In the family of roof barrier underlayment’s, ice and water shield is the premium application that protects the roofing system against all ice and water infiltration. Unlike the tar-impregnated paper of roof felt which is typically stapled to the roof and has lapped seams, ice and water shield is made from rubberized asphalt with an adhesive back that sticks to the roof deck and creates water tight seams.
Although technically Ice & Water Shield and Ice and Water Barrier are two distinct, yet similarly trademarked products, essentially they are manufactured from similar materials and provide protection against freezing and thawing cycles, wind-driven rains, and normal water flow around skylights, vents, chimneys and valleys.
Ice and water shield also serves a very valuable purpose in the event of ice damming when water backs up the roof and migrates between and under shingles. Because ice and water shield is adhered directly to the roof deck with sealed seams, there is nowhere for migrating water to infiltrate and ultimately cause damages.
Typically ice and water shield should be used along all gutter lines of roof pitches of 6/12 and less, although it is not uncommon to see it applied on steeper pitched roofs. It should also be applied in all valleys, along roof-to-wall flashing’s, around all skylights, vents, chimneys, and especially in all areas where metal pans or chimney saddles are utilized. Essentially it is best to use ice and water shield under any metal flashing(s) that have a seam which could potentially leak under the right inclimate weather circumstances.