FEMA’s New Guideline Explains How to Assess Exterior Glazing for Wind VulnerabilitiesOctober 11th, 2019 by Jordan Scott
As increasingly powerful hurricanes continue to make landfall in the U.S., resulting in extensive wind damage to critical facilities, the Federal Emergency Management Agency (FEMA) has developed FEMA P-2062: Guidelines for Wind Vulnerability Assessments of Existing Critical Facilities. The document provides design professionals with guidelines for assessing the vulnerability of critical facilities, including glass doors and windows, to wind pressure, wind-borne debris and wind-driven rain. The goal is to mitigate vulnerabilities to wind damage to avoid loss and disruption of service. The guideline incorporates observations and lessons learned from recent and past hurricanes, current building code requirements and other historic high wind events.
According to FEMA, the results of an assessment can be used by building owners; design professionals; entities that award repair, reconstruction or mitigation grants; as well as state, local, tribal and territorial government agencies developing mitigation plans.
The guideline’s list of five common wind vulnerabilities includes glazing breakage from wind-borne debris generated by hurricanes or tornadoes. The guide includes the example of a hospital in Florida where wind-borne roof aggregate broke the glazing of an intensive care unit, requiring evacuation during Hurricane Charley in 2004.
FEMA’s guideline recommends that if significant vulnerabilities are identified but there are not sufficient funds to mitigate all of them then the assessment team should first prioritize structural elements and exteriors walls, including glass curtainwalls, which have the potential to fail or collapse during wind speeds of 90 mph peak gust or less. If a weak glass curtainwall is identified, FEMA recommends evacuating areas in the vicinity of the weak element when winds above 60 mph peak gust are forecasted to minimize the risk of injury and death.
Assessing Exterior Glazing
Section 5.2 of the guideline covers exterior glazing and shutters, including impact-resistant systems. To perform a proper assessment of these elements, FEMA’s guideline requires that an assessor have knowledge of industry standards, manufacturers, system designs and current building code requirements.
The section includes two types of assessments for glazed assemblies: level one and level two. Level one assessments of exterior glazing are nondestructive and include research, information gathering and observations. For a level one assessment, an assessor should:
- Review project design and original construction submittal documents;
- Determine the age of the assemblies;
- Review repair and maintenance records to help determine the service history and condition of the assemblies, as well as reports of any performance-related issues;
- Research weather records and historical weather data for the area during the life of the building;
- Interview building occupants for reliable information about the service history of the building or any prior or current performance problems;
- Conduct a site inspection to determine through observation the condition of the assemblies, as well as to identify the type and treatment of the glass, including whether the glass is laminated or insulating and the thickness of each lite;
- Document anchor type, size, location and condition;
- Determine the condition of sealants and weather-stripping to help predict current air and water infiltration performance; and
- Check the interior finishes around windows and skylights for evidence of water intrusion.
If the level one assessment was sufficient enough to predict an assembly’s current performance or compliance with design criteria then no further assessment is necessary, according to the FEMA guideline. It only recommends a level two assessment if the level one assessment revealed that the glazing system has several more years of useful service life and the building is located where the basic wind speed is greater than 120 mph; the level one assessment did not provide all information needed; or the assumptions drawn from the level one assessment need to be confirmed. Level two assessments can include field testing, destructive analysis and theoretical analysis. The guideline recommends that for a level two assessment an assessor should:
- Conduct field air and water infiltration tests to confirm current field performance, likely using ASTM E1105-00, Standard Test Method for Field Determination of Water Penetration of Installed Exterior Windows, Skylights, Doors, and Curtain Walls, by Uniform or Cyclic Static Air Pressure Difference. Personnel and agencies experienced with field air and water infiltration testing should be used;
- Remove or partially disassemble typical assemblies;
- Analyze anchors and fasteners, which can be a critical step in determining predicted assembly performance;
- Review anchor substrates; and
- Conduct theoretical engineering analysis to develop performance criteria for existing assemblies when data are not available otherwise.