Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Birds Mouth Depth?

Birds Mouth Depth?

Birds Mouth Depth?

We have 2X12 roof rafters spanning 10'4 from ridge to wall which is less than 1/2 the distance code allows it to span. Code states a birds mouth cut can only cut into a rafter 1/4 of the depth...since a 2x6 can technically span the 10'4" is it possible to cut the birdsmouth 1/2 the depth of the 2 X 12 rafter?

RE: Birds Mouth Depth?

You will need to calculate the reduced shear capacity due to the notch and make sure it is still adequate for your loads. Take a look at section of the NDS to check this.
A 2x12 with a half depth notch at the end will have less shear capacity than a 2x6 of the same grade. This is due to the stress concentrations that happen at notched corners as well as how dimensional lumber is graded (chances are if you rip a 2x12 down into two 2x6's the grade of the resulting 2x6's would be less than that of the original 2x12 due to locations of knots and things of that nature). You lose capacity for both the stress riser and the (lack of) grading. So, it may work, but it is not as simple as saying, "I still have the same depth I would have if this were a 2x6, and a 2x6 works"

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close