What’s Under Your Shingles: Ice & Water Shield and Underlayment Explained

Shingles get all the attention because they’re what you see from the curb. But ask anyone who’s opened up a leaking roof: the layers underneath decide whether a Minnesota roof survives, and they’re also where cut-rate bids quietly save their money. Here’s what should be under your shingles and why it matters more here than almost anywhere else in the country.

Ice and water shield: the non-negotiable

Ice and water membrane is a self-adhering rubberized sheet that bonds directly to the roof deck and seals around every nail driven through it. Minnesota code requires it at the eaves, extending from the roof edge to at least 24 inches inside the exterior wall line, precisely because of ice dams. When meltwater ponds behind a dam and creeps under the shingles, this membrane is the last line of defense between that water and your ceiling.

Code is the minimum, not the target. On low-pitch sections, in valleys, around chimneys and skylights, and along walls where snow drifts pile up, we run additional membrane because those are exactly the spots we get called to fix on other people’s installs. When you compare bids, ask each contractor where the ice and water goes and how far up. The cheap bid usually stops at the legal minimum.

Underlayment: the backup plan for everything else

Above the membrane, the rest of the deck gets underlayment. For decades that meant asphalt-saturated felt paper, and some crews still use it because it’s cheap. We install synthetic underlayment instead: it’s dramatically stronger, doesn’t wrinkle when it gets damp, doesn’t tear out at the fasteners in wind, and holds up far better if weather hits mid-project. On a tear-off where the roof might sit exposed overnight, that difference isn’t academic.

Drip edge, starter strip, and the details

Metal drip edge kicks water off the roof edge into the gutter instead of letting it wick back into the fascia board. Starter strips give the first shingle course a sealed, straight anchor against wind. Neither costs much, and both are routinely skipped or reused on budget jobs. If your fascia boards keep rotting behind the gutters, missing or buried drip edge is the usual culprit.

None of this shows up in the curb-appeal photo, which is exactly why it’s worth asking about. When we quote a roof, the proposal spells out the membrane coverage, underlayment type, and edge metal by name, so you can compare apples to apples. Getting bids right now? See how we build a roof, or call (651) 565-1349 for a free estimate that puts the whole stack in writing.