Hurricane Impact Windows: Missile Impact Ratings, Code Requirements by State, and How to Spec Correctly

By Alex (COO) • • windows

Impact-resistant windows are tested to ASTM E1996 and E1886 standards using 9-pound 2×4 projectiles at 50 fps. Here is what the ratings mean, which states and counties require them, and how to spec the right product for each exposure category.

What Impact Resistance Actually Means

"Hurricane-rated" is not a single standard. Impact-resistant windows are tested to two interrelated ASTM standards: ASTM E1886, which measures the performance of the window assembly under missile impact, and ASTM E1996, which defines the test missiles and acceptance criteria. Understanding these standards is the difference between specifying the right product and buying the wrong one and discovering it on inspection.

The test is straightforward in concept: a 9-pound 2×4 wooden missile is launched from a cannon at the window at 50 feet per second (approximately 34 mph). The window must: 1. Withstand the impact without the missile penetrating the glazing 2. Remain in the frame after impact 3. Not develop an opening larger than a specified size (typically limited to less than 5% of the total glazed area)

A second missile impact test follows — the same missile strikes the same location a second time. The window must maintain structural integrity.

After the impact tests, the assembly is subjected to positive and negative design pressure (DP) loading — simulating wind loads on both sides of the building envelope.

---

The Rating Levels: What the Letters and Numbers Mean

ASTM E1996 defines several missile impact levels. The most common for residential and commercial fenestration:

| Rating | Missile Weight | Velocity | Application | |---|---|---|---| | E (or Basic) | 9 lb 2×4 | 50 fps (~34 mph) | Inland residential, standard hurricane zones | | F (or Enhanced) | 9 lb 2×4 | 70 fps (~48 mph) | Coastal high-velocity hurricane zones | | G | 9 lb 2×4 | 90 fps (~61 mph) | High-velocity hurricane zones, large missile exposure | | Large Missile (LA) | Various up to 9 lb | Up to 90+ fps | Per specific project specification | | Small Missile | 0.075 inch steel balls | 130 fps | Glazing adjacent to pedestrian areas, storefronts |

Miami-Dade Protocol goes further than ASTM E1996 in some respects. Products approved under the Miami-Dade Notice of Acceptance (NOA) have been tested to the most stringent protocol in the US. Miami-Dade certification is required for all impact products installed in Miami-Dade and Broward counties.

---

Design Pressure (DP) Ratings: The Wind Load Number That Matters

Missile impact testing is half the equation. The Design Pressure (DP) rating tells you what wind load the assembly can withstand after being impacted. DP ratings are expressed in pounds per square foot (psf) of positive and negative pressure.

For hurricane zones, minimum DP requirements:

| Exposure Category | Basic DP Required | Example Locations | |---|---|---| | Exposure B (suburban/urban, terrain with numerous closely spaced obstructions) | DP +30/-30 | Inland suburban subdivisions | | Exposure C (open terrain with scattered obstructions) | DP +40/-40 | Coastal plains, barrier islands | | Exposure D (flat, featureless terrain, open water) | DP +50/-50 | Beaches, open coastal areas, Keys |

A window tested to ASTM E1996 with DP +50/-50 can handle the equivalent of approximately 130 mph winds. A window with DP +35/-35 is rated for roughly 95 mph. Know the exposure category of the project site before specifying.

---

When Impact Windows Are Actually Required by Code

The requirement for impact-resistant fenestration is not universal in hurricane zones. Building codes distinguish between:

1. Essential windows — windows required to remain in place to maintain building envelope integrity during a storm 2. Standard windows — any window, where failure does not compromise the structural envelope

Florida: The Strictest Requirements

Florida Building Code (FBC) requires impact-resistant or shutter-protected windows in:

Louisiana

Louisiana's state building code (based on IBC with Louisiana amendments) requires impact-resistant fenestration in:

Mississippi and Alabama

Both states adopted IBC 2015 or later with coastal amendments. Requirements vary by county and are triggered by proximity to the Gulf Coast and design wind speed maps. Most coastal counties (Hancock, Harrison, Jackson in Mississippi; Mobile, Baldwin in Alabama) require impact-rated fenestration for new construction.

Texas Coastal Counties

Texas adopts the International Residential Code (IRC) and International Building Code (IBC) with state amendments. The Texas Department of Insurance regulates impact-resistant fenestration. Requirements are triggered by:

Texas coastal counties (Harris, Galveston, Nueces, Cameron, etc.) with design wind speeds exceeding 110 mph require impact-rated fenestration on new construction.

