ASTM E1300 Glass Design

Sizing Glass: Thickness Selection for Hurricane Pressure

Q: How do I determine glass thickness for hurricane windows?

Glass thickness for hurricane windows is determined by four main factors: design wind pressure (from ASCE 7 calculations), glass dimensions (width and height), support conditions (2-sided, 3-sided, or 4-sided), and glass type (annealed, heat-strengthened, or tempered). Use ASTM E1300 glass thickness charts with your specific parameters. In Miami-Dade HVHZ with 180 mph winds, typical residential windows require at least 1/4 inch laminated glass, often thicker.

Q: What is the minimum glass thickness for Miami-Dade HVHZ?

There is no single minimum thickness - it depends on the window size and wind pressure. However, typical minimums for impact-resistant glazing in HVHZ are: 1/4 inch (6mm) laminated for small windows under 20 sq ft, 5/16 inch (8mm) laminated for medium windows 20-35 sq ft, and 3/8 inch (10mm) or thicker for larger windows. These are general guidelines - actual requirements must be calculated per ASTM E1300.

Q: What is the difference between annealed, heat-strengthened, and tempered glass?

Annealed glass is standard float glass with no additional treatment - it is the weakest and breaks into sharp shards. Heat-strengthened glass is about 2x stronger than annealed and breaks into larger pieces. Tempered glass is about 4x stronger than annealed and breaks into small, relatively safe pieces. For hurricane glazing, laminated combinations using heat-strengthened or tempered glass provide both strength and post-breakage integrity.

Q: Why is laminated glass required for hurricane windows?

Laminated glass is required because it maintains integrity after breakage. The plastic interlayer (typically PVB or SGP) holds glass fragments together even when the glass cracks from debris impact. This prevents wind and rain from entering the building and maintains the building envelope. Miami-Dade requires laminated glass that passes large and small missile impact tests for HVHZ applications.

Glass is the weak point of any window. Under hurricane wind pressure, it flexes like a drum skin. Too thin and it shatters. This tool helps you find the right thickness to resist Miami-Dade HVHZ wind loads.

Calculate Wind Pressure Glass Types Guide

Glass Thickness Estimator

75 PSF

Glass

PVB

Glass

5/16"

Total Thickness

Window Width (inches)

Window Height (inches)

Design Wind Pressure (PSF)

Glass Type

5/16"
Min. Thickness

12.0

Glass Area (sq ft)

900

Total Load (lbs)

Glass Types for Hurricane Windows

Understanding glass types helps you specify the right product for your wind load requirements.

Annealed Glass

Standard float glass with no heat treatment. Weakest option, breaks into large sharp shards. Base strength reference (1x).

Heat-Strengthened

Heated then slowly cooled. About 2x stronger than annealed. Breaks into larger pieces than tempered. Good for laminated hurricane glass.

Tempered Glass

Rapidly cooled for 4x strength. Shatters into small cubes. Required for safety glazing locations. Often used in laminated assemblies.

Quick Reference Thickness Chart

Approximate glass thickness for heat-strengthened laminated glass at various sizes and pressures. Always verify with ASTM E1300 calculations.

Glass Size	Area (sq ft)	50 PSF	75 PSF	100 PSF	120 PSF
24" x 36"	6	1/4"	1/4"	5/16"	5/16"
36" x 48"	12	1/4"	5/16"	3/8"	3/8"
48" x 60"	20	5/16"	3/8"	7/16"	1/2"
48" x 72"	24	3/8"	7/16"	1/2"	9/16"
60" x 84"	35	7/16"	1/2"	9/16"	5/8"
72" x 96"	48	1/2"	9/16"	5/8"	3/4"

Glass Thickness FAQs

Common questions about glass selection for hurricane windows

How do I determine glass thickness for hurricane windows?

Glass thickness is determined by four main factors: design wind pressure (from ASCE 7 calculations), glass dimensions (width and height), support conditions (2-sided, 3-sided, or 4-sided), and glass type (annealed, heat-strengthened, or tempered). Use ASTM E1300 glass thickness charts with your specific parameters.

What is the minimum glass thickness for Miami-Dade HVHZ?

There is no single minimum - it depends on window size and wind pressure. Typical minimums for impact-resistant glazing: 1/4 inch laminated for small windows under 20 sq ft, 5/16 inch laminated for medium windows 20-35 sq ft, and 3/8 inch or thicker for larger windows.

What is the difference between annealed, heat-strengthened, and tempered glass?

Annealed glass is standard float glass - weakest, breaks into sharp shards. Heat-strengthened is about 2x stronger, breaks into larger pieces. Tempered is about 4x stronger, breaks into small safe cubes. For hurricane glazing, laminated combinations using heat-strengthened or tempered provide both strength and post-breakage integrity.

How does glass area affect required thickness?

Larger glass areas require thicker glass because the unsupported span increases. When glass flexes under wind pressure, the center deflects the most. A 4x6 foot window will deflect much more than a 2x3 foot window under the same pressure, requiring thicker glass.

Why is laminated glass required for hurricane windows?

Laminated glass maintains integrity after breakage. The plastic interlayer (PVB or SGP) holds fragments together even when cracked from debris impact. This prevents wind and rain from entering and maintains the building envelope. Miami-Dade requires laminated glass that passes large and small missile impact tests.