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

Discussion Forum

Discussion Forum

supporting long rafters

RTC | Posted in Construction Techniques on September 14, 2005 09:42am

hey guys, i’m doing a house with a pretty large gable roof. it’s 12′ to the ridge and 42′ outside to outside. the rafters will be about 25′ long with the tail. no ceiling joists. the second floor is inside the roof. it will have a few 6′ wide dormers on each side that plane with the wall face.the spans of the rafters will be broken up with walls and beams so we will be using 2×6. i was wondering if anyone had some pictures of long rafters.i’ve never done a roof this large on my own and it helps me to visualize.thanks.

RTC

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

Replies

  1. blue_eyed_devil | Sep 15, 2005 04:53am | #1

    Knee walls.

    blue

     

    1. RTC | Sep 16, 2005 07:41am | #3

      it's an icf house and the top plate is 4' above the subfloor.there are some walls that will be breaking up the span.originally the plans called for a wall running down each side about 8' in but we have altered the plans and haven't got them to the engineer yet.

      RTC

  2. Piffin | Sep 15, 2005 05:30am | #2

    You will not have room for any typical insulation in that 5.5" rafter space. Did the designer/arvchitect do any load calcs in this idea?

     

     

    Welcome to the
    Taunton University of
    Knowledge FHB Campus at Breaktime.
     where ...
    Excellence is its own reward!

    1. RTC | Sep 16, 2005 07:58am | #4

      i'm not exactly sure what you mean by typical insulation and load calcs.could you elaborate?

      RTC

      1. mojo | Sep 16, 2005 04:53pm | #5

        With standard fiberglass insulation, 5.5 inches will only get you R19 which is less than the R30 required or R38 recommended where I am in CT.  Using certain types of spray foam (closed cell is at least one) can provide insulation values that meet code in most areas with a 2x6 rafter.

        The load calc would be done by the HVAC contractor to determine the sizing of the HVAC equipment based on construction details including insulation properties.  More insulation in the proper places generally means the HVAC equipment can be sized smaller.

        1. RTC | Sep 16, 2005 07:15pm | #6

          i've never heard of required insulation values here in south texas?maybe i'm being ignorant.anyways, i wanted to use 2x12 rafters but the engineer called for 2x6 and the home owner doesn't want to spend the $$.

          RTC

  3. Piffin | Sep 17, 2005 03:42am | #7

    Mojo explained what I meant by typical insulation.
    When I refered to loads, I didn't mean heat and cooling loads, but live loads on the roof, from snow and wind.

    I realize that 2x6 is the common frame in Texas, having lived there, but i also know that placing a room in under the roof, Cape style, is not caommon there.

    Since you get no snnow, the engineer may be right that 2x6 us acceptable from the load/structural viewpoint, buit wrond RE: insulation. You don't need to worery so much about heating, but a second story of a house with inadequate roof insulation is going to be intolerably hot for human beings, unlesss the owner wants to spend a lot of money on AC to cool it. He should be considering this in his budget conscious mind.

    Another point that YOU should consider, is that a roof that is minimally OK for bearing the live laods on the roof, can still havea lot of bounce in it during high winds. That means that the Sheetrock will open the seams and show cracking at the joints from that structural flaw - excessive deflection.

    So have a heart to heart with the HO and explain to him that it is in his best interest and yours to have a better structure, and better insulation, both of which will pay for themselves in a few years. Before even going to the HO with htis, ask the engineer if he considered the fact that there will be living space immediately under the roof, or if he ONLY considered the minimal structural loading. He might say, "Ooops!"

     

     

    Welcome to the
    Taunton University of
    Knowledge FHB Campus at Breaktime.
     where ...
    Excellence is its own reward!

    1. JohnSprung | Sep 17, 2005 03:58am | #8

      > ....  a roof that is minimally OK for bearing the live laods ....

      He did say that the rafter span is broken up by walls and beams, so we don't know for sure if it's pushing the limits. 

       

      -- J.S.

       

      1. Piffin | Sep 17, 2005 04:59am | #9

        neither do we know if those partition walls are load bearing, direct to foundation, or if they merely transferr loads to midspans on floor/cieling joists below,so this is of course, acedemic, but meant to hilightr areas of concern for him to look into, to avoid liability and to help him formulate a plan to get everyone on the same page, so he can do the best job instead of merely adequate 

         

        Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

        1. RTC | Sep 18, 2005 03:35am | #10

          thank you so much for your input. i am pushing for deeper rafters, hopefully the cost diiference won't be a problem. but this being an icf home may cancel out the roof insulation problem, still i woyld rather use a 2x12.

          does anyone have any pictures of long span rafters ?nobody around here builds large gables.

          thanks

          RTC

    2. slykarma | Sep 18, 2005 09:22am | #11

      Piffin, you were ever the diplomat, so I'll say it instead: No way should 2x6 rafters be used on a 21' run. When the engineering comes back, the HO will see it in black and white.

      Looking in the Canadian code the options are either 2x12 @24" o/c or 2x10 @16" o/c (both SPF #2 & Better). That's at the very lowest load factor of 1.0 kPa which is appropriate for places like Vancouver and Victoria where snow is very rare but heavy rain is not. Those conditions would be reasonably applicable for the Texas coast area where RTC is.

      You would actually be buying fewer board feet if you went with 2x12 because of the wider spacing,  but I'm sure that 2x12 in those lengths is going to be a good bit more per BF than 2x10. Either way, those will be expensive, special order lengths of lumber, not to mention very heavy and tough to handle.

