Expert: Tom Petrilli - 11/8/2009

Question
What are the lines on tar paper to be used for? I have helped on a few roofs for friends and no one is really sure. Some claim it has something to do with aligning different types of shingles. I don't see how this is possible as the paper moves some just walking on it. Any movement or less than almost perfect overlap of the paper and squareness to the roof deck would show up as climbing or descending rows of shingles as courses are added. Thank you in advance for your answer!

Answer
Andrew,
The lines aren't really used by steep slope (shingle) roofers. When drying in the roof the white or sometimes red reference lines let the installer see that the paper is evenly overlapped; but thats really all. Every shingle, slate or shake installer I've ever known has laid out the roof with a chalk line; completely disregarding the marks on the paper.

Flat roofers use the lines that are printed on the paper; when installing BUR (built up roofing) the installers use alternating courses of hot asphalt with layers of felt paper. When the roof is finished they will wind up with either 3 or 5 plys of paper with hot tar between each course.  The lines on the paper are used to stagger the rolls as they are laid into the hot tar. Snapping chalk lines in hot tar is impossible so the roofers rely on the pre printed reference lines. The lines are typically printed at 3" and 18" from each end of the 36" wide roll.

You were right not to rely on the lines on the paper, they aren't precise and a shingle job needs precision.

Good question, thanks,

Tom
www.lyonscontracting.com