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
How-To

Framing a Bay-Window Roof

It's only a small hip roof, but its 45-degree corners befuddle many carpenters. Drawing bay roofs out full scale is key to fast and accurate framing.

By Scott McBride Issue 129
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Synopsis: Framing a hipped roof for a bay window is harder than it looks. This article explains how to lay out framing members with the help of full-scale graphic templates.


For as long as architects have been drawing bay windows, carpenters have been scratching their heads over how to frame the roofs. Victorian builders sometimes got around the problem by letting two-story bays die into a projection of the main roof above. Tract builders in the 1950s did likewise by tucking bay windows under overhanging second floors or wide eaves. A well designed bay window should match the proportions of the facade where it sits.

When a bay bumps out on its own, it needs a miniature hip roof to keep out the elements. Because the corners of bay windows aren’t square, neither is the roof above, and figuring the rafter cuts isn’t straightforward. I’ve built many of these roofs and have worked out a system that does the job without guesswork.

Roofs on manufactured or site-built bays are much the same

The skeleton of a bay roof consists of two parts. The first part is the cornice, an assembly of horizontal lookouts tied together by subfascias. (A subfascia will receive a finished material, in this case aluminum coil stock. If you’re planning to install a painted wood fascia, you can substitute the finished fascia material for the subfascia.) A horizontal ledger carries the lookouts where they are attached to the building.

The common rafters for the middle roof, hip rafters and jack rafters comprise the second part of the skeleton. The side roofs also require sloped ledgers to support the sheathing where it meets the building.

Bays can be site-framed or manufactured units. When the walls of a bay are framed on site, the horizontal lookouts double as ceiling joists. In that case, the lookouts bear directly on the wall’s top plates.

When I’m installing a manufactured bay, as I did for this article, the bay’s plywood headboard provides the ceiling. With the bay installed, I screw through the headboard to affix 2×4 plates above, parallel with the bay’s outside edges. I nail a second plate atop the first. This step makes room for a 3-in. frieze above the windows, which I think looks better than having the fascia directly above the glass. Raising the overhang lets in more light and provides room for insulation, which must usually be installed before the roof is sheathed. As a final plus, adding plates to the headboard provides a meatier surface for nailing the lookouts.

There are no rectangles in a hipped bay roof

A frequent mistake is framing the middle roof as a rectangle, using common rafters as hips. This error makes the side roofs steeper than the middle roof. The result looks clunky, and the disparity in pitch complicates the cornice details.

Bisecting the bay angle with a hip shapes the middle roof as a trapezoid and also ensures that the middle roof and the side roofs will be equally pitched.

Before attaching the plates, I draw the center line of each hip on the headboard, extending the line all the way to the house. To find the center lines, remember that the angle encompassed by a bay window is not its nominal angle, in this case 45°, but rather its supplement. (An angle plus its supplement equals 180°.) So the outer corners of a 45° bay each encompass an angle of 135°. The hips bisect these angles, so the hip center-line angle for a 45° bay is half of 135°, or 67.5°. The other common bay angle is 30°. The techniques in this article work on 30° bays, or bays of any angle for that matter, but you’ll have to adjust the angles accordingly.

To lay out the hip center line accurately, I use a framing square. Conveniently, a 5:12 angle on a framing square is equal to 67.5°, the hip angle of a 45° bay. I place 5 on the apex of the bay’s angle, 12 on either the front or side edge of the bay, and mark on the 5 side. Doubling 5:12 to 10:24, provides even greater accuracy.

I pencil plumb lines on the house wall where the hip center-lines intersect it. These plumb lines serve as references for locating the hip lookouts and hip rafters.

For a full-scale graphic template for all rafter cuts, click the View PDF button below. 

More on bay windows:

Video: How to Build a Bay-Window Roof — Veteran builder Rick Arnold demonstrates his simplified method for laying out and building a bay roof.

How to Install a Bay Window: Part 1 — Build the roof first to make the installation a little easier.

How to Install a Bay Window: Part 2 — With the roof built, it’s time to install the window.

Supporting a Cantilevered Bay — Before building that eye-catching bay on the side of the house, you have to get the floor framing right first.

Framing a Gable Roof Over a Bay — Cantilevering the ceiling joists beyond the walls makes this challenging roof detail stronger and easier to build.

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.

Flashing Boot Repair

Prolonged exposure to the sun and weather can compromise the rubber gasket on standard vent flashing. Use this to quickly and permanently fix failed seals or to help protect the gasket in new-construction applications.
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

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

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
×

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
View PDF

New Feature

Fine Homebuilding Forums

Ask questions, offer advice, and share your work

  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Up Next

Video Shorts

Featured Story

Putting Drywall Sanders to the Test: Power, Precision, and Dust Control

A pro painter evaluates a variety of drywall sanders and dust collection systems for quality of finish, user fatigue, and more.

Featured Video

SawStop's Portable Tablesaw is Bigger and Better Than Before

The 10-in. Jobsite Saw PRO has a wider table, a new dust-control port, and a more versatile fence, along with the same reliable safety mechanism included in all SawStop tablesaws.

Related Stories

  • Anneke Dunnington, Carpenter
  • Tall Deck on a Sloped Lot
  • One-Person Precision
  • Precut Bottom Plates in Doorways

Discussion Forum

Recent Posts and Replies

  • |
  • |
  • |
  • |
  • |
  • |
View More Create Post

Highlights

Fine Homebuilding All Access
Fine Homebuilding Podcast
Tool Tech
Plus, get an extra 20% off with code GIFT20

Video

View All Videos
  • FHB Podcast Segment: A Double Roof Discussion
  • Framing and Flashing a Small Deck
  • Details for Integrating an Addition
  • Podcast 596: Broken Trusses, Frost-Protected Foundations, and Air Control Methods
View All

Roofs

View All Roofs Articles
  • A More Resilient Roof
  • Better Plumb Cuts on Hips or Valleys
  • Pool Noodle Ladder Protection
  • Podcast Episode 662: Roof Venting, Roof Leaks, and High-Performance Framing
View All Roofs Articles

Fine Homebuilding Magazine

  • Issue 331 - June 2025
    • A More Resilient Roof
    • Tool Test: You Need a Drywall Sander
    • Ducted vs. Ductless Heat Pumps
  • Issue 330 - April/May 2025
    • Deck Details for Durability
    • FAQs on HPWHs
    • 10 Tips for a Long-Lasting Paint Job
  • Issue 329 - Feb/Mar 2025
    • Smart Foundation for a Small Addition
    • A Kominka Comes West
    • Making Small Kitchens Work
  • Issue 328 - Dec/Jan 2024
    • How a Pro Replaces Columns
    • Passive House 3.0
    • Tool Test: Compact Line Lasers
  • Issue 327 - November 2024
    • Repairing Damaged Walls and Ceilings
    • Plumbing Protection
    • Talking Shop

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 70%

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