Glass thickness is one of those specs that looks minor on a drawing sheet and becomes a significant cost driver at takeoff. A 1/4 inch change in glass thickness impacts framing depth, anchor spacing, structural load on the building, U-value, Sound Transmission Class, and per-square-foot cost. The opposite mistake is more expensive: under-specifying thickness, failing wind load or acoustic testing at inspection, and tearing out glass after install. This article breaks down the common commercial glass thickness specs, what each one is built for, and when to push up or pull back.
Common Commercial Glass Thickness Specs
Commercial glass thickness is written as the nominal assembly thickness, not as individual lite thickness. A "9/16 inch laminated" unit is two 1/4 inch (6mm) glass lites with a 0.060 inch PVB interlayer. A "1 1/16 inch IGU laminated" is a 9/16 inch laminated outboard lite + 1/2 inch air gap + 1/4 inch monolithic inboard. Here are the specs most commonly seen on Florida commercial projects.
| Nominal Thickness | Typical Build | Common Use |
|---|---|---|
| 1/4" monolithic | Single 6mm lite | Interior non-structural glazing, partition glass |
| 7/16" laminated | 2 x 3/16" + 0.030" PVB | Non-impact commercial, interior fire-rated frames |
| 9/16" laminated | 2 x 1/4" + 0.060" PVB | Standard Florida commercial impact, storefront, most punched openings |
| 11/16" laminated | 2 x 5/16" + 0.060" PVB | Large impact openings, high wind load coastal zones |
| 1" IGU (non-impact) | 1/4" + 1/2" air + 1/4" | Non-impact commercial with energy performance (rare in FL exterior) |
| 1 1/16" IGU laminated impact | 9/16" lam + 1/2" argon + 1/4" | Premium commercial impact with energy compliance |
| 1 5/16" IGU laminated impact | 9/16" lam + 1/2" argon + 9/16" lam | High-rise curtainwall, premium specification |
Every one of these specs has a purpose. The wrong question is "what's the thickest we can afford." The right question is "what does this opening actually need to do, and what's the thinnest build that meets every requirement."
1. Impact Rating Drives Thickness in Florida
On any exterior opening in a Florida commercial project within the wind-borne debris region — which is essentially all of coastal Florida — impact rating is the baseline requirement. Per the Florida Building Code, Chapter 16, impact testing is conducted to:
- ASTM E1886/E1996 Large Missile Impact (LMI): Required below 30 feet on most Florida commercial exterior openings outside HVHZ.
- TAS 201/202/203: Miami-Dade HVHZ protocol, required in Miami-Dade and Broward counties. More stringent than base Florida code.
- Small Missile Impact (SMI): Allowed above 30 feet on non-HVHZ projects, less demanding than LMI.
Passing Large Missile Impact requires laminated glass, which requires a minimum PVB interlayer of 0.060 inch or equivalent SGP. Below 9/16 inch total assembly, most standard glass makeups will not pass LMI testing. A 7/16 inch laminated lite can pass SMI and non-impact tests but rarely passes LMI without a specialty interlayer. In practical terms, if the project needs LMI impact rating, 9/16 inch laminated is the floor.
2. Wind Load Scales Thickness Up
Wind load design per ASCE 7-22 governs the glass thickness needed to survive design pressures without failure. The design wind pressure at a specific opening depends on building height, exposure category (B, C, or D), glazing zone on the facade (corner zones see higher pressures than field zones), and Hurricane Import Factor. For coastal Florida commercial projects, design pressures at upper floors or corner zones can hit +65/-85 psf or higher.
Glass thickness required to carry that pressure depends on the unsupported span — the distance between framing members. A 9/16 inch laminated lite might handle a 25 SF punched opening at +50/-60 psf without issue, but the same glass on a 60 SF curtainwall lite at a 20th-floor corner might require an upgrade to 11/16 inch or even a 1 5/16 inch IGU laminated with heat-strengthened lites on both sides.
The deflection criterion matters too. Under the Florida Building Code, glass deflection is limited to L/175 or less under design wind pressure, where L is the span. Thicker glass reduces deflection. On larger openings, thicker glass isn't about breakage resistance — it's about keeping the assembly flat enough to maintain seal integrity.
