Roofers earn their keep in the details. Shingles get the glory because they are visible from the curb, but the layer beneath them determines whether the system survives wind, heat, and sideways rain. Underlayment is the roof’s safety net and its daily workhorse. Choose it poorly and you court callbacks, insurance headaches, and early roof shingle repair. Choose it well and shingle roof performance jumps, you gain install speed, and homeowners see fewer problems over the next two decades.
What follows draws on years installing, repairing, and inspecting shingle roofs in different climates. The goal is practical guidance. You’ll find how each underlayment performs, where it succeeds, where it frustrates, and how to match it to roof shingle installation, repair, or replacement scenarios.
What underlayment actually does
Strip the marketing away and underlayment has four jobs. It manages liquid water that gets past the shingles, resists wind-driven rain during storms, protects the deck from UV and weather exposure during the build, and supports shingles against abrasion and sap bleed from the deck. On steep-slope roofs with asphalt shingles, the underlayment also plays a role in fire classification. A typical shingle roof relies on underlayment to remain watertight during installation and in those moments when ice dams or wind temporarily defeat the shingles.
Underlayment is not a magic membrane that substitutes for correct flashing. Even the best peel-and-stick is a dead loss if valley metal is sized wrong or step flashing laps the wrong way. I have seen pristine self-adhered membranes undercut by a single missed kick-out flashing at a wall. Underlayment buys margin, not immunity.
The main families of underlayment
Most residential shingle roofing uses one, or a combination, of these four categories.
- Asphalt-saturated felt Synthetic underlayments Self-adhered ice and water barrier Specialized high-temp membranes
That is enough taxonomy. The rest of this article looks at how each type behaves on an actual roof, with attention to climate, pitch, and budget.
Asphalt-saturated felt: the old reliable, with caveats
Felt, often called “tar paper,” has been used for generations. It comes in 15-pound and 30-pound designations, though the nominal weight has drifted over time. The thicker grade offers better tear resistance and slightly more cushion underfoot. On budget-driven roof shingle replacement jobs in mild climates, 30-pound felt remains a workable choice.
Pros that matter on site: felt lies flat on clean plywood, it is inexpensive, and it tends to be forgiving under hand nailing. Shingles seat nicely on it because the surface has bite. Felt also provides a modest vapor brake, which can help when you have conditioned attic spaces with accurate ventilation.
The downsides matter in wind and heat. Standard felt tears at fasteners when a gust hits an open deck. Once wet, it wrinkles and “telegraphs” through shingles, leading to hump lines that customers notice. Prolonged UV exposure during a weather delay dries it and makes it brittle. I have seen felt sheets go from taut to potato chip within a week of July sun. It can also become slick under frost or dew. If your crew is working on a steep 10:12 in spring, that slickness on an early start demands attention.
Use felt where budget controls the job, the install can proceed without long delays, the deck is flat, and the climate is moderate. Avoid it for coastal wind zones, high-altitude UV, and complex roofs where water management is tricky.
Synthetic underlayments: light, tough, and not all equal
Synthetics have become the default for many shingle roofing contractors because they are light, strong, and stable. Typical products use woven or spun polypropylene with a textured walking surface. A single roll often covers four to ten squares, so you move fewer rolls up the ladder and reduce seams.
The best synthetics impress for what they do during the install. They resist tearing when wind grabs a sheet. They hold fast at cap nails, letting you dry-in a big section before storms. They also shrug off a few weeks of UV without curling or chalking, which builds schedule breathing room. That stability keeps lines straight and shingles sit flat. If you have ever had to explain stair-step humps to a homeowner, you’ll appreciate this.
The caveat is slipperiness. Some synthetics deliver grip as advertised; others skate like ice when wet or dusty. Read the fine print and test a new roll on a small area. Crews quickly develop preferences. I have one foreman who swears by a heavier gauge synthetic with a grippy emboss because it feels like sandpaper under boots. Productivity rises when the crew trusts their feet.
Another difference hides in the temperature rating. Standard synthetics are fine under asphalt shingles on vented decks. When the roof sees high temperatures, such as over unvented cathedral assemblies or under metal details, you need high-temp rated products to avoid adhesive bleed or deformation.
Choose synthetics for most shingle roof replacement jobs, especially in windy, variable weather regions. They shine on larger footprints where speed and clean layout save hours. On complex roofs with many penetrations, their tear resistance around pipe boots and dormer cuts also pays off.
