Look! No Wind Slits in these Banners

JANUARY 12, 2016| SpeedPro of SF Peninsula

Look at the beautiful banner pictured below that SpeedPro Imaging of San Francisco Peninsula printed and installed at the Softball diamond at College of San Mateo (@csmbulldogs)  Do you notice something “missing’? How about the fact that the banner is not marred by those ugly semi-circular cuts that you see in banners all too often (including our title photo)?

What’s wrong about wind slits or vents in banners? That’s right.  No wind slits (!) — those slices made in the shape of a half-moon with the intent of giving the wind a way to blow through the banner and reduce stress.  When it comes to wind slits, we’re haters, even though many cities ordinances still require air relief for banners spanning streets.

1. They destroy the look of the graphic and can actually cause more vibration and tearing, and more importantly, all this damage is basically for naught, because:
2. They don’t really do much to relieve stress or to keep a banner from blowing down.

With the strong banner materials we use today, featuring tight weaves of nylon scrim reinforcement between layers of printable vinyl, the material is exceptionally durable when the correct weight is chosen for the project and intended duration. We usually use 13 oz. scrim banner for typical exterior banners, but the CSM banners will be up for years in a windy environment, so we specced a heavy 18 oz. block-out material and reinforced stitching. Combined with the right hardware (a pair of pole banner brackets designed for windy conditions), they’re not going anywhere!

So why do some people still use banner slits? Well, it’s largely mimicry, or simply a habit (“we saw other people doing it and it seemed like the thing to do”) and provides an outwardly visible and reassuring method to demonstrate a concern with mitigating the wind.  But in reality, it’s just a placebo– a “pill” that doesn’t do anything but still makes some people feel better.

What’s the scientific reasoning?

To understand why it’s ineffectual, take a quick look at the physics. If you calculate the area of a banner vs. the total area opened up by the slits, you can figure how much wind will pass through rather than hit against the surface. For example, imagine a banner that is 3ft x 7ft — that’s 21 square feet.   Let’s choose wind slits of a 6″ diameter. The area of each half-circle would be slightly over 14 sq. inches –remember Pi r2?…= (3.1415 * 9) / 2 [it’s divided by 2 since it’s only a 1/2 circle]. Now, let’s imagine ruining our banner by cutting ten of these little smiley-face monsters.  The ten of them together would be around 142 square inches — just under a square foot. So that’s 1/21, or less than 5% of the area of the banner that’s “relieved”. If someone is depending upon a 5% wind reduction to keep a banner from blowing down, they’re more of a risk-taker than I am. For more specifics regarding the science behind why wind vents don’t perform as people often believe, check out this wonderful blog about the research done at The University of Queensland in Australia.

There are many better answers, and we’re happy to help if you give us a call at 650.662.5450 or click here to fill out an inquiry form. Mesh banner can be great in many circumstances, and mostly it’s about proper installation and hardware. But don’t cut that beauty, please!