If your concrete garage is being underused as a usable space, i.e. Your car is stuck outside, and the garage is full of all sort of stuff (or ‘items various’ as my wife would say) then maybe you need to consider changing the use and converting it to a usable room. Depending on the usage of your converted garage, you may need building regulations approval, but if it is not being made any larger then generally planning permission would not typically be required. In both instances, it is worth checking with your local authority to be sure.
You need to clear out the garage of all unneeded items, and you will be surprised what you have in there, which is worthless and pointless. The sort of things which you would typically find in a typical garden shed would surprise you. When you have done this, you will have a clear empty shell so you can plan how you wish to proceed. The more straightforward thing to do is to use the garage as a glorified workshop, and this is easier to achieve.
If you wish to use a precast garage for full-time habitation, then it best to speak to an architect or builder experienced in this type of work. This way, you can ensure the work will meet building regulations which you would need to obtain. If there is a shortage of parking in your neighbourhood, then this might mean you might not get permission but can work in your favour sometimes. Also, if you have a listed building, then this might make a difference as well.
With the brick built garage, I had at my property; I decided to utilise the space better so cleared out all the junk leaving me with a garage which was more or less empty. I got a builder in to remove the garage doors, which were old and tatty and replaced them with some nice UPVC double glazed double doors. I also had the personal door replaced with a modern UPVC window.
The roof void in my garage consisted of timber joists, so I decided to fill the gap with two thickness of polystyrene. I use polystyrene as I cut this slightly oversize so when I squashed it into the void, it became self-supporting. When I had done this using plywood, cut to size, I screwed this into the garage ceiling. Before this, there were areas where I had to add some noggins where the joins were going to be.
The walls were treated similarly. I screwed into the wall some 50mm x 50mm pressure treated timbers at 16-inch spacing. (the 16-inch spacing meant that I had to only cut the plywood boards to the height of the garage) Again, I use polystyrene, but you could use fibreglass loft insulation which you can squash into place. Polystyrene was easier to use. After this, I lined the walls with thin plywood, which I screwed into place, but you could nail it. Reason for screws is that I could remove the panels to get behind with any electrical wires.
Please note that on a log cabin you would NOT fix timbers to the wall as they will expand and shrink throughout the year. You will find that the thickness of the cabin walls give the building plenty of insulation.
I was going to paint the plywood but found the plywood soaked up the paint and was somewhat patchy. I then decided to wallpaper the walls and then paint the wallpaper. Using an embossed wallpaper on the garage walls, this gave me a uniform surface. I added coving to the ceiling and skirting boards and painted them. The ceiling took four coats of paint to get a good finish, but the wallpapered walls only need two coats to get a top-class finish.
In the end, I have an immaculate highly functional modular room, which you could have as well if you have a concrete garage, which is easy to heat in the winter and does not get too hot in the summer. You could use this method in your garden shed as well and this, again, will be a great asset to your home. You could my experience to answer the query ‘how to insulate a log cabin’.
The only problem I got is that the wife has decided this room is highly suitable for her and her friends. Their hobby is craft and card making, and this is what they do most Wednesday nights.