Self-adhered ice and water barrier: the belt and suspenders
Self-adhered membranes do two things other layers cannot. They seal to the deck and seal around fasteners. When ice dams form, melting water backs up under the shingles and over the laps. A peel-and-stick membrane arrests that water at the deck, keeping it from finding nail holes. In valleys and low-slope transitions, that feature is worth the cost.
Code often requires ice barrier from the eave to a minimum of 24 inches inside the warm wall, measured horizontally. On typical overhangs and a 6:12 pitch, that can mean two courses. The same material belongs in valleys, along rake edges in extreme wind zones, and around chimneys and skylights. I also run it at dead valleys behind dormers because that is where leaks start after heavy, wind-driven rain.
There are two flavors: standard and high temperature. Standard SBS-modified asphalt membranes have served for decades. High-temp versions raise the softening point so they do not ooze under metal. Installers notice it when working in midsummer at the eaves, where dark drip edge can bake the membrane. On black roofs in southern zip codes, high-temp at the eave line and valleys avoids tar bleed, which can stain gutters and fascia.
Self-adhered membranes cost more and require cleaner decks. Dust, frost, and resin pockets reduce adhesion. On older plank decks with gaps and knots, use primer where needed and bridge gaps properly. Be mindful that once stuck, it is stuck. Plan your overlaps and avoid fishmouths that can telegraph through shingles.
Specialized high-temp membranes: when heat builds
Beyond standard ice barrier, some roofs demand high-temp underlayment across the field. Think dark shingles on unvented insulated assemblies, low-pitch roofs near the minimum allowed for shingles, and south-facing slopes that cook all afternoon. Temperatures at the deck can exceed 200 degrees Fahrenheit under some conditions. A membrane not rated for that will soften, slide, and potentially bond shingles in unintended ways.
If you are working in the Southwest or Gulf Coast and the attic ventilation is marginal or sealed, consider a high-temp synthetic underlayment for the field and high-temp self-adhered at critical zones. It is not hype. I have lifted shingles on five-year-old roofs in Phoenix and found standard synthetics brittle and powdery at the laps. A minor cost bump at install would have prevented it.
Matching underlayment to roof pitch
Pitch changes the water game. On a 4:12 roof, water moves slower and wind can lift edges. Manufacturers often require double coverage of underlayment at lower pitches, sometimes with cemented laps. On 2:12 to 4:12, follow the shingle maker’s instructions to the letter. Even a good synthetic needs generous overlap to resist capillary action. I prefer a continuous self-adhered layer on 3:12 sections, then standard synthetic above. That hybrid handles splash and driven rain without slowing the crew on the steeper portion.
On steep slopes, the priority shifts to walkability and tear resistance. Lightweight synthetics can feel like a drum. When the wind gets under them during staging, they rip around fasteners. A thicker synthetic with a textured face and cap nails at the right spacing holds up. Felt is serviceable on steep slopes if installed tight on a calm day, but you must button it down with caps, not staples.
Climate and regional considerations
Snow belts punish eaves. The ice dam question is not whether you get one, but how big and how often. Use self-adhered ice barrier from eave past the warm wall line, wrap valleys, and consider an extra strip along the rakes if the home sits in a drift path. Ventilation and insulation still matter most, yet the membrane buys time when life and weather outpace building science.
Coastal and hurricane regions prize wind uplift resistance and storm resilience. Synthetics paired with ring-shank nailing on shingles raise your wind rating. Add peel-and-stick along eaves and rakes, and at ridges in high exposure zones. I have seen ridge cap peel in gusts over 100 mph while a high-temp membrane underneath kept the deck dry until a temporary patch.
High UV locations like high plains and mountain towns need underlayment that tolerates exposure. Synthetic with 60 to 180 days UV rating helps when inspections, rain delays, or logistics push shingle day. Felt loses this race. In August sun at elevation, felt can fail in a week.
Hot-humid regions challenge adhesives and compounds. Choose high-temp variants and read the chemical compatibility notes. Some solvent adhesives for drip edge can attack certain membranes. Store rolls https://manuelvpbf081.image-perth.org/top-myths-about-roof-shingle-installation-debunked in shade, not in the truck bed. Heat-soaked rolls become gummy and difficult to unroll without fishmouths.
Decking matters more than many think
Underlayment performance starts with the deck. Plywood grips adhesives better than some OSB faces, although modern membranes stick fine to both if clean and dry. Old plank decks need work before you stick anything to them. Drive protruding nails, replace split boards, and fill gapped areas with plywood overlay if gaps exceed recommended widths. On one shingle roof repair over 1x plank in a 1920s bungalow, half an hour spent setting nails and vacuuming sawdust saved us a day of chasing blistered peel-and-stick.
