Alright, so here’s the thing nobody really talks about – your shingles? They’re kinda drama queens. You think they’re the tough guys up there taking on the sun, rain, sleet, and the occasional suicidal squirrel, but actually, they’re delicate. Like, deceptively delicate. The real MVPs? The stuff hiding under them. That boring, unsexy layer nobody brags about – the underlayment.
And believe it or not, picking the wrong one can wreck your roof faster than your cousin Greg wrecked his marriage with a karaoke mic and three whiskey sours.
Felt, Synthetic, or Some Frankenstein in Between?
Felt paper. The OG. People used it for decades. Some still swear by it, like those folks who won’t stop wearing cargo shorts. It’s like… fine. It works. Until it doesn’t. It tears kinda easy, gets soggy faster than a bowl of Corn Flakes left out on the porch, and if you leave it exposed during install for a couple days, it starts peeling like sunburn.
Synthetic underlayments came along acting like they were the answer to all problems. Some of them are – actually pretty decent. Strong, lighter, don’t absorb water like felt does. But then again, there’s like… a million brands. And half of them slap on some branding and charge you like it’s made from alien polymer found at Area 51. Nobody really regulates that stuff too tight. You might get gold, or you might get a glorified trash bag stapled under your shingles.
I remember this one job, guy insisted on the cheapest synthetic he could get. Said, “It’s all the same anyway, right?” Two summers later, I get a call. Water stains on the ceiling. Shingles looked fine. But peel one back? Underlayment had split like a cheap wallet. Probably from UV exposure during install. Moral of the story? The hidden stuff counts.
Roof underlayment is the roofing component installed directly over your roof decking. It lies between the decking and your asphalt shingles to provide an extra layer of protection from the elements. There are two types of roof underlayment for asphalt shingles: felt underlayment and synthetic underlayment. So, before we get to one which underlayment is best for asphalt shingles, you need to know the difference between the two types. Felt underlayment is the older of the two and comes in 15 lb and 30 lb rolls. The big difference between the two types of felt underlayment is that 30 lb is thicker, stronger, and less likely to tear than 15 lb.
https://www.billraganroofing.com/blog/best-type-underlayment-asphalt-shingles
Breathability vs. Waterproofing: A Loveless Tug-of-War
Here’s where folks get twisted. Some think underlayment should breathe. Others want it sealed up tighter than grandma’s Tupperware. And both kinda make sense, which is the annoying part.
Too breathable? Moisture from inside your attic might get out, sure, but rain that sneaks past your shingles can just… sit there. Making a tiny mold party. Too sealed? That moisture from inside can’t escape. Condensation starts forming like the inside of a cold Coke can. Either way, your wood deck ends up all swollen and sad.
There ain’t really a perfect answer. Depends on your climate. Dry places like Arizona? You might want breathability. But if you’re in the Carolinas with sideways rain three times a week and humidity that makes your pants stick to your thighs – go waterproof. Or try some hybrid and just hope the roof gods are kind.
Roofing underlayment is a barrier material that’s typically installed directly onto your roof deck. Depending on how your home was constructed, the skeleton of your roof is made up of rafters or trusses. The roof deck, also sometimes called roof sheathing, might be: Plywood, OSB, or Step sheathing. These boards are fastened onto the rafters or trusses to help stabilize the rafters or trusses and give structure to the entire roof.
https://www.owenscorning.com/en-us/roofing/blog/how-roofing-underlayment-helps-protect-your-home
Slippery Slopes and Sticky Situations
I once saw a guy eat it hard – like, cartoon banana peel hard – on a synthetic underlayment that had zero grip. It was windy, he had a bundle of shingles on his shoulder, and he went flying like a chicken with a rocket strapped to its back. Landed in a rose bush. True story. Walked it off somehow.
Point being – some underlayments are slick as ice. That’s not great if you’re, you know, a person walking on a roof. But also, when shingles go on top of something that slick, sometimes they don’t seal down right. Over time, that lets wind wiggle ‘em. And guess what? Wind loves a loose shingle. One tugs up, next storm peels it like Velcro. You got a leak. Maybe a family of raccoons moving in. It spirals fast.
The purpose of the shingle underlayment is to provide an additional moisture-resistant layer to back up your roof shingles. For many years, “felt-paper” served as the leading type of shingle underlayment. As continual improvements in the building materials industry came about, synthetic underlayments emerged as the preeminent underlayment material used today. Though pricier than felt, synthetic underlayments are lighter in weight, better at lying flat (which prevents ‘wavy’ shingle installations) and offer superior water resistance – so much so that the high end synthetic underlayments can serve as temporary, short-term roof covers.
https://www.certainteed.com/inspiration/projects/what-shingle-underlayment-and-how-does-it-help-protect-my-home
High Temp, Low Tolerance
Roofs bake. Like, literally cook. Black shingles on a 90-degree day? Surface temps can hit 160°F easy. If your underlayment starts melting at those temps — and yes, some do — you’ll get sticky messes, chemical smells, maybe even bubbles under the shingles. Bubbles! Like pizza crusts. Only way less tasty.
So if you’re somewhere that gets hot — Texas, Nevada, Death Valley, or just anywhere the sun hates you — get high-temp-rated underlayment. It ain’t a suggestion. It’s survival.
Also, PSA: metal roofs especially need underlayments that can take heat. That’s like putting aluminum foil in the oven. Stuff gets real spicy under there.
Ice Dams and That Whole Frozen Nightmare
In the North, where roofs suffer like unpaid interns during winter, underlayment choices can make or break things. Ice dams form, water backs up under the shingles, and bam — leaks that don’t show up until spring, when your ceiling suddenly looks like a tie-dye shirt.
There’s special stuff for this. Ice and water shield. It’s sticky, thick, and clings to your deck like an ex who won’t let go. But in a good way. You lay it at the edges, in valleys, around chimneys — basically the weak spots. It buys you time. Without it, even the best shingles are toast once that ice creeps up.
Saw a job once where the homeowner thought skipping it would “save some bucks.” February came, snow hit, then melted, then froze again. Ceiling collapsed in the nursery. Baby was fine, but their cat went missing for two days. Turns out it had crawled inside the drywall. So, yeah. Spend the $200 on ice shield.
Does It All Really Add Up?
Short answer? Yes. Long answer? Hell yes, but not always in ways you can predict. Some underlayments last decades. Others, they give up after one bad storm. And it’s not like you can check on them. Once the shingles go on, it’s a closed coffin. You hope it’s okay in there, but you don’t really know until stuff starts leaking or creaking.
And by then? It’s too late. Nobody wants to pull off a whole roof to fix what’s under it. It’s like trying to change your car’s axle without removing the tires. Painful, expensive, and makes you question every life choice that led to this point.
So yeah. Pick your underlayment like you’re choosing a co-pilot for a space mission. You want reliability, no drama, and preferably something that won’t burst into flames or dissolve in water. Simple.
Or just ask the guy who’s been on a roof in 115-degree heat with a hammer in one hand and regret in the other. He’ll tell you. The shingles get the glory. The underlayment does the work. Treat it right, and your roof won’t betray you.
Probably.