Ask a room of Texas building owners what FM 1-90 means and most will say the roof can handle 90 mph winds. That reading is wrong, and it leads to roofs that are either under-built for their site or over-built for no reason. Here is how wind uplift ratings actually work, what Texas codes require, and what to ask before you sign a roofing proposal.
What is a wind uplift rating?
A wind uplift rating is the suction pressure, in pounds per square foot (psf), that a complete roof assembly resisted in a lab test without failing. It rates the whole system, meaning the deck, insulation, fasteners, and membrane together, not any single product.
Uplift happens because wind moving fast across a flat roof lowers the air pressure above it, while air inside the building pushes up from below. The roof gets pulled and pushed at the same time. On a low-slope commercial roof, that combined force is what peels membranes and lifts insulation, far more than wind pushing sideways against the walls.
The building code recognizes three lab tests for membrane roofs: FM 4474, UL 580, and UL 1897. Each one loads a full sample assembly with rising pressure until something lets go. The rating is the last pressure level the assembly held.
Because the test covers the whole build, changing one component changes the result. A mechanically fastened TPO roofing system and the same membrane adhered over a different board are two separate assemblies with two separate ratings. Fastener layout matters too, which is why the pattern on polyiso insulation boards is part of the tested listing, not an installer preference.
Does FM 1-90 mean my roof can handle 90 mph winds?
No. In FM 1-90, the "1" stands for a Class 1 fire rating and the "90" means the assembly resisted 90 psf of uplift in the field of the roof. Wind speed is not part of the rating at all.
FM Global's corporate windstorm specialist lays out the naming and the math in a technical article on FM Global's wind data sheets: the 1 is the Class 1 interior fire classification, the 90 is the field-of-roof load in psf, and roof design should carry a minimum safety factor of 2.0. The reason for that margin shows up in FM's own testing. Moving the fasteners on a 4 ft by 4 ft insulation board from 12 inches off the board edge to 6 inches raised the failure point from 105 psf to 160 psf. Real installations vary board to board, so the design builds in room for it. In practice, a 1-90 assembly pairs with roughly 45 psf of calculated design pressure in the field.
FM 1-90 has become a default line in many specs, even on buildings FM does not insure. That habit is fine when the calculated pressures call for it. When they do not, you pay for capacity the building will never use, and the edges and corners can still be under-secured if nobody ran the zone pressures. If FM language is already in your spec, our guide to FM Global approved roofing covers what the approval itself requires.
What wind speed does the building code require for my Texas building?
Texas law applies the International Building Code to commercial buildings in its cities, including repairs and alterations, and each city adopts its own edition and local amendments. Lubbock enforces the 2021 IBC. Its current local table sets 107 mph for a typical commercial building and 118 mph for the highest-risk facilities.
Under the Texas Local Government Code, the IBC covers every commercial building in a municipality, plus any alteration, remodeling, enlargement, or repair of that building. Cities can adopt newer editions and local amendments, so the wind speed on your building depends on where it sits. If you own property in Amarillo, Midland-Odessa, or Abilene, confirm the adopted edition and that city's wind-speed table with the building department before design starts.
Lubbock's codified 2021 IBC amendments include the design table the city uses now. Ordinance 2025-O0116, adopted September 23, 2025, replaced the older speeds. The current table lists 100 mph for Risk Category I, 107 mph for Risk Category II, 113 mph for Risk Category III, and 118 mph for Risk Category IV, with allowable stress design speeds of 77.5, 83, 88, and 91.5 mph. The same code places Lubbock in the 250 mph zone of the ICC 500 storm shelter map. That figure governs tornado shelters, not ordinary roofs.
If a proposal still cites 115 mph for a Lubbock Risk Category II building, it is using the city's previous table. Ask for the pressures calculated from the current one before you compare bids.
Risk Category comes from how the building is used. Most offices, retail centers, warehouses, and light industrial buildings fall in Risk Category II. Schools and large-occupancy buildings typically land in III, while hospitals, emergency facilities, and designated shelters land in IV. Your design professional confirms the category, and it belongs on the construction documents.
How do you turn a wind speed into the uplift rating your roof needs?
A design professional converts the code wind speed into uplift pressures using your building's height, surrounding terrain, Risk Category, and roof zone. You then choose a tested assembly whose rating covers those pressures with the safety factor applied.
Wind speed is only the starting input. In Lubbock, a typical Risk Category II building starts at 107 mph under the city's current table. From there, taller roofs see stronger wind, and open, flat ground with few obstructions, which describes a lot of the South Plains, exposes a roof more than a building surrounded by other structures. The calculation follows ASCE 7, the wind standard the IBC references.
The output is not one number. It is a set of pressures for the field, the perimeter, and the corners of the roof. A complete proposal lists all three. Owners often run three different numbers together at this stage, so here is how they separate.
| Comparison | Code design wind speed | Assembly uplift rating | Warranty wind speed |
|---|---|---|---|
| What it measures | The wind your building must be designed for | The suction a tested roof assembly resisted in a lab | The wind events a manufacturer agrees to cover |
| Unit | mph | psf | mph (usually peak gust) |
| Who sets it | Your city's adopted building code | FM Approvals or UL testing | The roofing manufacturer |
| Lubbock example | 107 mph for a Risk Category II building | FM 1-90 = 90 psf in the field | Whatever speed the warranty names in writing |
| What it protects you from | Failed inspections and an under-designed building | Blow-offs at the design pressure | Paying for wind damage yourself |
Why do commercial roofs fail at the edges and corners first?
