Choosing the Right Pole – Flag Size Matters plus Wind Load Ratings for Light Pole Banners
Question: How do you choose the right size flag for different pole heights?
Answer: If you are speaking of national or state flags, there is a specific formula for each flag pole.
First, wind speed is the the first consideration. Regionally, the West Coast of the US is considered the lowest wind area, base on a 50 year high wind speed at 30 feet above ground, times 30% for wind gusts. So, if you want a 12’ x 18’ flag in Seattle, WA, it will need to be determined whether the flag pole you want to use can withstand an 85 mph wind x 1.3, or 111 mph winds.
Miami, on the other hand needs to be rated at 150 mph winds time 1.3, or 195 mph winds. They have more hurricanes in Florida than happens in Seattle. Maybe I could write a new song…”in Harborton, Hampton, and Hillsboro (OR), hurricanes hardly happen” (apologies to Lerner and Loewe’s My Fair Lady).
The next consideration is the wall thickness of the pole itself. As the height of pole goes up, the wall thickness will also increase. For instance, a 20’ pole, wind-rated for 120 mph while flying a 5’ x 8’ flag, will have an aluminum wall thickness of .188”; a 60’ pole will increase to a wall thickness of .25” to retain the same rating for the 120 mph wind with a 12’ x 18’ flag. And an 80’ flagpole, flying a 20’ x 30’ flag, will lose some wind speed rating to 105 mph, even though the wall thickness is now .375”.
Finally, as indicated above, the size of the flag will also be reflected in the wind load rating. The larger the size, the more pull the wind will put on the pole. The sizes indicated above are the maximum size recommended for the stated pole sizes.
The other factor will be the amount of ballast around the base of the pole. This will include concrete, the pole sleeve, and sand (and a little bit of mastic to keep the water from saturating the sand in the pole sleeve).
The company you purchase your flag and flag pole from will give you the proper calculations (usually in cubic yards) for the amount of pre-mixed concrete you’ll need to use to make sure the pole you select will give you the right amount of ballast weight for wind speed required by your state, municipal or county regulations.
Question: How do you install banners and flags on lamp poles?
Answer: Typically you’ll use either a single arm or double arm horizontal pole that’s attached to light pole or similar. There are fixed arm pole banner mounting arms and flexible arms.
Most pole banners are no larger than 36” x 72”, so the wind load is not the same as the flag poles discussed previously, but there can still be significant wind load on these banners. Generally, the top of these flags is no more than 20 feet above the ground, but if you have two 3 foot by 6 foot banners attached to a pole, watch out…you have a close equivalent 6 foot by 6 foot flag. Make sure the pole you’re attaching these banners to are able to withstand this type of wind, and if not, you may want to consider purchasing the spring-loaded arm type banner pole arms that will flex with the wind to release a strong wind load.