A shingle roof lives or dies by what you cannot see. The underlayment, that thin sheet between the deck and the shingles, decides whether wind-driven rain sneaks in, whether ice dams become leaks, and whether you get a quiet roof that lasts or a noisy one that curls and fails before its time. After twenty years of climbing ladders and pulling tear-offs, I’ve learned that the underlayment decision shapes everything that follows, from the pace of roof shingle installation to warranty coverage and insurance claims. Not every product belongs on every house, and not every line on a spec sheet plays out the same once crews and weather enter the picture.
This guide unpacks how felt, synthetic, self-adhered membranes, and hybrid systems compare in real conditions. If you are planning shingle roofing on a new build, weighing a roof shingle replacement, or debating a shingle roof repair after a windstorm, the nuances below will help you choose underlayment with intention rather than habit.
What an Underlayment Actually Does
Underlayment is secondary weather protection. Shingles shed most water, but not all of it, especially under wind uplift, driven rain, or ice dams. Underlayment backs up the shingles, covering the deck seams and giving water a pathway to the eaves rather than into the house. It also solves smaller, less obvious problems:
- Temporary dry-in during staging and weather delays, buying a roofer a few days of grace if storms hit before shingles are set.
It smooths minor deck imperfections so shingles lie flatter. It controls resin bleed from wood. It bolsters fire classifications and sometimes improves sound attenuation. Local codes often require specific fire and wind performance, and manufacturers tie their shingle warranties to approved underlayment types and fastener patterns. All of that lives under the shingles, but it matters on inspection day and ten winters later.
The Big Four: Felt, Synthetic, Self-Adhered, and Hybrids
Most shingle roofing contractors choose from three primary categories and one mix-and-match approach.
Felt underlayment, often called tar paper, comes in 15-pound and 30-pound felt. It is made from organic or fiberglass mat infused with asphalt. The 15-pound version is lighter, cheaper, and more common on low-budget or short-term roofs. Thirty-pound felt is thicker, offers better resistance to tearing and wrinkling, and gives a bit more cushion underfoot. Felt remains familiar and forgiving, especially in cooler, dry climates. It can wrinkle if exposed to humidity or direct sun for long and tears easily in wind, which can slow a crew’s day when a gust lifts a partially fastened sheet.
Synthetic underlayment is typically a woven or spun polymer sheet, often polypropylene or polyethylene blends. It is strong for its weight, resists tearing, and stays flatter after rain, which means straighter shingle courses and less telegraphed wrinkles. Many synthetics carry high walkability ratings and come with printed alignment lines that improve layout. They vary widely. Some budget synthetics are slick when frosty, while premium products have gritty coatings that grab boot soles and tool bags. Synthetics usually can be left exposed longer, anywhere from two weeks to six months depending on the manufacturer, a real advantage on complex builds or during a wet season.
Self-adhered membranes, often called peel-and-stick or ice and water shield, are rubberized asphalt or butyl sheets with a release film. They bond to the deck and self-seal around nails, which matters where water pools or backs up. Typical use zones include eaves for ice dam protection, valleys, around chimneys and skylights, low-slope transitions, and rake edges in coastal wind zones. Full-deck coverage with self-adhered membrane turns the underlayment into a near monolithic moisture barrier. That can be a smart strategy on very low-slope shingle roofs, but it changes how the roof breathes and may require ventilation tweaks to avoid condensation issues.
Hybrid systems combine a base layer of felt or synthetic with peel-and-stick at the high-risk areas. This is the most common approach on quality residential work. You get the tear resistance and walkability of synthetic or the low cost of felt, plus the self-sealing performance where water finds trouble.
Underlayment and Slope: Where Code Meets Physics
Slope dictates how water behaves under shingles. The steeper the pitch, the faster water leaves, and the less work the underlayment must do. On lower slopes, water lingers and can find seams and nail holes.
