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ANSI/SPRI GT-1: A Deeper Dive

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The roof assembly is an integral part of the building envelope, and your perimeter edge securement – including your gutter system – is the first line of defense to ensure your membrane is safely sealed, protecting against blowoffs and water damage. To provide quality assurance, the International Code Council updated International Building Code (IBC) to incorporate gutter testing requirements so that this critical component is ready for the elements. This article will guide you through the new ANSI/SPRI GT-1 testing standard that is part of the 2021 and 2024 IBC.

What is ANSI/SPRI GT-1?

After two years of development led by the Single Ply Roofing Industry (SPRI), ANSI/SPRI GT-1 became an official testing standard for gutter systems in 2016. The intention was to make low slope, commercial roof systems more secure. The ANSI/SPRI GT-1 standard improves the security of commercial roofs by creating standardized testing and performance measures for the gutters that secure load-bearing membranes. Since its standardization in 2016, ANSI/SPRI GT-1 was approved and included as a part of the International Building Code, beginning in the 2021 edition. 

Who are the key players?

American National Standards Institute (ANSI) is a private, not-for-profit organization that supports the U.S. voluntary standards and conformity assessment system. Encompassing practically every industry, the Institute represents the diverse interests of more than 270,000 companies and 30 million professionals worldwide.

Single Ply Roofing Industry (SPRI) is a national single-ply roofing association comprised of manufacturers and professionals. SPRI is a technical and statistical authority for the single-ply roofing industry and represents the industry’s sheet membrane and suppliers.

Factory Mutual (FM) is a conglomeration of insurance companies. To limit their exposure to loss, FM has developed testing standards for materials used on the properties they insure. All FM Approved products are listed on the RoofNav database.

American Society of Civil Engineers (ASCE) is the most respected engineering society in the US and represents civil engineers around the world. ASCE maintains the Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE 7), that is a vital part of many building codes.

How did we get here?

SPRI published “Wind Design Guide for Edge Systems Used with Low Slope Roofing Systems,” their first guide, in 1994. Four years later, the first edition of ANSI/SPRI ES-1 was created, having been derived from the original SPRI version. In 2003, ANSI/SPRI ES-1 was introduced into International Building Code. Gutters were not included until 2010, when ANSI/SPRI GD-1 was established. The following year, FM Global updated their edge metal testing standard, FM 4435, to match the ES-1 method, now known as ANSI/SPRI/FM 4435/ES-1. ANSI/SPRI GT-1 became an ANSI standard on May 26, 2016, after roughly two years in development, and was subsequently adopted into the IBC in 2021.This new standard further separated the design and testing standards for perimeter securement systems:

  • Design: Fascia, Coping, Gutters (ANSI/SPRI ED-1)

  • Testing: Fascia, Coping (ANSI/SPRI/FM 4435/ES-1)

  • Testing: Gutters (ANSI/SPRI GT-1)

Why have a testing standard?

ANSI/SPRI GT-1 provides a consensus for an expectable level of performance with real world practicality to protect owners, occupants, architects, and installers. When design professionals, fabricators, and installers are looking for a particular level of wind load resistance, ANSI/SPRI GT-1 has the answers. 

Is it required now?

ANSI/SPRI GT-1 is vital and – as states adopt the latest building code – increasing required throughout the United States. Though each state controls their building code, there are 21 states that already require ANSI/SPRI GT-1 testing as part of their building code, with four others requiring it at local levels as of October 2024. As other states look to follow, there is wisdom in getting ahead of the changes before it is required by your building code.  

Where is it referenced in IBC?

Like the ANSI/SPRI/FM 4435/ES-1 testing standard for edge metal systems, the ANSI/SPRI GT-1 for gutter systems is in Chapter 15 of International Building Code (Section 1504.5.1). 

“Gutters that are used to secure the perimeter edge of the roof membrane on low-slope (less than 2:12 slope) built-up, modified bitumen and single-ply roofs, shall be designed, constructed and installed to resist wind loads in accordance with Section 1609 and shall be tested in accordance with Test Methods G-1 and G-2 of SPRI GT-1.”

How do the ANSI/SPRI GT-1 tests work?

There are two tests conducted for ANSI/SPRI GT-1: G-1 (Horizontal Test Pressure) and G-2 (Vertical Test Pressure). There is a third test, G-3, that measures the resistance of the gutter system to test forces acting downward such as water, ice, and snow loads. Even though G-3 is part of ANSI/SRPI GT-1 testing, only G-1 and G-2 are directly cited in the 2021 IBC.

Test G-1: Horizontal Test Pressure measures the resistance of the gutter system to test forces acting outwardly (away from the building). The highest load held without failure is used to calculate the pressure by dividing the total force by the area of the gutter face.

Test G-2: Vertical Test Pressure measures the resistance of the gutter system to test forces acting upwardly tending to lift the gutter off the building. The highest load held without failure is used to calculate the pressure by dividing the total load by the total width of the gutter.

What's at stake?

When Hurricane Matthew devastated many portions of Florida, countless businesses and homeowners were faced with damages. In just one example, a 7,000 square foot large box retail building saw substantial damage from 80-90 MPH winds. The cause of the damage was most likely from a loose gutter and/or flashing, which led to the roof covering peeling back.

The situation was Deisgn Preventable, meaning that proper gutter/flashing securement would have resulted in no loss. Instead, the retail store was hit with a $70,000 Repair Cost claim, $1.7 million Content Cost claim and $1.75 million Business Interruption claim, for a total $3.52 million claim paid per insurance.
(Source: RICOWI Presentation Slides March 2019)

How to meet ANSI/SPRI GT-1 requirements?

With tested gutter solutions sized for every application, we can help you understand the ANSI/SPRI GT-1 Standard and update your low slope membrane gutter specifications. Available now, ANSI/SPRI GT-1 approved and backed by a 30-Year, 160 MPH Wind Warranty, Seal-Tite WR Gutter is your go-to solution from 5.25 - 7.75" and Seal-Tite XL Gutter is your XL solution from 8 - 14". 

Also, take advantage of our Gutter Calculator, which not only determines design pressures for ANSI/SPRI GT-1, but also calculates the size of the gutter required for specific projects. 

Searching for more information on ANSI/SPRI GT-1? Contact your local rep, who can assist you with any inquiries!

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