ThermalCraft Podcast
In the insulated metal panel (IMP) industry, one of the most common and costly design issues occurs when panel-spanning capabilities don’t align with girt-spacing requirements. These problems often aren’t discovered until late in the project, leading to redesigns, schedule delays, and additional costs.
To help architects, engineers, design-build contractors, and building owners avoid these challenges, ThermalCraft Principal, Dean Sol sat down with Brian Jaks, Professional Engineer and President of Greenspan Profiles, to discuss the fundamentals of exterior panel design, wind loading, and girt spacing.
According to Jaks, every successful wall design begins with understanding the loads the building must resist.
For exterior wall panels, wind loads are typically the governing factor. These loads are influenced by several variables, including:
Before determining girt spacing, engineers must first establish these design loads.
Girt spacing is ultimately determined by the span capability of the insulated panel. The span capability is affected by panel thickness, skin gauge, fasteners, attachment methods, and the supporting structure.
Many girt spacing issues originate long before construction begins.
Project requirements such as dock door heights, ceiling elevations, loading conditions, and building use all influence structural design decisions. Whether the facility is a cold storage warehouse, distribution center, winery, or rack-supported structure, those requirements must be considered alongside the building’s wind load demands.
The goal is to balance operational requirements with structural performance.
“You’re trying to marry what the building needs to do with the parts and pieces you’re going to use to build it,” says Jaks.
Today, most projects are designed using the International Building Code (IBC), which provides the methodology for calculating wind, snow, and seismic loads.
Design teams can determine wind pressures in two ways:
The faster, more conservative approach uses code tables that categorize buildings and provide required design loads.
The more precise approach uses code equations to calculate loads specific to the building’s geometry and location.
While some structural drawings provide detailed loading information, others require engineers to perform their own calculations based on the project’s design criteria.
One area that often causes confusion is the difference between structural loads and component-and-cladding loads.
Structural elements such as columns, beams, girts, and purlins are designed using one set of load requirements. Components and cladding—including insulated metal panels, clips, and fasteners—are designed using another.
Because components and cladding have smaller tributary areas, they often experience higher localized pressures than the primary structure.
This distinction is critical when evaluating panel spans and attachment methods.
Many girt spacing challenges occur in corner zones, where wind pressures can be significantly higher than in the field of the wall.
As wind moves around a building, it accelerates at corners and edges, creating areas of increased negative pressure. These corner zones often require tighter girt spacing than the rest of the structure.
However, for reasons ranging from fabrication efficiency to cost savings, many buildings are designed with uniform girt spacing throughout.
While that approach may simplify fabrication, it can create performance issues in high-load areas.
“For large distribution centers especially, it makes a lot of sense to use tighter spacing in the corner zones and save steel everywhere else,” Jaks notes.
Factory Mutual (FM) requirements add another layer of complexity.
While FM-approved designs provide a highly conservative approach to risk management, they often require substantially greater resistance than standard code requirements.
According to Jacks, FM design requirements can increase loading demands by approximately 30–40% through factors such as:
The result is stronger buildings—but also higher material, labor, and installation costs.
For owners not insured through FM, understanding the cost-benefit tradeoff is an important part of the decision-making process.