Most building codes and shingle manufacturers treat 2:12 to 4:12 as low slope for asphalt shingles. Many require special installation methods here, such as two layers of felt overlapped in a specific pattern or a full layer of self-adhered membrane. Above 4:12, standard single-layer underlayment is typically acceptable with proper laps. Below 2:12, shingles are often not approved, and your best move is a different roof system.
In my practice, the sweet spot for cost and performance on 4:12 and above is a good synthetic underlayment across the field and self-adhered at eaves, valleys, and penetrations. On 3:12 and 4:12 slopes in snow country, I favor extended peel-and-stick coverage from the eaves to at least 24 inches inside the warm wall, often more. On 2:12 to 3:12, I lean toward a full peel-and-stick deck if attic ventilation is robust and the sheathing is dry. These choices ease callbacks for shingle roof repair later.
Climate Pressure: Heat, Cold, Wind, and Rain
Underlayment performance shifts with climate.
Hot sun changes everything. I have watched low-grade felt bake into alligator skin in three days of July sun, then telegraph wrinkles through an entire plane of shingles. Synthetics handle UV better and keep crews moving without the rush to cover. In the desert Southwest or Gulf Coast, I spec synthetics with higher UV exposure ratings and a lighter color to reduce heat buildup, especially when a roof shingle replacement spans multiple days. High heat can soften self-adhered membranes, making them difficult to walk on and almost impossible to reposition. It pays to stage peel-and-stick early mornings and keep roll lengths manageable.
Cold snaps punish slick surfaces and brittle materials. Felt gets stiffer but still grips boots dependably. Budget synthetics can feel like ice at dawn. Premium synthetics with a textured face improve traction considerably. With peel-and-stick, cold affects adhesion; most manufacturers specify a minimum installation temperature. When I have to install below that, we use primers and hand-roll seams aggressively.
Wind exposure reveals the difference between paper statistics and rooftop reality. On coastal jobs or hills where the gusts run fast, felt can rip off the deck before it’s fully nailed. We learned to use cap nails or cap staples on synthetics, spaced tightly along the edges, and to limit how much is rolled out ahead of shingling. The stronger synthetics hold together better. On self-adhered, edge detailing matters more than the product brand. A ragged edge becomes a sail, and a lifted edge telegraphs into the shingle field.
Rain and humidity swell wood and can wrinkle felt as it dries. Synthetics stay stable. This stability makes for straighter shingle lines and cleaner shingle roofing in general. If you plan a phased roof shingle installation around unpredictable weather, synthetic underlayment is a friend.
Walkability and Crew Safety
Nothing torpedoes a schedule like a slip. Underlayment face texture, slope, dew, and boot selection all matter. I judge a material’s walkability not just by one dry afternoon but across a week with morning dew, a quick shower, and a little sawdust. Premium synthetics with a gritty surface hold up best. They also resist scuffs from tool bags and nail hoses that can polish a surface slick.
Felt remains predictable in the cool hours, though it can tear easily near edges where a worker’s weight lands on a fastener line. In my log of near misses, the slickest surfaces were budget synthetics on cold mornings and cheap peel-and-stick in full sun. Crews adjust, but the right surface saves ankles and time.
Fastening Matters More Than Marketing
Underlayment performs as installed, not as labeled. I see two recurring mistakes: using the wrong fastener and ignoring the manufacturer’s lap pattern. Plastic cap nails or cap staples create a large head that resists pull-through far better than smooth-head roofing nails. This matters when wind hits a partially covered roof or when a helper yanks a roll to square it up. Cap fasteners also reduce water ingress at the fastener during dry-in.
Lap patterns exist for a reason. Vertical and horizontal overlaps shed water in a designed direction. Misplaced edge laps create tiny gutters that capture and direct water into a seam. With felt, double coverage at lower slopes requires specific staggering. With synthetic, printed lines help, yet I still see seams wandering upslope. Take a breath, square the first course, and stay consistent.
