Installing roofing felt, also known as tar paper, is a critical step in creating a durable and weather-resistant roofing system. This underlayment acts as a protective barrier between the roof deck and the final roofing materials, such as shingles or tiles, safeguarding your home from moisture infiltration and extending the lifespan of your roof. Whether you’re a seasoned DIY enthusiast or a homeowner looking to understand the process, this comprehensive guide will walk you through the essentials of installing roofing felt. Roofing felt is installed over a clean, dry, solid roof deck before asphalt shingles are installed. The underlayment is generally applied horizontally from the lower edge of the roof upward so each higher course overlaps the course below and helps shed water toward the eaves. The exact overlap, fastening pattern, drip-edge detail, and underlayment requirements should follow the roofing manufacturer’s instructions and applicable building requirements.
Roofing underlayment is an important part of the roofing system because it provides secondary protection beneath the shingles.
During a complete roof replacement, S&K Construction And Remodeling LLC inspects the roof decking and installs the appropriate underlayment, ice-and-water protection, drip edge, flashing, shingles, and ventilation for the roofing system.
We provide roof replacement and roof repair throughout Northeast Ohio.
Schedule a free roof inspection and estimate today.
Understanding Roofing Felt
Roofing felt is typically made from a base material—either organic or fiberglass—that is saturated with asphalt to enhance its waterproofing properties. It comes in rolls, commonly 36 inches wide, and is available in different weights, with 15-pound and 30-pound felt being the most prevalent. The heavier the weight, the more durable and protective the felt.
Benefits of Installing Roofing Felt
- Moisture Barrier: It prevents rainwater or snow from seeping into the roof deck, thereby protecting the structural integrity of your home.
- Secondary Protection: In case the outer roofing material is damaged or blown off, the roofing felt provides an additional layer of defense against the elements.
- Uniform Surface: It offers a smooth surface for installing shingles, ensuring they lay flat and adhere properly.
- Fire Resistance: Some roofing felts have fire-resistant properties, adding an extra layer of safety to your home.
Tools and Materials Needed
Before embarking on the installation, gather the following tools and materials:
- Roofing Felt Rolls: Choose the appropriate weight (15-pound or 30-pound) based on your roofing needs.
- Utility Knife: For cutting the felt to the required lengths.
- Hammer or Staple Gun: To secure the felt to the roof deck.
- Roofing Nails or Staples: Galvanized to prevent rusting.
- Measuring Tape: For accurate measurements.
- Chalk Line: To ensure straight lines during installation.
- Ladder: For safe access to the roof.
- Safety Gear: Including gloves, safety glasses, and non-slip footwear.
Step-by-Step Guide to Installing Roofing Felt
1. Preparation
- Inspect the Roof Deck: Ensure the roof deck is clean, dry, and free from any protruding nails or debris. Repair any damaged or rotten sections to provide a solid foundation for the felt.
- Check Weather Conditions: Aim to install roofing felt on a clear, dry day to prevent moisture from getting trapped under the underlayment.
2. Install Drip Edge at the Eaves
- Purpose: A drip edge is metal flashing installed at the edges of the roof to direct water away from the fascia and into the gutters, preventing water damage.
- Installation: Starting at a corner of the eave, align the drip edge flush with the edge of the roof deck. Nail it in place using roofing nails spaced approximately 12 inches apart. Ensure the overlapping sections are seamless to facilitate proper water runoff.
3. Lay the First Course of Roofing Felt
- Starting Point: Begin at the lowest point of the roof, typically the eave. This positioning allows any water that penetrates the shingles to shed down the underlayment without seeping into the roof deck.
- Alignment: Unroll the felt parallel to the eave, ensuring it overhangs the edge by about 1/2 inch to 3/4 inch. This slight overhang directs water into the gutters.
- Securing the Felt: Using a hammer or staple gun, attach the felt to the roof deck. Place fasteners approximately every 12 inches along the edges and staggered across the middle to prevent wrinkling or shifting.
4. Overlap Subsequent Courses
- Overlap Measurement: Each new course should overlap the previous one by at least 2 inches. This overlap ensures that water flows over the layers without seeping underneath.
- Chalk Lines: Snap chalk lines to guide the placement of each course, maintaining straight and even rows.
- Upper Courses: As you move up the roof, continue this overlapping pattern until you reach the ridge.
5. Install Drip Edge at the Rakes
- Purpose: Installing a drip edge along the rake (the sloped edges of the roof) prevents wind-driven rain from entering under the roofing materials.
- Installation: Place the drip edge over the roofing felt along the rake edges. Nail it in place with roofing nails spaced about 12 inches apart, ensuring a tight fit.
6. Address Valleys and Roof Penetrations
- Valleys: In areas where two roof planes meet, creating a valley, lay an additional layer of roofing felt or a self-adhering waterproof membrane. Center it over the valley and ensure it extends at least 18 inches on each side for optimal protection.
