Granule loss is a normal process in the weathering and aging of any asphalt shingle.
Common causes of additional granule loss:
Traffic on roof;
Shingles applied on very slight slopes (2″ in 12″ or less), are prone to increased levels of granule loss due to the poor drainage capabilities of the roof.
A certain amount of granule loss is to be expected. Shingles are made with an excess of granules on the surface called “hitchhikers”.If the underlying asphalt is prematurely exposed, the appearance and service life of the shingle may be affected.