The MPI Fabrication
GT-1 Gutter System
A third-party-tested aluminum box gutter system for low-slope commercial roofing — evaluated by National ES Testing Service under the ANSI/SPRI GT-1 standard, with published pressure ratings for wind, uplift, and static load.
What Is GT-1?
GT-1 is a structural performance standard specifically developed for gutter systems used with low-slope roofing. It evaluates whether a gutter system — including the gutter profile, reinforcing components, straps, fasteners, supports, and attachment method — can resist the forces it may experience once installed on a building.
In plain terms, GT-1 testing answers a critical question:
Will this gutter system remain securely attached and maintain its shape when exposed to wind pressure, uplift, and the downward weight of water or ice?
A gutter is not considered GT-1 compliant simply because it is made from heavy material or resembles another tested gutter. The complete assembly must be tested as a system using the specified materials, dimensions, reinforcements, fasteners, attachment spacing, and installation method.
The Three GT-1 Tests
The ANSI/SPRI GT-1 standard evaluates gutter systems in three different directions.
Horizontal / Outward Pressure
Measures the gutter's resistance to forces pulling it outward from the building — typically wind acting on the face and leading edge of the gutter. Especially important on large commercial buildings and in high-wind regions where roof perimeters see the strongest pressures.
Vertical / Upward Pressure
Measures resistance to upward forces that attempt to lift the gutter off the building — simulating wind uplift acting beneath and around the gutter assembly. Verifies straps, rear supports, fasteners, and attachment points hold against separation.
Static / Downward Pressure
Measures resistance to downward forces from ponding water, ice, clogged outlets, and heavy rainfall. Verifies the gutter and its supports carry the load without losing securement or permanently deforming beyond the standard's limits.
The Tested Assembly
MPI Fabrication's certified assembly is a formed commercial box gutter manufactured from .040-inch aluminum, tested and reported by National ES Testing Service under ANSI/SPRI GT-1.
- .040-inch aluminum gutter body
- 8″ rear vertical · 6″ bottom · 5″ front face
- 1″ × 1″ return / box lip
- Hemmed .040 aluminum top straps
- 2″-wide, 16-gauge galvanized steel rear reinforcing supports
- Concealed #10–13 × 1½″ pancake screws
- Reinforcing supports and straps at 30″ on center
- 10-foot fabricated sections
Certified profile submittal — MPI GT-1 gutter
Why GT-1 Matters
Commercial gutter systems are part of the roof perimeter — one of the most wind-sensitive areas of a building. A gutter failure can create more than a drainage problem. It may damage the roof edge, fascia, membrane termination, wall panels, or surrounding property.
GT-1 testing provides documented evidence that the gutter assembly has been physically evaluated under controlled loading conditions.
Verified Structural Performance
Measurable pressure ratings — not just material thickness, appearance, or past experience.
A Defined Installation Method
The certification identifies the supports, straps, fasteners, attachment spacing, and blocking required to achieve the tested performance.
Better Submittal Documentation
Contractors get a profile drawing, material specs, installation details, test ratings, and third-party compliance documentation for approval.
Confidence on High-Wind Projects
Documented resistance to outward wind pressure, upward wind uplift, and downward static loading.
Local Custom Fabrication
MPI provides a tested commercial gutter system while offering the responsiveness, coordination, and fabrication flexibility of a regional manufacturer in Richmond Hill, GA.
Tested System Versus “GT-1 Equivalent”
A gutter should not be marketed as GT-1 compliant merely because it looks similar to a tested product. The rating applies to the tested assembly, including the gutter's dimensions, metal type and thickness, rear reinforcing supports, top straps, fastener type, fastener locations, support spacing, attachment into suitable blocking, and installation configuration.
The MPI report states that the test results apply to similarly produced gutters up to the tested maximum dimensions, provided the same material thicknesses or greater, the same support brackets, the same strap configuration, and the same installation requirements are used.
That distinction is important. GT-1 is not simply a label placed on a gutter. It is a documented relationship between the manufactured product and the way it is installed.
See the GT-1 System in the Field
MPI Fabrication's GT-1 gutter system was specified and installed on the New Midway Middle School roof in Liberty County, Georgia, in partnership with RPI Roofing.
Read the Midway Middle School Case StudySpecify MPI's GT-1 Gutter on Your Next Commercial Roof
Third-party tested. Published pressure ratings. Locally fabricated in Richmond Hill, GA. 24–72 hour standard turnaround for Southeast commercial roofing contractors.
Request a QuoteOr call (912) 755-0030
Important Note
The GT-1 rating applies to MPI's tested assembly, including the gutter's dimensions, metal type and thickness, rear reinforcing supports, top straps, fastener type and locations, support spacing, attachment into suitable blocking, and installation configuration.
MPI Fabrication offers a GT-1 tested gutter system when manufactured and installed in accordance with MPI's approved profile, material, reinforcement, fastening, and installation requirements.
Common Questions, Answered
What is an ANSI/SPRI GT-1 tested gutter system?
ANSI/SPRI GT-1 is a structural performance standard for gutter systems used with low-slope commercial roofing. It evaluates whether the complete gutter assembly — profile, reinforcing components, straps, fasteners, supports, and attachment method — can resist outward wind pressure, upward wind uplift, and downward static loading. MPI Fabrication's GT-1 gutter system is independently tested by National ES Testing Service under this standard.
What are the tested pressure ratings on MPI Fabrication's GT-1 gutter system?
MPI Fabrication's GT-1 tested aluminum box gutter system achieved 190 psf horizontal (G-1 outward wind pressure), 135 psf vertical uplift (G-2), and 160 psf static / downward load (G-3). These ratings apply to the complete tested assembly — .040-inch aluminum body, 16-gauge galvanized rear reinforcing supports, hemmed aluminum top straps, concealed pancake screws, and supports at 30 inches on center.
What are the dimensions of MPI Fabrication's GT-1 gutter profile?
The tested profile is a formed commercial box gutter: 8-inch rear vertical, 6-inch bottom, 5-inch front face, and a 1-inch by 1-inch return / box lip. It is fabricated from .040-inch aluminum and produced in 10-foot sections. The tested assembly includes 2-inch-wide, 16-gauge galvanized steel rear reinforcing supports installed at 30 inches on center.
Is every commercial gutter MPI Fabrication makes automatically GT-1 rated?
No. The GT-1 rating applies specifically to MPI Fabrication's tested assembly — the tested profile dimensions, material thicknesses, rear reinforcing supports, top straps, fastener type and locations, support spacing, and installation configuration. MPI Fabrication offers a GT-1 tested gutter system when manufactured and installed in accordance with MPI's approved profile, material, reinforcement, fastening, and installation requirements. Custom gutters outside the tested assembly are still available, but they are not covered by the GT-1 rating.
Who tested MPI Fabrication's GT-1 gutter system?
MPI Fabrication's GT-1 gutter assembly was independently tested by National ES Testing Service in accordance with the ANSI/SPRI GT-1 test methods. The performance report states that the testing applied to the complete formed gutter assembly — not simply the aluminum gutter shell by itself.
Why does GT-1 testing matter on a commercial roof?
Commercial gutter systems sit on the roof perimeter, which is one of the most wind-sensitive areas of any building. A gutter failure can damage the roof edge, fascia, membrane termination, wall panels, and property below. GT-1 testing gives architects, contractors, consultants, and building owners documented evidence — verified structural performance, a defined installation method, and third-party compliance documentation — instead of relying on material thickness or appearance alone.