Mezzanine Deck Types: Open Bar Grating

Painted 19W4 open bar grating on an observation catwalk

Open bar grating deck surface on an observation platform.


Let’s continue our exploration into the different types of decking used on our mezzanines.  Last time we talked about corrugated roof deck with resindek.  We mentioned that as a wood composite material it can swell if soaked, so it is not the ideal deck type for wet environments.  Today we’re going to talk about one deck type that excels in wet environments:  open bar grating.

The typical grating that we use is a 19W4 bar grating.   It’s made by taking steel bearing bars placed 1-3/16” on center and joining them together by welding wire rod cross beams perpendicular to the bearing bars every 4” creating an open grid.  The grating typically has either a painted or galvanized finish depending on the application.

Galvanized serrated 19W4 open bar grating on a mezzanine deck

Serrated and galvanized open bar grating on a landing bound for the outdoors.


Galvanized and serrated open bar grating is an ideal deck solution for outdoor applications.Open bar grating has many advantages as a decking material.  It is very strong and durable, and the grated surface provides excellent traction.  For particularly slick locations, such as oil factories or outdoors in icy environments, we offer a serrated version for even better grip.  As an open decking surface it easily allows water, air, and light to pass through the system.  This is why it is a particularly popular decking material for outdoor applications.

There is one common misconception about the open bar grating that I would like to note though.  We are often asked to put open bar grating in sprinkled environments, with the customer thinking that they will not need to add sprinkler lines below the platform.  Unfortunately this is not the case.  The decking and framing of the mezzanine system occlude the area below enough (even before factoring in the materials on top of the platform) that your fire inspector will still require you to sprinkle below the deck if it is sprinkled above.

Oddly enough, open bar grating’s strengths are also its weaknesses.  As a fabricated steel material, it is significantly more expensive than the resindek.  The grated surface makes it extremely difficult to roll pallets and such around on top without adding something like a layer of plywood in order to provide it with a smooth surface to roll across.  And as an open, porous material it allows things to flow through it, such as fingers, heels, dropped hardware (i.e. nuts, bolts, screws), or spilled material.

Commercial and residential roof hatches for pitched roofs

economy series roof hatch mounted on a pitched roof

Standard roof hatch on a pitched roof

We received this set of photos from a customer who used our “off the shelf” Economy Series Galvanized Roof hatch on a pitched shingle roof like you would find in many commercial and residential locations. The standard roof hatch comes with cap flashing and 1” thick rigid fiber board insulation along the curb of the hatch. For this installation, the customer removed the curb insulation from the hatch and bolted the hatch down to the roof. They wanted the most economical roof hatch solution that had a low profile to match the roof slope. Ordinarily we would suggest using a pitch corrected roof hatch on slopes greater than 3/12, but the infrequent use and need for a low profile roof hatch was more important to the customer than the advantages of the pitch corrected roof hatch. Below are some pros and cons of each setup to help you decide which solution is best for your situation.

Open roof hatch showing clearances on a sloped roof

Open roof hatch showing clearances on a sloped roof

Economy series hatch installed on a shingled, sloped roof

Economy series hatch installed on a shingled, sloped roof








Standard roof hatch on a pitched roof pros:

  • Low cost
  • Standard sizes most likely in stock for immediate shipment
  • Low profile on roof

Standard roof hatch on a pitched roof cons:

  • Cannot use roof hatch railing (roof hatch railing may be required by OSHA depending on your site conditions)
  • Increased strain on hardware – installation on pitches 4/12 and greater are not covered by warranty
  • Decreased opening area due to roof hatch angle (see above photos)
Sample pitch correction options for roof hatch curbs mounting on sloped roofs

Sample pitch correction options for roof hatch curbs mounting on sloped roofs

Pitch corrected hatch on a pitched roof pros:

  • Larger opening for exiting on a pitched roof
  • Less strain on the hardware
  • Roof hatch railing can be installed on pitch corrected curbs
  • Needed for warranty coverage on pitches of 4/12 and greater
  • Required for larger roof hatches on pitched roofs

Pitch corrected roof hatch on a pitched roof cons:

  • Slightly increased cost (made to order)
  • Increased lead time (made to order)
  • Taller curb on low end of roof may be more visible from ground level

Using the pitch corrected hatch for your pitched roofs over 3/12 gives you the standard manufacturer’s  warranty and can give you a larger opening to go through, but ultimately it comes down to your specific needs and what is most important for you. If you have any questions, please contact us.