Before you install metal roofing repair any damage to the wood under the shingles.
Install metal roof over electric riser.
Wrap flashing around electrical mast and close by crimping stainless steel clips supplied.
When installing a metal roof over an existing roof insulate the spaces between the wood strips with rigid insulation to prevent condensation before installing the roofing.
In a standing seam roof long single panels run vertically all the way from the eave to the ridge.
Then cover the entire roof with a layer of insulation and secure it with a staple gun.
Be sure the larger edge is laid so that the small edge of the next panel will overlap it.
Cut flashing opening to appropriate size for pipe.
Apply shingles up to lower edge of electrical mast.
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Align the first metal roofing panel so that it overlaps the edging by 1 2 to 3 4 of an inch and is square to the roof line.
Apply sealant to underside of base and secure base with roofing nails.
If you want to install steel over asphalt your best choice for installing metal roofing is to use a steel shingle system like the one shown instead of the more common and more expensive standing seam steel.