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Old 06-22-2012, 09:03 PM   #1
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Underlayment for metal roof


Hi we have a doublewide with a 3/12 pitch, going to put a metal roof on, exposed fasteners, tearing off old roofing. I'm taking off the top row of sheeting on both sides of the peak, and even though it does have shuts in the eves I'm running some 8 foot long cardboard ones down to them and blowing in insulation. I would like to know what you think about this, putting a row of ice and water down on the eaves, and in the valley, then covering the rest with synthetic, then single bubble refelective foil, with 1x3s then metal. Just wondered if this sounds alright, my first metal roof.

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Old 06-22-2012, 09:09 PM   #2
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Underlayment for metal roof


Bah, too many components. That bubble wrap will get you nothing unless you plan on shipping it somewhere.

Just do solid ice/water on the whole damn thing. Especially since it's rolled rib, you are going to need the self-sealing properties when all your fasteners start to leak.

Make sure you use an HT (high temp) ice/water that says it is suitable for metal and tile.

Just re-read it. Please tell me you aren't putting it on batts. In the real world, your 29ga "roofing" has a span rating of 0"

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Old 06-22-2012, 09:41 PM   #3
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Underlayment for metal roof


I know what you mean about the screw fasteners, dosen't make sense to put all those holes in your roof, but there's no way I can afford standing seam, the price on that is just way out of line compared to the other steel roof. I
Heard the foil wrap had refelects 97 percent of the suns heat. People around here-- Michigan--- are using it now
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Old 06-23-2012, 02:50 AM   #4
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I Heard the foil wrap had refelects 97 percent of the suns heat. People around here-- Michigan--- are using it now
Only people I've heard that from are the mfrs of the products. There may be independent studies out there but I have not seen any. Maybe someone else here knows of some.

Eliminate some of those extras and your budget could allow for a hidden-fastener system.
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Old 06-24-2012, 09:57 AM   #5
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Anybody else with experience with the foil?
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Old 06-24-2012, 12:31 PM   #6
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Underlayment for metal roof


Only works with an airspace so you need a gap to make it work.

Radiant barriers are proven but largely relegated to the Southern 1/4 of the US.

You would be better suited to put some rigid foam on the roof as that would work in both the summer and the winter if you have an insulated roof deck (Which I suspect with they type of construction that is prevalent in your home).
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Old 07-06-2012, 05:38 PM   #7
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I'm not sure the physics work on a radiant barrier under a metal roof...metal roofs already have their own inherent emissivity (the basic property that makes the foil work) but if you can handle the aestetics, a reflective white coating on top of the roof (factory installed or put on by you) will make a big difference in summer months.

All reflective or radiant solutions offer reduced payback as you go further north, for various reasons.

I like Old N' Broken's suggestion of covering the whole roof with Ice and Water Barrier - basically a second layer of waterpoof protection, that is self gasketing. Make sure you use a "High Temp" or "Tile and Metal" Grade Ice and Water Barrier.
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Old 07-06-2012, 06:22 PM   #8
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I have installed lots of the Metal roofing you are talking about. Mostly on farm building and a few houses.
I find that screws will back out, Valley's are impossible to seal properly, and chimneys and vent stacks can be problematic.
Not in favour of it for a house.
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Old 07-07-2012, 09:42 AM   #9
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I'm not sure the physics work on a radiant barrier under a metal roof...metal roofs already have their own inherent emissivity (the basic property that makes the foil work) but if you can handle the aestetics, a reflective white coating on top of the roof (factory installed or put on by you) will make a big difference in summer months.
The Solar Reflectance and Thermal Emittance ratings on most metal roofs do certainly mitigate the impact of a radiant barrier, however, if a customer wants a darker roof to match their aesthetic requirements, a well placed radiant barrier does have energy efficiency value.
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Old 07-07-2012, 01:04 PM   #10
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Underlayment for metal roof


better off with a high quality shingle then use barn siding on your roof

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