Then snap lines for every course or every other course.
How to snap a chalk line for roofing.
I snap a line for every other course.
By bob vila using a chalk line is a quick way to give yourself a straight line as a building guide.
First shake up the chalk inside your tool or add chalk if it does not have any.
3 tabs i snap the same baseline then square off that for a vertical bond line then i measure over half the width of a tab and snap a parallel line.
This saved on nail holes.
If you have a well functioning chalk snap line you can slowly play out the line without.
Even small moisture amounts will cause chalk dust lines as well as any black or lead pencil marks to permanently damage steel surfaces.
Once you have the chalk line over the second mark lift off the string and allow it to snap back onto the surface.
These chalk lines will serve as a guide for subsequent even numbered rows of shingles and odd numbered rows respectively.
Snap a vertical chalk line from the inside edge of the first shingle on the second row to the top of the roof and from the inside edge of the first shingle to the top of the roof.
The chalk will mark a straight line along the surface between the two points.
I too am a diyer and not a professional roofer.
But then i work on a 4 12 roof so you may have to use nails to hold the free end on your 9 12 roof.
I snap chalk lines solo by wrapping the free end of the string on a brick and pulling tight on the other end.
When it comes to the use of chalk near steel roofing and siding the following warning should have been added.
Get your chalk reel.
If i must past a obstruction i snap a line through higher and use it as a reference point for the shorter actual lines.
Hook the chalk line clip over the nail head or screw and reel out the string to the other end point along the straight surface.
The line produced by the chalk snap line is fuzzy and sometimes hard to follow when cuttting along it.
Then hook one end of the chalk snap line to your beginning point.
Snap horizontal chalklines to help you keep the courses straight.