Metal Roofs

A metal roof can be installed directly over existing shingles with or without strapping, but using wood strapping (furring strips) is generally recommended by most installers and manufacturers to protect the metal and manage moisture. Strapping (typically 1x4 wood boards) creates a vital gap between the rough shingle surface and the metal panels, allowing heat and moisture to escape.

Good Question, it depends on what profile of metal roof you are installing and the shape of the shingled roof it is going to be installed onto. There are many steel shingles profiles that can be installed directly on to the shingles, there are others (R-panel (ribbed exposed fasteners) that require the roof to be strapped to accept the new steel panels. If you are installing Standing Seam (hidden fastener) Metal roof the roof needs to be ripped off, substrate inspected, high temp ice and water and synthetic installed then panels are installed directly to the roof deck to achieve flat even look. Hope this helps. In a perfect world you would always remove materials and start fresh.