Approval Standard for Class 1 Exterior Wall Systems
Class Number 4881
2. Select Product
3. Design to Product Specs
Step 1: Define
FM Global Property Loss Prevention Data Sheet 1-28 is intended to provide general guidance to building designers regarding wind considerations for building components and cladding and their immediate supports. Inward and outward pressure for enclosed and partially enclosed buildings are determined by building designers and FM Approved exterior wall panels tested per Approval Standard 4881 for natural hazards exposure, where available, are used. Panels with appropriate ratings will have to be selected in accordance with guidelines in sections 3.1.6 and 3.1.7, using a safety factor of 2.0.
You may obtain the FM Global Property Loss Prevention Data Sheet 1-28 from www.fmglobaldatasheets.com. Registration is required.
Step 2: Select Product
Metl-Span’s FM 4881 Windload Ratings-Fastening Patterns 1, 2, 4, 10/wp-content/uploads/2022/11/Metl-Span-FM-4881-Listing-06-Feb-2018.pdf and 11
Step 3: Design to Product Specs
Compare Metl-Span 4881 testing to the rest of the IMP market.
If designed around our product, competitors’ product may not meet rating requirement and must be addressed in project specifications.
Additional Notes about FM 4881:
- FM 4881 is more aggressive than other test methods required by code.
- A safety factor of 2.0 is required, the assembly cannot fail and it has to maintain pressure.
- Ratings are listed as positive pressure/negative pressure (1.4 times positive pressure).
- Where expansion fasteners are required, they have to be installed directly through the support steel into the panel skin. Offset clips are not allowed. The inside skin of the panels has to bear on support members that are minimum 14 gauge thick and a maximum of ½” thick.
- A plaque showing the wind rating must be posted in a readily visible location on the completed building project.
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