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FIELD TECHNIQUE: A Tested Edge



   Author: MetalMag


THE ROOF IS WIDELY RECOGNIZED as one of the most vulnerable parts of a building. Of the various components of a roof, the roof edge is the most critical because of the way in which wind acts on a building.

Commonly, the roof edge receives little attention. It is considered an add-on accessory; however, careful selection of an appropriately tested roof edge is necessary to guard against the effects of potential wind damage.

In addition to longevity issues, a tested roof edge is required by building codes in many states and municipalities. The following information will walk you through the often confusing landscape of testing standards, code requirements and key issues related to choosing the appropriate performance tested roof edge for each project, highlighting ANSI/SPRI ES-1, "Wind Design Standard for Edge Systems Used with Low Slope Roofing Systems."

INDUSTRY BACKGROUND
SMACNA
The Sheet Metal and Air Conditioning Contractors' National Association (SMACNA), Chantilly, Va., has long been involved in providing guidance about metal gauges, cleat gauge and fastener placement through its recommended details.

It is important to note the association's details are prescriptive in nature rather than performance based and they provide no performance numbers to match testing requirements.

NRCA
The National Roofing Contractors Association (NRCA), Rosemont, Ill., also has been instrumental in providing guidance to roofing contractors and other design professionals. NRCA supplies details for edge metal terminations but is not and has no plans to become a roof edge manufacturer.

NRCA has created a sublisting process offered to NRCA members, but only limited details and select gauges have been approved. For the ES-1 requirement to be met, a sheet-metal fabricator (contractor) must be individually approved and listed by NRCA and Intertek Testing Services NA Inc. (ITS), Boxborough, Mass.

According to NRCA, the sublisting process includes:

1. Payment of fees to NRCA and/or ITS and execution of sublisting agreements
2. Payment of initial setup fee to NRCA and execution of a sublisting agreement
3. NRCA authorizes and/or ITS to begin the sublisting processes, which generally requires:

  • Payment of fees
  • Factory audit manual reports
  • Inspections of the sheet-metal fabricator's shop
  • Execution of sublisting agreements
  • Use of approval labels on all listed edge metal flashings
  • Follow-up inspections to ensure continued compliance
For contractors to meet the ES-1 requirement, they must use an approved detail and be an approved contractor. Both items must be in place for a metal edge to actually meet the code.

Roofing contractors should fully understand the different testing methodologies to supply the appropriate product for each project.

FM GLOBAL
Various organizations have provided guidelines and recommendations for roof edge design. One of the most familiar is that created by FM Global, Johnston, R.I. FM Global is formed of a conglomeration of insurance companies that has developed testing standards for materials used on the properties it insures in an effort to limit its exposure to loss. FM Global's standard became popular to use even on buildings that were not FM Global insured because the roofing industry had no standard of its own.

Over time, it became apparent that a consensus standard created by the roofing industry was greatly needed. This especially was true in consideration of the potential damage a poorly designed roof system can do. As a result, the ANSI/SPRI ES-1 standard was created.

Design professionals should not confuse FM Global testing with ANSI/SPRI ES-1 testing; they are two separate and unique testing methods. Specifiers carefully should list which testing requirements are needed for each building project. Likewise, roofing contractors should fully understand the different testing methodologies to supply the appropriate product for each project.

ANSI/SPRI ES-1
OVERVIEW
The key players of the standard are the American National Standards Institute (ANSI), Washington, D.C., and Single Ply Roofing Industry (SPRI), Waltham, Mass. ANSI is a nonprofit organization that does third-party endorsements of performance testing processes and procedures. SPRI is comprised of manufacturers and professionals in the single-ply roofing industry.

The standard was canvassed throughout the industry to develop consensus and followed these steps on its way to becoming an international code:

1. Developed by SPRI
2. Approved by ANSI
3. Approved by the International Code Council, Falls Church, Va.
4. Written into the 2003 International Building Code (IBC) and subsequent versions

IBC
The 2003 IBC and recent 2006 IBC include the requirement that roof edges be ANSI/SPRI ES-1 tested. 2006 IBC 1504.5 states: "Low-slope membrane roof system metal edge securement, except gutters, shall be designed and installed for wind loads in accordance with Chapter 16 and tested for resistance in accordance with ANSI/SPRI ES-1, except the basic wind speed shall be determined from Figure 1609."

More than half the United States has adopted the 2003 IBC or subsequent versions statewide, and countless municipalities have done likewise. The trend is clear, and ES-1 testing is something all roofing and design professionals will need to become familiar with.

