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 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.


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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.

Good luck

-->  The unaimed arrow never misses....
-->  If can, can. If no can, no can... Hawaiian Pidgin

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.




I have done a few metal roofs and also been involved with the design for houses we have built. This is what I would do: At 2' centres I would install 2x4 strapping across the rafters. Pretty much what you have now with your 2x3's, although I don't know the centres. Then I would nail down a 7/16 OSB or 1/2" plywood sheathing over the entire roof. Then tar paper and ice shield as Randy says (or to local codes).

If its new construction I can pre-drill the entire skid of steel roofing on the ground so that the screws will hit the strapping.

If you want to add insulation after the sheathing is down than this is the perfect time. You can put down several inches of foam and (check with them and the roof suppliers on this) either use a long screw to again hit the strapping or add a 1x4 strapping on the foam and then the steel but still making sure your long screws are in those 2x4's.

The point is that you get 1 1/2" of screw in wood and not just a little bit in the sheathing.

David's point is controversial. I wonder where that house is located? The purpose of vapour barrier is to prevent warm moist air cooling to the point it condenses. If that happens within a wall cavity you get moisture conditions that allow decay fungi to grow.

If you are in an area where the moist warm air is inside and it's cold outside the vapour barrier is absolutely installed inside. If the opposite is true. Florida being a good example with warm outside and air conditioning, then the vapour barrier should still be installed on the warm side but now that is outside.

Who knows what to do if you are in the Carolinas????

Bob Warren
Khita Log Builders Ltd.
"still 2' of snow at my house...I know which side is cold"
Is this your attic space?
No  it is the second floor living area

So there is no ceiling like sheetrock or wood?

Cathedral etc.?

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.


there is sheetrock for the ceiling with insulation between the roof and the sheetrock but the metal roof still condensates on the under side and sometimes drips inside so that is why I think sheathing and tar-paper then the metal will alleviate this problem because if the roof condensates on the underside then, it will run off the tar paper instead of going inside the home

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.

Yes you are right ''no easy fix'' we have vented one side by installing soffit and fascia and plan on doing the other side as well.But the next step we feel is installing sheathing ''OSB'' and tar paper or a synthetic covering under the metal and then reinstalling the metal with new screws.


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