roofing over shingles or not

Gary Shamblen
3/3/2015
I AM PREPARING TO PUT A NEW METAL ROOF ON OUR HOME. I HAVE BEEN RESEARCHING THE METHODS FOR DOING THIS. I FIND QUITE A BIT OF DIFFERENCE BETWEEN CONTRACTORS. AMONG THOSE WHO LEAVE EXISTING SHINGLES ON: ONE USES 1" X 4" FURRING STRIPS 24" APART, THEN INSERTS 24" WIDE X 3/4" THICK RIGID INSULATION BOARD BETWEEN THOSE. THE ROOFING IS ATTACHED TO THESE STRIPS, SHEETING BOARDS, AND THE TRUSS RAFTERS; ANOTHER USES A BLANKET INSULATION OVER THE SHINGLES AND ATTACHES THE ROOF; THEN I SAW ONE INSTALLING THE METAL ROOF DIRECTLY OVER THE SHINGLES; AND YET ANOTHER ONE INSTALLED 30MM. THICK UNDERLAYMENT AFTER REMOVING THE SHINGLES. WHEN DRIVING THE SCREWS SOME STARTED THEIR SCREWS ALONG THE EDGE RIB AND WORKED ACROSS THE SHEET COMPLETELY INSTALLING ALL SCREWS ONE RIB AT A TIME. I SAW ANOTHER RUN HIS SCREWS ACROSS THE SHEET ONE RIB AT A TIME FROM BOTTOM TO TOP. IBEYOND THE EDGE SAW ALL KINDS OF FLASHING, VALLEY TIN, RIDGE PIECE, ETC. SOME USED A DRIP EDGE, OTHERS JUST EXTENDED THE SHEET ABOUT 1-1/2". CAN SOMEONE GIVE ME THE STRAIGHT AND NNARROW OF HOW TO DO THIS?
Eric Novotny
An informed customer is the Best Customer!
3/4/2015
You have to check with the panel manufacturer for what their prescribed installation methodology is. As far as the insulation question goes, I would never put blanket on the top side of the roof. I don't care for going over shingles but I certainly would opt for the rigid foam option. Who is the panel maker on both?

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