Opinions about wind slits in banners vary. The purpose of these semi-circular cuts in the vinyl banner material is to relieve the wind load that can shred a banner to pieces. Sign makers often use anything from soup cans to coffee cans as templates for cutting slits with an Xacto knife or utility knife.
To understand how damaging high winds can be, read my story: The Effect of Wind Loads on Vinyl Banners.Amazingly the pressure of a 75 mile per hour wind on a 3’ x 30’ banner spanning a city street is about 1890 lbs.
Concerned that high winds could send banner material, cables and anchoring mechanisms flying putting passers-by at risk of injury, some well-meaning communities have required wind slits in banners. To some extent, these wind slits do reduce wind loads by 6% to 15%, according to the estimates of experts.
Here’s the rub. In my example, that’s only a reduction of the wind pressure of 283 lbs, at best. The pressure of that 75 mph wind is still more than 1600 lbs. What’s more, the wind slits have weakened the banner material, making it easier for the wind to rip it apart.
When customers insist that you cut wind slits in their banners, you should explain that they are not that effective. In addition, they detract from the aesthetics of the banner. In short, they’re ugly!
Another consideration that you should bring to the attention of your customer is that most manufacturers will not warranty their banner material if it is cut with wind slits.
Instead of defacing a great looking banner with wind slits, you have an alternative: Use the right material for the application. If the banner is subjected to potentially damaging winds you could print the graphics on a 75/25 banner mesh. Mesh material is much more effective at reducing wind load than cutting wind slits in vinyl banner material. Using mesh material is a great option for banners strung across streets.
When printing graphics on both sides of pole banners or over the street banners, another option is to use 18 oz. vinyl blockout banner with a 1000 x 1000 denier scrim. This heavier material provides at least one year of durability for outdoor applications. Proper installation also improves the likelihood that a banner will survive damaging winds.
