You will need to lay some 1 by 4 inch pine boards lengthwise every two feet on your roof.
How to put shingles over a metal roof.
This is what it looks like when you install a steel shingle roof system over an existing asphalt shingle roof.
Advantages of metal roofs in general.
Attach them to your roof with 3 inch wood screws in each corner.
Apply roofing felt all over your roof you need to make the roof as straight as possible.
Venting the eaves to vent the roof holes are cut in the old roof above the soffit which pulls air through the soffit vents underneath.
Make a slat board base on top of the shingles.
Installing metal roofing over shingles 1.
Thus wood strips would be.
Move from bottom to top.