I’m replacing some painted roof deck that’s 0.035 inches thick. What gage number do I need?

Based on the “Typical Actual Thickness” shown in the table below, your existing deck is 20 gage (GA), but this may or may not be the gage that you need.  To answer that question, you should ask an engineer to select the deck gage based on support spacing and design loading.  If that is not possible, we recommend that you make the following two checks:

1.  Measure the thickness of the existing material and use the table below to determine the likely gauge.  If your measured thickness falls in between the values shown here, you should select the lower gage number to make sure your replacement decking is at least as strong as what you are replacing.

2.  Compare that gage and the span length on your project to the current maximum allowable spans published by Factory Mutual, reproduced here.  If your deck type and gage are not listed, contact D-MAC for assistance.


To be conservative, we recommend that you order the heavier gage determined by steps 1 and 2.  If you have any questions about selecting your deck gage, please ASK D-MAC!

This table contains the Uncoated Thicknesses that are published by the Steel Deck Institute (SDI) along with Typical Actual Thicknesses that we at D-MAC added based on our measurements of finished products.
Design Thickness: The bare metal thickness used to calculate the strength of the metal deck.
Minimum Thickness: The minimum allowable bare metal thickness (95% of the design thickness).
Typical Actual Thickness: The thickness you can expect to measure in the field of a clean (not rusted) flat portion of the metal deck for painted and galvanized deck.