Q: We have a major leakage problem and are getting a new roof. What is the best underlayment to protect the valleys in my roof from leaking: ice and shield guard, metal flashing, or double rolled shingles?

— Jerry, Collinsville, IL

A: Tom Silva replies: First, your roofers should lay down an ice and water shield over the entire roof. Made of polyethylene and rubberized asphalt, this membrane prevents water that has slipped under shingles from penetrating to ceilings below. The valleys should then be covered with metal flashing or weaving. I would also recommend two layers of the ice and water shield on the lower section of the roof (along the eaves), around chimneys and beside the dormers.
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