The story about ice and waters:
Ice and water is installed under roofing to prevent water caused by ice dams from leaking into a building. If there are fastners used than the ice and water barrier seals around the fastner.
Ice and water shield surfaces come in three main forms; granular, sand and mat. Granular, sometimes referred to as mineral, surfaces are covered with granules that are about the same size as shingle granules. Granular surface rolls also tend to be a little heavier than rolls with a different type of surface. A sand surface has a fine layer of sand attached to the face of the ice and water shield. A mat surface, sometimes called film, poly or fabric, has no granules or sand attached to the surface. Surface selection on ice and water shield is important because some ice and water shields can become very slick when water is on their face.
High temperature (HT) rolls are good to use when your roof deck is going to get over 150 degrees Fahrenheit. If you’re installing a metal roof you may want to use a high temp ice and water shield. Metal roofs will also require an ice and water shield with a non-abrasive surface so that the bottom surface of the metal will not be abraded as it expands and contracts.
Ice and water barrier comes in different thicknesses,but as long as it is 40 mil thick it will all do the same job.
When used on a residental application there are two ways recommend by the manufacturer. One is under drip edge and down on to fascia with drip edge over. Two is drip installed first and ice and water sealed to drip edge.