How To Install Felt Paper On A Roof: A Professional Step-by-Step Guide
Installing felt paper—also known as roof underlayment—creates a critical secondary weather-resistant barrier beneath asphalt shingles or metal roofing systems. By adhering to building code overlaps, choosing the correct weight, and fastening securely against wind uplift, you protect the roof deck from moisture infiltration and ice damming.
Pre-Operation & Equipment Checklist
Proper preparation ensures both personal safety and structural integrity before any roofing material touches the plywood deck. Roof underlayment must be laid over a clean, dry, and structurally sound wood substrate to perform correctly.
- Essential Gear, Tools, and Materials: 15 lb or 30 lb asphalt-saturated felt paper, pneumatic cap stapler or hammer tacker, corrosive-resistant roofing nails with plastic caps (tin caps), utility knife with hook blades, chalk line, roofing hammer, tape measure, ladder, OSHA-compliant personal fall arrest system (harness, lanyard, and anchor), and non-slip footwear.
- Mandatory Prerequisite Knowledge and Standards: Review local building codes, ensure the roof deck (OSB or exterior-grade plywood) is completely free of protruding nails, protruding splinters, or debris, and verify that the drip edge is correctly installed along the eaves before underlayment application.
- Estimated Budget and Duration Benchmarks: Material costs typically range from twenty to fifty dollars per roll depending on weight (organic felt vs. synthetic variants). A standard residential roof layout takes between two to four hours for a two-person crew to complete.
Step-by-Step Roofing Underlayment Installation Workflow
Step 1: Clean and Prepare the Deck Edge
Inspect the entire plywood or OSB roof deck for gaps, warping, or fastener heads sticking above the surface plane. Install the metal drip edge along the eaves (horizontal lower edges) directly against the roof deck, and install drip edge along the rakes (sloped side edges) directly over the underlayment, or follow local code specifications regarding eave drip edge integration. Sweep the deck clear of sawdust, grit, and wood scraps to prevent punctures in the felt paper.
Warning: Never walk backward on an unanchored or wet roof deck. Always secure your fall protection harness to a rated structural roof anchor before staging materials at height.
Step 2: Snap Reference Lines and Roll Out the First Course
Snap horizontal chalk lines parallel to the eave line to ensure your felt paper runs straight across the roof plane. Begin at the bottom-most edge (eave) of the roof, unrolling the felt paper horizontally from left to right. Align the bottom edge of the felt paper flush with or overhanging the eave drip edge by approximately one-quarter to one-half inch to direct water runoff away from the fascia.
Step 3: Fasten the Base Course Securely
Tack the starting edge of the felt paper, pull the roll taut across the deck to eliminate wrinkles and air pockets, and secure it using a hammer tacker or pneumatic cap stapler. Drive fasteners approximately every 12 inches along the horizontal laps and every 6 inches along the perimeter edges.
Pro-Tip: Use plastic cap nails (often called cap staples or ring-shank roofing nails with plastic disks) rather than standard narrow-crown staples if rain is forecasted before shingle installation; caps seal tightly around the fastener shank and resist pull-through caused by high winds.
Step 4: Overlap Subsequent Courses Upward
Unroll the second course of felt paper directly above the first, adhering to strict overlap guidelines. For 15 lb or 30 lb felt, overlap the top edge of the lower course by a minimum of 2 inches (or follow the printed horizontal lap lines on the paper). For slopes under 4:12 down to 2:12, double-coverage underlayment is typically required, necessitating a 19-inch overlap for 36-inch wide rolls. End laps—where one roll ends and another begins horizontally—must overlap by a minimum of 4 inches.
Step 5: Integrate Valleys, Penetrations, and Flashing Details
Continue running courses upward toward the ridge line, maintaining proper shingle-style overlaps so upper layers always shed water over lower layers. At roof valleys, run a continuous 36-inch wide strip of felt paper down the center of the valley first, then lap the field felt over it by at least 12 inches. Around roof penetrations such as plumbing vents, chimneys, and skylights, cut the felt paper tightly around the obstacle and seal the joint with approved roofing cement or flashing tape.
Roofers and Underlayment,Tar Paper, Roofing Felt,or Synthetic
Technical Specifications of Roofing Underlayments
| Underlayment Type | Typical Weight / Coverage | Recommended Slope Application | Vapor Permeability | Wind Uplift Resistance |
|---|---|---|---|---|
| No. 15 Organic Felt | ~15 lbs per 100 sq ft | Standard slopes (4:12 and greater) | Moderate | Moderate (requires cap nails) |
| No. 30 Organic Felt | ~30 lbs per 100 sq ft | Low-slopes and high-end residential | Low-to-Moderate | High durability against foot traffic |
| Synthetic Underlayment | Lightweight polymer weave | All slopes (down to 2:12 with sealing) | Varies (engineered breathable or non-breathable) | Excellent tear resistance |
Common Site Failures and Field Fixes
- Root Cause: Felt paper wrinkles, buckles, or ripples after getting wet from morning dew or unexpected rain before shingle installation.
- Actionable Fix: Cut along the crest of the bubble or wrinkle with a utility knife to relieve tension, press the flaps flat against the deck, and secure them with roofing nails or dab a trowel of asphalt roofing cement underneath before nailing down.
- Root Cause: Fasteners pull through the felt paper or tear the material during high-wind events prior to shingle loading.
- Actionable Fix: Replace standard narrow-crown staples with plastic cap nails or tin-cap roofing nails, which distribute holding pressure over a wider surface area and prevent tearing.
- Root Cause: Felt paper degrades, cracks, or crumbles due to being exposed to UV radiation and weather elements for too long.
- Actionable Fix: Strip away the damaged sections back to sound material, slide a new patch underneath the upper course by at least 6 inches, and fasten securely. Always cover felt paper with finished roofing materials within the manufacturer's specified exposure window (typically 30 to 90 days).
Frequently Asked Questions
How much should felt paper overlap?
Felt paper must overlap horizontally by at least 2 inches, and vertical end laps must overlap by at least 4 inches. If you are installing on a low-slope roof between 2:12 and 4:12 pitch, local building codes usually require a double-coverage method with a 19-inch horizontal overlap.
Should I use 15 lb or 30 lb felt paper?
No. 15 lb felt is lighter, more economical, and suitable for standard-sloped residential roofs with quick shingle installation turnarounds. No. 30 lb felt is thicker, resists foot traffic and tearing much better, provides a flatter surface, and is preferred for premium architectural shingles or environments with prolonged exposure windows.
Can felt paper get wet before shingles are installed?
Felt paper is water-resistant, not waterproof. Brief, light rain showers will not harm it if it is installed correctly and allowed to dry completely. However, prolonged saturation can cause organic felt to buckle, wrinkle, or absorb moisture that transfers to the wood deck, requiring replacement if warping occurs.
How do I install felt paper around roof vents and chimneys?
Roll the felt up to the penetration, cut an X-shape or custom slit to fit tightly around the base of the pipe or chimney, and secure the edges with roofing nails. Overlap the upper edge of the felt with step flashing or counter-flashing, and seal any exposed edges with approved polyurethane roofing sealant.
Protect your home investment by combining professional-grade underlayment installation with durable, weather-tested shingle systems. Connect with our certified roofing specialists today to secure professional installation services and extend the lifespan of your roof.
