Use 1 1 4 inch.
How to install metal roofing over shingle roof.
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.
Installing the metal roofing over 1x4 s allows the ability to also install additional insulation under the metal roof.
If you want to install steel over asphalt your best choice for installing metal roofing is to use a steel shingle system like the one shown instead of the more common and more expensive standing seam steel.
You will need to lay some 1 by 4 inch pine boards lengthwise every two feet on your roof.
Installing metal roofing over shingles is the best solution.
The vast majority of installations of the metal roofing systems produced by my company are over existing shingles.
In a standing seam roof long single panels run vertically all the way from the eave to the ridge.
Steel shingles weigh about 1 4 what asphalt shingles weigh and aluminum shingles weigh about 1 8 what standard shingles weigh.
The metal used for the roof can be tin copper aluminum or steel.
Install the metal edging.
Make a slat board base on top of the shingles.
Install your metal edging around the perimeter of your roof.
How to install a metal roof over shingles.
The low weight of metal roofing is one thing that encourages this.