Primers can make or break adhesion in cold weather. Most self-adhered ice barrier products specify a lower limit for deck and ambient temperature, often around 40 degrees Fahrenheit. Below that, primer helps. Do not try to beat physics. If the deck surface is frosted, adhesion will be unreliable no matter what label says. Wait for sun or use temporary synthetic and return for peel-and-stick.
Fasteners and laps: small choices, big outcomes
Cap fasteners matter. Plastic caps distribute load and prevent tear-through in synthetics and felt. Staples leave crescent cuts that tear under gusts. If you want to keep a dry-in intact overnight, use cap nails at the manufacturer’s pattern. On high ridges, tighten the spacing. Yes, it takes minutes longer. It saves hours after a squall.
Laps need to follow the printed guide lines. On synthetics with grid patterns, align fights wrinkles, which makes shingle layout smoother. Sealant at laps is rarely required for synthetics but often specified for felt in low-slope areas. With self-adhered membranes, roll the laps with a weighted roller for a full bond. The extra step visualizes as a simple pass, but it seats the tack and stops micro-channels that can run water.
Where mixing products makes sense
A hybrid approach often wins. Run high-temp self-adhered membrane at eaves, valleys, sidewalls, and penetrations. Cover the field with a quality synthetic. Use 30-pound felt only in well-protected interior planes if budget is tight and weather is stable. This combination controls costs while guarding the known leak points. Inspectors like it, and crews can keep pace.
On complex roofs with multiple dormers, I often add peel-and-stick under the first three courses above roof-to-wall intersections. The extra three feet of insurance catches water that rides up under shingles when wind hits a gable end. On solarium tie-ins or cricket transitions, the additional membrane eliminates the tiny drips that lead to ceiling stains a year after a roof shingle replacement.
Performance under foot and crew safety
Nothing slows a job or risks health like slippery underlayment. The marketing language on the wrapper is not enough. Before committing a large order, lay a sample sheet on a test slope and walk it with the boots your crew uses. Dust from cutting shingles can turn even good surfaces slick. Establish a cleanup rhythm: blow off granules before laying the next run of underlayment or before staging bundles.
On cold mornings, frost on synthetics can be deceiving. A membrane with an embossed surface reduces the skating effect, but it is not a cure. In my crew, we start on sunny slopes first in shoulder seasons, then rotate. It keeps production up and knees intact.
Cost and value, not just price per roll
Homeowners see a material line item and balk. Explain that underlayment is not a commodity. For a typical 30-square roof shingle installation, upgrading from felt to a solid synthetic may add a few hundred dollars in materials. Self-adhered ice barrier at eaves and valleys adds a bit more. Compare that to the cost of one interior leak repair and repaint, or to the lost goodwill after a storm exposes a weak dry-in. The cost delta fades.
For the contractor, faster staging, fewer wind-tears during install, and fewer callbacks result in better margins. Synthetics can shave half a day on large roofs because you are not fighting wrinkles or replacing wind-torn felt. When amplified across a busy season, that time turns into extra jobs booked.
Warranty and code alignment
Manufacturers write warranties to their products and assemblies. Many shingle makers now package-system warranties that require specific underlayments. If you aim for enhanced wind or algae warranties, read the document. You may need a branded synthetic or high-temp ice barrier at critical areas. Inspectors likewise follow local amendments. Northern townships often mandate ice barrier to a certain line inside the warm wall. Coastal codes can require enhanced fastening schedules and peel-and-stick along rakes.
Documentation matters. Photograph the underlayment installation before shingles cover it. Capture laps, cap nail patterns, and the extent of ice barrier. Those images settle 99 percent of future questions during a roof shingle repair diagnosis.
Repair versus full replacement: adjust the playbook
On shingle roof repair jobs, the underlayment decision narrows to the immediate area. If you are opening a valley to chase a leak, switching to a full-width high-temp membrane during the repair is smart, even if the old roof used felt. Tie-in carefully: tuck the new membrane under the old underlayment upslope, and over it downslope. Stagger laps to avoid a straight water path. If the existing roof shows widespread underlayment failure, communicate the risk. Patch repairs on brittle felt can hold, but they are temporary in the grand scheme.
For roof shingle replacement, you have the chance to correct old sins. Upgrade ice barrier coverage, use a better synthetic, and straighten layout. Replace rotten decking and fix ventilation. A new underlayment will not save an attic that runs 140 degrees Fahrenheit all summer. Balanced intake and exhaust will.
