martin wilburn
With garage below getting rooms to be warm can be challenging, you need to look at insulation and drafts. You can add insulation between the floor boards and ceiling below but you must maintain ventilation here are you will get condensation build up, you can over board the garage ceiling with insulation such as kingspan while appearing excessive up to 200mm would make a huge difference. Also make sure that there aren't any gaps for cold air in the garage to get through into the floor space above as these create cold drafts. You should be able to make that room habitable for a lot less than doing the garage conversion
