Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Building & Construction

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 08-23-2012, 02:52 PM   #1
Member
 
Join Date: Aug 2012
Posts: 112
Share |
Default

Joist & rafter span calculators & lumber


I'm not sure on how this is done. I want to determine if I should use 2 x 6 or 2 x 8 lumber for the joists & rafters. The building is only 18' x 24' and is a post & frame construction. I know there are tables for this but I don't know how to work with them. I want to use 24" on center for the joists & rafters. I don't have to worry about any live loading like snow or ice . the joists are from top wall plate to top wall plate, making up the attic area. there is no ceiling or drywall that will be hung on the joists. Its just plain framing. this is a workshop. Just want to know if I can do it with 2 x 6's
for the joists I was going to add purlins or strongbacks to stiffen them up across the 18' span. Anyone care to ad there .02's worth. I should ad that there will be no storage in the attic area either. The only load I have is dead load of the structure itself.

Thanks
Maddog1

maddog1 is offline   Reply With Quote
Old 08-23-2012, 03:20 PM   #2
Member
 
Join Date: Apr 2012
Location: UK
Posts: 710
Default

Joist & rafter span calculators & lumber


Is this what you mean?
The rafters might sag a bit depending on what your roof finish is, but if it's all well-nailed, should hold up.
Permit??
Attached Thumbnails
Joist & rafter span calculators & lumber-mini-scan0229.jpg  

tony.g is offline   Reply With Quote
Old 08-23-2012, 03:59 PM   #3
Member
 
GBrackins's Avatar
 
Join Date: Apr 2012
Location: Fairhaven, Massachusetts
Posts: 2,807
Default

Joist & rafter span calculators & lumber


here is a link to the American Wood Council's Online Span Calculator http://www.awc.org/calculators/span/...rcalcstyle.asp

and this link will give you the American Wood Council's Span Tables for Joists and Rafters http://www.awc.org/pdf/STJR_2012.pdf

to be able to calculate these members you need to know the code required loads they must support. will there be solid walls along the perimeter or will this be an open structure?
__________________
Gary

"You get what you pay for, and sometimes free costs more!"
GBrackins is offline   Reply With Quote
Old 08-23-2012, 06:05 PM   #4
Member
 
Join Date: Aug 2012
Posts: 112
Default

Joist & rafter span calculators & lumber


Hi;
Your drawing shows it correct. The roof slope will be 7'' on 12". The roof will be architectural shingle. Thinking I will do 24" on center for the rafters. And yes, I do plan on taking out a building permit for this.

I could use 2x8's, but a tight budget makes me think how much do I really need. I do think the joists might sag a bit, even if they are placed Crown up. That's why I mentioned I might install purlins or strongbacks. I would run a 2x4 across the top of the joists, (at a right angle to the joist) one on each side. Then to that I would glue & nail & 2x6 to the 1 1/2' side of the 2x4 & then toe nail the 2x6 into the top of the joist as well. Thanks for your looking.

Maddog1
maddog1 is offline   Reply With Quote
Old 08-23-2012, 10:05 PM   #5
Residential Designer
 
AndyGump's Avatar
 
Join Date: Sep 2010
Location: Orange County CA.
Posts: 1,258
Send a message via Skype™ to AndyGump
Default

Joist & rafter span calculators & lumber


According to the 2009 IRC 2x8 C.J.s would just make the grade as long as your Building Department will allow it at 10 lb dead load and 10 lb live load, no storage.
At 24" O.C.

Andy.
__________________
Residential Drafter/Designer
www.draftinginoc.com
AndyGump is offline   Reply With Quote
Old 08-24-2012, 01:34 AM   #6
Member
 
Join Date: Apr 2012
Location: UK
Posts: 710
Default

Joist & rafter span calculators & lumber


Quote:
Originally Posted by AndyGump View Post
According to the 2009 IRC 2x8 C.J.s would just make the grade as long as your Building Department will allow it at 10 lb dead load and 10 lb live load, no storage.
At 24" O.C.

Andy.

Codes typically stipulate figures for live and dead loads, but in this instance, the OP has told us there is no storage, and there will be no ceiling boards/insulation etc. The only vertical load the joists will be carrying will therefore be their own self-weight.

Each joist will weigh approx 50-55 lbs, so the bending stress will come in at less than 200 lbs/sq.in. Most timbers will take a minimum of 800lbs/sq in.

As for deflection, it will be around 0.3" and if we allow a limit of 1/240 span,
the sag will be well under this.
The ceiling joists will of course be subject to tension (acting as ties) and will need to be fixed firmly to the rafters/wall plate.

Whether 2x6s for the rafters wil be OK is another matter; we don't know the dead or live loads he has to allow for.
tony.g is offline   Reply With Quote
The Following User Says Thank You to tony.g For This Useful Post:
GBrackins (08-24-2012)
Old 08-24-2012, 07:43 AM   #7
Member
 
Join Date: Aug 2012
Posts: 112
Default

Joist & rafter span calculators & lumber


After reading the replies to my post on rafters & joists, Im changing my thinking a little. Im now considering that if I go with 2x6's rafters & joists, I should probably move them to 16" on center rather than 24" on center. I would still achieve some cost savings on the 2x6 lumber.

Next consideration would be to go to 2x8's on 24" center. I think either would work. But in the end, I guess the wise thing to do is talk to my building inspector & let him know what I'm up to. Maybe he will tell me what he will be looking at on an inspection, if they ever inspect it at all. Keep in mind this is not a residential use building. Its an outbuildin for my tractors & a small workshop so I can get the needed room to work on my stuff & hobbies. As long as the building is structurally safe to be in, is all I care about.

Maddog1

maddog1 is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
max joist span gkaro Building & Construction 15 01-12-2012 10:58 PM
Remodel bonus room above gargage (need floor joist advance 22" span) Brianhoup Building & Construction 26 01-11-2012 10:40 PM
Joist span question simonb Building & Construction 17 08-29-2011 10:45 PM
Dryer duct hole thru band joist & floor joist justplumducky General DIY Discussions 12 10-05-2010 12:31 PM
joist span? apowens Carpentry 17 05-04-2007 07:54 AM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.