- Roof Penetrations: For elements like vent pipes or chimneys, cut the roofing felt to fit snugly around these penetrations. Seal the edges with roofing cement to prevent water infiltration.
7. Finalize at the Ridge
- Overlapping: When both sides of the roof are covered with felt up to the ridge, overlap the felt from one side over the other. This overlap provides continuous protection across the roof peak.
- Securing: Fasten the felt securely along the ridge, ensuring it remains flat and wrinkle-free.
Common Mistakes to Avoid
- Inadequate Overlapping: Failing to overlap the felt sufficiently can lead to water seepage. Always maintain the recommended overlap measurements.
- Poor Fastening: Using too few fasteners
What Is Roofing Felt?
Roofing felt is a type of roof underlayment installed between the roof decking and the finished roofing material.
Traditional roofing felt is made using a base material saturated with asphalt.
It provides a secondary layer beneath asphalt shingles and helps protect the roof decking while the complete roofing system works together to shed water.
Roofing felt is sometimes called:
Tar paper
Roof felt
Felt paper
Asphalt felt
Roof underlayment
Is Roofing Felt the Same as Roof Underlayment?
Roofing felt is one type of roof underlayment, but the terms are not exactly interchangeable.
Modern roof underlayment options may include:
Traditional asphalt-saturated felt
Synthetic underlayment
Self-adhered waterproof membranes
Specialty roof-deck protection products
The correct product depends on the shingle manufacturer, roof slope, building requirements, weather exposure, and roofing system.
Roofing Felt vs Synthetic Underlayment
Traditional roofing felt has been used under asphalt shingles for many years.
Synthetic underlayment is another common option on modern roof replacements.
Synthetic products may offer advantages involving:
Tear resistance
Lighter weight
Walking traction
Larger roll sizes
Weather exposure
Installation efficiency
However, the best product depends on the roofing system and manufacturer’s requirements.
Do not make a blanket statement that synthetic is always better.
15-Pound vs 30-Pound Roofing Felt
Traditional roofing felt is commonly associated with No. 15 and No. 30 felt designations.
Heavier felt generally provides greater material thickness and durability than lighter felt.
However, homeowners should not select underlayment based only on the traditional felt designation.
The roofing system, manufacturer instructions, roof slope, weather conditions, and applicable requirements should determine the appropriate underlayment.
Does the Roof Deck Need to Be Dry Before Installing Felt?
The roof deck should be clean, dry, structurally sound, and free of debris before underlayment and shingles are installed.
Damaged or rotten plywood and OSB should be repaired before covering the roof.
GAF installation instructions specifically require roof decking to be dry before shingle installation.
This gives you a perfect internal link to:
What Plywood Is Used for Roofing?
Which Direction Is Roofing Felt Installed?
Roofing felt is generally installed horizontally across the roof beginning near the eave.
Each course above overlaps the lower course so water moving down the roof stays on top of the underlayment layers rather than running underneath them.
Installation continues upward toward the ridge.
The exact lap dimensions should follow the specific underlayment manufacturer’s instructions.
How Much Should Roofing Felt Overlap?
The required overlap depends on the underlayment product, roof slope, and manufacturer’s installation instructions.
Some traditional underlayment applications use relatively small horizontal overlaps on standard roof slopes, while lower-slope roofing may require additional protection.
Homeowners should follow the specific roofing system instructions rather than assuming every felt product uses the same overlap.
How Does Roof Pitch Affect Underlayment?
Roof slope can change the underlayment requirements beneath asphalt shingles.
Ohio residential provisions allow asphalt shingles on slopes of 2:12 or greater and require additional underlayment treatment in the 2:12-to-4:12 range.
This is why contractors need to measure roof pitch before deciding how the underlayment and shingles should be installed.
Internally link this to:
Steep vs Shallow Pitch
7/12 Roof Pitch
12/12 Roof Pitch
What Goes First: Drip Edge or Roofing Felt?
Drip-edge sequencing depends on where it is being installed and the roofing system requirements.
A common asphalt-shingle detail places underlayment over the drip edge at the eaves while rake-edge drip metal may be installed over the underlayment.
The roofing contractor should follow the applicable manufacturer and building requirements for the specific roof.
The current article already uses this general sequence, so keep the concept but avoid treating one installation detail as universal.
What Is Ice and Water Shield?
Ice-and-water shield is a self-adhering waterproof membrane used in vulnerable areas of the roof.
Depending on the roofing system, it may be used around:
Eaves
Valleys
Chimneys
Skylights
Roof penetrations
Walls
Other leak-prone areas
It is different from ordinary roofing felt because it adheres directly to the roof deck and provides greater protection against water intrusion.
