Why the Nails in Your Shingle Bundle Can Rust Before the Shingles Do

Most homeowners never see the nails on their roof. They sit under the course above, and they stay put for as long as the roof does. That is why the coating on a nail gets so little attention. In St. Louis the coating does real work, because the fasteners go through a freeze and thaw cycle that wets and dries the metal several times each winter. A nail that rusts early can leave a stain on the shingle face and lose some of its grip long before anyone looks up at the roof.

What the coating is protecting

A roofing nail is a short steel shank with a head. Steel rusts when water and oxygen reach it, and the coating is the barrier that slows that down. Two coatings show up often on asphalt shingle nails. Hot-dip galvanized nails carry a thick zinc layer bonded to the steel. Electro-galvanized nails carry a thinner zinc layer applied by a different process. Stainless steel and other specialty finishes also exist, and they cost more. The difference matters because the zinc is the sacrificial layer. Once it wears through at the head or along the shank, the steel underneath begins to corrode.

The nail does not need the same protection everywhere. Most of the shank is sealed inside the shingle layers and the deck, so it stays dry. The head sits under the course above, but moisture still reaches it at cut edges, along the rake, near the ridge, and wherever wind drives water under the edge of a shingle. Those are the places where a coating gets tested first, and they are also where a failed head shows up as a rust streak running down the shingle.

Why freeze and thaw matter here

St. Louis winters do not hold a steady cold. A warm spell lets snow melt on the south slopes, the meltwater runs toward the eave, and then a hard freeze locks it in place. Each freeze and thaw cycle pushes moisture into small gaps and holds it against the metal. Ice damming at the eave adds another source of wet, because the water that gets past the ice sits right against the lowest row of nails. A coating that is thin at the head ages faster under those conditions than the same nail on a shaded north slope that stays drier.

Hail adds a different risk. A hit that breaks a tab can leave a nail head bare, and a bare head starts to rust sooner than the coated shank around it. The spot is small, but it is a spot where rust can start. When a crew inspects or repairs a roof after a storm, the fastener condition at the damaged area is worth noting along with the shingle surface, so the record shows what was found and where.

Material and spec

Nail length matters as much as coating. A nail that is too short will not reach far enough into the deck to hold, and one that is too long can penetrate the deck and show through on the attic side. The right length depends on the thickness of the shingles, the underlayment, and the sheathing under them. The roofer should state the length for your job, not just say roofing nails. Ring shank nails are common for asphalt shingles because their grooves grip the wood, but that is a separate question from the coating.

Stainless nails cost more and are less common on a standard asphalt roof. People ask about them when they want a fastener that will not rust at all, and they make sense on some jobs, such as roofs with exposed metal trim where rust stains would show. For a plain asphalt roof, a properly galvanized nail is the usual choice. The real question is whether the coating is the one the product's installation instructions call for, and whether the quote names it.

Keep in mind that shingle nails are not the only fasteners on the roof. Drip edge, starter strip, and flashing each use their own fasteners, and those pieces carry their own coatings. Ask about all of them, not only the nails in the shingle field. A coating that suits the shingle nail can still be the wrong choice for a drip edge fastener driven along the same eave line.

What it costs

The price difference between a standard galvanized coating and a heavier one is usually a small line on a roof quote, but it is still a line item, and it should be visible. Quotes sometimes fold fasteners into a general materials figure, which makes it hard to tell which coating was priced. Ask for the fasteners to be listed separately, with the coating and the quantity. That way a change in fastener shows up on paper before the crew starts, and you can see whether the price moved with it.

Fastener quantity is worth asking about too. A roof is priced by the square, and the number of nails per square depends on the nail pattern the product calls for. If the quote says nothing about fastener count, you cannot check whether the crew loaded what was priced. This is a small detail, but it is one that separates two quotes that otherwise look alike on the first page.

What to ask

• Which coating is on the nails, written on the quote, and does it match the installation instructions for the shingle product on your roof?
• What is the nail length for this deck and underlayment, and who checked it against the sheathing thickness?
• Are the drip edge, starter and flashing fasteners on their own lines, with their own coatings and quantities?
• If a nail head is exposed by a cut or a torn tab, what does the crew do before the next row goes on?
• Will you receive photos of the nails in a cut section, at the rake, and at the ridge once the roof is finished?

If Keys Roofing is the contractor on your job, call the office at (314) 220-2333 and ask that the fastener line appear in the written scope. The scope with its photos and measurements is what you keep, and it is the record that shows which nail went into your roof and what coating it carries.