- Ice and water shield (a self adhering membrane or SAM)
- Metal flashing in the valley
*Ice and Water Shield: Ice and water shield should always be used in the valleys, and in most cases it is a sufficient form of protection, placed beneath the shingles to protect the valleys of your roof. Ice and water shield is a self-adhering bituminous membrane much like a sticker. Sometimes referred to as a SAM, ice and water shield is akin to a large sticker. It typically comes in a roll that is 3 feet wide and weighs about 90 pounds. This should be applied as the primary underlayment beneath all shingles in the valleys of your roof, as these areas are designed to channel the water, and are thus points of high vulnerability. Ice and water shield should also be used around all chimneys, vent pipes, and any other protrusions coming through the roof.
*Metal Flashing: Contrary to what many believe, metal flashing is not always a better alternative to ice and water shield. In fact, it should never be used an alternative; metal flashing in the valleys should only be used in addition to a SAM. Metal flashing is either a strip of steel or aluminum that should be placed over top of a SAM in certain situations. For example, if there is a superfluous amount of leaf build up in a particular valley, metal might be a welcomed alternative to the sandpaper-like texture of a composite shingle. The slippery metal will only help to shed the leaves and water from the valley.
A valley on a roof that has a very gentle pitch (anything below a 4 pitch) would be yet another welcoming scenario for valley metal. In this situation, the water and debris that might otherwise just collect in the shallow valley will be channeled off the roof more efficiently.