Wind Uplift Ratings Explained for Property Managers

In short: A wind uplift rating tells you how much upward suction a commercial roof assembly survived in a controlled test — not the wind speed it can endure, but the pressure it resisted. FM ratings like 1-60 and 1-90 express that resistance in pounds per square foot; UL 580 classes (30, 60, 90) certify an assembly passed fixed pressure thresholds. As a property manager, you do not need to run the numbers yourself — you need to know where your building's rating lives, whether it matches the wind zone, and that edge flashing is rated separately.

Why does wind try to lift a roof instead of pushing it down?

Most people picture wind as something that pushes. On a roof, the dangerous force pulls.

When wind flows over a building, it accelerates over the roof surface and creates negative pressure — suction — above the membrane, much like air moving over an airplane wing creates lift. The effect is strongest at perimeters and corners, where airflow separates and turbulence concentrates. Building scientists call these zones the field, perimeter, and corner, and corners can see uplift pressures multiples higher than the middle of the roof.

This is the mechanism behind most commercial wind damage: the membrane, insulation, or flashing was adequate for the field but marginal at a corner, and one strong gust partially detached it. The roof can look perfectly intact afterward — until the next rain finds the seam the wind left behind. Uplift ratings exist to quantify exactly how much suction an assembly can take before that happens.

What do FM ratings like 1-60 and 1-90 actually mean?

FM Approvals — the testing arm of FM Global — runs one of the two dominant uplift test programs. The process is straightforward to understand: a full roof assembly (deck, fasteners, insulation, membrane) is built on a large test frame, clamped to a pressure vessel, and subjected to increasing suction until something fails. The assembly's rating is set at the pressure level below the failure — so if the system failed at 105 pounds per square foot, it earns a 1-90 rating.

A few things worth knowing about the FM scheme:

• The number is a pressure, not a wind speed. 1-60 means the assembly earned approval at 60 psf of uplift resistance; 1-90 means 90 psf. FM's minimum approval level is 1-60.
• The test runs to failure. Failure can be a membrane tear, a seam delamination, screw pullout, or any other component giving way — the rating reflects the weakest link of that exact assembly.
• The rating belongs to the assembly, not the membrane alone. A 1-90 approval describes a specific stack-up: a particular deck, fastener pattern, insulation, and membrane installed as tested. Swap a component and the rating no longer applies unless the manufacturer documents that combination.
• FM 1-28 and 1-29 are the design references. FM's loss-prevention data sheets describe how engineers calculate the uplift pressures a roof will actually face (1-28) and how above-deck components should be secured (1-29). The rating is only half the story; the other half is whether the design pressure for your site is within it.

For property managers, the practical takeaway: if your roof spec or contractor submittals list "FM 1-90" (or similar), that number is your benchmark. Ask whether the installed assembly matches the tested configuration, especially the fastener pattern — attachment density is what the rating is really buying.

What are UL 580 classes, and how do they differ from FM?

UL 580 is the other major uplift standard, run by UL (formerly Underwriters Laboratories). It tests the resistance of roof assemblies using a 10-foot-by-10-foot mockup subjected to both positive pressure from below and negative pressure (vacuum) from above, including oscillating pressures that simulate gusting.

The UL classes are fixed thresholds, verified during this run:

• Class 30 — withstood a total pressure differential of 45 psf
• Class 60 — withstood a total pressure differential of 75 psf
• Class 90 — withstood a total pressure differential of 105 psf (48.5 psf positive pressure combined with 56.5 psf negative pressure)

Two distinctions from the FM approach matter. First, UL 580 is not run to failure — the assembly is tested only to the specified limit of its claimed class. Second, UL 580 applies both to structural panels installed over open framing and to roof coverings attached to solid substrates when the two are specified as a system. You will most often see UL classes on metal roof panels, while FM ratings dominate single-ply and built-up assemblies — though either can appear on a spec sheet depending on the system.

Do not try to convert between the two schemes arithmetically (1-90 and Class 90 are tested differently and are not interchangeable labels). What matters is that the assembly's certified class meets or exceeds the design requirement for the building.

Does the uplift rating cover edge flashing and metal?

Often, no — and this is the most overlooked gap in wind design.

Uplift pressures peak at perimeters and corners, which is exactly where edge flashing, fascia, and coping sit. Yet the membrane's FM or UL rating does not automatically certify the edge system. Edge metal is governed by a separate standard, ANSI/SPRI ES-1, the wind design standard for edge systems used with low-slope roofing. ES-1 tests flashing and fascia against wind pull-off so the perimeter's resistance can be matched to the same wind environment as the field.

For a property manager, the question to ask after any roof project is simple: is the edge system ES-1 tested, and does its rating suit our wind zone? A roof with a strong membrane rating and untested edge flashing has its strongest protection in the zone that needs it least. When wind damage investigations find a roof that peeled from the edge inward, missing or under-rated edge metal is a frequent culprit.

How do you find your building's wind uplift rating?

The rating exists in paperwork, not on the roof itself. Here is where to look, in order:

1. Original specifications and contractor submittals. The roof spec should name the assembly and its tested rating. Submittals from the installer document what was actually built.
2. Manufacturer product data. Membrane and panel manufacturers publish ratings for approved system configurations — look up the assembly as installed, not just the membrane product.
3. FM Approval Guide / RoofNav. FM's online database lists approved assemblies and their ratings; a contractor or consultant can cross-reference your configuration.
4. Your roof consultant or contractor. If records are missing, a professional can identify the deck, attachment, insulation, and membrane in the field and determine which published rating — if any — the configuration matches.

If no documentation turns up at all, treat the rating as unknown rather than assuming the minimum. Unknown is a legitimate answer, and it is the starting point for a professional assessment — a roof that has survived twenty years has proven something, but it has not proven its rating.

What should a property manager actually do with the rating?

You are not expected to engineer wind loads. But the rating gives you four practical levers:

• Match it to the zone. Ask your roofer or engineer whether the installed rating meets the design uplift pressure for your building's wind zone, height, and exposure. Buildings change use, codes get updated, and yesterday's adequate rating may not be today's.
• Prioritize perimeters and corners. Since uplift concentrates at edges, inspection and maintenance dollars go furthest there. Loose flashing, open terminations, and corroded edge fasteners are where rating capacity erodes first.
• Protect the rating during repairs. Any reroof section, overlay, or major repair should use an assembly with a documented rating at least equal to the original — and the edge system should be addressed at the same time, not deferred.
• Document before storm season. Photograph the roof's condition, keep the rating documentation with your building files, and schedule a post-storm check after any event with reported gusts or debris. If a claim ever becomes necessary, the combination of a documented rating and documented maintenance is your strongest position. For help documenting storm-related changes, contact our team.

Uplift ratings are one of the few places in roofing where the engineering is genuinely legible to a non-engineer: a number, earned in a test, describing what your roof was proven to withstand. Know the number, keep the paperwork, and make sure the edges got the same attention as the field.

Frequently asked questions