Evaluation of Single Ply Roofing Blisters—How Big Is Too Big?

There are numerous reasons why a single ply roof system may develop blisters over the service life of a roof: insufficient adhesive, damaged insulation, water infiltration, or other causes. But when does a blister become so large that it is in danger of advancing during periods of high wind? This paper explores how an investigator may evaluate a blister or localized area of damage in a single ply system to determine if it is at risk of progressing into a blow-off condition. Single ply membranes resist the advancement of blisters though a combination of tensile resistance and peel strength of the membrane from the substrate. As the blister gets larger, the angle of membrane peel increases, resulting in a non-linear decrease in the resistance to failure. When the peel strength of the blister perimeter length is exceeded by the applied wind load, the blister can advance to catastrophic failure.