Why a garage door fails so easily A garage door, which is often the largest opening in a home, is only held in place by the rollers in the track.
When the wind blows at the door, it creates positive pressure – the higher the wind speed, the greater the pressure. As the pressure increases, the door bows inward and the ends of the door are pulled toward each other (or toward the center of the door) as well as causing the roller to tilt an angle.
Since the front of the tracks are flat, the rollers pull right out of the tracks and the door comes in as a unit as depicted below:
The garage door pulling out of the tracks can occur on a double garage door (the most common size is 16′ wide and 7′ high for a total surface area of 112 sf) at about 70 to 80 mph (just the beginning of hurricane force winds) when the pressure is about 12 to 16 pounds per square foot (psf) which means there is a total pressure on the door of about 12 psf x 112 sf or 1,344 to 1,792 lbs. This can be seen in the product demonstration video of testing on this website where the testing on basic garage door is stopped at 70 mph wind speed, just prior to the door pulling out of the tracks.
The exact wind speed or pressure required to cause a garage door failure depends upon many factors. Single car garage door, most commonly 8′ wide and 7′ high or 56 sf, fail at higher wind speeds since the total pressure (wind speed pressure times surface area of the door) is less than with a double door. To achieve about 1,500 lbs of pressure on a single door of 56 sf, a wind pressure of about 26 psf is required which is about 100 mph (a category 2 hurricane). The larger door, the more likely it is to fail as it must withstand greater pressures. When the wind is blowing at the side of the home opposite the garage door, there is negative pressure or suction on the garage door as the wind comes around the corner of the home and creates “lift” like on an aircraft wing. All tested and approved hurricane products must protect against both positive and negative pressures. In negative pressure, the garage door situation works in reverse. The door bows outward instead of inward. The more the door bows, the more the two ends of the door are being pulled toward the center of the door. The track is curved in the rear so it rolls until the door is freed and is sucked out as pictured below:
Since the wind direction can vary during a hurricane, garage doors must be protected against both positive and negative pressures. Remember, a hurricane has cyclical winds and direction of the wind can be significantly different from the direction from which the hurricane is approaching depending upon where the home is located relative to the path of the eye of the storm. It is a total fallacy to believe that since hurricanes may normally approach from the East, for example, that the east-side of a home is more vulnerable and a West-facing garage door does not require protection. All openings on all sides of a home require protection especially the largest opening, the garage door.
Wind-rated garage doors protect against bowing by large horizontal beams, normally one per section or panel of the garage door. However, once the door is prevented from bowing, a second source of failure exists the tracks must not pull loose from the home. Wind-rated garage doors normally have heavier tracks than non-rated doors and they always have better systems for fastening the tracks to the wall more securely. Secure Door® protects against bowing inward with the vertical brace(s) behind the door, against the outward bowing by securing to the hollow throat of the hinges on the door with metal “arms” attached to the brace and the hinges as well as reinforcing the tracks by carrying most of the pressure load by effectively breaking the door into several load sections like studs in an interior wall. By way of example, at a wind speed of 150 mph (about 50 psf) and pressure on a 16′ w x 7′ h double garage door of 112 sf of about 5,600 lbs, with three braces on the door, the door is broken into four sections so each track carries 700 lbs (which they should be capable of doing without reinforcement if installed correctly) and each brace will carry 1,400 lbs.
Retrofitting a garage door with horizontal braces places more weight on the door, requiring the springs to be adjusted to balance the door, and then must be augmented by better attachment of the tracks. Even if all of this is done well, the performance of the end result is difficult to assess. In contrast, Secure Door® has been tested and is Florida Building Code approved to give assurance to prospective buyers that the system will perform. Secure Door® adjusts vertically to permit its use on garage doors from 7′ to 8′ in height as well as being adjustable to fit snuggly to a door with no horizontal bracing or fit behind braces up to 5″ deep or any depth between 0 and 5″ for those older doors that had some horizontal bracing but insufficient bracing to protect against today’s higher wind speed standards.