March 7, 2021
Composition

Mastering Roof Inspections: Asphalt Composition Shingles, Part 2

Mastering Roof Inspections: Asphalt Composition Shingles, Part 2

ORGANIC SHINGLES

Organic shingles haven’t been made since about 2008, but many were installed over the years and you will continue to see them for a while.

The cellulose used for the tile mat comes from recycled wood and cardboard chips, rags and paper.

Cellulose mat, also called felt, is typically thicker than fiberglass mat.

To produce shingles, the cellulose mat was first saturated with thinner asphalt to about 170% by weight. This flexible core was then interposed within a second layer of thicker asphalt, creating a kind of asphalt sandwich.

Due to their thicker and more flexible double layer of asphalt, organic shingles can be more durable in cold climates than fiberglass shingles.

Often times, it is possible to repair a damaged section of the roof instead of replacing the entire slope, or to replace just one slope instead of the entire roof. Although some vendors may stock commonly used organic shingles, homeowners who need to match existing shingles will find this increasingly difficult.

Distortion

As organic shingles age, they slowly lose volatiles. Volatiles are compounds that boil at a low temperature. They dissipate over time, mainly through evaporation.

Volatiles are added to the asphalt mix to help make the shingles flexible, durable, and waterproof. Since its loss is mainly due to evaporation, the loss will occur more quickly in hot climates or in homes with poor roof ventilation.

As the volatiles dissipate, the cellulose mat becomes drier and more absorbent.

Mastering Roof Inspections: Asphalt Composition Shingles, Part 2

The absorption of moisture causes the tiles to expand and deform.

Mastering Roof Inspections: Asphalt Composition Shingles, Part 2

Since organic shingles near the end of their useful life can contain considerably more moisture than fiberglass, they can exhibit extreme distortion, as you can see here.

Mastering Roof Inspections: Asphalt Composition Shingles, Part 2

These organic shingles are obviously at or near the end of their useful life. Many of the volatile compounds that helped keep these shingles waterproof and flexible have been dissipated.

Mastering Roof Inspections: Asphalt Composition Shingles, Part 2

Moisture cycles, which repeatedly get wet and dry over the long term, have caused the carpet to warp.

Mastering Roof Inspections: Asphalt Composition Shingles, Part 2

The deterioration of the asphalt layer has weakened the bond between the asphalt layers and caused widespread delamination.

It is not uncommon to see organic shingles on the same roof deteriorating at different rates.

Mastering Roof Inspections: Asphalt Composition Shingles, Part 2

The spacing between shingles that deteriorate at different rates often appears as a diagonal pattern across the roof.

This condition is caused by the mixing of shingles from different batches. The diagonal pattern is created by shifting successive courses as the shingles are installed.

Different batches of shingles may have slight differences in the quality and thickness of the asphalt.

Mastering Roof Inspections: Asphalt Composition Shingles, Part 2

In the long term, these differences will cause shingles from different batches to deteriorate at different rates.

Mastering Roof Inspections: Asphalt Composition Shingles, Part 2

The exception is when installing a tile type that is not installed diagonally. On this roof, most of the T-lock shingles are of the same type. Only two packages are different and were installed at opposite ends of the slope, at the ridge and eave.

Mastering Roof Inspections: Asphalt Composition Shingles, Part 2

If left on the roof long enough, organic shingles end their life looking like this.