Copper flat-lock is a type of roofing system that involves laying copper sheets in a flat, interlocking pattern. The sheets are usually fastened to the roof deck with nails or screws, and the seams between the sheets are sealed with a sealant to prevent water infiltration. Copper flat-lock roofing is known for its durability, longevity, and ability to withstand harsh weather conditions. Flat-lock roofing is often used on residential and commercial buildings and is a popular choice for historical renovations due to its traditional, classic appearance.