Ask This Old House

Preventing Ice Dams; Applying Closed-Cell Spray Fo

General contractor Tom Silva explains to a homeowner how ice dams form and how to prevent them. He then works with an insulation contractor to apply closed-cell spray foam insulation in an attic. Then Tom, along with host Kevin O'Connor, landscape contractor Roger Cook, and plumbing and heating expert Richard Trethewey, asks, "What Is It?" Afterward, Richard shares a tip about connecting gutter downspouts. And Roger heads to Philadelphia to plant two trees on a busy city street.