The MicroMetl’s Sales Department too often receives requests for Hold Down Brackets to meet wind code requirements. The common misconception; the brackets alone installed on a standard rooftop curb will fulfill wind code requirements. Perhaps the misconception is due to other names given to these brackets, sometimes called Hurricane, or Wind Brackets.
HVAC Hold Down Brackets are used to secure an HVAC rooftop to a roof curb. Wind Certification requires a Professional Engineer’s (PE) Stamp of Approval to verify a HVAC rooftop unit can safely withstand high wind gusts, sustained winds or storms, without separating from the roof curb, or the roof curb separating from the roof.
Most important, a wind certified curb alone does not meet the criteria necessary for certification. Certified instructions must be followed precisely when securing the curb to the roof, and building structure. Otherwise the improperly secured, now airborne HVAC unit will accompany the sharp sheet metal of the connected curb torn from the roof.
A Hold Down bracket is a necessary part of Wind Rated Roof Curb. However, a Hold Down Bracket alone, added to a curb, without a Wind Rated PE Certified Stamp DOES NOT fulfill any wind code requirement! It is the entire system together.
What is a Hold Down Bracket?
The Hold-Down Bracket screws into the base rails of a HVAC unit, while the other end is secured by screws into the roof curb. A series of these brackets prevent the unit from being blown off the roof curb by securely connecting them to each other.
What is a wind requirement?
An HVAC Rooftop unit is designed to be placed upon a roof curb. The unit is usually set in place using a large crane. In many areas of the country, wind pressures are low enough where the weight of the unit is sufficient to keep it securely in place for the life of the unit. In areas of the country subject to hurricane winds, more than the weight of the unit is required to secure the unit to the curb.
In August of 1992 along came Hurricane Andrew; South Florida’s most costly hurricane. The Category 5 Winds were determined to be 165 MPH causing a staggering $25-$26.5 billion in damages — in Florida alone.
Most codes discover their origins in California and the West Coast. However, the aftermath of hurricane Andrew placed Florida as the leading authority for Wind Curb Calculations. Since the devastation of 1992, The Florida Building Code (FBC) for wind has become de facto throughout the United States.
Specifically speaking for MicroMetl, our Structurally Calculated Wind Rated Curbs adhere to the 2010 Florida Building Code (FBC) & 2012 International Building Code (IBC). A wind rating is a compilation of the sum of its parts. No one part can satisfy the code requirements. The brackets are connected to the rooftop unit, which is connected to the curb, which is anchored to the building. MicroMetl curbs and brackets have been designed by following the wind load. Each MicroMetl component between the unit and the roof have been designed to ensure that the force of the wind acting on the unit is transmitted through the Hold Down brackets into the curb, and into the roof as intended. Each sequential requirement specifies screw types & quantities, metal gauge, anchoring techniques, bracket types, and more.
So what requirements comprise a wind rated system, and fulfills wind code requirements? As previously noted, it is the entire system together. A PE will evaluate the dimension & weight of the roof top unit connected by specifically engineered hold down brackets. They further consider the specifically engineered curb connected to the roof, by an engineered connection to a building’s structure.
Do you need a PE stamped certificate?
Don’t be misled by any manufacturer which insinuates that brackets alone are all you need to meet required wind codes. I discovered one company not only calling their product — Wind/Seismic Brackets, but they offer a spec sheet associating them to all the standard wind codes as “Assumptions For Calculations.” This is dangerous, and misleading.
Hold Down Brackets are a great add-on to secure your rooftop unit. However, if your goal is to meet code… You must have a wind rated curb stamped by a PE! The PE Stamp ensures that a professional engineer registered in the state of the project has reviewed the curb and hold down bracket design. Furthermore, the stamp confirms the design is adequate for transmitting the intended wind loads from the roof top unit to the roof. Without a PE Stamp, the user runs the risk of utilizing an inadequate curb or bracket that could potentially fail during hurricane winds.