To limit the probability that the shingle fastening will be unable to resist uplift forces from wind, vibration and gravity, which could lead to the displacement of shingles, which could lead to water penetrating directly to roof decking or sheathing, which could lead to precipitation or meltwater ingress, which could lead to deterioration, which could lead to the structural failure of roofs or walls or of assemblies protected by roofs or walls, which could lead to harm to persons.
To expand the application of Sentences 9.26.7.4.(1) and (2) to include constructions where relatively narrow shingles, or shingles that do not rely solely on fasteners, are used.