The conditions for placing batts include the provision that there must be a gap between the wall and the insulation itself. This is to prevent getting mould on the insulation.
Another idea is to use foil board. You will have to run some timber battens on the steel framework and glue the foil board onto it. This would be the quickest way to insulate the area. You could also sandwich the current insulation that you have between Tunnelcore 2250 x 1220 x 2.5mm Black Double Walled Plastic Board also known as Corflute.
I suggest cutting the Corflute into a rectangle that fits into the gap between the steel framing, place the insulation in, and then place another Corflute panel to the front. This will prevent the insulation from sagging and keep it away from the steel wall. You can run zip ties through them to keep them together. It's like making a stiff insulation sandwich. - EricL
I have lined a few sheds. Glass bats need to be supported so if you use them on walls you will need to line the inside. The trick is to leave no gaps. In Tamworth I have used R2 and R2.5 in the walls and lined one with gyprock, the other with 12mm non-structual ply (can be screwed straight to steel frame and split aircon can be screwed straight to it).
When you buy your bats, foam or glass, remember they come in different widths so match them to your frame it saves a lot of cutting and wastage. Heat rises so once you line the walls most of your heat will be lost through the roof and any gaps it is important to insulate the ceiling.
If you are not putting in a ceiling I would look at insulating under the roof you can get fibreglass bats with foil on one side or foam this is where you will lose most heat. I would suggest R3.5 on the ceiling or under roof. Ring someone local who fits insulation and enquire (or go to a display home in the nearest town and enquire) or failing that I have been known to rock up to a building site and ask. - JDE
In our shed and studio we have used a product called aircell on the ceiling and batts in the walls. Although we haven't had temperature sub zero we believe they are doing a good job of maintaining a more comfortable temperature than without. - DIYgals