The ES-1 document is ANSI/SPRI ES-1, "Wind Design Standard for Edge Systems Used with Low Slope Roofing Systems," and it can be downloaded for free from SPRI's Web site, www.spri.org.

TESTS
The ANSI/SPRI ES-1 standard is comprised of three tests that measure the ability of edge treatment to resist the pull of the roof material inwardly. The RE-1 Test is a static test, and the RE-2 and RE-3 Tests are cycle test, which allow for a realistic simulation of wind, which acts on a building in periodic gusts rather than one long, continuous gust. It also is important to understand the corners of a building receive the most wind-uplift stress and stress will suddenly increase and decrease with wind-gust strength.

RE-1 Test

  • A static test with a 100-pound (45 kg.) load every foot is used for ballasted systems while a calculation based on fastener placement is used for mechanically attached systems.
  • The membrane is pulled at a 45-degree angle to the roof deck to simulate a billowing membrane.
  • The edge is tested until failure occurs, which is when the membrane comes free of the edge termination or the termination comes free of its mount. The edge is considered to have passed if the test force at failure on a 12-inch- (305-mm-) wide sample meets or exceeds the force.

RE-2 Test
  • A load is applied to the face of the fascia incrementally and held for at least 60 seconds. The load is removed and then increased in increments of 25 lb/ft2 (120/kg/m2) until 150 lb/ft2 (730 kg/m2). Then increments of 10lb/ft2 (50kg/m2) are used.
  • The edge is tested until failure occurs, which is the loss of securement of any component of the roof edge system or deformation that would result in the loss of weather protection at the edge.

RE-3 Test

  • Simultaneous loads are applied to the face and top. The back leg and top and the front leg and top are tested individually on separate samples. The lowest test results will be used.
  • The loads are applied incrementally in the same manner as the RE-2 Test.
  • The edge is tested until failure occurs, which is the loss of securement of any component of the roof edge system or deformation that would result in the loss of weather protection at the edge.

KEY FACTORS
The equation for calculating the design pressure is found in ANSI/SPRI ES-1. This calculation involves five key elements and should be calculated as follows:

























1. Building Height
The building height should be the height at which the roof edge is to be installed. If there are multiple roof levels, each level is considered a different building height.

2. Wind Speed
Use the ANSI/ASCE 7-02 document "Minimum Design Loads for Buildings and Other Structures." This document provides wind maps of the United States and its territories, which are to be used to determine the wind speed for a particular region.

3. Building Location (Exposure Level)

  • Exposure B: urban and suburban areas, single-family dwellings
  • Exposure C: open terrain with scattered obstructions
  • Exposure D: flat, unobstructed areas; open water for 1 mile (1.6 km) or greater

4. Building Occupancy Factor (Importance Factor)

  • Category I: buildings and other structures that represent a low hazard to human life in the event of failure (agricultural facilities, certain temporary facilities and minor storage facilities)
  • Category II: all buildings and other structures except those listed in Categories I, III and IV
  • Category III: buildings and other structures that represent a substantial hazard to human life in the event of failure (buildings where more than 300 people congregate; elementary and secondary schools and day-care facilities with a capacity greater than 250 people; health-care facilities with a capacity of 50 or more resident patients but not having surgery or emergency treatment facilities; and jails or detention facilities.
  • Category IV: buildings and other structures designed as essential facilities (hospitals and other health-care facilities having surgery or emergency-treatment facilities; fire, rescue and police stations; emergency-vehicle garages; and communication centers and other facilities required for emergency response)

5. Special Terrain Characteristics
Obstructions or special terrain characteristics, such as hills, escarpments, etc., influence the wind patterns on your building.

RECOMMENDATIONS
No area of the country is exempt from wind-related roofing damage, and one of the leading causes of commercial roofing damage has proven to be improperly designed and installed edge details. Conservative estimates show that 75 percent of all wind-related roofing failures are attributed to insufficient or poorly installed perimeter metals.

Conservative estimates show that 75 percent of all wind-related roofing failures are attributed to insufficient or poorly installed perimeter metals.

Design professionals should recognize the value of a performance tested roof edge and the quality assurance provided through ANSI/SPRI ES-1 design standards. The addition of this standard to the 2003 and 2006 IBC further aids in protecting buildings from wind-uplift forces, in any area of the country, especially in coastal areas and hurricane zones.

It is important to frequently check your local code requirements because additional states, counties and municipalities are in the process of adopting the 2003 and 2006 IBC. Understandably, it can be difficult and sometimes confusing to keep track of each locality's requirements. To avoid the risk of not meeting the code, specify ES-1 tested roof edges.


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