Impact rating (large-missile test)
An impact rating certifies that a door assembly survived the large-missile test: a nine-pound 2×4 fired from an air cannon at roughly 50 feet per second, followed by thousands of pressure cycles on the damaged specimen. It is the wind-borne-debris half of hurricane certification, mandatory in Florida’s HVHZ.
What the certification demands, and where
The rating is earned in a lab with a cannon. Test standards (the Florida Building Code’s HVHZ protocols and the ASTM missile-impact family behind them) prescribe the projectile, the velocity, the strike locations and the pass criteria; large-missile testing applies to assemblies protecting enclosed spaces up to specified heights — garage doors squarely included. The strike is followed by the cyclic-pressure sequence, and the certified result is, as with wind-load, an ASSEMBLY: the sections, glazing, struts, track and fasteners that stood in the lab. Substitution voids in the same quiet way.
Geography again writes the requirement. Miami-Dade and Broward — the High-Velocity Hurricane Zone — mandate impact protection outright, with Miami-Dade’s NOA system the strictest paperwork in American building products (approvals expire annually and Broward-only approvals do not travel south). The rest of Florida requires opening protection in mapped wind-borne-debris regions, where an impact-rated door is one compliance path alongside tested shutters. Beyond Florida, coastal Gulf and Atlantic jurisdictions adopt debris provisions by local code, and the TDI’s windstorm program folds impact products into its inspection regime. The Index on this site’s codes hub carries the county-level detail.
Impact certification, at a glance
| Element | What it is | Why it matters |
|---|---|---|
| Large missile | nine-pound 2×4, end-on, ~50 ft/s | the codified real-world debris |
| Strike locations | prescribed, including weak points | no cherry-picked center hits |
| Cyclic pressure phase | thousands of cycles on the damaged door | certifies wounded performance |
| NOA (Miami-Dade) | the approval document, annually renewed | expired paper fails the permit |
| Glazing package | tested with the assembly | field glass voids the rating |
| Small-missile variant | gravel-class projectiles, higher elevations | rarely governs garage doors |
Buying and living with the rating
Impact and wind-load travel together
HVHZ doors certify both halves — pressure AND debris. Shopping in rated territory means one label carrying both stories; shopping elsewhere, the impact tier is the optional second question after DP.
Check the NOA’s date, not just its existence
Miami-Dade approvals expire annually; a door legitimately certified last year can fail this year’s permit on paperwork alone. Current-at-permit is the standard the county actually enforces.
Repairs are certification events
A debris-struck rated door that visibly survived may still need section replacement to remain CERTIFIED — the post-storm inspection is about the paper as much as the steel.
The premium is bounded
Impact packages add real money but less than folklore suggests, especially against the shutter systems they replace — and insurers in debris regions discount for exactly this line item.
Impact rating questions
Why test with a flying 2×4, of all things?
Because that is what hurricanes actually throw. Post-storm damage surveys found lumber — framing pieces from failed structures upwind — among the most common and most penetrating debris in residential wind fields, so the standards codified it: a nominal nine-pound 2×4, end-on, at specified speed, striking prescribed locations including the assembly’s weakest points. The test is deliberately ugly and deliberately specific; a rating earned against a literal flying stud communicates more than any abstract pressure number could.
The door survives the hit — why the pressure cycling afterward?
Because the storm does not stop after the debris strike. The test’s second act loads the DAMAGED specimen through thousands of positive and negative pressure cycles — simulating the hours of gust and suction that follow a puncture in a real event. Passing means the assembly holds the pressure boundary while wounded: dented, even pierced, but still keeping the storm outside the envelope. It is the difference between a door that merely resists debris and one certified to keep doing its structural job after taking the hit.
Do windows in an impact-rated door break the rating?
Only if the glazing is not part of the certification. Impact-rated doors with windows use tested glazing packages — laminated or polycarbonate systems certified with the door — and in the HVHZ every glazed opening in the assembly must carry that pedigree. The practical rules: order windows WITH the rated door rather than adding them, never field-glaze a rated section, and when replacing a damaged pane in rated territory, match the certified package. The versus and cost pages’ glass caveats sharpen to legal requirements here.