Tar paper

Tar paper is similar to roofing felt,[1] historically a felt-like fabric made from recycled rags impregnated with melted asphalt, and today evolving into a more complex underlayment of synthetic mesh or fiberglass strands waterproofed by synthetically enhanced asphalt.

Grade papers are rated in minutes: the amount of time it takes for a moisture-sensitive chemical indicator to change color when a small boat-like sample is floated on water.

It is sold in rolls of various widths, lengths, and thicknesses – 3-foot-wide (0.91 m) rolls, 50 or 100 feet (15 or 30 m) long and "15 lb" (7 kg) and "30 lb" (14 kg) weights are common in the U.S. – often marked with chalk lines at certain intervals to aid in laying it out straight on roofs with the proper overlap (more overlap for flatter roofs).

[2] Older construction typically used a lighter-weight tar paper, stapled up with some overlap, as a water- and wind-proofing material on walls, largely displaced in recent decades by breathable plastic housewrap, commonly in 8-or-10-foot (2.4 or 3.0 m) widths.

In the 19th and early 20th centuries, shacks of wooden frames covered with tar paper were a common form of temporary structure or very low-cost permanent housing in the rural United States and Canada,[3][4] particularly in the temperate American South.