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Design for the Chapter 15 IBC wind resistance of low-sloped ballasted roof systems with confidence

Henry 790-11 Waterproofing System has been evaluated to align with the Chapter 15 IBC ANSI/SPRI RP-4 wind resistance requirements for low-sloped ballasted roof systems.

Of all the many IBC Section 1504 assembly performance requirements that architects must follow, “ANSI/SPRI RP-4: Wind Design Standard for Ballasted Single-Ply Roofing Systems” may be one of the most challenging.

The goal of ANSI/SPRI RP-4 is relatively simple – it is intended to help architects design and specify low-sloped ballasted roof systems – pavers, aggregate rock, green roofing vegetation, etc. – to meet proper wind resistance requirements. But the standard itself is rather complex, as it comprises a range of building- and project-specific criteria, including building type, building exposure type, building height, parapet height, local wind conditions, and more.

Essentially, ANSI/SPRI RP-4 requires a custom wind analysis and roofing system assessment for every project across North America. In practice, it generally involves a mix of calculations, product guidelines, and other theoretical assumptions. As a result, recommendation of an over-engineered ballasted roofing system is not uncommon. “As many building professionals have found out the hard way, relying on theoretical calculations rather than actual testing involves a fair amount of risk,” says Michael Whitfield, President of Green Roof Outfitters, which is a total amenity deck product manufacturer.

However, based on a recent series of successful wind resistance tests conducted by a third-party, it’s no longer a necessary risk. Henry Company now offers multiple assemblies that are evaluated to meet or exceed ANSI/SPI RP-4 maximum allowable wind speeds.

Pioneering wind resistance tests from Henry
Working with third-party industrial testing providers and Green Roof Outfitters, Henry devised a series of lab trials that tested the wind resistance of various green roofing systems designed with the Henry 790-11 Hot Rubberized Asphalt Waterproofing System. Wind resistance tests mimicked a range of real-world wind-flow situations that maxed out at Category 5 Hurricane conditions.

The results demonstrated that the green roofing systems designed with Henry 790-11 would withstand lateral winds of up to 165 MPH and evaluated wind uplift pressures of up to 350 PSFs. Liz Morris, Henry Director of Vegetated Roofing, puts the results into context: “Architects and builders in all types of wind conditions can be confident that Henry Green Roof Systems will function as intended, and remain in place, even in extreme wind conditions.”

Look to Henry for help early in the process
Thanks to the findings of the evaluated wind resistant systems, architects now have access to an unprecedented range of low-sloped ballasted roof assemblies backed by data that demonstrates they can withstand wind uplift ratings of up to 350 PSFs. Rather than having to rely on a given manufacturer’s technical bulletins or project calculations, architects can now look to Henry for lab-tested, engineer-validated systems that meet the IBC Chapter 15 ANSI/SPRI RP-4 wind resistance requirement.

In any climate zone, high winds can damage and destroy roofing with wind-born debris during storms. But the biggest concern is displacement of the roofing from pressure pushing it up from underneath. This is where the whole roof can end up in the parking lot, or on top of the building next door. Add on thousands of pounds of plants and soil, and it is clear why this is a primary green roof design considerations.

The key for success is to start working with Henry early in the design of the building, preferably during the schematic design stage. Henry is here to help architects and owners select a system that will meet ANSI/SPRI RP-4 requirements with real-world data.

For assistance on the design and specification of a low-sloped ballasted roof system Contact Henry today to schedule a wind resistance consultation.

Schedule a meeting with your Henry Advisor today