Winterguard Metal Underlayment: this product is a high temperance ice and water shield that goes along the bottom edge of the roof in the valleys around any penetration points (as in pipes, chimneys, skylights, or along the edge of the house where there is flashing). If your sawfit is deeper than 2 foot your roof will require an extra row of ice and water to protect your home from any potential ice damage.
More Information on Waterproofing Underlayment >>
More Information on Lightweight Synthetic Underlayment >>