I move in to a house which has a brick which was built in last ten years, I would like to convert half of it in to general use room l cheap mini gym/mini man cave. Had handy man round to quote me for the work but it he didnt think I needed a breathable membrane just 15mm insulation plaster board. Does any one have any other suggestions on this could be done cheaper. I wanted to stud out the wall and add loft insulation. The garage is bone dry and there are no leaks.
If you want building regs then he is giving you BS. All the U value requirements have just gone up (walls a lot!!). It needs to be properly looked at and specified: what are the current walls? If you don't want BR then do what you like but be prepared for grief potentially when the kids put the house on the market to put you into a home!
Cheapest answer is clear it out and whitewash the walls. Better alternative to 15mm insulation which is next to useless anyway
So if you're not going to make it "habitable", just do what you thought; if you can afford the space, use 75mm or 100mm Jablite in studwork, insulate the ceiling and perhaps the floor, depending on your intended use. Wall/insulation/DPM/plaster boards/ paint.