[Closed] metal garage roof - how to solve condensation

String a dust sheet or two across. Won't pole your problem but should stop the drips if you angle it down at one end.

Only sure way is to insulate it with expanding foam so that the whole sheet is covered, not just the dips on the underside. To do it properly, i'd suggest a 2 part expanding foam. Probably cost around 120 quid for what you'd need

What FM said, get it sprayed with foam.

think I'll string up my large tarp for now, and do something proper in the summer.

cheers

put it at an angle across the roof so that the moisture runs across it rather than puddles in the middle - also be aware that you may have water dripping off the edges.

As above. Also look at something like Celotex - it comes in large sheets and is pretty good insulation - easy to handle and fix as it's so light.

I use foil-covered bubble insulation (like [url= http://cgi.ebay.co.uk/8-Double-foil-bubble-insulation-4-5sqm-rolls-/260698345864?pt=LH_DefaultDomain_3&hash=item3cb2d51188 ]this[/url]) on my garage door. It makes a notable difference to the temp in the garage/workshop and also makes the place much brighter. Relatively inexpensive, too.

Any suggestions on what spray foam should be used?

I used cellotex panels on a metal shed room which suffered similar problems. Was a pretty quick and low mess fix.

Ventilate it.

As above, couple of vents have reduced the damp in my garage.

Air brick is another option.

there is plenty of ventilation.
Main door has gaps at the bottom, all around the roof there are gaps between the metal corrugations and the wood exterior.
The problem only occurs when it's really cold / lying snow on the roof. It's made worse when I bring in a wet bike.

It's a concrete panel garage, so not easy to add extra ventilation either.