With self-adhered membranes, substrate preparation controls adhesion. Dusty OSB, high-resin knots, or cold sheathing all undermine bond. Primers improve grip in marginal conditions, and rolling with a weighted roller seats the membrane, especially at laps and around fasteners.
Real Costs: Material, Labor, and the Cost of a Leak
Material prices move, yet the pattern stays stable. Felt is cheapest per roll. Synthetics cost roughly 1.5 to 3 times felt, depending on brand and thickness. Self-adhered membranes cost several times more per square than felt or basic synthetics. That is only part of the math. Labor, waste, and risk matter.
Felt is heavy and fragile in wind. Labor slows on gusty days, and waste rises with tears. Synthetics cover quickly, with longer roll lengths and fewer tears, which can offset the higher material cost. A two-person crew often lays synthetic 20 to 30 percent faster than felt, especially on roofs with long runs. For roof shingle replacement jobs where speed reduces homeowner disruption, that productivity makes a real difference.
Self-adhered takes longer to stage and apply but simplifies detailing. Around skylights, chimneys, and dead valleys, peel-and-stick saves time and reduces future shingle roof repair calls. For a homeowner, the avoided leak might be the most valuable return. A single ceiling repair can erase the savings of a cheaper underlayment selection.
Manufacturer Warranties and Insurance Expectations
Shingle manufacturers publish approved underlayment lists for their roofing systems. If you want an enhanced warranty, check the fine print. Some require a particular synthetic underlayment from the same brand family and specify coverage percentages of self-adhered at eaves and valleys. Deviating from the list might void parts of the warranty even if the installation looks textbook.
Insurance adjusters also notice underlayment. After storms, claims move faster when the dry-in uses cap fasteners and the material is intact. I have watched adjusters photograph cap spacing and lap lines. On homes with ice dam claims, they often ask how far the self-adhered membrane runs inside the warm wall. Being able to say two feet, three feet, or to the first rafter line can shorten the debate.
Ventilation and Moisture: The Hidden Balance
A roof is not hermetically sealed. It breathes through the attic or conditioned roof assembly. Underlayment choices affect how moisture moves. Felt is vapor-permeable to a degree, allowing the deck to dry a bit faster. Many synthetics are far less permeable, though industry offerings vary and some advertise limited permeability. Self-adhered membranes are essentially vapor barriers.
If you cover a full deck with peel-and-stick in a mixed or cold climate, pay attention to attic ventilation. The combination of vapor barriers above and below can trap moisture from indoor air, especially in winter, leading to deck rot from the underside. If you run a full adhered layer, confirm that soffit and ridge vents actually flow, and use baffles to maintain clear air channels. On tight homes with bath fans dumping into attics, underlayment will not save you. Fix the ventilation and duct the fans outside before laying even the first course of shingles.
Matching Underlayment to Project Scenarios
A few typical project profiles help translate the options into decisions.
For a simple gable, 6:12 pitch, temperate climate, and a homeowner planning to stay ten years, a premium synthetic across the deck with peel-and-stick at eaves and valleys is a solid, cost-effective choice. It keeps lines straight, speeds installation, and protects where water lingers. If budget is tight, 30-pound felt with the same peel-and-stick at critical areas still makes a respectable system. I avoid 15-pound felt unless this is a short-term roof or an outbuilding.
For a coastal home with frequent tropical storms and a 7:12 roof, wind resistance and fast dry-in are key. Choose a high-tensile synthetic approved for the shingle system and use dense cap fastening patterns, particularly along edges and ridges. At rakes and eaves, either an extended strip of peel-and-stick or a nailed metal drip edge over quality synthetic helps control uplift paths. Valleys should be peel-and-stick. A conscientious shingle roofing contractor will also talk about starter strip adhesion and high-wind nailing patterns, because underlayment alone cannot carry that load.
