Organic-Mat Shingle

An organic-mat shingle is an asphalt shingle whose core is a felt made from cellulose fibres such as recycled paper, rag or wood pulp. It was the standard form of asphalt shingle for most of the 20th century before glass-fibre mats took over.

Construction

Organic shingles were built in more steps than modern glass-mat products. The felt was first saturated with a soft asphalt, then coated on both sides with a harder, stabilised coating asphalt, surfaced with mineral granules on top, and backed with sand, talc, slag or limestone dust. Organic shingles contain about 40% more asphalt per unit area than fibreglass shingles, which made them heavier and somewhat more flexible.

Performance

• Cold weather: organic shingles were less brittle in low temperatures, which made them popular in northern climates and in Canada.
• Tear strength: most organic shingles exceeded 2,000 g on the Elmendorf tear test, above the 1,700 g minimum set for glass-mat shingles in ASTM D3462.
• Fire: the absorbent felt limited the best available fire rating to Class B, compared with Class A for glass-mat products.
• Moisture: the felt could absorb water if the coating was damaged, leading to curling, blistering and "fishmouthing".

Before the early 1980s, some organic felts contained asbestos fibres, which matters when old roofs are removed.

Decline

Glass-mat shingles were introduced in 1960 and overtook organic shingles in the United States by about 1982. Most manufacturers stopped making organic shingles in the mid-to-late 2000s, and the last North American maker, Building Products of Canada, ended production in 2011.

Today

Organic shingles are no longer sold new in North America, but many remain on older roofs. Inspectors identify them by their thickness, flexibility and a fibrous, paper-like core at a cut edge.