۲ ROOFING SYSTEMS
The Description section discusses roof assembly materials, including roof decks, air and vapor retarders, roof insulations, and roof coverings. The Application section discusses system selection criteria, warranty considerations, key elements of drawings and specifications, and construction contract administration. The Details section discusses and presents various details. The remaining sections are Emerging Issues, Relevant Codes and Standards, and Additional Resources.
This Guide is intended to give a relatively brief introduction to roofing, to weigh pros and cons of various materials that are not available in other reference documents, and to provide some suggestions for enhancements beyond systems that simply comply with code and warranty minimums. It addresses the basics, but does not delve deeply into the subject. After gaining a general understanding of the roof assembly options and various issues associated with them, the designer has a choice to make: Either elect to further expand your skills and knowledge, or work with professional roofing contractors or roof consultants. Years ago, it was uncommon for designers to work with a roof consultant or call upon a trusted contractor for advice. But the complexities brought on by the BUR alternatives now demand the inclusion of a roof consultant as part of the design team, if this expertise is not developed within the designer’s office.
Delivering a successful roof project involves two distinct phases. The first phase is the design process. It is imperative to identify all of the criteria and required performance characteristics early in the design process. A roof system should be selected that optimally responds to an integration of the project’s requirements and the system selection criteria. After the roof system is selected, the specifics of the system (such as deck type, insulation type(s) and thickness, fastener patterns, and warranty requirements) are developed and details are designed. This phase is culminated with the preparation of specifications and drawings that communicate the designer’s design concept and requirements to a professional roofing contractor for execution of the work.
When specifying roof assemblies, designers have many materials from which to choose. This section provides a brief overview of the primary roof deck, air barrier, vapor retarder, insulation, and roof covering materials used in the U.S. For further information on these materials, refer to The NRCA Roofing Manual (published by the National Roofing Contractors Association). Roof system selection criteria are discussed in the Application section. Combining the various materials into assemblies is also discussed in The NRCA Roofing Manual and for roofing systems on Federal buildings see United Facilities Criteria UFC 3-110-03.
A design concern when designing roofs in cold climates is the possibility of falling ice and snow, as described in Considerations for Building Design in Cold Climates by Mike Carter, CET and Roman Stangl, CET.
The term roof system refers to the air barrier or vapor retarder (if present), roof insulation (if present), and the roof membrane, flashing, and accessories.
Low-slope Roof Coverings (slope less than or equal to 3:12):
- Built-up Roofs (BUR)
- Mesh Reinforced Elastomeric Coatings (MREC)
- Modified Bitumen (MB)
- Atactic Polypropylene (APP)
- Styrene-Butadiene-Styrene (SBS)
- Styrene-Ethylene-Styrene (SEBS)
- Thermoplastic Single-Plies
- Polyvinyl Chloride (PVC)
- Thermoplastic Polyolefin (TPO)
- Ketone Ethylene Ester (KEE)
- Thermoset Single-Plies
- Ethylene Polypropylene Diene Monomer (EPDM)
- Thermoplastic Single-Plies
- Sprayed Polyurethane Foam (SPF)
- Metal Panels
- Hot and Cold fluid-applied roofing membranes
Steep-slope Roof Coverings (slope greater than 3:12):
- Metal Panels and Shingles
- Asphalt, Wood, and Synthetic Shingles
- Wood Shakes
- Clay and Concrete Tile