FHB Logo Facebook LinkedIn Email Pinterest Twitter X Instagram Tiktok YouTube Plus Icon Close Icon Navigation Search Icon Navigation Search Icon Arrow Down Icon Video Guide Icon Article Guide Icon Modal Close Icon Guide Search Icon Skip to content
Subscribe
Log In
  • How-To
  • Design
  • Tools & Materials
  • Restoration
  • Videos
  • Blogs
  • Forum
  • Magazine
  • Members
  • FHB House
  • Podcast
Log In

Fine Homebuilding Project Guides

Roofing

Guide Home
  • Tools and Materials
  • Roof Replacement and Reroofing
  • Roof Ventilation
  • Waterproofing
  • Installing Asphalt Shingles
  • Installing Other Types of Roofs
  • Roof Maintenance and Repair
How-To

Adequate Roof Venting

Builder Mike Guertin gives sound advice on gable, ridge, and soffit vents.

By Mike Guertin Issue 257 - Feb/Mar 2016
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Q:

I am having the shingles replaced on the roof of my ranch-style house. The roofer is concerned about attic ventilation and recommends installing a ridge vent and closing off the existing gable vents. He also says that the rectangular metal soffit vents may not be adequate and recommends installing more to eliminate the risk of the roof sheathing rotting. There are five vents in each soffit, and they measure about 4 in. by 16 in. each. Is it necessary to close off the gable vents? If so, how can I do that? Do I have to remove them and fill in the void with siding?

And how do I know how many soffit vents to install?

Mark Villar, Middletown, CT

A:

Editorial Adviser Mike Guertin replies: If the roof sheathing hasn’t begun to rot already, it’s unlikely that replacing the roof shingles will cause it to occur. Still, it’s a good idea to address ventilation to reduce attic heat in the summer and to reduce the chance for ice dams in the winter.

Most likely, the roofer is recommending closing off the gable vents when adding a ridge vent to prevent short-circuiting of the air. When gable vents are left open, air can enter through the gables and bypass the soffit vents. If air flows in through the gables and out the ridge vents, the entire roof doesn’t receive the full effect. The air isn’t entering through the soffit vents, traveling up the underside of the roof, and exiting through the ridge vent. You don’t have to remove the gable vents, though. Just screw a piece of rigid foam or plywood over the vent from the inside. When the siding is replaced, the old gable vents can be removed and the openings filled.

The standard equation for older homes that don’t have air barriers and vapor retarders (now required) is 1 sq. ft. of vent area for every 150 sq. ft. of attic floor. If your house is 26 ft. wide by 48 ft. long, you have a 1248-sq.-ft. attic floor and need 8.32 sq. ft. of total vent area. If, however, the attic floor has been air-sealed and has a vapor retarder between the inside of the house and the attic, the equation is 1 sq. ft. of vent area for every 300 sq. ft. of attic floor.

Ideally, this 8.32-sq.-ft. total vent area is split: 4.16 sq. ft at the ridge and 4.16 sq. ft. at the soffits. Each type of vent has a range of effective vent area per linear foot—this is called the net free vent area (NFVA). Ridge-vent NFVA ranges from 14 sq. in. to 18 sq. in. per lin. ft. (Check manufacturers’ instructions for the ratings of specific products.) If 46 ft. of ridge vent (often it does not extend to the ends) is installed and the product has an NFVA of 15 sq. in. per lin. ft., we can take 46 ft. and multiply it by 15 sq. in., which equals 690 sq. in. Converted to square feet (690 divided by 144), the total is 4.8 sq. ft. This ridge vent supplies 4.8 sq. ft. of NFVA, which is just over half of 8.32 sq. ft.

You can’t have too much soffit venting, but it’s worth noting the minimum requirements. Usually, 4-in. by 16-in. soffit vents are rated for 26 sq. in. of NFVA each. With a total of 10 vents, you have a total of 260 sq. in. (1.8 sq. ft.) of soffit-vent area. Since you need at least 4.16 sq. ft. of NFVA, you’ll need to add 14 more of the 4-in. by 16-in. soffit vents (for a total of 4.3 sq. ft. of NFVA in the soffits). If the soffits are wide enough, you can remove the existing vents and replace them with 8-in. by 16-in. vents, which provide 65 sq. in. of NFVA per vent. With 10 of these large vents, you’ll end up with a more adequate 4.5 sq. ft. of NFVA in the soffits.

From Fine Homebuilding #257, pp. 80-81, January 6, 2016

Fine Homebuilding Recommended Products

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

Ladder Stand Off

Stability is key when working off a ladder or accessing the roof, and this lightweight aluminum stand-off makes any extension ladder safer and more comfortable to use.
Buy at Amazon

Peel & Stick Underlayment

Often required by code, this durable, slip resistant, self-sealing, and self-adhered roofing underlayment is easy to install and ensures maximum protection along roof eaves, rakes, and valleys.
Buy at Amazon

Roof Jacks

All-steel construction makes these roof brackets durable and long lasting, and their adjustability allows you to create a flat, safe standing surface on most any pitched roof.
Buy at Amazon
Previous: A Crash Course in Roof Venting Next: Attic-Ventilation Strategies

Guide

Roofing

Chapter

Roof Ventilation

Sign up for eletters today and get the latest how-to from Fine Homebuilding, plus special offers.

