A Deeper Dive: Backnailing
A Closer Look at a Confusing Term
Have you ever come across a term that seems more confusing than helpful? That was my reaction when I ran into “backnailing” while scanning a list of inspection definitions. I knew the concept—but the word raised more questions than it answered. So I decided to take a closer look, not just at the term itself, but at how much words really matter when you’re inspecting a roof.
___
Every so often, a term pops up that seems like it should clarify something—but instead makes me pause. Today’s example? Backnailing.
I was scanning through a list of inspection-related definitions when this one caught my eye. At first glance, it looked straightforward:
A technique used in flat roof installation where the rear edge of roofing membrane sheets are secured with nails or fasteners before being covered by the next overlapping sheet…
Seems simple enough, right? But the more I thought about it, the more questions I had. Is this a term that home inspectors really need to know? Is it even used consistently in the trades?
I decided to dig deeper.
One Word or Two?
Even the spelling is unsettled. You’ll find it written as both backnailing (one word) and back-nailing (hyphenated). The hyphenated form shows up in some formal glossaries, but many construction pros—especially those writing from the field—favor the single word.
And that makes sense. In construction terminology, compound words like backfilling, reflashing, and underlayment tend to lose their hyphens over time as they become part of everyday vocabulary. Following that pattern, I lean toward backnailing as the more natural form.
Still, don’t be surprised if the internet hasn’t made up its mind yet.
Expanding the Definition
Once I started looking around, I noticed that some sources were using backnailing to refer not just to flat roofs, but to all kinds of roofing situations. That got me wondering if the term originated in one specific context—say, torch-down or membrane roofing—but has since been borrowed and adapted by people applying it more broadly.
That wouldn’t be the first time a trade term took on a life of its own.
And then there’s this: I’ve done roofing. Years ago, while working on my father’s house, I learned how to lay shingles the same way many people do—by reading the diagrams and instructions printed on the paper wrapped around each bundle of shingles. Nail placement, overlap — it was all there. But I never saw the word backnail.
So I started asking myself: Is this term actually useful to a home inspector? Or is it only meaningful when something goes wrong?
When the Nails Show Themselves
Here’s the catch: if a flat roof is properly backnailed, you won’t see the nails at all. They’re hidden beneath the next layer of membrane. So knowing the term doesn’t necessarily help unless you're dealing with a defect.
But when backnailing is done poorly—when fasteners are placed too close to the edge or left exposed—you get a visible condition that matters. That’s when it becomes more than just a technical term—it becomes part of your report.
Let’s call that condition what it is:
Exposed Fasteners (Flat Roofing)
A defect in flat roof installation where fasteners intended to be covered by overlapping membrane sheets remain visible. These exposed nails or screws compromise waterproofing, creating potential pathways for water entry. The condition may result from installer error, poor measurements, membrane shrinkage, or lack of overlap. Even if these fasteners have been sealed with roofing cement or caulk, they remain a sign of substandard installation and may contribute to premature roof failure.
So if the nail is in the general vicinity of where a backnail should be—but isn't adequately covered by the next sheet—it’s still called backnailing. Just improper backnailing. And if it’s visible? It’s your job to recognize the risk and report it, no matter what the installer intended.
Don’t Let the Word Get in the Way
Here’s the takeaway: You don’t need to know the word “backnailing” to be a good inspector.
You need to:
Recognize visible conditions (like exposed fasteners)
Understand why they matter (water intrusion, reduced service life)
Communicate clearly and usefully (without burying the client in jargon)
Technical terms can help when you’re talking to roofers or writing training materials. But when you’re on a roof—real or metaphorical—what matters most is what you see, what it means, and how you explain it.
So if you’ve never used the term backnailing before, don’t worry. If you’ve ever spotted exposed fasteners on a flat roof and recognized them as a problem, you already know what matters.