Q: Why are the shingles bubbling or bumpy? A: Small bubbles or bumps will sometimes develop on the surface of roofing materials. This is referred to as blistering that will generally appear within 2-3 years of product installation. Small rash blisters, 7mm (1/4�) or less, will not normally affect the performance of the shingle. Larger blisters, often up to 2.5cm (1�) in diameter, can shorten the life of the shingle as they often break exposing the underlying components of the shingle. Causes include trapped moisture, inadequate ventilation of the attic, excessive use of adhesive, or the use of non-compliant adhesive.