When you picture a roof, you picture shingles. That's natural — they're the part you see. But here's a truth that separates a roof that survives Maine winters from one that leaks: the shingles are really just the raincoat. The layer underneath them is the wetsuit — the last, waterproof line of defense when ice and water try to sneak past. Skimp on that hidden layer and it won't show on installation day. It'll show in February, as a stain spreading across your bedroom ceiling.
What underlayment actually does
Underlayment is the protective sheet installed over the bare wood deck, beneath the shingles. It's a secondary barrier: if wind-driven rain or melting snow ever gets past the shingles, the underlayment is there to stop it from reaching the wood and your home. It comes in traditional felt or modern synthetic versions — synthetic is generally lighter, tougher, more tear- and water-resistant, and lies flatter, which is why many roofers favor it. Either way, it's a quiet, essential layer most homeowners never knew was doing so much work.
Ice-and-water shield: the Maine essential
This is the one that matters most up here. Ice-and-water shield is a self-adhering, fully waterproof membrane installed at the roof's most vulnerable spots — the eaves, the valleys, around penetrations. It actually seals around the nails driven through it. Its job is to stop the specific villain of a Maine winter: the ice dam.
How ice dams attack — and how the shield stops them
Heat escaping into your attic melts snow on the roof. That water runs down to the cold eaves, refreezes, and builds a dam of ice. Water then pools behind the dam and, with nowhere to go, works its way up and under the shingles — where ordinary roofing can't stop it. Ice-and-water shield is the sealed, waterproof barrier that blocks that backed-up water from ever reaching the deck and your ceilings.
Want a roof built for Maine winters — not just for looks?
We install proper underlayment and ice-and-water shield as standard, because up here it's not optional. Get a free, honest estimate and see exactly what goes into your roof.
The corner cheap roofs love to cut
Here's why this article matters when you're comparing quotes. Because underlayment and ice-and-water shield are invisible once the shingles go on, they're exactly what a lowball bid quietly skips or minimizes to hit a cheaper number. You'd never see it — until the damage does. When you compare roofing estimates, ask specifically about the underlayment and how much ice-and-water shield is included, and where. A roof that's fully protected at the eaves and valleys costs a little more and saves you from the far larger cost of water inside your home.
It's a system, not a single layer
One honest point to close on: no single layer makes a roof watertight by itself. A great roof is a system — shingles, flashing, underlayment, ice-and-water shield, and proper attic ventilation and insulation, all working together. The membranes stop water that gets through; good ventilation and insulation reduce the ice dams in the first place. Get the whole system right, installed properly, and your roof shrugs off the worst a Maine winter can throw at it. That's what we build, every time.
"After years of ice-dam leaks with our old roof, they explained exactly what was missing and did it right. Two brutal winters later, not a drop inside. Worth every penny."
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Frequently asked questions
What is roofing underlayment?
A protective layer over the wood deck, beneath the shingles, providing a secondary barrier against water. It comes in felt or synthetic versions and is a big part of keeping a roof watertight.
What is ice-and-water shield and why does Maine need it?
A self-adhering waterproof membrane at the eaves and valleys that seals around nails and blocks water backing up from ice dams. In Maine's climate it's one of the most important defenses against interior water damage.
Is synthetic underlayment better than felt?
Synthetic is generally lighter, stronger, more tear- and water-resistant, and lies flatter. Many roofers prefer it, though quality installation matters most.
Can you skip ice-and-water shield to save money?
It's a common corner cut on cheap roofs — and a costly one in Maine, where ice dams can drive water under the shingles. Don't let a low bid leave it out.
Do these prevent all leaks?
They dramatically reduce the risk, but a watertight roof is a system — shingles, flashing, ventilation, and membranes together, all installed properly.
This article is general guidance. Proper materials and placement depend on your roof and code — ask your roofer what's included in your system.