Some important aspects of roof system designs are often not addressed, resulting in incomplete contract documents and as a result sometimes incomplete craftsmanship.
Some important aspects of a roofs design that are often overlooked are (And some of the codes behind them):-
• Fire-resistance classification
• Uplift resistance
• Roof slope and drainage attributes
THE FIRE-RESISTANCE CLASSIFICATION for your project
The building code contains provisions requiring roof assemblies to have specific fire-resistance properties. IBC 2012 contains provisions for external and internal fire-resistance classifications of roofing systems.. IBC 2012 Section 1505—Fire Classification contains provisions for roofing systems to be tested in according to ASTM International E108, or Underwriters Laboratories 790, both titled “Standard Test Methods for Fire Tests of Roof Coverings.” ASTM E108 and UL 790 are separate and independently maintained documents that provide the same test protocols and classification criteria. ASTM E108 or UL 790 testing results determine a Class A (most severe fire exposure), Class B (less severe fire exposure), or Class C (lowest level of fire exposure) classification.
TEST AND MEASURE UPLIFT RESISTANCE for low slope
Construction scopes that try address wind design for low-slope membrane roof systems are often not adequate enough. Roofing system designers should not place the responsibility for determining roof system or individual component design wind loads on manufacturers, installers or roofing contractors. Nor should roof system designers rely on specifying wind speed warranties as a substitute for building-code–required wind design. It is important to look at factors such as wind speeds, building height, risk category, wind exposure, and internal pressure coefficients as applied to a specific building—all of which are necessary for properly determining a roof system’s design wind loads for building code compliance.
Building code provisions for uplift resistance for roof assembly components are located in IBC 2012 Chapter 15—Roof Assemblies and Rooftop Structures. General wind resistance provisions for roofs are in IBC 2012 Section 1504.1 Wind resistance of roofs. The section states: “1504.1 Wind resistance of roofs. Roof decks and roof coverings shall be designed for wind loads in accordance with Chapter 16 and Sections 1504.2, 1504.3 and 1504.4.” IBC 2012 Chapter 16—Structural Design prescribes the minimum structural loading requirements for use in the design and construction of buildings and other structures. The referenced Chapter 15 sections provide category-specific requirements for resisting design] wind loads in roof assemblies, as determined in accordance with Chapter 16. For low-slope membrane roof systems, provisions in IBC 2012 Sections 1504.3 and 1504.4 are relevant. Section 1504.3 contains the following relevant provisions:
“1504.3 Wind resistance of nonballasted roofs. Roof coverings installed on roofs in accordance with Section 1507 that are mechanically attached or adhered to the roof deck shall be designed to resist the design wind load pressures for components and cladding in accordance with Section 1609.
“1504.3.1 Other roof systems. Roof systems with built-up, modified bitumen, fully adhered or mechanically attached single ply
through fastened metal panel roof systems, and other types of membrane roof coverings shall also be tested in accordance with FM 4474, UL 580 or UL 1897.”
Section 1504.3 applies to roof systems that do not use ballast to resist wind-uplift loads, such as adhered and mechanically attached roof systems. Roof system designers are required to demonstrate that the proposed fastening schedules will resist the wind uplift loads. Section 1504.3.1 contains additional provisions for nonballasted low-slope roof systems (roof systems with slopes less than 2:12). Membrane roof systems are required to demonstrate building code–required uplift load resistance, using one of three referenced testing methods.
Responsibility for determining and clearly identifying wind design data, including design wind loads for roof systems, is required
by building codes. Therefore, roof system designers should note design wind loads for subject buildings in contract documents. Roof systems designers may retain structural engineers or other qualified consultants to help them fulfill their design responsibilities.
KEEP ROOF DRAINAGE POSITIVE
NRCA recommends low-slope membrane roof systems be designed to provide positive drainage. The criterion for judging proper slope for drainage is that there be no ponding water on the roof 48 hours after a rain during conditions conducive to drying. Roof membrane manufacturers also generally recommend that a roof assembly have a positive slope to drain and should allow for short durations of ponding water.
IBC 2012 Section 1507—Requirements for Roof Coverings requires that low-slope membrane roof covering systems have a
design slope of a minimum of one-fourth unit vertical in 12 units horizontal (2% slope) for drainage, and one-eighth unit vertical in 12 units horizontal (1% slope) for coal-tar built-up roofs.
In general, slope is incorporated into the roofing system by design:
• Sloping the structural framing or deck. This method is more complex than for non-sloped structures and requires coordination
during the design process to ensure proper placement of roof drains, scuppers, tapered insulation and other drainage components.
• Designing a tapered insulation system. This method is appropriate for both new construction and reroofing projects, as well as in cases where a roof deck will not provide adequate slope to drain.The tapered insulation also can contribute thermal resistance as part of meeting the code requirement for minimum insulation value.
• Using an insulating fill that can be sloped to drain. Lightweight insulating concrete, thermosetting insulating fill, and spray polyurethane foam (SPF) are examples of systems that can be installed over level or irregular roof assembly surfaces to achieve positive slope.Geographical location, structural considerations, compatibility with other components, and the geometry of the area to be sloped must be considered in determining the feasibility of this option.
• Proper location of roof drains, scuppers, and gutters. The roof system designer should determine the location of drainage elements. For reroofing, modifications to existing drainage elements, such as raising or lowering a drain or scupper, may be necessary to provide proper drainage. Adding drains or scuppers can lead to conflict with existing building elements, and the additional drainage elements have to be integrated with existing building systems. There’s also added cost to consider.
Most often, a combination of methods will be used to create adequate roof slope and drainage.
Contract documents should clearly indicate the slope and drainage method for roof systems. At a minimum, the following roof slope and drainage-related information should be included by roof system designers in contract documents:
• Roof slope and drainage elements, such as roof drains, scuppers, and gutters, should be clearly and completely shown.
• Mechanical documents should indicate placement of rooftop equipment. The equipment and associated support elements should not interfere with anticipated drainage paths.
• Structural documents should indicate the type of roof deck and may include sloping elements and mechanical equipment supports.
• Roof-related drawings should be coordinated. Details should be appropriate for the type of roof system being specified.
• Roof-related specifications should include anticipated roof system elements and be consistent with information shown on construction drawings.
So, this is was brief overview of how contracts, building codes need to go hand in hand, to make sure the contractors are clear about the project they will be working on. In the DFW area, Roofing Fort Worth and Dallas roofing has made a lot of full roof installations and a lot of roof repair fort worth so done so many projects with a fully detailed scope, and proper contracts, and then results have been more customer satisfaction, less law suits, etc.