Residential Roofing Glossary

Decking, also called roof sheathing, is the flat panel material — typically plywood or oriented strand board (OSB) — nailed directly to your roof’s structural rafters. It forms the solid base layer onto which all other roofing materials are fastened. Damaged or rotted decking compromises the integrity of the entire roof system and must be replaced before new shingles or underlayment are installed.

Underlayment is a water-resistant or waterproof barrier material installed directly on top of the roof decking and beneath the outer roofing material, such as shingles. It provides a secondary layer of protection against wind-driven rain and moisture infiltration. Available in felt or synthetic varieties, underlayment is a critical component that helps prevent interior water damage if the primary roofing material is ever compromised.

An ice and water shield is a self-adhering, waterproof membrane applied to the most vulnerable areas of a roof, including eaves, valleys, and around penetrations like chimneys and skylights. It is specifically designed to prevent water damage caused by ice dams — a condition where melting snow refreezes at the roof’s edge and forces water back up beneath shingles, potentially causing significant interior leaking.

Flashing refers to thin strips of corrosion-resistant metal — typically aluminum, galvanized steel, or copper — installed at roof joints, transitions, and penetrations to prevent water from seeping into the structure. Common flashing locations include areas around chimneys, skylights, vents, and where a roof meets a vertical wall. Improperly installed or deteriorated flashing is one of the most common sources of residential roof leaks.

A ridge cap is the specially formed roofing material applied along the peak of a roof — known as the ridge — where two opposing roof slopes meet. It seals this critical junction against wind and water intrusion while also contributing to the roof’s overall ventilation and finished aesthetic appearance. Ridge caps are available in shingle-style or pre-formed metal versions depending on the roofing system used.

A roof valley is the internal angle formed where two sloping roof planes intersect and direct water toward the eaves. Because valleys concentrate heavy water flow from multiple roof surfaces, they are among the most leak-prone areas of any residential roof. Valleys are typically reinforced with metal flashing or specialty underlayment to handle the increased volume of runoff and protect against premature wear.

A drip edge is an L-shaped metal flashing installed along the outer edges of a roof — at the eaves and rakes — designed to direct water away from the fascia and into the gutters. It also helps prevent wind from lifting the edges of shingles and discourages insects and small animals from accessing the space beneath the roofing material. Most building codes require drip edge installation as a standard component of any residential roofing system.

Architectural shingles, also referred to as dimensional or laminate shingles, are a premium type of asphalt roofing shingle constructed from multiple bonded layers of material. This multi-layer design creates a textured, three-dimensional appearance that mimics the look of wood shake or slate. Compared to traditional three-tab shingles, architectural shingles offer superior durability, a higher wind resistance rating, and a significantly longer lifespan, making them the most commonly specified shingle in modern residential roofing.