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!
  • Students Click Here

*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


Vaulted Ceiling with Knee Wall - Bracing Option

Vaulted Ceiling with Knee Wall - Bracing Option

Vaulted Ceiling with Knee Wall - Bracing Option

Interestingly framed vaulted roof -

The roof is a vaulted roof that sits on knee walls (aka stub walls), so the bottom of the rafters are 3' above the floor. There are no ceiling joists or collar ties as the room has a vaulted ceiling. There is another wall (parallel to the outside wall) inset 16" from the outside knee wall and between these walls there is full sheathing. Basically this creates a moment type connection that actually seems to work when modeled.

See attached.

What are your thoughts on this?

Also - this roof happens to have a hip on one end and a dormer on the other and it only acts over a small portion of roof. In the bigger picture this is probably helping things but I'm not inclined to rely on this or try to analyze it that way.


RE: Vaulted Ceiling with Knee Wall - Bracing Option

If it works, then it works. Good. Perhaps these could be placed every 4 feet or so if the framing can span that far, and depending on the thrust seen.

The only thing extra you need is metal strapping to the rafters and plates at the ends of the wall to take the uplift.

As an alternate to the plywood, you could also use a diagonal member, but it seems that the plywood is simpler.

Mike McCann
MMC Engineering

RE: Vaulted Ceiling with Knee Wall - Bracing Option

What is the spacing on the 2x12's and the floor joists. I assume they are 16" on center. Then what is the spacing of the OSB diaphragm. Is it just in one location or does it repeat along the walls at a certain spacing. Is the OSB just on one side or both sides of the studs.

RE: Vaulted Ceiling with Knee Wall - Bracing Option

Thanks for the input.

These are at every rafter which are 16" oc. They are on 1 side but another side could be added.

Interesting notes:
If I argue that the there is no "holddown" or reaction capacity of the lag screws in withdrawl, the analysis still seams to work as there is a moment between the floor wall and rafter due to the restraint of the plywood. However the difficult part is how to accurately analyze the moment transfer from the sheathing to the rafter and wall.

If I say that the the restraint of the lag screws is valid (which it should be) then the behavior is similar to a brace as Mike notes.


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!


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