - he didn't like to comment. We've since had 2 builders, a structural surveyor and a loft conversion company over. All agree that the back section is perfectly fine in terms of modern standard joists and insulation, but the small front area you walk over to get to the room itself could do with some joist reinforcement if to be used more regularly. Some (including the surveyor) have said the staircase is fine , others have said it should be replaced with a formal staircase to pass building regs.
We've had a lot of other work done to the house so already covered fire doors etc.
Now - to do the loft 'properly' we seem to be looking at around 30-40k with staircase. It would have the benefit of requiring our 3rd bedroom to be knocked into making that room a bit larger too. But it's a v large amount of money.
Particularly if it sounds like what we have up there already may not be so far off building regs anyhow.
To add some context- we very much need this space....but as a spare room for when DHs family who live abroad come to visit, not for any of us. So whilst it would be a bedroom, it wouldn't be being used daily. This is also what makes me shirk at spending so much on an occasional use room.
We've had alternative quotes of circa 15k just to make good what we have, with new window, plastering, decorating etc.
This would leave us money to recarpet the rest of the house which badly needs it and not wipe out our entire savings.
We live in the SE so I'm very concerned that if we spend 30-40k on top of the 60k We've already invested extending this property and doing a new bathroom, we could end up actually making a loss as the SE is due a housing price fall by all accounts.
So...all things considered, what would you do???