Rooftop equipment such as HVAC units, exhaust fans, cooling towers, mechanical units, and other service equipment can become a major wind-loss risk if it is not properly secured. FM requirements affect rooftop equipment anchorage by requiring the equipment, its supports, and its connection to the building to resist the wind forces expected at the facility. For commercial properties seeking FM property-loss protection, anchorage should be designed as part of a complete structural load path rather than treated as a simple roofing detail.
FM Global’s Data Sheet 1-28, Wind Design, specifically addresses wind forces for anchorage of roof-mounted equipment other than solar panels. FM explains that inadequately secured rooftop equipment can be displaced by wind and damage the roof covering, potentially creating an opening through which wind-driven rain can enter the building.
What Does FM Require for Rooftop Equipment?
The central issue is wind resistance. Rooftop equipment experiences uplift, lateral forces, and other wind effects during severe storms. The anchorage system must transfer those forces safely from the equipment into its supports and ultimately into the building’s structural system.
This means the design should consider more than the strength of individual bolts. A complete load path may include:
- The equipment cabinet or frame
- Equipment supports, rails, curbs, or structural frames
- Bolts, welds, clips, and other connectors
- Roof deck or structural members
- The building’s primary structural system
FM emphasizes that the weakest component in this load path can determine the overall resistance of the system.
Equipment Location Matters
Wind pressure is not necessarily uniform across a roof. Roof edges, corners, and elevated portions can experience more severe wind effects than interior roof areas. Consequently, rooftop equipment located near roof edges or corners may require greater anchorage capacity.
The building’s geometry, height, exposure, wind conditions, equipment dimensions, and surrounding conditions can all affect the required design loads. FM Data Sheet 1-28 provides guidance for determining wind pressures used for roof-mounted equipment anchorage, while structural design of the supporting building members may require evaluation under applicable building codes and structural standards.
FM Approval and Equipment Supports
Where FM protection requirements apply, using appropriately FM Approved products and systems can be important. FM Approvals uses testing and certification to verify that products and systems meet defined property-loss-prevention performance requirements. FM Approved products are listed through FM’s Approval Guide and RoofNav resources.
However, an FM Approved component does not automatically mean that every installation is adequately anchored. The complete installation still needs to provide the required load path and comply with the applicable project design.
Why Anchorage Can Affect the Roof
Improperly anchored equipment can move during high winds, damaging membranes, flashing, insulation, curbs, and other roof components. Once the roof assembly is breached, water intrusion can cause damage far beyond the original equipment failure.
FM specifically recommends anchoring or strapping roof-mounted equipment to the roof deck as part of windstorm protection.
For this reason, contractors should avoid treating equipment anchorage as an afterthought. Penetrations through a finished roof also need appropriate flashing and waterproofing so that the anchorage solution does not create a new leak point.
What Should a Commercial Building Owner Check?
Before installing or replacing rooftop equipment, a building owner should confirm:
- The required wind design loads for the building location and roof area.
- The equipment manufacturer’s anchorage requirements.
- The strength of the curb, frame, or support structure.
- The connection between the support and structural deck or framing.
- Whether FM Approved components or an FM-recognized roof assembly are required by the property’s insurance or risk-management program.
- Whether penetrations and flashing are properly integrated with the roofing system.
FM’s plan-review guidance also calls for detailed information about roof layers, securement, fastener spacing, flashing, and existing structural deck conditions when reviewing roofing projects.
Bottom Line
FM requirements make rooftop equipment anchorage a structural and roof-system issue, not simply an equipment-installation detail. The equipment, supports, connectors, and building structure must work together to resist the expected wind forces while protecting the roof from damage and water intrusion.
For commercial buildings in Florida and other high-wind areas, a qualified roofing contractor and structural professional should evaluate rooftop equipment anchorage whenever equipment is installed, replaced, relocated, or modified. Shieldline Roofing can help commercial property owners evaluate roof conditions, flashing, penetrations, and coordination requirements as part of a broader commercial roofing project.
Related Questions
- What does FM Data Sheet 1-28 cover?
- What does FM Data Sheet 1-29 cover for roof securement?
- Should rooftop equipment be secured or shut down before a hurricane?
- Who is qualified to certify that an installed roof meets FM requirements?
- How do rooftop equipment and screens become debris in a hurricane?
- How does a large rooftop equipment cluster create localized high-pressure zones?
- How do rooftop screens and equipment change wind loads on the roof?
Commercial Roof Replacement / Re-Roofing
