Design Pressure (DP) Ratings on Impact Windows Explained

The Short Answer

Design Pressure (DP) is a standardized measurement of how much wind pressure a window or door can withstand without failing. The number — DP-30, DP-50, DP-70 — represents the pounds per square foot (psf) of pressure the product was tested to resist. In Miami-Dade’s High Velocity Hurricane Zone, a typical one- or two-story home needs roughly +40 to +50 psf and −43 to −62 psf, with corner windows, taller homes and waterfront lots needing more. A DP rating does not convert to a single wind speed: the same 175 mph design wind produces different pressures depending on building height, exposure, the window’s size and whether it sits near a corner.

What Is Design Pressure?

Design Pressure is a structural performance rating developed by the American Architectural Manufacturers Association (AAMA) and codified in North American Fenestration Standard/Specification for windows, doors, and skylights (NAFS). It represents the uniform load — steady pressure applied across the entire surface — that a window or door can withstand in both positive (wind pushing inward) and negative (wind suction pulling outward) directions.

The test is straightforward in concept but rigorous in execution:

The complete window assembly (frame, sash, glass, hardware) is mounted in a test chamber.
Air pressure is gradually increased to 150% of the target DP rating and held for 10 seconds.
The pressure is released, and the assembly is inspected for permanent deformation.
For hurricane-zone approval, an impact-tested unit is also cycled 4,500 times inward and 4,500 times outward at stepped pressures up to its full design pressure (TAS 203 in the HVHZ, ASTM E1886 elsewhere).
The assembly must also resist water infiltration at 15% of the DP rating (20% for heavy commercial AW-class products).

If the window passes every phase without permanent deflection, hardware failure, or seal breach, it receives the DP rating.

The Formula

The pressure an opening must resist comes from ASCE 7-22, which the 2023 Florida Building Code adopts:

q = 0.00256 × Kz × Kzt × Kd × Ke × V²

p = q × (GCp − GCpi), then × 0.6 to get the allowable (ASD) pressure that product ratings use

Where:

V = Basic wind speed in mph, set by the building’s risk category (175 mph in Miami-Dade and 170 mph in Broward for homes)
Kz = Velocity pressure exposure coefficient (varies with height and terrain)
Kzt = Topographic factor (hills, ridges — usually 1.0 in flat South Florida)
Kd = Wind directionality factor (0.85 for windows and doors)
Ke = Ground elevation factor (1.0 at sea level)
GCp = External pressure coefficient (higher near corners and for smaller openings)
GCpi = Internal pressure coefficient (±0.18 for an enclosed house)

This is why you cannot simply convert wind speed to DP without knowing the building-specific factors. A window rated for 140 mph winds at ground level in a suburban neighborhood may be inadequate on the 30th floor of a Brickell tower.

DP Ratings Explained with Real Examples

DP-30 (30 psf)

Where it is used: Non-hurricane regions, interior or sheltered openings
Status in Miami-Dade: Below the pressures Miami-Dade’s county chart lists for any exterior opening on a home (the chart’s lowest value is +30 / −33 psf, for very large openings)

DP-50 (50 psf)

Where it is used: Common for standard residential installations in Miami-Dade and Broward
Status in Miami-Dade: Covers most mid-wall openings on one- and two-story homes on inland lots. Small corner windows on those same homes can need more than −50 psf of suction. The code sets no single DP minimum; each opening’s requirement comes from the wind load calculation.

DP-60 (60 psf)

Where it is used: Corner windows on two-story homes, waterfront homes facing open water (Exposure D), and many three-story homes
Status in Miami-Dade: Frequently required for small corner windows and on waterfront lots

DP-70 (70 psf)

Where it is used: Waterfront homes near the 60 ft low-rise limit, corner openings on exposed sites, and many mid-rise condominiums
Status in Miami-Dade: Common on oceanfront and bayfront buildings in Miami Beach, Key Biscayne and Brickell

DP-80+ (80 psf and above)

Where it is used: High-rise towers, critical facilities, hurricane shelters
Status in Miami-Dade: Common in towers and on large-format glazing, where project-specific engineering sets the numbers

How Building Height Affects Your Required DP Rating

Wind speed increases with height above ground level due to reduced surface friction. The Florida Building Code accounts for this using the velocity pressure exposure coefficient (Kz), which raises the wind load as height increases.

The table shows ASCE 7-22 pressures for a small (10 sq ft) window on a Miami-Dade home at 175 mph, rounded up to whole psf.

Mean roof height	Kz (Exposure C / D)	Mid-wall window, inland (C)	Corner window suction, inland (C)	Mid-wall window, waterfront (D)	Corner window suction, waterfront (D)
15 ft (1 story)	0.85 / 1.04	+41 / −44	−54	+49 / −53	−66
25 ft (2 stories)	0.94 / 1.13	+45 / −49	−60	+54 / −58	−72
35 ft (3 stories)	1.01 / 1.20	+48 / −52	−64	+57 / −62	−76
60 ft (low-rise limit)	1.13 / 1.32	+54 / −58	−72	+63 / −68	−84

Larger openings need somewhat less: a 50 sq ft slider leaf on a one-story inland home needs about +36 / −40 psf. Buildings over 60 ft use a different ASCE 7 method and project-specific engineering.

This is why a Brickell condo owner on the 25th floor needs dramatically higher-rated products than a Kendall homeowner in a single-story ranch. The wind speed at 250 feet is roughly 30-40% higher than at ground level.

Large Missile Impact vs. Design Pressure

This is where many homeowners get confused. Design Pressure and large missile impact resistance are separate, independent requirements.

