ACCURATE ROOFING THICKNESS MEASUREMENT: THE HAAG PANEL & MEMBRANE GAUGE
By Amber Prom, P.E., and Steve Smith, P.E.
Whether you’re an engineer, insurance adjuster, roofing consultant, or contractor, if you commonly find yourself collecting data out in the field, you rely on a kit of tools to assist you. From tape measures, cameras, levels, or chalk, the precision and reliability of your tools is crucial. If your tools are unreliable, you can end up with an incorrect assessment and/or cost estimate.
What is the Haag Panel & Membrane Gauge?
The Haag Panel & Membrane Gauge (HPMG) is a unique tool that every field investigator should have at the ready when inspecting metal roofing panels or single-ply roofing. While many inspectors measure metal roofing panel thickness using a standard sheet metal gauge, the HPMG has been carefully designed by Haag Research & Testing to accurately measure most every metal roofing panel you will encounter in the field, accounting for the thickness of any coating that may be present. In fact, as a testament to its accuracy, many insurance companies now require that metal thickness be measured with an HPMG when inspecting for possible damage. Non-HPMG or standard metal thickness gauge measurements are rejected.

Compatible roofing materials
The HPMG is compatible with:
- Single-ply membranes (excluding modified bitumen, self-adhering, and fleece-backed)
- Steel and aluminum metal panels.
How to Identify Aluminum vs. Steel Roofing Panel Material
Correct material identification is essential before taking measurements. For metal roofing panels, it can be difficult to determine if you are looking at aluminum or steel panels. The Haag Panel & Membrane Gauge™ includes a rare earth magnet (strong, permanent magnet made from rare earth alloys) to help determine panel type
- Steel panels will attract the magnet
- Aluminum panels will NOT react to the magnet
- Some stainless steels may not react to the magnet, and are generally shinier, more reflective, heavier, and harder to scratch than aluminum. (*See “Stainless Steel and Aluminum: How to Distinguish Between Them?“1, or other online guides for ways to differentiate.)
All steel roofing panels have either a metallic coating (galvanized or Galvalume®), or a paint coating. Measuring coated metal roofing panels with a standard sheet metal gauge gives artificially thick readings, making a determination of gauge/thickness incorrect, and resultantly the associated cost estimate more expensive than it should be.
The HPMG is fabricated in the USA using high precision manufacturing methods. Gap thicknesses are quality checked by Haag’s IAS accredited Laboratory to maintain the tool’s accuracy.
how to use the Haag Panel & Membrane Gauge
- Identify the type of material (See info above; use the magnet to help determine aluminum or steel).
- Start with the widest slot. Hold the gauge loosely in one hand at a 30-degree angle to the material, drag the slot along the edge of the panel or membrane. Note that the slightest burr (rough edge on the material after cut) will misrepresent thickness. Do not force the gauge onto the material.
- Stop at resistance. When dragging the tool, the slightest resistance constitutes refusal. The slot prior to refusal is the estimated panel thickness.
- Take multiple measurements to qualify your results, and record all findings


Key Features of the HPMG
- Standard metal roofing panel thickness slots range:
- Steel: 29 to 18 gauge
- Aluminum: 0.18 to 0.80 inch.
- Standard single-ply membrane thickness slots range:
- 45 to 90 mil
- A built-in magnet to assist in material identification (steel vs. aluminum)
- A machined hole to attach the HPMG to a clip or lanyard.
- Straight edge to visually demonstrate dent depth.
- Durable metal construction to resist wear, bending, or corrosion.
- Compact size to fit into small pockets and not obstruct images when taking photographs.
- Unique shape to help measure in tight places (like panel ends extending into gutters).
- The HPMG can be easily photographed when documenting your file.
- Designed and manufactured in the United States.
Why Accuracy in Thickness Matters
The HPMG is the top-of-the-line tool when it comes to determining roofing panel and membrane thicknesses accurately in the field. Without it, your thickness measurements could be inaccurate. This can
- Add significant costs to your estimates
- Increase bids unnecessarily
- Lead to more expensive claim settlements.
Add a Haag Panel and Membrane Gauge to your gear and take your measurements with confidence, backed by Haag’s proven expertise in forensic consulting since 1924.
Source– 1. Delmet Stainless Steel, “Stainless steel and aluminum: how to distinguish between them?”, https://www.delmetelectropolishing.com/n/37-stainlesssteelandaluminumhowtodistinguishbetweenthem.html

Amber Prom, PE, is Director of Curriculum for Haag Education and a Forensic Engineer for Haag, a Salas O’Brien Company. Based near Denver, Ms. Prom is a Registered Professional Structural Engineer with 16 years’ experience in structural design, project management, forensic engineering, and engineering management/ training. Amber previously worked as Professional Development Manager, Project Engineer/ Technical Lead, and Principal Consultant for 8 years. She was responsible for training all new hires and providing continuing education/training for existing experts within the Civil/Structural and Building Consultant Divisions. She built this training program from the ground up for 100+ experts throughout the U.S. and Canada. As a Project Engineer/Principal Consultant, she conducted forensic engineering investigations related to building components which had failed, become damaged, did not operate/function as intended, or were constructed deficiently. She was also the Technical Lead for processes, including performing field investigations, documenting/photographing, equipment use, etc.
Ms. Prom’s previous experience also includes working as a Design Engineer, where she designed a multitude of industrial power plant elements electrical transformer containment areas and foundations, miscellaneous electrical buildings and foundations, 140-ft cantilevered stair tower, multi-level steel platforming, among many others. She was a Project Manager for commercial projects, including those in high seismic areas, hurricane-prone areas, and high snow-load regions.

Steven R. Smith is a Forensic Engineer and Director of Research & Testing for Haag, a Salas O’Brien Company. Mr. Smith is an experienced forensic engineer who began his career with Haag in 1998. He spent seven years working as Haag’s Senior Lab Technician while earning a Bachelor of Science in Mechanical Engineering degree from The University of Texas at Arlington. He has been involved with the lab throughout his career and has been able to leverage his extensive and practical engineering field experience with research and testing projects. Mr. Smith has authored or co-authored several Haag publications, including Repairing an Existing 36-Inch Laminated Asphalt Shingle Roof with Metric-Sized Laminated Asphalt Shingles, Effects of Hail-Caused Dents on the Thermal Performance of Insulation Under Single-Ply Roofing, Testing of Impact-Resistant Asphalt Shingles, and Hail Effects on Air-Conditioner Performance. He also contributed to other publications as a laboratory technician, including Hail Damage Threshold Sizes for Common Roofing Materials, Hail Damage to Tile Roofing, and Hail Impact Resistance of Asphalt Shingle Overlays.
Mr. Smith’s areas of expertise include roofing system evaluations, components and cladding, code and standard compliance, and mechanical equipment evaluations. He is a licensed Professional Engineer in Texas, Arkansas, Oklahoma, Missouri, Minnesota, and Wisconsin. He is a member of the American Society of Mechanical Engineers (ASME) and Pi Tau Sigma National Honor Society. Prior to joining Haag, he trained at the Navy Nuclear Power Training Command Center in Orlando, Florida and was stationed aboard the USS Arkansas (CGN-41), where he maintained reactor and steam plant chemistry, performed radiological controls, and operated mechanical equipment in the propulsion plant.