As long as the plywood under the shingle roof is in good condition this way can provide many benefits.
How to install standing seam metal roof over shingles.
The purlins are screwed or nailed down to the roof deck depending on how the metal roofing manufacturer has testing for their roofing panels and then the metal is installed to the purlins.
In contrast standing metal seam solutions can only withstand winds up to 80 miles per hour.
First of all if you install a standing seam metal roof over asphalt shingles there will be a so called telegraphing effect where shingles can punch horizontal lines in standing seam panels.
Snap the panels together and fasten along the opposite side and top of the panel.
In a standing seam roof long single panels run vertically all the way from the eave to the ridge.
Unlike steel and aluminum shingles standing seam panels should not be installed over the existing asphalt shingles.
Snap first two to three inches of panel together and slide the panel tight against the eave trim or with the gap depending on the temperature.
If you want to install steel over asphalt your best choice is to use a steel shingle system like the one shown instead of the more common and more expensive standing seam steel.
The system is designed around the patent pending 138t shingle recover clip and 138t symmetrical standing seam panel.
The second way to install a metal roof over a shingle roof is with the use of purlins or battens.
In contrast steel shingles are small panels installed in horizontal rows much like other shingles.
3 install 1x4 purlins down over the shingles before installing the metal roof the third way to install a metal roof over shingles is by applying 1x4 purlins over the shingle roof.
Complete and separate roofing systems such as standing seam metal roof systems that are designed to transmit the roof loads directly the buildings structural systems and that do not rely on existing roofs and roof coverings for support shall not require the removal of existing roof coverings.
There are two main reasons.
This is by far the most common way to install a metal roof.
This method has its benefits as well.
The main challenges when installing a metal roof directly over shingles with no underlayment are clip alignment and abrasion on the underside of.
Mcelroy metal has introduced a method for installing standing seam metal roofing directly over asphalt shingles without a tear off.
In a standing seam roof long single panels run vertically all the way from the eave to the ridge.
Better steel shingle systems like the one shown install over a framework of 2x2s.
Place sealant over underlap rib before sliding hem over the eave trim.