Evaluation of Wind Damage To Shingles

When wind passes over and around a building, it
generates inward or outward pressures on the
walls and inward or outward (uplift) pressures on
the roofs. Inward (positive)pressures are
generated on the windward side of the building as
the wind blows against a wall or roof surface such
​as asteep roof. This positive pressure does not
damage shingles unless the tabs are lifted such
that the pressure can get underthe tab. Outward
(negative/suction/uplift) pressures aregenerated
when the wind passes by a wall, passes away from
a wall (leeward side of the building, that is, the
​side not facing the wind), passes over a shallow
sloped roof, or passes overthe leeward slope of
the roof. It is this negative or suction pressure
​that lifts a tab or a shingle strip.

The magnitude of the positive or negative/suction pressures on the shingles of a building is determined not only by the speed of the wind, but also by the orientation of the roof slope to the direction of the wind and the location of the shingles onthe roof slope. For example, the shingles at the edges of awindward roof slope are exposed to higher
uplift pressures than
the shingles near the
center of the roof
slope. This extra
uplift pressure is
generated at the
edges by the
additional pressures
from the secondary
movement of the
wind as it encounters
the wall and then
rushes up over the
roof. High uplift
pressure are
generally found along
the eaves, along the
rakes, along the ridge,
along the hips, and
along other
discontinuities or
changes in the roof

It is an accepted industry practice that an asphalt shingle should be inspected at least once per year. This is a regular maintenance issue and is required to reduce the risk of damage from winds because unsealed or poorly sealed tabs are more vulnerable to lifting by normal and expected wind.

In closing, the cause of damage to shingles proposed to be due to exposure to excessive winds requires methodical consideration. The evaluation includes the consideration of the weather data, the reported weather conditions prior to the reported discovery of the damage, the review of surrounding objects for wind damage,the review of the pattern of the damage, and the close-up examination of the shingles themselves. All of these provide clues to identify the true damage-producing mechanism.

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