3. Sound Transmission Class Drives Thickness Up
Thickness and asymmetry drive acoustic performance. STC (Sound Transmission Class) ratings by common glass build:
- 1/4" monolithic: STC 27
- 9/16" laminated: STC 34–37
- 1 1/16" IGU (symmetric 1/4" + 1/2" air + 1/4"): STC 32
- 1 1/16" IGU laminated inboard (asymmetric 9/16" lam + 1/2" air + 1/4"): STC 40–42
- 1 5/16" IGU laminated both lites (asymmetric thickness): STC 44–48
The important move is asymmetry: two different glass thicknesses in an IGU defeat coincident frequency dips that reduce STC in symmetric assemblies. Airport-adjacent, nightlife-adjacent, and urban hospitality projects benefit from thicker, asymmetric laminated IGU builds — and the STC jump from 34 to 44 is a perceptible reduction in indoor noise level. See the companion piece on noise-reducing glass for Florida businesses for acoustic spec detail.
4. Thermal Performance: Thicker IGUs, Better U-Values
U-value and SHGC on a commercial IGU depend on low-E coating placement, spacer type, and fill gas — but thickness matters through the air gap dimension. A 1/2 inch argon-filled air gap outperforms a 3/8 inch air gap by roughly 10% on U-value. On the Florida Energy Conservation Code compliance paths, U-value targets of 0.35–0.45 for commercial fenestration typically require a full 1 1/16 inch IGU with a 1/2 inch argon cavity. Trying to hit those targets with a thinner unit is difficult without going to triple-glazing, which is rare in Florida commercial work.
5. Framing Depth Follows Glass Thickness
This is the operational implication that most spec writers miss. A 9/16 inch laminated impact lite fits comfortably in a 2 inch x 4-1/2 inch storefront frame — ESWindows ES-8000, ESWindows ES-9500 equivalent. Pushing to 1 1/16 inch IGU laminated requires deeper framing: 2-1/2 inch x 6 inch to 2-1/2 inch x 7-1/2 inch sections. On interior coordination, that means more wall depth, more drywall return, and more opening framing on the structural drawings.
On curtainwall, the implication is bigger. Thicker IGUs drive deeper frames — often up to 2-1/2 inch x 10 inch or more on high-performance systems. Structural weight per SF can double from 8–9 lb/SF on a 1 inch IGU to 16–18 lb/SF on a 1 5/16 inch IGU laminated both sides. That weight feeds back into the structural engineer's slab edge detail and the anchor schedule.
6. Cost Implications
Glass thickness cost scales roughly linearly on laminated, and less than linearly on IGU (because the assembly labor is the same).
Framing runs 25–35%, labor 15–25%, hardware and miscellaneous 10–15%. Spec'ing the right thickness is not about picking the lowest-priced — it's about hitting every required performance target without overshooting.
7. When to Go Thicker
- Large uninterrupted openings. A 10 foot x 10 foot lite on a coastal project needs a thicker build than a 5 foot x 5 foot lite at the same pressure.
- Corner zones on tall buildings. Wind pressures at corner zones run 20–30% higher than field zones; glass thickness should follow.
- Airport- and highway-adjacent projects. STC 40+ requires thicker, asymmetric builds.
- Blast resistance specifications. Government, embassy, and select corporate projects spec blast-rated glass that requires SGP interlayer and thicker assemblies.
- Critical security installations. Banks, jewelers, and specific retail applications may spec UL 752 ballistic glass, which requires meaningfully thicker assemblies.
8. When Standard Thickness Is Enough
- Punched openings under 25 SF on buildings under 60 feet tall. 9/16 inch laminated impact typically covers wind load and impact with margin.
- Interior partitions and office fronts. 1/4 inch or 3/8 inch monolithic is fine where impact is not required.
- Standard storefront under canopy. Where the opening is shielded and the project is not in the wind-borne debris region, SMI or non-impact specs with thinner glass may apply.
Real Project Examples
Reference builds on recent Florida commercial projects give a sense of how the specs play out in the field. The Lake Park Innovation Center storefront uses standard 9/16 inch laminated impact on ESWindows ES-8000 at grade openings. Villa L'Onz multifamily new build uses 1 1/16 inch IGU laminated impact on residential openings to hit both impact rating and thermal performance. Panther National Clubhouse, as a large-opening resort-style project, uses heavier builds on key architectural openings to handle span and pressure.
Spec'ing Right on Your Next Job
ACG's takeoff process includes glass spec recommendations on each opening based on span, pressure, code requirements, and performance intent. Send plans for a line-item proposal with glass builds called out. GCs in West Palm Beach, Tampa, or anywhere in Florida can get detailed specs inside 48 hours through the bid portal. New construction scopes flow through the new construction glazing workflow with full shop drawings, engineering, and PE-stamped submittals. ACG is CGC-licensed Florida (CGC1531993), 350+ commercial projects, 1M+ SF installed — factory-authorized on ESWindows and other commercial systems. Contact (772) 486-7711.