Garage Door System GuideA steel sectional door is the most common residential garage door in North America. The number of layers, the gauge of the steel, and the paint finish are the specifications that separate a builder-grade door from a premium one. This page pulls the definitions and numbers directly from manufacturer literature.
Single, double, and triple-layer construction
Steel doors are built up in layers. A single-layer door is one skin of steel with no insulation. A double-layer door adds insulation behind the exterior skin, and a triple-layer door sandwiches the insulation between an exterior and an interior steel skin for the most rigid and best insulated build.
Clopay sells its steel doors in one, two, or three-layer construction across the Classic, Modern Steel, Gallery, and Bridgeport lines, letting buyers pick a build to match budget and climate. Amarr builds its Designer's Choice line in triple-layer construction, which pairs the interior steel skin with the insulation core for quiet operation and strength.
Steel gauge and paint finish
Gauge measures the thickness of the steel skin, and the number runs backward: a lower gauge number means thicker, more durable steel. Manufacturers protect that steel with multi-coat paint systems that resist corrosion and fading.
Amarr coats its heavy-gauge steel in a five-layer paint system for long-lasting durability, and offers eight factory paint colors plus access to more than 800 Sherwin-Williams colors through its Color Zone program. Overhead Door backs its Thermacore steel with hot-dipped galvanized steel and two coats of baked-on polyester paint on the interior skin.
Insulation drives the upgrade
The jump from single to triple-layer is really a jump in insulation. Polystyrene panels slot into double-layer doors, while injected polyurethane fills the entire cavity of a triple-layer door and bonds to both skins, which is why premium doors post the highest R-values.
Clopay's Intellicore is a proprietary polyurethane foam injected into premium doors that expands to fill the structure, reaching R-values up to 18.4. Overhead Door's top Thermacore model uses two inch thick foamed-in-place polyurethane between two steel layers for a third-party verified U-factor of 0.10.