Wood slats under metal roof...

Old 12-30-13, 12:34 AM
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Wood slats under metal roof...

Would like to get some feedback on this "idea"... I am putting on a new metal roof...will tear old rolled roofing off down to decking...replace, repair, etc as needed. A friend of mine told me that in warmer climates (i.e. Phoenix) he has seen where they have screwed 1 x 4 wood slats vertically, spaced over the rafters and then run 1 x 4 slats horizontally on top of the vertical slats...spaced perhaps 3' apart. Thus you have a 1 1/2" clearance from the deck the the underside of the metal roofing...which would be screwed into the the vertical slats. The spacing of the vertical slats would not necessarily have to be over the rafters if the decking is good...but instead would be spaced according to the width of the panels. The reasoning is that this space allows for air flow to help in cooling the roof/attic...as the metal roof heats ups the warm air underneath moves upward to the ridge cap and vents out...keeping the attic as much as 20 degrees cooler. Does anyone have any experience with this or any ideas or foresee any issues with this idea... Let me know what you think...and thanks for your feedback.
Old 12-30-13, 04:52 AM
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Welcome to the forums!

It is commonplace to install metal roofs over strapping that is affixed to the rafters. When the roof has decking, you install roofing felt [tar paper] and then the metal. I'm not sure I'm following your scenario 100% but metal roofing has to have support closer than every 3'
Old 12-30-13, 05:25 AM
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we replaced several rotted metal roofs w/' onduline ' a few yrs ago - work'd great - iirc, we had to 1st install purlins then roofing was a snap much less $ than new metal.

we also repaired several w/sealoflex - no $ interest in either
Old 12-30-13, 06:27 AM
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I'm not getting the logic of adding anything to the tops of all the joist before Purlins. Id just do the outside edges so drip edging can be attached before the roof goes on.
That would make an 1-1/2 opening on the outside edges to cover up.
It's best in your area I would think to have soffit and a ridge vent.

If this is a house and not a barn or shed I'd strongly suggest going with a standing seam metal for far less chances for leaks.
Old 12-30-13, 11:56 AM
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Metal Roof

The vertical roof panels get attached to the horizontal strapping. Vertical strapping under the horizontal strapping would allow vertical air flow above a sheathed surface.
Old 02-26-14, 04:22 PM
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Metal roof

Though new to this forum, not new to installing metal roofs. It is better to have the stripping - even on a roof that has plywood decking - because you can have an air gap and add in the 4x8 sheets of insulation that are common with a metal roof.

That being said, it is better, but not REQUIRED according to zoning codes. Metal can actually (though I wouldn't do this unless you just couldn't afford the stripping) be screwed directly to the roof if you have the right underlayment. Again, not that I like that, but it is usually ok and up to code to do so. That is because putting metal on top of an existing shingle roof or shaker roof or whatever - is considered a roof-over system. A roof on top of a roof. But again, stripping it out and then adding insulation first is a better option. It helps big time with the temperature in the attic as well.

An installation of a metal roof to this one customer's home reveals this. When just HALF of the metal was put up, he said his air conditioner started kicking on and off. He said this never happened with the shingle roof. They ran all summer. And that was just with half the metal roof on.

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