At a guess i would place the strapping no further apart than 16.
Metal roof strapping spacing.
Correctly measure the spacing of furring strips for a metal roof to further decrease condensation.
The gauge of the metal 24.
Galvanized sheet steel strapping about 1 1 2 in.
12 if installing over existing shingles the roof should be strapped with minimum 1 x 4 strapping at 24 centres panel installation should begin at the gable end of the roof opposite the prevailing rain bearing.
Wider panels allow for greater spacing between rafters.
To determine how far apart to set rafters measure the width of the metal panel and then the width of the first hill and valley of the panel.
If there are gutters installed on the eaves the eave flashing should be installed to overhang the lip of the gutter by about 1 2 inch.
A metal roof must also allow for some overlap on each side of the panels which will reduce the effective width of the panel.
Should it be installed over the existing asphalt or strapping 2.
Place corner pieces where panels will meet bends at the edge of the roofing.
26 or 29 is a variable that must be considered as is the type of fastener and the pitch of the roof.
Wide holds down the roofin case of severe wind uplift.
Standing double locking seam does this tend to sweat on top of asphalt shingles.
Use 1 1 4 inch nails to cover the outline of the roof with strips of metal eave flashing also called edging.
Will need to install your metal roof.
In case some moisture finds its way into the roof.
Question from june in new hampshire.
Edit answer for another 41 minute you need to check the installation instructions from the manufacturer depending on whether the purlins firring strips are 1x or 2x material and how wide thickness metal gage of roofing steel or aluminum type of seams design wind and snow loading whether designed to be walked on or not etc i have seen it vary from as little as 4 inches clear gap between firring strips on lightweight aluminum to as much as 4 feet on very heavy gage steel.
Insulation and the underside of the metalroofing.