Common mistakes I still see and how to avoid them
- Skipping cap nails. Staples rip out. Use caps at the specified spacing. Short ice barrier at eaves. Measure to the warm wall, not just a single course. Two courses are often needed. Wrinkled felt under three-tab shingles. Those wrinkles print through. If felt gets wet and buckles, cut relief slits, let it dry, and patch before shingles. Self-adhered membrane on dirty decks. Sweep, vacuum, and prime in cold weather. A little dust kills adhesion. Ignoring temperature ratings. Standard membranes under metal or dark shingles on unvented assemblies will creep. Use high-temp where heat builds.
A few brand-agnostic buying tips
Stick with underlayments that publish third-party test data for tear strength, UV exposure tolerance, and temperature range. Look for clear install instructions that match the jobsite realities you face, like permitted exposure days and cap nail patterns. Talk to your shingle supplier rep about which products play well together. Compatibility beats improvisation when a warranty is on the line. Finally, buy extra peel-and-stick for penetrations. Running out mid-dormer costs more in time than carrying an extra roll on the truck.
Installation rhythm that works
A clean flow reduces mistakes. Dry-in the eaves with self-adhered membrane first, including a starter strip along rakes if you are in a wind zone. Set valley membrane next. Then roll synthetic on the field, straight and tight, snapping a control line at the first course. Cap nail as you go; do not plan to return to fasten later. Stage shingles after the underlayment is fully secured and the forecast is your friend. When thunderstorms lurk, prioritize drying-in penetrations and transition points. That sequence has saved me more grief than any clever trick.
When to call a pro
DIYers tackle shed roofs with decent success, but whole-house roofs demand a practiced eye. If the roof has multiple intersecting planes, skylights, chimneys, or low-slope sections, a shingle roofing contractor earns their fee in details you do not see until the first bad storm. If you hire, ask to see photos from recent jobs showing underlayment coverage, not just final shingle glamour shots. Good contractors keep those images because they know how valuable they are.
Final thoughts from the field
The underlayment you choose should reflect climate, pitch, deck condition, budget, and the crew that will install it. No single product wins everywhere. If you work where ice builds, peel-and-stick buys you peace at the eaves and in valleys. If you fight wind and tight schedules, a robust synthetic underlayment pays for itself. Felt still has a place on simple, fair-weather projects with tight budgets, but its margin for error is thin.
When a homeowner calls about a ceiling stain after a nor’easter, the problem usually traces to one of three places: a missing or short ice barrier, a weak or torn underlayment seam in the field, or an unprotected transition at a wall or dormer. Invest your time and money in those zones. The shingles will look fine from the street. The underlayment is what keeps the house dry when it counts.
Express Roofing Supply
Address: 1790 SW 30th Ave, Hallandale Beach, FL 33009
Phone: (954) 477-7703
Website: https://www.expressroofsupply.com/
FAQ About Roof Repair
How much should it cost to repair a roof? Minor repairs (sealant, a few shingles, small flashing fixes) typically run $150–$600, moderate repairs (leaks, larger flashing/vent issues) are often $400–$1,500, and extensive repairs (structural or widespread damage) can be $1,500–$5,000+; actual pricing varies by material, roof pitch, access, and local labor rates.
How much does it roughly cost to fix a roof? As a rough rule of thumb, plan around $3–$12 per square foot for common repairs, with asphalt generally at the lower end and tile/metal at the higher end; expect trip minimums and emergency fees to increase the total.
What is the most common roof repair? Replacing damaged or missing shingles/tiles and fixing flashing around chimneys, skylights, and vents are the most common repairs, since these areas are frequent sources of leaks.
Can you repair a roof without replacing it? Yes—if the damage is localized and the underlying decking and structure are sound, targeted repairs (patching, flashing replacement, shingle swaps) can restore performance without a full replacement.
Can you repair just a section of a roof? Yes—partial repairs or “sectional” reroofs are common for isolated damage; ensure materials match (age, color, profile) and that transitions are properly flashed to avoid future leaks.
Can a handyman do roof repairs? A handyman can handle small, simple fixes, but for leak diagnosis, flashing work, structural issues, or warranty-covered roofs, it’s safer to hire a licensed roofing contractor for proper materials, safety, and documentation.
Does homeowners insurance cover roof repair? Usually only for sudden, accidental damage (e.g., wind, hail, falling tree limbs) and not for wear-and-tear or neglect; coverage specifics, deductibles, and documentation requirements vary by policy—check your insurer before starting work.
What is the best time of year for roof repair? Dry, mild weather is ideal—often late spring through early fall; in warmer climates, schedule repairs for the dry season and avoid periods with heavy rain, high winds, or freezing temperatures for best adhesion and safety.