AG metal and Condensation.

I maybe over thinking this, but I started re-researching metal roofs, and the one main thing I'm concerned with is condensation..

From what I understand, you get condensation forming and possibly trapped on the bottom of any metal roof when the outside is 35 or lower, and worse if the space below is heated.. I watched a video of a barn raining inside that got my attention! Imagine the water damage that could slowly occur..

I like the durability and the price of a AG metal, but wonder what it would take to address the issues. I don't want to talk about hidden fastener standing seam now.

I think I figured out how to prevent screws from backing out by using a new epdm flat top serrated wafer screw I found..
But regarding the condensation, I think the only solution would be by adding vertical battens over the existing trusses for a air path before the horizontal battens, and using a foil faced bubble wrap type condensation barrier over the battens before the metal.

But isn't the main issue how to prevent heat and moisture from escaping the house and reaching the bottom of the cold metal? In most cases it's a re-roof, and installing a vapor barrier is unrealistic. Along with common static mushroom vents cut into the roof that would need to be patched and replaced with a ridge vent. Is the foil face bubble wrap condensation barrier enough?

Are there any other better steps I can take to minimize the condensation? In my case, I only have static vents close to the peak and no overhang or soffit vents. So I could get fancy and extend the 2x4 vertical battens out and over the edge to make a overhang and soffit. But this is allot of expense just to take care of condensation..

Thanks!

Thank you Mr Miller..

My home has static mushroom vents close to the peak (which my luck, would be located under each panel seam), but no overhang or soffit vents. I wonder how it can work with no low intake, but I haven't noticed ice dams..

I wouldn't have asked this question unless I hadn't found a few reports of issues with condensation including battens rotting out, condensation dripping from under a porch roof and the barn raining inside video. But these probably weren't "typical construction".. One was a sips roof. Another one the home owner insulated and drywalled the roof joists etc..

So what your saying, if the attic has "typical construction", one can install a metal roof right over the underlayment without additional ventilation or condensation barrier, and no condensation will form or be trapped?

Thanks!

Mike,

Can we get some pictures of the attic? Is the roof deck solid?

I 100% agree Mr Miller.. Its a mobile home with shingles and Ive been told "don't mess with the ventilation the mobile home engineers designed." I read one topic here where the home owner removed the cardboard under the sheathing and then later realized, after it was raining inside his home, it was the condensation barrier..

Since I cannot install a soffit overhang and low intake ventilation air (not enough free air space due to shallow rafter tails and top plate) , my only metal option is for a cool metal roof like houstoncoolmetalroofs.com design, but I imagine they didn't come up with the idea. I cant find allot of forum talk regarding Houston cool roofs. Maybe I should be searching "Texas cool roof"? They claim houstoncoolmetalroofs do not need "typical construction" meaning the attic can be fully insulated because of the radiant barrier on top facing the metal, and the large ventilation air space..

Is it a well thought out and proven design?

Thanks!
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My roofer and I might just do sleepers and a metal roof because we decided to postpone the roof until next spring as the repairs have held tight in the last week of rain. I'm pretty sure its not a 2:12 pitch Mr Miller. I figured 4:12 because it had shingles.. But I have not measured.

What might happen is my roofer will remove old shingles and install a underlayment designed to withstand UV for 6 months. That will give me time to install the 2x4 or 2x6 sleepers and battens.. But what I'm wondering if how to safely add more R-value.. Should I remove a row of sheathing and blow fiberglass into the truss space? Or just reduce the sleeper air space with 2" of polyiso between them, or install polyiso before the sleepers, maybe laying them on the 4" side to distribute weight and reduce thermal conductivity? Not sure how I would locate the existing trusses to screw into them with a layer of polyiso or underlayment covering the nails though..

And then what to do with the old static vents? Cover them and cut a 4" ridge vent? I'm pretty sure the static vents didn't do much to vent the attic without soffit vents, but more to allow moisture to escape..