Why Ice and Water Shield Matters in Northeast Ohio
Northeast Ohio roofs experience freezing temperatures, snow, ice, and repeated freeze-thaw cycles.
When ice dams form near the eaves, water can back up underneath shingles.
Ohio residential roofing provisions address ice-barrier protection in locations with a history of ice damming and require the protection to extend into the roof area beyond the exterior wall line under applicable conditions.
This makes proper eave protection especially important on Northeast Ohio roof replacements.
Can Roofing Felt Stop an Ice Dam Leak?
Traditional roofing felt should not be treated as a substitute for an approved ice-barrier system.
Ice dams can force water backward underneath shingles.
Areas susceptible to ice damming may require self-adhering ice-and-water protection or another approved ice-barrier assembly.
The entire system should follow the roofing manufacturer and applicable building requirements.
How Is Underlayment Installed Around a Roof Valley?
Roof valleys carry large amounts of water because two roof slopes drain into the same area.
The underlayment and valley protection should therefore follow the specific valley design and roofing manufacturer’s instructions.
Depending on the roofing system, the valley may use:
Self-adhered membrane
Additional underlayment
Metal valley flashing
Closed-cut shingles
Open-valley construction
Do not rely on one generic felt overlap measurement for every roof valley.
How Is Roofing Felt Installed Around Vent Pipes?
Underlayment around a plumbing vent should be carefully integrated with the pipe boot and roofing system.
The pipe boot and flashing create the primary water-shedding detail around the roof penetration.
Simply cutting roofing felt around the pipe and applying roofing cement is not a substitute for proper flashing.
Internally link this to:
Should Roof Vent Pipe Be Covered?
How Is Underlayment Installed Around a Chimney?
Chimneys require a properly designed flashing system.
Underlayment should integrate with:
Step flashing
Counterflashing
Chimney cricket where required
Roof shingles
Waterproof membrane where appropriate
Roof cement alone should not be treated as the permanent flashing system around a chimney.
Internally link this to your chimney article.
Can Roofing Felt Get Wet?
Roofing underlayment can sometimes experience limited weather exposure during construction depending on the particular product.
However, roofing contractors should protect the roof deck and underlayment from unnecessary moisture.
If materials become saturated, damaged, torn, wrinkled, or compromised, they should be inspected before the roofing installation continues.
Exposure limitations vary by manufacturer and product.
Can Shingles Be Installed Over Wet Roofing Felt?
Roofing shingles should be installed according to the manufacturer’s requirements over an acceptable, properly prepared roof assembly.
The roof deck should not be covered while saturated or damaged.
If rain occurs during a roof replacement, the contractor should evaluate the decking and underlayment before continuing.
Internally link this to your Roofing in the Rain article.
Common Roofing Felt Installation Mistakes
Installing underlayment over wet decking
Insufficient overlaps
Incorrect fasteners
Wrinkles in the felt
Torn underlayment
Incorrect drip-edge sequencing
Poor valley installation
No ice-and-water protection where required
Covering rotten decking
Improper chimney flashing
Improper pipe boot integration
Installing shingles before the roof assembly is ready
Using roofing cement as a substitute for proper flashing
Ignoring manufacturer instructions
Should Roofing Felt Be Replaced During a Roof Replacement?
Yes, during a complete tear-off roof replacement the existing underlayment is normally removed with the old roofing system so the roof decking can be inspected.
Once the roof is stripped, the contractor can identify:
Rotten plywood
Soft decking
Water damage
Old underlayment
Improper flashing
Ventilation problems
Previous roof repairs
New underlayment and other protective roofing components can then be installed as part of the new roofing system.
Roofing Underlayment During a Northeast Ohio Roof Replacement
S&K Construction And Remodeling LLC provides complete asphalt shingle roof replacement throughout Northeast Ohio.
During roof replacement, we remove the existing roofing materials, inspect the roof decking, and install the appropriate roof-deck protection, ice-and-water membrane, drip edge, flashing, shingles, and ventilation for the roofing system.
Proper underlayment is especially important in Northeast Ohio because roofs are exposed to heavy rain, snow, ice, wind, and repeated freeze-thaw cycles.
We provide roof replacement, roof repair, storm damage inspections, and roofing estimates throughout Cleveland, Lake County, Ashtabula County, Geauga County, Trumbull County, Summit County, and surrounding Northeast Ohio communities.
Need your Roof Underlayment Replaced?
Roofing felt and synthetic underlayment protect the roof deck beneath the shingles and are important parts of a complete roofing system.
If your roof is aging, leaking, storm damaged, or ready for replacement, S&K Construction And Remodeling LLC can inspect the shingles, underlayment, roof decking, flashing, ventilation, and other roofing components.
We provide roof inspections, roof repair, storm damage services, and complete roof replacement throughout Northeast Ohio.
Schedule your free roof inspection and estimate today. 440.235.3124
