There are several roof systems available for Pre-Engineered Metal Buildings (PEMB) that can have a significant impact on the price of a building project due to a large range in both the cost of materials and the amount of labor required for installation. Generally, these roof systems fall into two categories: Standing Seam Roof (SSR) systems or Screw Down Roof systems.
Screw Down Roof systems are the most economical option for steel buildings and can be used in applications such as workshops, agricultural buildings, and sawmills. It consists of lapping steel panels that are through-fastened to the roof purlins. The roof fasteners typically have a long-life alloy capped head, but are also commonly available in stainless steel as an upgrade. A sealing washer (pre-installed on the fastener) is what provides a seal. Care must be given throughout the installation to install each fastener properly. Over or under tightening of the fasteners, or damaged/missing sealing washers can result in a roof leak. Tape sealant is applied at the panel laps in conjunction with stitch screws. Common roof panel thicknesses are 26 gauge or 24 gauge.
Standing Seam Roof systems use panels that have a raised seam and are supported by clips that must first be fastened to the roof purlins, but the attachment between the roof panel and the clip does not require a fastener. Clips are typically available in different height options and in a fixed, or sliding style to allow for thermal expansion of the roof panels. Thermal blocks can also be installed in conjunction with the clips to decrease thermal conduction between the roof panel and roof purlin.
There are a variety of mechanically sealed SSR systems as well as snap-together systems. Mechanically sealed SSR systems require use of a seaming machine in the field that is designed and calibrated for a particular roofing product or brand.
The combination of a sealed and raised seam with a minimal number of through-fasteners gives standing seam roof systems superior weather tightness compared to a screw down roof system, but since SSR systems require more components, and are more complicated to manufacture, they also have a greater material cost, and take more time to install.