Proper Design Improves Roof Longevity
What is the best roof system? Facility executives contemplating a roofing project probably ask themselves that question on a daily basis. Although there are strong opinions from all sectors of the industry on that matter, the truth is that there is no one answer. Each building is different, and the circumstances surrounding each project could alter the roof system choice. The success of a roof system depends on meeting five criteria: design, materials, workmanship, weather and maintenance.
1. Proper Design
Key components to proper design include wind uplift calculations, drainage design, thermal factors, perimeter edge design and existing building conditions. All of these items should be considered for all roof projects.
In the past decade, facility executives have become more active in specifying the types of application methods that they require at their facilities. This has forced designers and contractors to apply systems that comply with the facility executive's constraints. Oftentimes facility executives are concerned with noise, smoke and access to interior work areas during construction. Providing systems that address those constraints and still provide waterproofing protection to the facility can be challenging.
Proper design also includes selecting materials and systems that are compatible with existing building conditions. For instance, the type of deck and slope of the deck will influence the types of materials that are applied. Consideration of the geographic and environmental conditions of the building's location also plays a role in system selection. Buildings located in high-velocity wind zones and areas prone to frequent hailstorms require special design considerations.
Proper design should always be completed with the intent of providing a long-term roofing system. Designing a system around an owner's limited budget should be designated as a short-term repair and should be fully documented as such.
The design standards referenced in bid documents are important for proper roof application. Strategically placed throughout bid documents, these acronyms are more than simply "CYA" phrases used by designers. They are inserted to assure the installed roof system meets the requirements of the roofing industry, as well as those of local and national building codes and insurance providers. When properly presented in the bid documents, the standards can be a valuable asset to the installing contractor.
The responsibility for deciphering the standards and determining how and where they apply in the design documents falls to the specifier. Providing a statement such as "comply with [insert standard]" is simply inadequate when it does not provide the exact design standard requirements for the system.
For instance, in the case of Factory Mutual Global (FMG) wind uplift requirements, the specifier should go beyond the statement "apply in accordance with FMG 1-90, Approval Standard 4470 for Class 1 Roof Covers," and state the required attachment method for the specified deck and insulation components. This includes items such as providing the exact number of fasteners required per square foot to comply with the standard or referencing the manufacturer's FMG test approval document. When this information is not clearly identified by the specifier, the contractor is forced to provide bids based on assumptions.
Identifying standards by their exact names or numbers is also critical, as most standards have several different classifications. For example, the statement "complete the metal coping in accordance with National Roofing Contractors Association (NRCA) details" is vague and confusing because there are several variations to this type of detail. The most prominent standards used in roof system design come from ASTM International, FMG, Underwriters Laboratories (UL), various details from manufacturer literature, NRCA, or the Sheet Metal and Air-Conditioning Contractors' National Association (SMACNA). The specifier should either state the exact standard or be prepared to allow a contractor to complete the detail based on its own interpretation.
The latter practice can lead to inaccurate bids because each contractors' interpretation will be different. It can also lead to on-site disputes, change orders, confrontations between specifier and contractor, and in the end, an unsatisfied owner. The specifier must determine applicable standards for the roof system, list them in clear and concise language, and where necessary, define the methods required to meet those standards during installation.
Although the responsibility of determining design standards for a roof system rests with the specifier, the contractor should have a basic understanding of them and why and where they are required. And the facility executive should understand the specification process well enough to be able to manage it effectively.