And the Answer is: Do Not Vent
The working theory for many years was that wind vents would reduce the wind load on any given banner. In other words, wind would blow threw instead of pulling on and possibly tearing the banner. This theory was so widely accepted that some governments made vents mandatory for banners installed in certain locations. Springville, Utah went as far as to regulate that at least 20% of the area of a banner must be made up of holes.
But, wind tunnel tests conducted by aerodynamic specialists not only disproved the theory that slits, flaps or holes will reduce wind resistance but have scientifically proven they can be a detriment due to vibration and fabric stress within the banner. They tended to increase the wind load rather than reduce it. "The holes allow the fabric to ripple and catch more wind increasing the drag factor.” [i]
The aerodynamic specialists concluded (somewhat tongue in cheek) that “if you have a banner tied in such a way that it will remain flat in the wind, then it seems that the benefits of adding vents are minimal unless you want to make your banner into Swiss cheese.”
Here in the city and county of Denver, while permits are required for some outdoor signage, the city doesn’t dictate vents or no vents. That stated, to recommend the best substrate we always ask our clients about the install location of the banner and how long it will be up. Based on the research and our professional experience, SpeedPro Denver suggests a few materials that work with the wind without marring your design with holes. Here are a few examples:
Scrim: Commonly used for outdoor signage since it is scratch- and water-resistant but can be penetrated for grommets for easy hanging. Scrim banners are made of vinyl and reinforced with polyester cording. The material construction is what gives it strength and durability. Its smooth, flat finish makes this surface ideal for large-format inkjet printing.
Heavy duty: Ideal for fluttering flags that will go with the wind instead of fighting it, this vinyl substrate has high tear resistance due to the multi-layer design. Typically hemmed and with grommets, it is also ideal for prints that will be inserted into re-usable stands to announce the current sale or holiday specials.
To read more about the research referenced in this story, click the link below.
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[i] “Do wind vent holes in banners make a difference? We used a wind tunnel to find out” article published by Novella April 2016, Matthew Mason, The University of Queensland and Jonathan Roberts, Queensland University of Technology https://blogs.qut.edu.au/science-engineering-education-research/2016/04/25/do-wind-vent-holes-in-banners-make-a-difference-we-used-a-wind-tunnel-to-find-out/