Does G90 Type B Metal Deck Add Strength or Only Corrosion Resistance?
G90 adds corrosion resistance, not strength. The load capacity of 1.5" Type B deck comes from its gauge (22 to 16) and its 50 ksi ASTM A653 steel. The zinc coating does not count toward it. G90 has a heavier zinc layer than G60, which suits coastal, humid and unconditioned Florida buildings. We supply G90 Type B in every catalog gauge.
Strength comes from gauge and steel grade
Catalog section properties and allowable loads are calculated on the base steel design thickness under ANSI/SDI RD-2017, C-2017, NC-2017 and SD-2022. To carry more load or span farther, go to a heavier gauge. A heavier coating will not help.
Corrosion: where G90 earns its place
Florida combines salt air, high humidity and long periods of rain. G90's thicker zinc layer protects longer when the deck underside is exposed to that air, or when moisture can reach the top of the deck during construction or from roof leaks.
- Coastal and barrier island buildings
- Open canopies, breezeways and unconditioned warehouses
- Roofs with lightweight insulating concrete (pair with vented deck)
Specify both properties
Your documents should name the gauge and the coating, for example 20 gauge, G90, 50 ksi. Send the plans and we will run a takeoff and quote the deck to match.
1.5" Type B section properties are the same for G60 and G90 (catalog, 50 ksi)
| Gauge | Design thickness (in) | Se+ (in3/ft) | Mn/Ω (in-lb/ft) |
|---|---|---|---|
| 22 | 0.0295 | 0.165 | 5158 |
| 20 | 0.0358 | 0.221 | 6656 |
| 18 | 0.0474 | 0.299 | 9331 |
| 16 | 0.0598 | 0.386 | 11806 |
Related Questions
Is G90 the same as hot-dip galvanized structural steel?
Both use zinc, but they are applied differently. G90 deck is cut from coil that was galvanized continuously before forming, under ASTM A653. Structural members are often galvanized after fabrication, under a different standard. On deck, the zinc protects the cut ends sacrificially, so the edges do not need to be coated again.
Does G90 make the deck heavier?
Only slightly, from the extra zinc. For dead load, structural design uses the catalog design weight for each gauge: 1.6 psf at 22 gauge, 2.0 at 20, 2.6 at 18 and 3.0 at 16. Your engineer may also add an allowance for coating.