Metal Roof Installed Over Purlins

The second way to install a metal roof over a shingle roof is with the use of purlins or battens.

Metal roof installed over purlins. I was driving by a new building being constructed and it has wood trusses with 2x4 horizontal purlins looks to be about 2 oc spacing on the trusses. They then installed the metal directly to that. The purlins are screwed or nailed down to the roof deck depending on how the metal roofing manufacture has testing for their roofing panels and then the metal is installed to the purlins. The purpose of the purlins is to provide a solid foundation for the metal roofing panels and trim to be screwed to.

They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top. It helps direct water away from the meeting points and keeps the roofing dry. I have been playing around with the ribbed metal roof but pricing is pretty high over shingles obviously. Flashing is metal trim that fits over joints where two sections of roof meet.

The flashing should overlap the edge of the roof by one inch to help direct water. Choosing to install a metal roof this way can save you some dough and garner all of the benefits of a metal roof in the humid climate of florida. Doesn t provide the flattest surface for the metal roofing to be installed over each course of shingles is about a 1 8 higher than the course just below it. They give added support to the roof and also provide a nailing surface for the end panels and drip edge.

A metal roof can be installed over a shingle roof but you ll need to make sure the plywood under your shingle roof is in good enough shape to handle a new metal roof over top. Metal roof purlins are installed horizontally under metal roofs. Bend the flashing into a v shape to fit over the top roof ridge and the corners where the panels meet. Metal roofing panels rated for architectural use attached to purlins horizontal pieces of wood or metal fastened to roofing trusses are structurally sound when installed according to your roofing manufacturer s instructions and local building codes.

For many applications a layer of plywood underneath your metal roofing is an unnecessary expense.