On a Mount Lebanon roof, ice and water shield belongs along every eave, running from the roof edge to at least 24 inches past the inside face of the exterior wall. It also belongs in all valleys, around chimneys, skylights, vents and pipe boots, at roof-to-wall junctions, and on any low-slope section such as a porch or dormer roof.

That short answer covers most homes in the township. The longer answer depends on your roof’s pitch, your overhang depth, and how well your attic breathes. I’ve watched plenty of leaks show up in January on roofs that looked perfectly fine in July. Below, I’ll walk through where this membrane matters, where it’s wasted, and where installers get it wrong.

Why Mount Lebanon Winters Are Hard on Roof Edges

Our winters aren’t brutal. They’re indecisive — and that’s worse. A stretch of 38-degree afternoons followed by 22-degree nights sets up the exact freeze-thaw rhythm that builds ice dams.

Here’s what happens. Warm air escapes the attic, heats the roof deck, and melts the snow sitting on it. That meltwater trickles down toward the eave, which hangs out over cold outside air and never warms up. It refreezes there. Repeat this for a week and you’ve got a ridge of ice holding a pond of water behind it, sitting under your shingles.

Shingles shed water. They don’t hold it back. Once water sits still, gravity stops helping and capillary action takes over, pulling moisture up under the courses and into the deck. That’s the failure mode a self-adhered membrane is built to stop. Good roof leak protection starts with accepting that shingles alone won’t win this fight.

Where should you put an ice and water shield?

Think in zones, not in square footage. Every spot where water can pool, change direction, or meet an interruption is a candidate.

The eave measurement trips people up, so be specific with your contractor. The 24 inches is measured from the inside of your exterior wall, not from the gutter. On a home with a 24-inch overhang, that’s roughly four feet of coverage — meaning one 36-inch roll won’t do it. You need a second course, lapped correctly.

Where Should Ice and Water Shield Be Installed on a Mount Lebanon Roof?

Mount Lebanon housing stock changes the math. Many homes here date to the 1920s through the 1950s, and those roofs weren’t designed the way modern ones are. Deep eaves, steep pitches, cross gables, dormers stacked on dormers — beautiful from the street, complicated from a ladder.

Cape Cods and Tudors in the township often have finished attic space with knee walls. Insulation is thin at the perimeter, so heat pools right where the roof meets the wall. Those roofs need membrane well past code minimum, sometimes six feet up the slope. Dormer cheek walls deserve it too, since snow packs into those inside corners and stays for weeks.

Then there are the additions. A sunroom or family room tacked onto the back of a house creates a low-slope roof draining under a steeper one — a classic trouble spot. I’d cover the entire lower roof, no exceptions, and carry membrane up the transition wall. Anyone quoting ice and water shield Mount Lebanon homeowners can actually rely on should be pointing at these areas before you ask.

Should an ice and water shield cover the whole roof?

Usually, no. It’s an appealing idea — more protection sounds better — but full coverage creates a problem on a vented roof assembly.

The membrane is a vapor barrier. Put it under the entire deck and any moisture that gets into the sheathing from below has nowhere to go. Plywood stays damp, and over years that shows up as delamination or rot. You spent money to trap water in your roof deck.

There are exceptions. Roofs under 4:12 pitch, roofs with recurring leak history, and homes with unvented spray-foam attics can justify wall-to-wall coverage. Metal roofs and low-slope porches often get it too. Outside those cases, targeted coverage plus a quality synthetic underlayment across the rest is the better assembly.

Should an ice and water shield be nailed down?

The membrane bonds to the deck by adhesive, not fasteners. You peel the release film and roll it down, working from the low edge upward so each course laps over the one below.

That said, fasteners do enter the picture. Drip edge, starter course and shingles all get nailed through it — and that’s fine, because the modified bitumen seals around each shank. That self-sealing property is the entire point. In cold weather, some installers use a few cap nails at the top edge to hold a course while the adhesive grabs, which is acceptable if they stay high enough to be covered by the next lap.

What matters more is surface prep. Cold, damp, dusty or frosted decking kills adhesion. If the membrane isn’t fully bonded, it can tent under the shingles and channel water instead of stopping it. Any competent roof installation Mount Lebanon crew will warm and clean the deck rather than slap membrane onto whatever they find.

What are the common problems with ice and water shields?

The material rarely fails. Installation does. Here’s what I see most.

Wrong measurement at the eave. One 36-inch course on a deep-overhang home leaves the interior wall unprotected — exactly where leaks show up on your ceiling.

Overlaps running the wrong way. Laps have to shingle downhill. Reversed seams funnel water into the deck.

Trapped moisture. Full-deck coverage on an under-ventilated attic causes deck rot and condensation problems that homeowners often mistake for a roof leak.

Wrinkles and fishmouths. Air pockets telegraph through the shingles and eventually crack. Roll it flat, roll it slow.

Membrane instead of flashing. No amount of sticky underlayment replaces properly formed step flashing at a chimney or sidewall. It’s a backup layer, not a substitute for metal.

Attic Ventilation Changes Everything

Membrane manages the symptom. Air sealing and ventilation treat the cause. If your attic is leaking heat, ice will keep forming regardless of what’s under your shingles.

Look at your soffit vents. On older township homes I frequently find them painted shut, blocked by blown-in insulation, or missing baffles entirely. Fix the intake, add insulation at the perimeter, and roof temperatures even out. The University of Minnesota Extension’s guide to preventing ice dams explains the building science better than most contractor literature does.

Soffit condition also affects sequencing on a replacement project. If you’re weighing which component to tackle first, Should I Replace My Roof or Soffit First in Pittsburgh? covers that decision in detail.

What to Ask Before You Sign a Roofing Contract

Ask three questions and you’ll learn a lot fast.

First: how many courses of membrane at the eaves, and how did you calculate that? A real answer references your overhang. Second: which valleys, penetrations and wall junctions are included? Vague answers mean vague work. Third: will you photograph the underlayment before shingles go down? Reputable crews already do this, and those photos are worth keeping.

Also confirm the product is compatible with your shingle warranty. Mixing brands is common and usually fine, but manufacturer coverage sometimes depends on it. Get the specific product name in writing.

The Bottom Line

Ice and water shield is cheap insurance placed exactly where your roof is weakest. Eaves, valleys, penetrations, wall junctions, low slopes. Not everywhere — just everywhere that matters.

Get the measurements right, get the laps right, and pair it with an attic that breathes. Do that, and February stops being something you worry about.