My question is we have a metal roof on our home and they put 2x3'' boards across the rafters and then put the metal over that. I have been wanting to take the metal off and install plywood or OSB under it and then put the metal back down with tar paper under the metal so condensation would be able to run off instead of dripping inside .We need to get the proper way this should be done so as to fix the condensation problem.We understand that it is from heat loss from inside the house and are going to beef up the insulation once this is done to further help this problem but need guidence in the underlayment procedures and any input will be greatly appreciated.
My answer may be controversial, but here goes.
I watched a segment of Homes on Homes. He was rehabbing an older home that was incorrectly done. He stated that in the past the vapor barrier was place next to the warm side to reflect the heat back into the home. He stated that now the vapor barrier should be closest to the cold side with insulation next to the vapor barrier.
Now, my knowledge. I have sky lights. The warm side is directly below. The condensation forms on the cold side and runs off my roof... simple. If there is warm next to the roof then the metal should act like a vapor barrier and the condensation should form on the roof, much like my sky lite. You may want to try an experiment and use insulation next to the metal to see if your metal roof can act like my sky lights.
I do know that is is standard practice to use stringers to put on a metal roof. However, we recently had our roof replaced, and they did exactly as you stated, plywood, 30 weight tar paper and then the metal roof. It will be difficult to remove your metal, but very possible because of the screws used.
The proper method for installing metal roofing over a heated space (a house) is to put down OSB or plywood sheathing, then ice & water at least two rows up with roofing felt for the rest and then the metal roofing.
Metal roofing over sleepers is generally only done in areas like barns or large storage buildings where there is no insulation under the roof.
So there is no ceiling like sheetrock or wood?
Wow....what bad contractors.
If you like the exposed metal (like barn style), they should have built up (foam) the roof to begin with.
This is why I do alot of my own work.
Let me be clear. The foam should not leave a gap where wet air can exist. My example is a skylight in Western Washington that has condensation on it all the time. But it is on the outside and then runs off the roof.
Think of a Styrofoam cup. It gets wet on the outside when the temp of the surface reaches the dew point. If you put a cover on the outside, it will still get wet on the outside. But put two cups together, no moisture, no gap...
Often the most complex problem is solved with a stupid example...
Yeah...sounds like you don't have proper "venting".
They should have put "baffles" between the fiberglass and the metal roofing / between the raftes, which would have left an air space and then vented at the ridge (of course you would have needed soffit vents as well).
Your roof is not "cold enough" (as close to the outside air temp as possible).
Of course it might be under insulated too.
I am wondering....did they just put "bird stops" and seal off the eaves and leave no air space for venting?
No easy fix.