North Carolina, South Carolina, and Georgia

Requirements in these states are more situational. The IRC and IBC trigger impact-resistance requirements based on:

Most new coastal construction in these states above the 110 mph design wind speed contour requires impact-rated fenestration.

---

Primary vs Secondary Protection: When You Can Skip Impact Windows

The building code allows two approaches to meeting the hurricane protection requirement:

1. Primary protection: Impact-resistant windows that require no additional covering 2. Secondary protection: Standard windows with code-compliant storm shutters, impact-rated panels, or other covering systems that are deployed before the storm

The secondary protection approach is valid in most jurisdictions — but the shutters or panels must be:

For rental properties, vacation homes, or commercial buildings where occupants may not be present before landfall, primary protection (impact windows) is almost always the better choice. There is no opportunity to deploy shutters if no one is there to do it.

---

How to Spec Impact Windows Correctly

Step 1: Determine Exposure Category and Design Wind Speed

Use ASCE 7-22 (or the version adopted by the jurisdiction) to establish:

This information comes from the project structural engineer or the local building department's design wind speed map.

Step 2: Match the ASTM Rating to the Hazard

Step 3: Verify the Testing Agency

Not all impact ratings are equal. Look for testing agencies recognized by the Florida Building Commission or the building official in the jurisdiction. Recognized testing laboratories include:

A window that claims "impact tested" but is not listed with a recognized agency may not be accepted by the building department.

Step 4: Confirm the Glazing Type

Impact-resistant windows use either:

Both pass the missile impact test. Verify which is used in the product being specified, as laminated glass requires slightly different handling and cleaning procedures.

---

The Cost Reality and How to Budget for It

Impact-resistant windows cost 40–70% more than standard fenestration at equivalent performance levels. A standard double-pane vinyl single-hung at U-0.30 might run $180–$250 installed. A comparable impact-rated vinyl single-hung with laminated glass and DP +40/-40 rating runs $300–$450 installed.

On a typical 18-window single-family home in a coastal zone, that is an additional $2,200–$4,500 in fenestration cost.

The delta narrows significantly when sourcing direct from international manufacturers — Buildtana supplies Miami-Dade certified and Florida Building Code compliant impact windows at 20–40% below typical US dealer pricing. For multi-unit projects, the savings compound quickly.

---

Common Specification Mistakes

1. Specifying ASTM E1996 Level E when Level F is required Level E passes the 50 fps missile test. Level F (70 fps) is required in higher-velocity zones. Mixing these up creates a compliance issue on inspection.

2. Not checking the Miami-Dade NOA for county-specific requirements Miami-Dade and Broward counties require NOA-listed products. Products tested to ASTM standards alone but not listed with Miami-Dade are not compliant in those counties.

3. Assuming all "hurricane-rated" products are equivalent There are significant performance differences between products that pass the basic ASTM E1996 test and those that carry a full Miami-Dade NOA. The testing protocol is more rigorous and the field verification requirements are stricter for Miami-Dade.

4. Overlooking the DP rating in favor of the missile rating A window that passes the missile impact test at DP +30/-30 is only rated for approximately 95 mph winds. The missile test and the pressure test are separate requirements. Both must be met for the application.

5. Specifying impact windows without checking the installation nailing fin requirements Impact windows in high-velocity zones typically require enhanced nailing fin attachment schedules — more fasteners, higher withdrawal resistance — that are not always specified in the window product literature. Check the installation instructions and coordinate with the structural engineer.

---

Bottom Line

Hurricane impact windows are not a single product grade — they span from basic ASTM E1996 Level E (50 fps, inland zones) to Miami-Dade NOA certified (most stringent protocol). The right product depends entirely on:

1. Design wind speed at the site 2. Exposure category 3. Whether the project is in Miami-Dade or Broward (requires NOA) 4. Whether the building is classified as an essential facility

Contractors who verify these four parameters before specifying avoid failed inspections, expensive product substitutions, and callback claims. Impact-resistant windows that do not meet the actual site requirements are not a bargain — they are a liability.

---

This article is for informational purposes. Specific code requirements vary by jurisdiction and are subject to local adoption of IBC/IRC versions. Verify all specification requirements with the local building department and a qualified fenestration consultant before specifying impact-resistant products.

Key Facts

Industry Statistics

Get a Free Quote from Buildtana →