Pole baren

How can I keep the roof of my barn from sweating? [img]/forums/images/icons/confused.gif[/img]

You can't keep it from sweating. It's the nature of the beast, cold metal + humidity = condensation. What you can do is minimize the sweating and keep it from dripping on you by adding insulation(dow board or equivalant) between the trusses right up to the bottom side of the metal. Sort of like a press fit. Or you can spray the bottom side of the metal with foam. Hope this helps.

Would better air circulation help?

Yes it does help Mike. I've got a big exhaust fan that is on a temp. gauge. Unless I've got the stalls full of horses it will do a good job keeping the condensation down.

Perhaps people underestimate just how much moisture there is in a barn environment. Animals (both liquid and water vapor from breathing), perhaps a wash stall, hay, etc. it can get kind of humid. We oriented our barn so the center aisle is east to west and, unless there's bad weather, the end doors are always open. The stalls all have outside (and inside, of course [img]/forums/images/icons/tongue.gif[/img] ) dutch doors and the upper door is always open. Keeps the air moving.

You will also get moisture leaching up from the ground itself. This can also happen even if there is a concrete slab in the barn if no vapor barrier (plastic sheeting) was installed under the concrete.
A combination of ventilation - some type of airflow across the botton of the roof panels and insulation will go a long ways towards reducing, maybe eliminating the sweating. Ridge vents will also help to draw air up away from the underside of the panels.
One thng about some of the spray on insulation is that over time, they can sometimes start shedding small particles of insulation material - winds up looking like dust all over everything.