search
cart
facebook twitter linkedin youtube instagram Spotify Podcasts Apple Podcasts Spotify Podcasts Apple Podcasts
  • Sign In
  • Create Account
  • Sign Out
  • My Account
  • NEWS
  • TOPICS
    • Cool Roofing
    • Event News
    • Latinos in Roofing
    • Low Slope
    • Legal
    • Metal
    • Project Profiles
    • Roofing Supply Pro
    • Roofing Safety
    • Steep Slope
    • Sustainable Roofing
    • Technology
  • EXCLUSIVES
    • Best of Success
    • Contractor Profile
    • IRE Show
    • Roofing Contractor of the Year
    • Top 100
    • Young Guns
    • State of the Industry
    • Century Club
  • MULTIMEDIA
    • Videos
    • Podcasts
    • Interactive Spotlights
    • Roofing Quizzes
    • IRE Videos
    • Webinars
    • Photo Galleries
  • PRODUCTS
    • New Products
    • Featured Products
  • COLUMNS
    • Editor's Note
    • Exit Planning
    • Legally Speaking
    • Safety Advice
    • Technical Details
    • Guest Column
  • EVENTS
    • International Roofing Expo
    • Webinars
    • Best of Success Conference
    • Industry Events
  • DIRECTORY
    • Associations
    • Distributors
    • Manufacturer/Supplier
    • Business Services
    • Get Listed
  • MORE
    • Roofing Contractor eNews
    • RC Store
    • Roofing Supply Pro
    • Custom Content & Marketing Services
    • Market Research
    • Sponsor Insights
    • Company Spotlights
    • Classifieds
      • Auctions
      • Business For Sale
      • Business Opportunities
      • Equipment For Sale
      • Positions Available
      • Products
      • Safety
      • Software
      • Services
      • Training
    • Contact Us
  • EMAGAZINE
    • eMagazine
    • Advertise
      • Media Kit
      • Editorial Calendar
      • Contact
    • Archive Issues
  • SIGN UP!
Columns

TechnicalDetails: Underlayments for Steep-Slope Shingle Applications

By John D'Annunzio
March 11, 2006
Most roofing experts would agree that it is a best practice to apply underlayments on steep-slope shingle applications. Underlayments provide benefits to the roof system at the deck and shingle components. These benefits add to the long-term weatherproofing success of the roof system. Another primary reason for their use is that most building codes require the application of underlayments on steep-slope roofs.

Photo courtesy of Carlisle Coatings and Waterproofing.


Most roofing experts would agree that it is a best practice to apply underlayments on steep-slope shingle applications. Underlayments provide benefits to the roof system at the deck and shingle components. These benefits add to the long-term weatherproofing success of the roof system. Another primary reason for their use is that most building codes require the application of underlayments on steep-slope roofs. It is imperative that the contractors familiarize themselves with the codes in their work areas. Installations that are not completed in accordance with codes can be very costly to remedy, particularly in this case, where the remedy would include the removal of the steep-slope covering. Underlayments are also required to achieve a Class A fire rating for the roof system.

Underlayments serve as a weatherproofing barrier protecting the deck from moisture prior to shingle application and can be applied to dry in the roof in advance of the shingle installation. This is of particular importance on new construction projects, where there can be a lengthy lapse between deck installation and shingle application. Moisture absorption in the deck could lead to delamination or warping of the deck surface, providing an unsuitable long-term substrate.

In the completed system, the underlayment provides secondary protection against moisture infiltration, preventing water from entering the interior spaces if the shingles are lifted, displaced or torn. The underlayment also provides added protection to the applied shingles by separating the contact of wood resins and the shingles. Some wood resins can have an adverse effect on the shingles, contributing to deterioration over time. Underlayments also serve in leveling the deck by bridging over any slight irregularities and creating a flat and even surface for the shingle application.

Types of Underlayments

Underlayments used in steep-slope applications are generally one of four material classifications: organic felts, fiberglass mats, composites, or modified bitumen sheets. The most common type of steep-slope shingle underlayments are asphalt-saturated nonperforated organic felts. There are two designations of these sheets: Type 15 (No. 15) and Type 30 (No. 30). The designation denotes the once-used pound per square foot weight of the material. The sheets are manufactured in a multi-step process using an organic mat, fiberglass mat, or a combination of each. The initial process involves saturation of the sheet, which is accomplished by impregnating the fibers of the dry felt with asphalt and filling all voids. The next step is the coating process, which is completed by applying mineral stabilized coating asphalt to the top and bottom of the sheets. In some cases, a final step of a mineral surfacing application is completed to one or both sides of the sheet. Eaves flashing or "ice shield" protection is typically manufactured from self-adhered modified sheets or coated felts.

Most underlayments are distributed in rolls that are 36 inches wide. However, specialty underlayments are manufactured for specific applications. For instance, 18-inch rolls are produced for use as interlayments on wood shake applications.

Underlayment Application Procedures

Underlayments should always be applied over dry substrate surfaces. Moisture on the surface or entrapped in the substrate may enter the underlayment. Wet underlayments can contribute to shingle damage by creating blisters, buckling or wrinkling of the shingles. The deck substrate should be relatively flat, rigid and free of irregularities such as openings, cracks, deformations and delamination. All irregularities should be corrected prior to the installation of the underlayment.

Prior to underlayment application, local codes should be reviewed to determine the proper underlayment attachment methods and if eaves flashings are required. These circumstances are guided by geographic boundaries. Eaves flashings are typically required in Northern climates, and strict fastener attachment is required in high-velocity wind zones. Application should be completed in accordance with the manufacturer's latest printed specifications.

