Does this garage conversion sound reasonable?

[Berk23]

Had a quote to convert our detached garage into office space.
We're having no windows, garage door is staying with a stud wall about a foot beyond it.
Walls, insulation and ceiling with spot lights. We did quote for underfloor heating and a replacement side door.

The quote is £18.5k, does it seem reasonable? It was more than I was expecting especially since there's no windows being put in or the garage door being bricked up.

Forgot to add, it's a small single garage

Sounds about right. Building costs have gone up massively

Does that adhere to building regs without windows? Some areas you need planning permission as well, although it depends what you're doing.

Don’t you need some kind of escape route?

even if it does meet building regs, a windowless, airless room for an office sounds awful. My single stone built garage with a window, up and over and single door has been very hot the last few days.

18k sounds a lot to me but I’m in the north.

No idea what a building company would charge but DH did ours for £1600, no heating though, otherwise sounds very similar to yours. It's being used as a gym and utility room rather than a home office. It remained remarkably cool during the recent heatwave due to the level of insulation he has put in.

Hmm it is a lot. My husband has just done ours. We had no windows too, just a glass-paned door (which we paid £1400 to get put in). I think we've spent at least 2k on the rest but hard to know for sure as he's constantly popping to Wickes 'for a few bits'. We didn't do new lights and I'd say wall and floor insulation are good but ceiling pretty poor.

So bear in mind you are paying for labour and a professional finish and maybe that's just what it costs? I would get a few more quotes though.

We’ve had quotes for £30k for a double garage but we’re putting in windows and doors. Going to be a utility room, gym and store room. Apparently about £1000/m2 at the moment. Almost double what it would have 2-3 years ago.

I wouldn't spend that on a box with no windows. It sounds awful.

Not necessarily. As I said we have done similar with a glass-paned door which is equivalent to the size of a window. In fact I am typing this now in a room with a solid door and one window in my house. One glass door is not thaaaat different. Not as good as being in the home, but a good solution when you need extra space.

That is fair enough @HappyMediocreTime but OP doesn't mention a glass door.