Wind pressure peaks where air separates from the building at the roof edge. FM Global data shows perimeter pressures running up to 68% higher than the field of the roof, and corner pressures up to 153% higher.
| Roof zone | Uplift compared with the field |
|---|---|
| Field of the roof | 100% (baseline) |
| Perimeter | Up to 168% (up to 68% higher) |
| Corners | Up to 253% (up to 153% higher) |
The same FM Global analysis warns that a roof cover or deck not designed for those higher edge pressures can be lost in moderate winds. Building codes historically gave little direction on perimeters and corners, which is part of why FM wrote Data Sheet 1-29 with prescriptive fastening for those zones. A roof that is fastened at one spacing all the way across is under-secured exactly where the wind is worst.
Edge metal carries its own code test, ANSI/SPRI ES-1, which covers fascia, gravel stop, and coping. If a bid says "install edge metal" without naming a tested system or the design pressure it resists, ask before you sign. We go deeper on how edges, coping, and terminations let go in our guide to commercial roof flashing failures, and the wall side of the problem in parapet wall waterproofing.
Do you need a TDI windstorm inspection when you replace your roof?
Only if the building sits in the Texas designated catastrophe area: 14 coastal counties plus parts of Harris County east of Highway 146. There, a roof replacement needs a Texas Department of Insurance windstorm inspection and certificate of compliance to qualify for Texas Windstorm Insurance Association coverage.
TDI's windstorm inspection guide explains the two certificates. TDI issues a WPI-8 when the work is inspected during construction by a TDI inspector or an appointed engineer, and a WPI-8-E when a Texas licensed professional engineer inspects completed work. Inspecting after the fact is harder and can cost more, so coastal owners should line up the inspection before the tear-off. Roof repairs under 100 square feet that do not involve the decking are exempt.
Inland, including Lubbock, Amarillo, Midland-Odessa, and Abilene, there is no TDI windstorm program. Your roof answers to the city permit and the adopted building code. That does not make West Texas a low-wind market. It means the responsibility for getting the numbers right sits with your design team and contractor rather than a state inspector.
Is your roof warranty's wind speed the same as its uplift rating?
No. A warranty wind speed is a manufacturer's promise about which wind events it will pay for, while the uplift rating is a lab result. The two are set independently, and one does not guarantee the other.
Manufacturers offer standard and enhanced wind coverage, usually stated as a peak gust speed in mph. Higher coverage typically comes with stricter attachment, fastening, or edge requirements, and sometimes an inspection. Read the exclusions, and make sure the covered speed is written into the warranty itself, not just mentioned in a sales conversation.
A Lubbock roof can be designed to code at 107 mph, carry an FM 1-90 field rating, and still have a warranty that covers less than the code wind speed. Each number answers a different question. You want all three on paper.
What should you ask your roofing contractor about wind uplift?
Ask for five things in writing before you sign: your Risk Category, the uplift pressures by roof zone, the tested assembly listing, the edge metal standard, and the warranty wind speed. A contractor who designs to the numbers will have every answer ready.
- Risk Category. It sets the starting wind speed, so it should match how your building is actually used.
- Design pressures for field, perimeter, and corners. One number for the whole roof is a red flag.
- The tested assembly listing. Ask for the FM or UL listing that matches the exact deck, insulation, fasteners, and membrane being installed.
- Edge metal tested to ANSI/SPRI ES-1. Fascia and coping should name the system and the pressure it resists.
- Warranty wind speed. Get the covered speed and the conditions attached to it in the warranty document.
Two proposals at the same price can describe very different roofs. These five answers are usually where the difference shows. For more questions worth asking at bid time, see our guide on how to choose a commercial roofing contractor in Texas.
Frequently asked questions
Is a higher wind uplift rating always better?
Not automatically. A higher rating costs more, and what protects your building is matching the rating to the calculated pressures in each zone, especially the corners.
Does hail affect wind uplift performance?
It can. Hail cracks membranes, crushes insulation, and loosens seams, which gives wind a way underneath, so a roof hit by a major storm should be checked before the next wind season, ideally with an infrared thermal roof inspection to find wet insulation you cannot see.
Can an existing roof's uplift resistance be improved without a full replacement?
Sometimes, through steps like re-securing perimeter metal, adding fasteners in perimeter and corner zones, and repairing failed seams. A coating does not add attachment strength, which is one of the limits we cover in roof coating versus replacement.
Who calculates wind loads for a reroof in Lubbock?
A registered design professional runs the calculation using the adopted code and ASCE 7, often alongside the manufacturer's tested assembly data. Ask to see the zone pressures on paper before any materials are ordered.
The short version
FM 1-90 means 90 psf, not 90 mph. Your city's code sets the wind speed, an engineer turns it into pressures for the field, perimeter, and corners, and the tested assembly has to cover all three. In Lubbock that starting speed is 107 mph for a typical commercial building under the current 2021 IBC table. Get those numbers, the edge metal standard, and the warranty wind speed in writing, and you will know exactly what your roof is built to handle.
We can walk the roof, confirm the Risk Category and zone pressures against the code your city actually enforces, and tell you whether the proposed assembly covers them. Request a roof inspection or call (806) 404-1250.