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Roofing

Roofing

A complete resource that includes the best materials and the right techniques to build a sturdy, leak-free, attractive roof on any house

View Project Guide

View All Project Guides »

Become a member and get unlimited site access, including the Roofing Project Guide.

Start Free Trial

Tools and Materials
  • Roof Coverings
  • Roofing Materials
  • Power Tools
  • Handy Helpers
  • Staging and Ladders
  • Safety Equipment
Roof Replacement and Reroofing
  • Preparing the Old Roof
  • Sheathing
  • Installing the New Roof
Roof Ventilation
  • Venting Basics
  • Installation
Waterproofing
  • Underlayment
  • Drip Edge
  • Flashing Adjoining Walls
  • Dormer and Skylight Flashing
  • Chimney Flashing
  • Vent Flashing
  • Gutters
Installing Asphalt Shingles
  • Calculating Shingles
  • Layout
  • Installation
  • Valleys
Installing Other Types of Roofs
  • Cedar Shingles
  • Metal
  • Low-Slope Roofs
  • Slate and Tile
Roof Maintenance and Repair
  • Assessing the Problem
  • Repairing Asphalt-Shingle Roofs
  • Other Roofing Repairs

Fine Home Building

Newsletter Sign-up

  • Fine Homebuilding

    Home building tips, offers, and expert advice in your inbox.

  • Green Building Advisor

    Building science and energy efficiency advice, plus special offers, in your inbox.

  • Old House Journal

    Repair, renovation, and restoration tips, plus special offers, in your inbox.

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters

Follow

  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X
  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X

Membership & Magazine

  • Online Archive
  • Start Free Trial
  • Magazine Subscription
  • Magazine Renewal
  • Gift a Subscription
  • Customer Support
  • Privacy Preferences
  • About
  • Contact
  • Advertise
  • Careers
  • Terms of Use
  • Site Map
  • Do not sell or share my information
  • Privacy Policy
  • Accessibility
  • California Privacy Rights

© 2025 Active Interest Media. All rights reserved.

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

  • Home Group
  • Antique Trader
  • Arts & Crafts Homes
  • Bank Note Reporter
  • Cabin Life
  • Cuisine at Home
  • Fine Gardening
  • Fine Woodworking
  • Green Building Advisor
  • Garden Gate
  • Horticulture
  • Keep Craft Alive
  • Log Home Living
  • Military Trader/Vehicles
  • Numismatic News
  • Numismaster
  • Old Cars Weekly
  • Old House Journal
  • Period Homes
  • Popular Woodworking
  • Script
  • ShopNotes
  • Sports Collectors Digest
  • Threads
  • Timber Home Living
  • Traditional Building
  • Woodsmith
  • World Coin News
  • Writer's Digest
Active Interest Media logo
X
X
This is a dialog window which overlays the main content of the page. The modal window is a 'site map' of the most critical areas of the site. Pressing the Escape (ESC) button will close the modal and bring you back to where you were on the page.

Main Menu

  • How-To
  • Design
  • Tools & Materials
  • Video
  • Blogs
  • Forum
  • Project Guides
  • Reader Projects
  • Magazine
  • Members
  • FHB House

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Popular Topics

  • Kitchens
  • Business
  • Bedrooms
  • Roofs
  • Architecture and Design
  • Green Building
  • Decks
  • Framing
  • Safety
  • Remodeling
  • Bathrooms
  • Windows
  • Tilework
  • Ceilings
  • HVAC

Magazine

  • Current Issue
  • Past Issues
  • Magazine Index
  • Subscribe
  • Online Archive
  • Author Guidelines

All Access

  • Member Home
  • Start Free Trial
  • Gift Membership

Online Learning

  • Courses
  • Project Guides
  • Reader Projects
  • Podcast

More

  • FHB Ambassadors
  • FHB House
  • Customer Support

Account

  • Log In
  • Join

Newsletter

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Follow

  • X
  • YouTube
  • instagram
  • facebook
  • pinterest
  • Tiktok

Join All Access

Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features.

Start Your Free Trial

Subscribe

FHB Magazine

Start your subscription today and save up to 81%

Subscribe

We hope you’ve enjoyed your free articles. To keep reading, become a member today.

Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine.

Start your FREE trial

Already a member? Log in

Privacy Policy Update

We use cookies, pixels, script and other tracking technologies to analyze and improve our service, to improve and personalize content, and for advertising to you. We also share information about your use of our site with third-party social media, advertising and analytics partners. You can view our Privacy Policy here and our Terms of Use here.

Cookies

Analytics

These cookies help us track site metrics to improve our sites and provide a better user experience.

Advertising/Social Media

These cookies are used to serve advertisements aligned with your interests.

Essential

These cookies are required to provide basic functions like page navigation and access to secure areas of the website.

Delete My Data

Delete all cookies and associated data