Expensive to complete loft room?

[Pleaselettheholidayend]

Currently buying a house where the loft room appears to be half converted. Has velux windows, radiators and sockets but I don't think floor properly boarded, needs insulation and plastering and proper stairs fitting.
Doesn't need extending out from the roof as its a good space already. Obviously we will get quotes but anyone have experience of completing a project like this and what sort of budget should we expect?

How long is a piece of string!
Obviously at the moment it’s just a loft, so shouldn’t be classed as a bedroom / office space / play room on the sale listings. It may well be that it’s not feasible to put in a staircase to make it into another bedroom compliant with building regs if that’s what you’re hoping. In order to comply and be classed as another bedroom you will need a proper staircase and fire doors on all internal doors throughout the house.
https://www.checkatrade.com/blog/cost-guides/fire-door-installation-cost/

You need to see the paperwork that shows that the work completed so far has been inspected by building control.
There’s two ways to get building control

1. submit the plans to building control for the work you are planning to do and then obvious issues will be raised at the planning stage by building control and then inspections will occur at set points during the works. This is the best option and what should have happened
2. There isn’t a plan and building control inspect the works as you go along. For some projects this is fine but not for lofts.

A really good joiner is the main trade you will need.

check if planning permission was required and if yes did they get it.

Check to see if BR have been and accepted the work done so far. They won't have a certificate just yet as it isn't finished but just to make sure that what has been so far meets building regs.

Thank you, will make sure to ask builders when we have quotes. We don't want anything fancy, just to make it into an office space. Looking at the regs I think it should meet the head height criteria, looks like the main barriers will be staircase angles when installed and fireproof doors. But handy to know, very new to getting Reno work done!

It’s the people selling the house you need to ask about building regs.
Yes any builders you use will have to comply but you most likely won’t need a builder just a joiner.

If the current owners haven’t gone through building control there might be a serious issue such as the joists aren’t sufficient to hold the weight of a room

@Autumn1990 AHH ok - house is a probate so probably will be tricky to get any proof but I can ask solicitors if there's any paperwork/certificates relating to the work already done. I think the house was renovated in the 80s and not much done since so we shall see...

My parents loft is done out like a room. It can never be listed as a proper room as the beams for the floor aren't big enough and if we made them big enough then there wouldn't be enough head height. I'd take a builder round to the property with you and see what you're actually dealing with here

You need to get someone who plans loft conversions and can do structural calculations to visit and check it can be converted and meet the current building regs otherwise you’ve just got a nice storage space