When a commercial building needs a new roof, a roof recover can sometimes be installed over the existing roof instead of completely removing the old system. However, FM Global does not treat the existing roof as something that can simply be covered and forgotten. For FM-insured properties, the condition, construction, attachment, drainage, structural capacity, and fire and wind performance of the existing roof can all affect whether a recover is acceptable.
FM Global’s Property Loss Prevention Data Sheets provide engineering-based guidance for roofing projects, including modifications to existing buildings. FM also identifies roof repairs and replacements as projects that may require plan review.
The Existing Roof Must Be Evaluated
Before installing a recover system, the existing roof should be inspected to determine whether it is a suitable substrate. FM guidance emphasizes identifying deficiencies such as leaks, deteriorated membranes, loose or missing fasteners, damaged flashing, poor drainage, ponding water, damaged insulation, and other conditions that could compromise roof performance.
A recover should not be used to conceal significant existing problems. Wet or water-damaged insulation, structurally inadequate components, or severely deteriorated roofing materials may need to be removed or corrected before the new roof is installed.
The condition of the existing roof is particularly important because the new system depends on the existing assembly for support and, in many cases, for its load path.
FM Looks at Structural and Wind Performance
FM’s approach is performance-based. The additional weight of a recover must be considered, particularly when installing a new roof over an existing metal roof or other structural system.
For existing metal roofs, FM guidance states that a licensed professional engineer should demonstrate that the structure can support the gravity loads, including the additional weight of the recover. The wind and gravity load path must also properly engage the existing supporting structural framing.
The recover can also change the roof’s geometry, drainage characteristics, and wind exposure. If the proposed system substantially changes the roof configuration, additional structural analysis may be necessary.
The New Recover Must Have Appropriate FM Approval
Another major consideration is the compatibility of the proposed recover assembly with the existing roof. FM guidance calls for appropriate FM Approved wind-uplift-rated assemblies, where available, and states that a new roof cover should be specifically FM Approved for recover construction over the particular existing metal roof system when applicable.
This means contractors should not assume that an FM Approved roofing product is automatically approved for every recover application. The specific roof assembly, substrate, attachment method, insulation, membrane, and other components matter.
FM Approvals provides third-party certification for roofing assemblies and other products, while approved products and systems can be identified through FM’s approval resources.
What Happens to the Existing Roof?
The answer depends on its condition and the proposed recover system.
A sound existing roof may remain in place if the proposed assembly is appropriate and meets applicable FM requirements. Defective components, however, may require repair or removal. For example, FM guidance for certain metal-roof recover applications requires existing exposed fasteners to be retightened, additional fasteners to be installed when necessary to meet wind requirements, and severely deteriorated areas to be addressed before liquid-applied roof systems are installed.
Drainage must also remain adequate. Existing drains, scuppers, and other drainage components should be evaluated so the additional roof layers do not create unacceptable ponding.
When Should a Recover Be Avoided?
A recover may be inappropriate when the existing roof has extensive wet insulation, severe deterioration, inadequate structural capacity, unacceptable attachment, major drainage problems, or conditions that prevent the new system from achieving its required FM performance.
In these situations, full roof replacement may provide a safer and more defensible solution than covering existing problems with another roof layer.
Key Takeaway
FM generally treats an existing roof during a recover as an active part of the roofing assembly—not merely as material that can be covered. Its condition, structural capacity, attachment, drainage, fire characteristics, and compatibility with the proposed recover system must be evaluated.
For an FM-insured commercial property, Shieldline Roofing can help assess the existing assembly, identify deficiencies, and develop a recover or replacement approach that considers FM requirements, manufacturer specifications, and applicable building requirements. For complex projects, the roofing design should be coordinated with the building owner, qualified roofing professionals, and the appropriate engineer or FM representative.
For official guidance, FM Global makes its Property Loss Prevention Data Sheets available as engineering guidelines for reducing property-loss risks.
Commercial Roof Repair in Florida
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