For a snow-belt ranch with long eave runs and a 4:12 pitch, ice dams are the enemy. Run self-adhered membrane from the eaves to at least 24 inches inside the warm wall. On deeper overhangs or poorly insulated walls, I push that to 36 inches inside. Above that, synthetic underlayment saves cost without sacrificing performance. Make sure attic insulation is even and ventilation is clear. I have reduced shingle roof repair calls by half on these houses by being generous with peel-and-stick at the eaves and paying attention to bath fan ducting.
For a low-slope addition at 3:12 tying into a steeper main roof, transitions leak if you skimp. I like full peel-and-stick on the low-slope plane, lapped correctly up under the synthetic on the main slope, with metal transition flashing and careful counterflashing at the step. That recipe keeps both planes behaving, and it shortens the punch list on final walk-through.
For historic homes with plank decks and uneven surfaces, felt can conform a bit better to irregularities, but synthetics prevent plank gaps from telegraphing into the shingle field. Before choosing, I walk the deck after tear-off, set loose nails, replace rotten boards, and sheet over with OSB or plywood where gaps are excessive. Underlayment cannot compensate for structural voids. If the homeowner wants minimal change, a heavier felt with generous cap nailing and peel-and-stick in valleys meets both performance and aesthetic goals, as long as the deck is sound.
Noise, Heat, and Indoor Comfort Considerations
Underlayment has small but real effects on how a roof sounds and heats. Felt deadens the hollow drumming of rain slightly better than thin synthetics. On metal roofs the difference is bigger; on shingles it is subtle, yet in https://dallasnsbz963.huicopper.com/roof-shingle-repair-for-skylight-leaks-a-practical-guide attics over bedrooms I have had sensitive clients notice. Thicker synthetics narrow the gap.
Color and reflectivity of exposed underlayment during staging affect attic heat on hot days. Light-gray synthetics build less heat than black felt while the roof waits for shingles. Once shingled, the difference disappears, but during installation those few degrees can help keep adhesives manageable and crews alert.
Repair and Replacement: How Underlayment Choices Age
When a hailstorm or fallen branch forces roof shingle repair, the underlayment you see tells you how the roof was built. Synthetics often come off in large, intact sheets even after ten years, making selective replacement manageable. Old felt tends to tear, especially around nail lines, which pushes a repair toward a larger replacement area. Self-adhered membrane in valleys proves its value; if water ran in those channels under shingles, the membrane usually shows scuffs and debris but no deck staining. I have also pulled shingles off a poorly primed peel-and-stick zone to find the membrane slipping, a reminder that prep matters as much as product.
On full roof shingle replacement, the biggest underlayment-related budget surprises are layered systems. Two or three layers of felt from past reroofs add labor to remove and dispose, and codes in most jurisdictions now require removing down to the deck rather than overlaying. Peel-and-stick adhered directly to plank decks pulls splinters and requires careful scraping, a time sink that crews must plan for.
Building a Clean Edge: Eaves, Rakes, and Penetrations
Leak paths concentrate at edges and holes. A clean underlayment detail here often saves a frantic weekend call.
At eaves, install drip edge metal under the underlayment if you are not using peel-and-stick, and over the peel-and-stick if you are. The goal is to direct water into the gutter, not behind the fascia. On homes without gutters, be deliberate about the overhang and seal shingle starter strips fully. At rakes, drip edge goes over the underlayment. Ice and water shields that wrap the rake edge add insurance in wind zones.
Valleys deserve full-width peel-and-stick with a centered shingle valley or a metal W-valley over it, depending on design. I have seen more rot here than anywhere else on a shingle roof. The underlayment gives you a second chance.
Penetrations like plumbing vents, skylights, and chimneys need staged layers: field underlayment, then flashing, then additional peel-and-stick that laps shingle-style over the uphill side of the flashing. A neat, redundant wrap keeps wind-driven rain from working under the flange and into the deck.
How to Talk With Your Contractor
Homeowners do not need to dictate every roll and fastener, but a frank conversation clarifies expectations and aligns warranty coverage. Ask which underlayment the crew prefers for your slope and climate, and why. Request the product data sheet and confirm it is approved for your chosen shingles. If you are in a cold region, ask how far self-adhered will run from the eaves. If the project is a roof shingle replacement on a tight schedule, bring up UV exposure windows and walkability, because those affect how the crew sequences the work.