      If traditional span-reducing options such as collar ties or knee walls are not acceptable, my personal  preference would be to use TJIs,  there is a 9.5" depth that would be perfect for this application. Lighter and stiffer than solid lumber, easy to  handle.  But if the HO is balking at the cost of 2x12 compared to 2x6 then he ain't gonna go for TJs.

      RTC: if you haven't already insisted on it, get the thing engineered. That is one major call-back if you go ahead with 2x6 and then it fails because of overspanning.

      Wally

       

       

       

       Lignum est bonum.

      1. Piffin | Sep 18, 2005 05:55pm | #12

        You may have missied in your reading that he said it had already been engineered. it was my diplomatic side recommending that he review that with the engineer tactfully pointing out a few things. I have no idea where the kneewals are or whether they can be considered load bearing.I would prefer the TJIs also for my own choice, but he is in Texas.There is no way in maine, canada, or texas that a collar tie does anything to reduce load spans 

         

        Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

        1. slykarma | Sep 18, 2005 06:37pm | #13

          Maybe we are running into issues of differences in terminology here. I remember a while back we found that in Canada we have a different definition for cripples than you do in the states.

          In my trade school framing text, collar ties are defined as "horizontal members used to strengthen the rafter and reduce the unsupported span. They are attached to opposite pairs of rafters." Lignum est bonum.

          1. Piffin | Sep 18, 2005 06:42pm | #14

            Now prove that they do anything to reduce spans. A dictionary doesn't do it. That dictionary doesn't even clarify whether these are what we here call either rafter ties or collar ties 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          2. slykarma | Sep 18, 2005 06:46pm | #15

            What is the difference between rafter tie and collar tie? Lignum est bonum.

          3. Piffin | Sep 18, 2005 06:52pm | #17

            a cileing joist functions as a rafter tie to resist outward thrust of the rafters on a wall.
            A collar tie is placed in the upper third of the rafter space and resists upward lifting forces that would tear a ridge apart - required in southern building codes where hurricanes and tornadoes are common. 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          4. slykarma | Sep 18, 2005 07:03pm | #18

            I guess when I think about it a horizontal tie can do little to support snow load even tho that book says it does. Resultant force is still downward  directly below ridge.  Wouldn't be the first time the book has been wrong or at least inaccurate.Lignum est bonum.

          5. Piffin | Sep 18, 2005 06:50pm | #16

            I'll take part of that back. I think in terms of vertically applied snow laods on rafters.Buta true collar tie resists the upward load of wind sucking a roof surface away from itself. It would also take a horizontal wind load andtransfer that load to the opposite rafter and thence to the wall supporting it.but they do nothing to resist snow loads 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          6. blue_eyed_devil | Sep 18, 2005 07:20pm | #19

            Slykarma, I was taught a ton of stuff that was wrong in my carpentry apprenticeship trade school (union school).

            One of our instructors always insisted that trusses were the bane of construction and that all trussed roofs would be severly sagging in the next couple of years. The only roofs that I see sag are the conventional ones!

            Don't believe everything you hear.

            blue 

          7. Piffin | Sep 18, 2005 08:09pm | #20

            even when ya hear it here, hear?;) 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

      2. RTC | Sep 19, 2005 02:56am | #21

         yeah like piffin said,the plans are enginereed. there's  lots of walls and beams.most of the 2x6 are in spans of  13' or so.

        the engineer is a good guy and knows what he is doing. the hard part for me is installing this roof and planning what height the interior walls should be to land right on a midspan seat cut or should i even do seat cuts or just sit the rafters on the walls/beams.

        basically i'm trying to find a way to simplify this roof install.i'm new at this.

        oh yeah we've got collar ties

        RTC

        Edited 9/18/2005 7:58 pm ET by RTC

        1. blue_eyed_devil | Sep 19, 2005 03:09am | #22

          the engineer is a good guy and knows what he is doing. the hard part for me is installing this roof and planning what height the interior walls should be to land right on a midspan seat cut or should i even do seat cuts or just sit the rafters on the walls/beams

          Since you're having such a hard time for such a fundamental aspect of rough frame, I'll offer this tidbit.

          Snap (draw) out the roof in full scale on your first floor deck.

          blue 

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Video Shorts

Categories

  • Business
  • Code Questions
  • Construction Techniques
  • Energy, Heating & Insulation
  • General Discussion
  • Help/Work Wanted
  • Photo Gallery
  • Reader Classified
  • Tools for Home Building

Discussion Forum

Recent Posts and Replies

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

Up Next

Video Shorts

Featured Story

An Easier Method for Mitered Head Casings

Making mitered head casings is a breeze with this simple system.

Featured Video

How to Install Cable Rail Around Wood-Post Corners

Use these tips to keep cables tight and straight for a professional-looking deck-railing job.

Related Stories

  • Guest Suite With a Garden House
  • Podcast Episode 688: Obstructed Ridge Vent, Buying Fixer-Uppers, and Flashing Ledgers
  • FHB Podcast Segment: Finding the Right Fixer-Upper
  • Keeping It Cottage-Sized

Highlights

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

"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.

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

Fine Homebuilding Magazine

  • Issue 332 - July 2025
    • Custom Built-ins With Job-Site Tools
    • Fight House Fires Through Design
    • Making the Move to Multifamily
  • 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

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

Enjoy unlimited access to Fine Homebuilding. Join Now

Already a member? Log in

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