How Roof Shingles Should Be Installed, And How to Tell If Yours Weren't

Most homeowners never watch their roof go on. You leave for work, you come back, there are new shingles up there and the yard is clean. Whether it was done right is something you find out in year three, or year twelve, or the first time a real storm comes through.

This is what actually happens on a correct shingle installation, in order, and what it looks like when a step gets skipped. You are not going to install your own roof after reading it. But you will be able to ask a roofer the two or three questions that separate the ones who do it properly from the ones who do it fast.

It starts with tearing everything off

The old roof comes off down to the wood. All of it.

Roofing over an existing layer is legal in most of Pennsylvania and it is the single biggest corner a roofer can cut. It saves a day of labor and a dumpster. It also traps heat against the new shingles, adds weight the framing was never designed to hold, hides whatever is rotting underneath, and voids most manufacturer warranties the day it is finished.

If a bid comes in noticeably cheaper than the others, this is usually why. Ask directly whether it includes a full tear-off.

The decking gets inspected while it is bare

This is the only moment in a roof’s life when anyone can see the wood. A good crew walks it, finds the soft spots, and replaces them.

Rotted decking is the one line item nobody can price accurately up front, because it is invisible until the old roof is off. An honest bid handles it as a per-sheet cost rather than pretending it will not happen. If your roofer never mentions decking at all, they are either planning to nail over whatever they find or planning to surprise you with an invoice.

Ask for photos. We send them from the roof before anything goes back down.

Ice and water shield goes on first, at the edges

This is the layer that matters most in this climate and the one most often minimised.

Ice and water shield is a self-adhering membrane that sticks directly to the decking and seals around any nail driven through it. It goes along the eaves, up the valleys, and around chimneys and skylights.

Here is why it matters here specifically. Snow melts on a warm roof, runs down to the cold overhang past the heated part of the house, and refreezes. That ridge of ice dams up more meltwater behind it, and the water sits there and works its way back up under the shingles. Shingles shed water travelling downhill. They do nothing at all against water travelling uphill. Only the membrane stops that.

Code in most of our area requires it to a set distance up from the eave. Cheaper crews do exactly that minimum. We run it further, and through every valley, because an ice dam has never once consulted the code minimum.

Then underlayment across the rest

Synthetic underlayment covers everything the ice and water shield did not. It is the secondary barrier, the thing keeping the deck dry if wind drives rain up under a shingle.

Felt paper is the older option. It is cheaper, it tears when crews walk on it, and it wrinkles when it gets damp, which telegraphs through the finished shingles as visible lines across the roof. Synthetic costs slightly more and does none of that.

Drip edge, then flashing, then shingles

Drip edge is the metal strip along the eaves and rakes that kicks water out into the gutter instead of letting it curl back underneath and rot the fascia. It is inexpensive and it is skipped constantly.

Then the flashing. Everywhere something comes through the roof, a chimney, a plumbing vent, a sidewall, a skylight, gets new flashing. Reusing old flashing is the most common reason a brand new roof still leaks.

Chimneys specifically need step flashing woven into each shingle course as it goes up, plus counterflashing cut into the mortar joint above it. If someone runs a bead of black tar around your chimney and calls it flashed, it will crack inside two seasons and you will be exactly where you started.

Only then do shingles go on, beginning with a proper starter course along the eave. A starter strip has its adhesive along the bottom edge, positioned to grab the first row and stop wind getting under it. Cutting up regular shingles to use as starter puts that adhesive in the wrong place, and the first row is precisely where wind attacks.

Nailing is where most failures actually happen

Every shingle has a nail line printed on it. Four nails per shingle in normal conditions, six on steep pitches and in high wind areas. They go in that line, driven flush. Not angled, not sunk through the mat.

Two things go wrong here, and both are invisible from the ground once the next row covers them:

Nailing too high. Driving nails above the line means the row above does not overlap them, so each nail head sits exposed under a shingle instead of clamped between two. It is faster, because the installer does not have to aim. It is also why some roofs lose shingles in a storm the house next door shrugs off.

Overdriven nails. A nail gun set too hot pushes the head straight through the shingle mat. The shingle is now hanging on a hole.

Neither is something you can inspect afterwards. It is a reason to care who is physically on your roof, beyond whose name is on the truck. Our crew works for us and nobody else, and Justin is on site while they work, which is the only quality control in this trade that actually functions.

Ridge vent last

The ridge gets cut open and a vent runs along the peak. Paired with soffit intake down below, that moves air continuously through the attic.

Skip it and the attic cooks. Heat builds under the deck and bakes the shingles from underneath, and in winter that warm deck melts snow which refreezes at the cold eaves and makes ice damming worse. Bad ventilation will take a thirty-year shingle down to fifteen, and void the warranty on the way.

What you can check yourself from the ground

Once the crew has gone, walk the perimeter and look for:

• Straight courses. Shingle rows should run parallel to the eave. Waves or drifting lines mean nobody snapped chalk lines.
• Metal at the edges. Drip edge should be visible along both the eaves and the rakes.
• Clean chimney work. New metal stepped into the shingles, not a smear of tar.
• A vent along the peak, rather than a couple of box vents near the top.
• Nails in your driveway. There should be none. We run a magnet over the whole yard, and cleanup comes up in our reviews more than anything else we do.

Then in the attic, on a bright day with the lights off: no daylight anywhere except the vents, and no damp on the underside of the deck after rain.

Should you shingle a roof yourself?

For a shed or a detached garage, with a helper and no fear of heights, it is a reasonable weekend project.

For a house, no, and the reason is not difficulty. It is that roofs only ever fail at the details, and the details are the flashing, the valleys, the nailing pattern and the ventilation. Those take years to learn and minutes to get wrong. The shingles themselves are the easy part.

Beyond that, a self-installed roof carries no manufacturer warranty and no workmanship warranty, and any insurance claim later becomes a much harder conversation.

If you want someone to look at yours

We have been putting roofs on across Beaver, Butler, Allegheny and Lawrence counties for thirty years, roughly two thousand of them. Justin does every inspection and writes every bid himself, and if your roof has a few good years left in it, that is what he will tell you.

The estimate is free and often same day. Call or text (724) 494-5614, or send a photo of whatever is bothering you and we will tell you what we are looking at.