No. 17
1998-09-28
Printable version

COLOUR SHADING OF ASPHALT SHINGLE ROOFS

As a roof is viewed from different angles, and/or different lighting conditions, certain areas may appear darker or lighter. This inconsistency in colour is commonly called "shading".

Shading usually results from slight variations in texture which normally occur during shingle production. The variations necessary to cause shading are so slight that they cannot be detected during the manufacturing process. When light is reflected from a given roof, its appearance will vary as the viewer walks past the building. The impact will depend on the position of the sun and the overall light intensity. When the sun is directly overhead, the shading may disappear. The perception of shade differences may also vary under cloudy skies or if the shingles are wet.

Shading is most frequently a problem in the case of black and other dark coloured shingles. Since only a small amount of light is reflected from a dark surface, even the slightest differences in shingle texture may cause this problem. In the case of white and other light coloured shingles, the total amount of light reflected is considerably greater. This results in a decrease in observable shading differences. Blends, made of a variety of colours tend to camouflage this effect, and make observable differences even less noticeable. Lighter blends will reduce shading more effectively than darker blends.

The backing material, used to keep the shingles from sticking together in the bundle, can rub off onto the granular surfacing material of the shingle packed next to it. This may also result in an apparent shade difference once the shingles are on the roof. As well, shingles can develop minor staining when stacked too high and/or when stored for extensive periods. Under these conditions, the lighter oils contained in the asphalt coating simply seep between and permeate neighbouring shingles. Again, this can give a temporary visual shade difference between lots of shingles, but it will be eliminated by natural weathering.

To reduce the potential for shading:

•  Shingles are generally packaged with a date/production code on each bundle. Never mix shingles with different production codes on the same roof. This could result in shading, or worse, drastic colour variations between shingled areas.

•  Manufacturers recommend that shingles be applied starting from the bottom of the roof, then working across and up. This will blend shingles from one bundle to the next and minimize any shade variations. Always follow the application instructions printed on the shingle bundle wrappers.

•  Use blends rather than solid colours to reduce observable shading.

•  Allow sufficient time for any transferred backing materials or oil stains to weather out.

•  Never stack bundles of shingles higher than the manufacturer's recommendations. Rotate shingle inventories to ensure material is not stored for unnecessarily long periods.

Shading is an optical problem, and in no way affects the durability of asphalt roofing systems. Despite the best efforts of the shingle manufacturer and the shingle installer, some slight shading is normal and simply unavoidable.

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