If a bid lists “standard underlayment,” get specifics. Prices can vary by a few hundred dollars between felt and a quality synthetic on a typical house, but the lifetime cost of a leak dwarfs that difference. A trustworthy shingle roofing contractor should welcome these questions.
A Field-Driven Comparison
Not all products with the same label behave the same, but patterns emerge from years on ladders.
Felt, at its best, is inexpensive, familiar, and workable in cold weather. It lays nicely in still air and helps quiet minor rain resonance. It tears in wind, wrinkles in humidity, and has a short UV window. If you choose it, use the heavier weight and do not push exposure time.
Synthetic underlayment delivers a flatter deck, faster staging, better tear resistance, and longer exposure tolerance. The better ones are kind underfoot with coarse textures, while budget options can be slick. Costs run higher, but on most jobs I earn it back in speed and reduced waste. It is the versatile choice for most shingle roof projects.
Self-adhered membrane is your shield at weak points and low slopes. It self-seals around nails and bonds to the deck, which is exactly what you want at eaves and valleys. Full-deck coverage provides a strong safety net, but it raises ventilation stakes and complicates future tear-offs. Use it where water collects, and treat adhesion temperatures and priming seriously.
Hybrid systems combine strengths in a way that fits most homes and budgets: synthetic across the field, peel-and-stick at eaves, valleys, and penetrations, with crisp metal edge details. That is the package that has given me the fewest callbacks for shingle roof repair.
A Short Homeowner Checklist
- Confirm slope-specific underlayment requirements and how they will be met, especially between 2:12 and 4:12. Identify where self-adhered membrane will be installed, and how far it will extend past the warm wall at eaves. Verify fastener type and spacing for the field underlayment, with cap nails or cap staples at edges. Align manufacturer approvals so shingle and underlayment match warranty terms, and keep the product labels for your records. Walk attic ventilation with your contractor and resolve bath fan venting before dry-in.
When the Edge Cases Drive the Choice
Some roofs are quirky. Cathedral ceilings with tongue-and-groove decking and minimal venting complicate moisture movement. In those cases I prefer synthetic for the field to avoid a full vapor barrier above, while still using peel-and-stick at the eaves and around penetrations. On cabins that rely on winter wood heat and run higher interior humidity, I stretch peel-and-stick coverage at the eaves beyond code minimums and add ice belt flashing because experience says the first thaw after a midwinter freeze pushes water uphill under shingles.
In wildfire-prone regions where Class A fire ratings matter, check the assembly listing. Some assemblies assume a specific underlayment type beneath asphalt shingles to achieve the rating. Substituting a non-listed product can reduce the classification, an unpleasant surprise at inspection or during insurance underwriting.
If a roof has a history of condensation from unbalanced ventilation, do not expect a thicker or pricier underlayment to solve it. Fix the airflow and insulation details. A better underlayment will resist the symptoms a little longer, but wood rot and mold ignore brand names.
The Takeaway for Planning a Shingle Roof
Underlayment is not an afterthought. It is the quiet layer that forgives mistakes, buys time when weather shifts, and turns a good shingle layout into a resilient roof. On most homes, a quality synthetic paired with self-adhered membrane at high-risk areas strikes the right balance of cost, speed, and durability. Felt still earns a place on modest projects and cool-weather installs when handled with discipline. Full peel-and-stick decks solve specific problems but demand ventilation awareness and careful deck prep.
Partner with a shingle roofing contractor who can explain these trade-offs in the context of your roof shape, your climate, and your plans for the house. Whether you are lining up a roof shingle installation on a new home, scheduling a roof shingle replacement after two decades of service, or trying to avoid yet another shingle roof repair in a stubborn valley, choosing the right underlayment is the most cost-effective decision you make where no one will ever see it.
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.