by Kenton Shepard and Nick Gromicko, CMI®
The purpose of the series “Mastering Roof Inspections” is to teach home inspectors, as well as insurance and roofing professionals, how to recognize proper and improper conditions while inspecting steep-slope, residential roofs. This series covers roof framing, roofing materials, the attic, and the conditions that affect the roofing materials and components, including wind and hail.
A variety of different kinds of damage can be done by those working on a roof. The roof may be walked on for a variety of reasons, including for maintenance on the gutters, chimney and roof, and for work on other components, such as air-conditioning, electrical, HVAC and communications equipment. Splitting is the type of damage of main concern.
Chemicals may be applied to a wood roof for a number of reasons. People may try to extend the life of the roof, make it more fire-resistant, and remove and prevent biological growth by applying a wide variety of chemicals, some of which are inappropriate and some of which are damaging to the roof.
Biological Surface Growth
Various types of biological organisms will grow on wood roofs if conditions are right. These include moss, lichen and algae. Their presence on a roof indicates elevated moisture levels. Moss and algae, especially, will hold moisture against the roof, encouraging decay. Zinc or copper strips may be nailed across the roof near the ridge to help prevent algae growth. Copper is generally more effective and sometimes will kill existing algae. Moss has shallow roots and can be removed by scrubbing.
Stay off mossy wood roofs. Moss on wood is slippery!
Algae are more difficult to remove, and chemicals may be required to kill it. In your report’s wording, you should recommend that “appropriate” chemicals be applied by a “qualified contractor.” Using the wrong chemicals may discolor the roof or damage or kill landscaping. It may also put toxic chemicals into the soil around the home, which can be especially dangerous to children and pets.
Wood decay, which is the same as wood rot, is caused by fungi. It often happens in shake and shingle butts first because butts are thicker and hold moisture longer. Because they may contain large numbers of fungi that can spread to and damage the surrounding roof, shakes and shingles with visible decay should be replaced. Heartwood contains extractives that make it more resistant to decay than sapwood. This means that edge-grain shakes and shingles resist decay better than flat-grain.
Decay may be caused by different conditions.
Cap Shakes and Shingles
Cap shakes and shingles are butted together and fastened with nails or staples. Although butt laps should alternate as caps and are installed to help shed runoff properly, this is a quality issue, and it won’t be what you’ll find on the roof when inspecting most homes. Don’t call it a defect if you don’t find caps done this way.
Caps fail in several ways.
Learn how to master a roof inspection from beginning to end by reading the entire InterNACHI series: Mastering Roof Inspections.
Take InterNACHI’s free, online Roofing Inspection Course
Mastering Roof Inspections
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Inspecting Underlayment on Roofs
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