Underlayment application should begin parallel to the eaves and should completely cover the entire deck area. Each course should overlap the preceding course by a minimum of 2 inches. If two or more pieces are required to complete a full course, the end laps should be a minimum of 4 inches. The end laps should be staggered throughout the installation, with end laps in succeeding courses a minimum of 6 feet from the end laps in the succeeding course. At all hips and ridges, the felt should be set a minimum of 6 inches on each side of the slope and it should be extended a minimum of 4 inches up all vertical surfaces. The underlayment should be laid flat and be free of all wrinkles and depressions, providing a smooth surface for the shingle application.

The most common attachment method is mechanical fastening to the substrate. The appropriate fastener/nail depends on the type of substrate and the manufacturer's specific requirements. Attachment methods should be determined by specific wind uplift requirements in the geographic location. Typical application rates over wood decks are one fastener every 9 inches at the side laps and two rows of fasteners in the middle rows staggered every 18 inches on center. In recent years, self-adhered underlayments have become more prominent in the industry and may be used in certain geographic zones.

Share This Story

Looking for a reprint of this article?
From high-res PDFs to custom plaques, order your copy today!

Jdannunzio
John A. D’Annunzio is President of Paragon Roofing Technology Inc., a construction engineering firm he founded in 1989. He is the editorial director of Architectural Roofing & Waterproofing and a technical columnist for Roofing Contractor. He has published more than 100 articles and has written four books on building exterior issues. For more information, visit www.paragonroofingtech.com. He can be reached at 248-936-8744.

Recommended Content

JOIN TODAY
to unlock your recommendations.

Already have an account? Sign In

  • Roofing Contractor Group Publisher Jill Bloom

    Physics, the Power of Authenticity and You

    In February's Publisher's Note, Jill Bloom describes a...
    Columns
    By: Jill Bloom
  • The Family Food Fare supermarket in Midland, Mich.

    ‘Rooftop Ninja’ Discovered Living on Roof, Inside Grocery Sign

    A bizarre tale out of Midland, Mich.: a woman dubbed the...
    Roofing News
    By: Bryan Gottlieb
  • A before and after heat measurement comparison

    How Hot is Too Hot in the Attic?

    If the ventilation is working, how hot should the attic...
    Columns
    By: Paul Scelsi
You must login or register in order to post a comment.

Report Abusive Comment

Manage My Account
  • eMagazine Subscription
  • Sign Up for the eNewsletter
  • Online Registration
  • Manage My Preferences
  • Subscription Customer Service

More Videos

Sponsored Content

Sponsored Content is a special paid section where industry companies provide high quality, objective, non-commercial content around topics of interest to the Roofing Contractor audience. All Sponsored Content is supplied by the advertising company and any opinions expressed in this article are those of the author and not necessarily reflect the views of Roofing Contractor or its parent company, BNP Media. Interested in participating in our Sponsored Content section? Contact your local rep!

close
  • An overhead view of a residential block
    Sponsored byCBIZ CompuData

    From Spreadsheets to Strategy: How Roofing Companies Can Transform Financial Operations

  • Snow Guard Solutions for Metal Roofs by S-5!
    Sponsored byS-5!

    Safeguard Your Building: How Snow Guards Prevent Costly Roof & Property Damage

  • A hand holding a wooden block that reads 'EVOLVE'
    Sponsored byWatercress Financial

    Embracing Change: A New Era for the Roofing Industry

Popular Stories

Agentes de ICE arrestaron a casi una docena de empleados de una empresa de techos en Lowell, Massachusetts. Los arrestos son parte de una redada federal más amplia contra la contratación no autorizada y las violaciones migratorias en Boston.

ICE Redondea a Equipo de Techos Afuera de Boston

Florida has become the focal point for construction-site raids, attracting national attention and altering labor dynamics throughout the industry.

Florida Emerges as the Epicenter of ICE Raids

QXO CEO Brad Jacobs will share the company’s strategic vision today at the Wolfe Research Global Transportation & Industrials Conference in New York following its acquisition of Beacon Roofing Supply..

QXO’s Brad Jacobs Charts Growth at Wolfe Research Conference

Roofing Contractor Webinar

Events

December 3, 2025

The Premier Roofing Conference: Best of Success

Join roofing professionals from across the nation at the 2025 Best of Success conference, the ultimate destination for roofing professionals seeking the latest industry insights and networking opportunities. Pick up strategies for critical challenges like workforce shortage with innovative solutions, explore the latest advancements in roofing technology and sustainable practices, and gain valuable insights from industry leaders on navigating the evolving roofing landscape.

View All Submit An Event

Related Articles

  • Technical Details: Essential Elements For Successful Roof Applications

    See More
  • Technical Details: How to Determine Proper Fasteners for Roof Applications

    See More
  • Common Shingle Application Mistakes

    See More
×

Be in the forefront of the roofing industry!

Join thousands of professionals today. Shouldn’t you know what they know?

JOIN NOW!
  • RESOURCES
    • Advertise
    • Contact Us
    • Directories
    • Store
    • Want More
  • SIGN UP TODAY
    • Create Account
    • eMagazine
    • eNewsletter
    • Customer Service
    • Manage Preferences
  • SERVICES
    • Marketing Services
    • Reprints
    • Market Research
    • List Rental
    • Survey/Respondent Access
  • STAY CONNECTED
    • LinkedIn
    • Facebook
    • Instagram
    • YouTube
    • X
  • PRIVACY
    • PRIVACY POLICY
    • TERMS & CONDITIONS
    • DO NOT SELL MY PERSONAL INFORMATION
    • PRIVACY REQUEST
    • ACCESSIBILITY

Copyright ©2025. All Rights Reserved BNP Media.

Design, CMS, Hosting & Web Development :: ePublishing