In a conventional roof system, insulation is installed under the roof membrane. This is the most common low-slope roof application. Placing insulation in a conventional roof system poses some disadvantages. Among the many types of roofing systems available is the built-up roof system (BUR), which is generally applied to “flat or low-slope roofs”.
The traditional flat roof system used for more than 100 years, is also known as a “mop-on” or “tar and gravel system”. A “docked” roof is a conventional roof that is built on site. It uses roof beams, hanging beams, strut beams, struts, straps, neck flanges, rafters and ridges. Single-layer roofs are lightweight, flexible, cost effective, and quick and easy to install.
A lattice roof is a type of roof construction that is commonly used today throughout residential construction. Reinforcements generally rely on the outer walls only to support the roof structure, leaving the inner walls more or less built in the middle as partitions dividing the house. Trusses are a designed wooden net that, when built, forms the entire roof system. Benefits of conventional and constructed roofs include multi-layer protection, thermal and UV performance, fire and lift stability, strong tensile strength and durability for high roof traffic and multiple weather conditions.
In conventional low-slope roof assemblies, also known as exposed membrane roof assemblies, the membrane is on the outside of the insulation and roof structure, exposing it to outdoor conditions including temperature, solar heat gains, cooling of the night sky, abrasion and dirt. Conventional framed roof systems are ceiling beams that rest on the outer walls and meet each other on a trestle board that is generally supported by means of posts that go down onto any available inner wall, causing that wall to bear load. A new conventional roof was installed in a test facility, using 3 different roof membrane colors (white, gray and black) and 3 different insulation arrangements for a total of 9 unique roof assemblies. Prior to 1970, both roof trusses and conventional roof structures were used, and before 1950, almost all homes had conventional framed roof systems.