Garage Conversion - Fairly Straight Forward?

Hi

We have an internal garage which we want to turn into a habitable room, it's going to be a playroom and a gym. I realise we will need building regs.

Walls are cavity as there is a bedroom above already so walls have insulation, albeit to mid 80s standards when it was built.

It already has a large bay window to the side, a door from the house and both lighting and electric circuits.

In terms of a conversion, I am thinking we would need to :

1. Block up the garage door which would involve digging out suitable footings first.
2. Batten the walls and go over them with insulated PB to get us to the required U value for building regs, same with the ceiling.
3. DPM on the floor to lap up above the existing brick DPM, insulate it and then go over with floor boards.

Considering the window, door entry from the house and the electrics are already done, this seems like it should be a no brainer for a conversion if we want extra room downstairs and reasonably straight forward?

Toying with the idea of getting a firm in to block up the door and doing the rest DIY or just getting someone in to do the whole lot

Cheers

Got one quote so far. £13800.

Making me re think if it’s worth while and if it’s possible to do a lot DIY and just get the door bricked up by someone

If you are a competent diy'er, and not in a great rush, (though even if you were you may still be quicker than some builders!), then I would sit down and plan exactly what you want to achieve. Then work out what materials you would need and how much they would cost. Add an extra 10% to the cost to allow for mistakes/rise in cost of materials etc
I would then sit down and draw up some plans, (they don't need to be architecturally precise, just something you can follow), and activelt seek out potential problems or improvements. Sometimes you can get halfway through a job and suddenly think/realise you could have made a small change earlier on to make a big difference.
Then set yourself a realistic schedule/timetable on what and when to do certain jobs. Be honest with yourself and realise you will not set up a stud wall as quick as a joiner. You will not plaster/board out a wall as quick as a tradesman etc.
Once you have done this put it down for a few days and do something completely different to take your mind off it. It's amazing how something can sometimes pop into your head when you are not thinking about it that could make something easier/quicker.
After this break take up your paperwork and sit down to go through it all again with a fresh mind. Once you are convinced you have done the best you can, your costings are all correct and your timetable is feasible, (don't forget to add potential lieu days off due to bad weather/illness etc), then set a start date and away you go.

All this prep work may actually show you that certain parts are beyond your capabilities, and you will need to get someone in to do those sections, which means amending your plans/schedules.