If i must past a obstruction i snap a line through higher and use it as a reference point for the shorter actual lines.
How to snap a chalk line for roofing.
First snap a line for the top of the starter course whose bottom will be flush with the waterproof shingle underlayment wsu or felt underlayment which overhangs the drip edge by 1 2 inch.
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.
By bob vila using a chalk line is a quick way to give yourself a straight line as a building guide.
Never snap chalk lines on steel sheeting.
These chalk lines will serve as a guide for subsequent even numbered rows of shingles and odd numbered rows respectively.
This saved on nail holes.
When it comes to the use of chalk near steel roofing and siding the following warning should have been added.
Snap a chalk line the next time you need to mark a straight edge as part of a home improvement job.
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.
Get your chalk reel.
Then snap lines for every course or every other course.
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.
I snap chalk lines solo by wrapping the free end of the string on a brick and pulling tight on the other end.
First shake up the chalk inside your tool or add chalk if it does not have any.
Even small moisture amounts will cause chalk dust lines as well as any black or lead pencil marks to permanently damage steel surfaces.
I snap a line for every other course.
Once you have the chalk line over the second mark lift off the string and allow it to snap back onto the surface.
If you have a well functioning chalk snap line you can slowly play out the line without.
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.
Snap horizontal chalklines to help you keep the courses straight.