The hidden science of sealants, fasteners and flashings

By Jesse Sanchez. 

The true strength of a metal roof isn't what meets the eye, it's what's out of sight that matters. 

What makes a metal roof truly reliable isn’t its sleek surface or sharp lines; it’s the hidden components underneath. According to ASC Building Products, long-term performance depends on what most people never see: sealants, fasteners, underlayment, clips and flashing. These critical elements work behind the scenes to protect the structure, while the visible panels simply finish the look. A roof might appear solid from the street, but it's the construction below that determines whether it will stand up to time and weather. 

In a series of in-depth technical videos, Jeff Haddock, technical services manager from AEP Span, outlines the often-overlooked components that ensure a metal roof’s integrity. From concealed non-skinning butyl sealants that remain tacky for decades, to the nuanced choice between fixed and floating clips, the details are crucial and easy to get wrong. 

One critical takeaway: using the wrong sealant in the wrong location can cause serious problems. “We’ve seen cases where a curing sealant was used in a dynamic joint,” Jeff said, “That seal line can actually shear off and then the benefits of utilizing that sealant are gone or it cracks or breaks away. You could have water infiltration if the improper sealant was used.” 

Choosing the right fastener for a metal roof is far more technical than it looks; every detail matters, from head shape to corrosion resistance. It’s not simply a matter of matching screw to substrate. Head profile, thread count, drill point style, corrosion resistance and even UV exposure must all be factored in.  

Trim and flashing aren’t one-size-fits-all components; they need to be measured and fabricated to fit the specific demands of each project. Relying on catalog dimensions can lead to gaps, exposure and failure, especially on custom builds. The focus should be on how the detail functions, not just its size on paper. This level of precision becomes even more critical when a weather-tight warranty is involved. Securing that warranty isn’t just about checking a box; it requires proper planning, detailed reviews, field inspections and the use of approved materials like factory-applied sealants. If the system isn’t built to spec from the start, the warranty won’t apply. 

Metal roofs promise decades of durability, but only if the unseen components are selected, installed and maintained with care. When the right fasteners and sealants are used from the start, they provide long-term protection that holds up well beyond the initial installation, ensuring performance that lasts, not problems that surface later. 

Learn more about the hidden science of sealants, fasteners and flashings and how getting these details right from the start can mean decades of reliable, weathertight performance!