Requirement	Tests For	Standard
Design Pressure (DP)	Structural resistance to wind pressure	AAMA/WDMA/CSA 101/I.S.2/A440
Large Missile Impact	Resistance to 9 lb 2×4 lumber fired at 50 ft/s	ASTM E1996 / ASTM E1886

A window can have:

High DP but no impact rating (common in non-hurricane regions)
Impact rating but low DP (unsuitable for high-rise installations)
Both high DP and impact rating (required for Miami-Dade HVHZ)

In the High Velocity Hurricane Zone, every impact window must pass both tests. The Miami-Dade Notice of Acceptance (NOA) and Florida Product Approval documents list both the DP rating and the impact test level for each approved product.

What the Label on Your Window Means

Impact windows that pass Miami-Dade testing carry a permanent label, usually etched into the glass corner or a non-removable sticker on the frame. The label contains:

Manufacturer name and model number
Miami-Dade NOA number or Florida Product Approval number
DP rating (e.g., “DP ±50”)
Impact test level (e.g., “Large Missile Level D”)
Glass thickness and interlayer type

If your window has no label, it may not be impact-rated at all. Unlabeled windows are common in homes built before 1992 (pre-Hurricane Andrew) or in unpermitted installations.

DP is one line on that label. For the full picture, including large vs small missile impact, HVHZ approval, and how to check an NOA or FL number, see our guide to hurricane window ratings.

Common Misconceptions About DP Ratings

Myth: “A higher DP rating means thicker glass.”

Fact: Not necessarily. DP is a system rating, not a glass rating. A DP-70 window may use the same glass thickness as a DP-50 window from the same manufacturer but with a reinforced frame, upgraded hardware, and additional anchoring. The frame and installation method contribute significantly to the overall rating.

Myth: “If one window in my house is DP-50, they all must be.”

Fact: Required ratings vary from opening to opening. Hurricane winds can come from any direction, so the code does not treat one side of the house differently. What changes the requirement is the opening’s size, its height, and whether it sits in the corner zone of the wall, where suction is about 23% higher. Many installers standardize on the highest required rating for simplicity.

Myth: “DP ratings are just a marketing number.”

Fact: DP ratings are legally mandated and inspection-verified. Miami-Dade building inspectors check window labels against permit documents during the final inspection. Installing a DP-30 window where DP-50 is required will fail inspection.

How to Determine the Right DP Rating for Your Project

For New Construction

Your architect or structural engineer calculates the required DP for each opening based on:

Building height and geometry
Exposure category (C for most South Florida lots, D for shorelines facing open water)
Basic wind speed (175 mph in Miami-Dade and 170 mph in Broward for homes)
Risk category (homes are Risk Category II)
Opening size and whether it sits in the corner zone

The engineer specifies the minimum DP on the construction documents, and your contractor orders products that meet or exceed that specification.

Want a planning number first? Our free wind load calculator estimates the positive and negative pressure for each window and door on a home in Miami-Dade, Broward or Palm Beach. Treat it as an estimate: the permit still needs a sealed calculation. If you just want to see how wind speed relates to pressure, the wind speed to psf calculator converts mph to psf and back, and explains why a DP rating is not a wind speed rating.

For Replacement Windows

Replacement windows must meet today’s code pressures for each opening, not the rating of the windows being removed. Older windows were often installed under earlier codes with lower wind speeds.

Get the pressures: your contractor submits a sealed wind load calculation with the permit. In Miami-Dade, one- and two-family homes and townhouses up to 30 ft mean roof height can use the county’s wind load chart for openings where the building department accepts it.
Check the product: look up the NOA on the Miami-Dade Product Control Search or the Florida Product Approval number on floridabuilding.org, and confirm both ratings meet the opening’s numbers at the size you need.

A reputable installer like National Glass will verify the required DP before ordering products and will not substitute lower-rated units to cut costs.

DP Ratings and Your Insurance

Insurance companies do not directly discount premiums based on DP ratings. Instead, they use the wind mitigation inspection (OIR-B1-1802 form), which verifies that your openings are impact-rated — not the specific DP.

However, if you file a claim after a storm and your insurer discovers that your windows were under-rated for your location (for example, DP-50 windows installed where DP-70 was required), they may argue that the installation did not meet code and reduce or deny the claim.

For this reason, installing the correct DP for your location is both a code compliance issue and an insurance protection issue.

What National Glass Recommends

At National Glass, every order starts from the sealed wind load calculation for the home. These are our typical starting points in Miami-Dade; corner windows and taller homes often need more:

Location	Typical starting specification
Inland Miami-Dade (Kendall, Pinecrest, Doral)	DP-50, Large Missile
Coastal Miami-Dade (Miami Beach, Key Biscayne, Coconut Grove waterfront)	DP-60, Large Missile
Oceanfront / open water	DP-70, Large Missile
Mid-rise and high-rise (Brickell, downtown)	DP-70 to DP-80+, Project-specific engineering

We source products from ES Windows, PGT, MrGlass, and ECO Window Systems — all manufacturers with extensive NOA portfolios that include options at every DP level. Our engineers review your specific building conditions before specifying products, ensuring you are neither under-protected nor overpaying for unnecessary capacity.

Get Expert Guidance

If you are unsure what DP rating your home requires, or if you suspect your current windows are under-rated, schedule a consultation with National Glass. We review your home’s location, height, and exposure, verify existing product approvals, and recommend the right specification for your situation.

Call (305) 599-0909 or visit natglass.net for a free assessment.

Last updated: April 2026. Design Pressure information is based on AAMA/WDMA/CSA 101/I.S.2/A440-17 and the Florida Building Code 8th Edition (2023). Always verify current code requirements with a licensed engineer or the Miami-Dade Building Code Compliance Office.