I have a pre-cast concrete garage with a non asbestos corrugated roof. It suffered with terrible condensation and was always freezing cold in winter or boiling hot it summer. After 10 years the roof started to split. I drilled small holes at the end of the splits to stop them spreading. Doing that made the split turn 90degree! Eventually a roof panel came down and landed on the tank on the Jota and dented it
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I stripped the whole lot off and installed a metal profiled and insulated roof on the original trusses. I raised the floor with 2 x 2 inch battens and cut celotex insulation to suit. I did the same with the walls. I covered all this with 18mm marine ply and painted it white. I laid interlocking 7mm heavy duty tiles on the floor over the ply. For the metal doors I used a multi layer metallic blanket from Wicks and tapped this to the doors.
The problem with using a heater is the condensation it produces especially in a cold garage when by nature the bikes and tools are cold, condensation forms on the surfaces and causes corrosion. I use a dehumidifier, it's brilliant, the garage is only a couple of degrees warmer than outside but the air is dry, no condensation at all and dry air is warmer and easier to work in. The dehumidifier I use is a RubyDry, it uses 280w/hour on its lowest setting, this is the setting I use 24/7. Obviously it's not cheap to run it but it's only during the winter and to be honest it will cost more to clean and fix the corrosion off the bikes if I didn't use it.
I empty the catch tank every two days and pour away 5 litres of water every time. That's a lot of moisture attacking your pride and joy!
