by Kenton Shepard and Nick Gromicko

    

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.

   

PROPERTIES of ROOFING MATERIALS

  

Let’s examine the properties that affect the impact-resistance of some of the common steep-slope roof-covering materials.

 

Resistance to hail damage depends upon a number of factors.

 

Type of Roof-Covering Material

 

The type of roof-covering material is one factor.  Some types of materials and profiles are more resistant to damage than others. Metal roofs seldom suffer functional damage from hail. Many thousands of asphalt shingle roofs are damaged by hail every year.

 

Roofing Material Condition

 

 

 

The condition of the roofing material is another factor. These photos show a 20-year-old asphalt shingle roof which has suffered general granule loss. 

 

 

You can see it accumulated in the gutters.

 

 

This condition was probably contributed to by widespread blistering, an example of which is shown above.

 General granule loss is NOT considered to be functional damage.

 

 

 

The thickness of the roofing material will also affect the severity of damage.  Assuming that we’re comparing similar materials, such as thick and thin asphalt shingles, thicker materials will typically resist damage better than thinner ones.

 

Nature of the Substrate

 

The characteristics of the substrate will also affect the severity of damage. 

 

 

Thick, solid, smooth, single-layer substrates will improve the ability of the roof-covering material to absorb impact, and this reduces the chances of functional damage. Solid wood decks supply solid substrates. Layers of old roof-covering materials offer poor support against hail impact.

 

Part of the Roofing Material Hit

 

The amount of damage will also be affected by the part of the roofing material that’s hit. 

 

The edges of roof components, such as wood and asphalt shingles, are more fragile and subject to damage than material in the middle of the components, since the edges have less surrounding material for support.

 

Ridge and hip cap shingles are poorly supported, so they are more likely to suffer hail damage.

 

Temperature of the Roofing Material

 

The temperature of the roofing material can also have an effect.  Certain roof-covering materials, such as asphalt shingles, become increasingly brittle at lower temperatures. Brittle materials are less able to absorb impact without damage, so cold materials are more likely to be damaged by hail.

 

To review, the impact-resistance of a roof-covering material will be affected by the thickness of the material, the nature of the roofing, and the condition of the roof-covering material.