Diamond-built

Collar Tie

Recommended Posts

Does X7 have a collar tie feature? I have to put collar ties down a 1/3 and every 1/3. 

Share this post


Link to post
Share on other sites

You can create them using general framing member. You could use this for your strongback in your other post as well. Lets you create whatever size framing member you need. Create your first one and set it where you want it then use the multiple copy tool to place more at desired intervals.

Share this post


Link to post
Share on other sites

I just draw them in, in section elevation view, it would be nice to have a tool, b/c I have them in just about every non-beam ridge condition.

Share this post


Link to post
Share on other sites

Most engineers have done away with collar ties because they don't do that much. A metal strap at the ridge can do as well or better.

Share this post


Link to post
Share on other sites

Not mine, he wants them on every job when not having a bearing ridge including a metal strap

Share this post


Link to post
Share on other sites

Here's a discussion: http://www.finehomebuilding.com/how-to/qa/removing-collar-ties.aspx

 

The author neglects to consider the main purpose of the ties, which is to keep the rafter tops spreading during wind uplift, but this is done much more cheaply through metal straps. They might also reduce the deflection on very steeply pitched and undersized rafters in an existing structure.

 

Here's a better technical article: http://www.finehomebuilding.com/pdf/021240018.pdf

  • Upvote 1

Share this post


Link to post
Share on other sites

The only time collar ties do any good is when they are specifically designed to be functional by an engineer or architect

 

We try to create a truss effect even when there are no manufactured trusses. Ceiling and rafter joists at the same spacing. Much better than not.

Share this post


Link to post
Share on other sites

Ceiling ties (i.e. joists) can have a truss effect, if properly nailed. If you tried to use a collar tie for truss forces, it would require so many nails that the wood would split. (Same is true for ceiling joists in a low pitched roof.) Also, for a truss effect, you really need "triangles" of framing. If you think you are getting any real truss-like benefit out of a collar tie (i.e. in the top third of the rafter) you are deluding yourself.

Share this post


Link to post
Share on other sites

Here's a discussion: http://www.finehomebuilding.com/how-to/qa/removing-collar-ties.aspx

 

The author neglects to consider the main purpose of the ties, which is to keep the rafter tops spreading during wind uplift, but this is done much more cheaply through metal straps. They might also reduce the deflection on very steeply pitched and undersized rafters in an existing structure.

 

Here's a better technical article: http://www.finehomebuilding.com/pdf/021240018.pdf

Interesting articles Richard.

 

I've installed engineer designed collar ties with no rafter ties or ceiling joists but they were engineered carefully and installed properly. Always use the metal straps over the ridge.

 

My current house had a concrete tile roof with 2 x 6 rafter ties every 4 ft. O.C. They were probably enough to keep the rafters in place, the ridge board from sagging and the walls from splaying outward but the framer only used a couple or 3 16d's at the lap with the rafters.

 

That wasn't enough and over time that nailed joint began to fail and the ridge sagged, the walls moved and the fascia bowed under the stress. I talked to my engineer and learned that the connection of the rafter ties to the rafters where they lap was very important. I jacked up the roof over a couple weeks, nailed the cr@p out of the rafter/rafter tie lap, and created a truss system with plywood gussets. Held fine until we tore it off for a second story addition.

Share this post


Link to post
Share on other sites

Ceiling ties (i.e. joists) can have a truss effect, if properly nailed. If you tried to use a collar tie for truss forces, it would require so many nails that the wood would split. (Same is true for ceiling joists in a low pitched roof.) Also, for a truss effect, you really need "triangles" of framing. If you think you are getting any real truss-like benefit out of a collar tie (i.e. in the top third of the rafter) you are deluding yourself.

FYI, been doing it that way for 40 years--no problems, talk to a structural engineer that knows. you'll learn.

Share this post


Link to post
Share on other sites

FYI, been doing it that way for 40 years--no problems, talk to a structural engineer that knows. you'll learn.

 

 

My experience mirrors Richard's approach.  I have never spec'd ties and my engineer has never required them.  However I do not think there is a downside to using the ties.

 

I either have a ridge BEAM with no ties or ceiling joists OR I have a ridge BOARD with ceiling joists in the lower 1/3rd of attic area.   The higher up from the top plate the ceiling joists are,  the more nailing is required.  I am not surprised by Larry's comment in regards to trying to use the collar ties as ceiling joist/truss config.

 

I always strap rafters over ridge when using the ridge BEAM approach,  rarely if ever do I use straps if I take the ridge BOARD ceiling joist approach.

 

We are always learning,  thank you Richard for your posts in regards to collar ties.

Share this post


Link to post
Share on other sites

FYI, been doing it that way for 40 years--no problems, talk to a structural engineer that knows. you'll learn.

Well, then you've probably been wasting the homeowner's money for 40 years. I've talked to MANY structural engineers, and run the numbers myself.  Here's an example calculation of tension forces in a collar tie, if you used it that way: http://mathscinotes.com/2010/11/the-mathematics-of-rafter-and-collar-ties/ You can see that the tension forces in that collar tie are running over 2000 lbs. Given that a 16d nail can handle somewhere around 100 lbs in shear, you would be looking at using around 20 nails in the rafter/collar tie connection. Or a couple of bolts, which likely wouldn't hold without splitting the wood. As the pitch gets shallower, the forces get larger.

 

Of course, as dshall mentions, they probably won't do any harm.

Share this post


Link to post
Share on other sites

The only time collar ties do any good is when they are specifically designed to be functional by an engineer or architect

 

You guys are forgetting about this condition. And I think my" Licensed Structural engineer" for 40 plus years, might just know more about this. I have had plan check corrections regarding this, he calls them and --no problem after. Richard, I hope you structures don't collapse, best of luck.

Share this post


Link to post
Share on other sites

It's gonna' be one of those days.

 

"Ding, Ding, Ding... and in this corner weighing in at 74 years of combined experience...."

Share this post


Link to post
Share on other sites

I am not surprised by Larry's comment in regards to trying to use the collar ties as ceiling joist/truss config.

In this case the framer used rafter ties which are basically ceiling joists tied to the rafters at the lap over the top plate. Perfectly valid method to brace a roof in lieu of engineered collar ties. In this case the framer just threw them in and didn't nail the ends enough. I think my engineer recommended 10 10d nails per lap?

Share this post


Link to post
Share on other sites

Well, then you've probably been wasting the homeowner's money for 40 years. I've talked to MANY structural engineers, and run the numbers myself.  Here's an example calculation of tension forces in a collar tie, if you used it that way: http://mathscinotes.com/2010/11/the-mathematics-of-rafter-and-collar-ties/ You can see that the tension forces in that collar tie are running over 2000 lbs. Given that a 16d nail can handle somewhere around 100 lbs in shear, you would be looking at using around 20 nails in the rafter/collar tie connection. Or a couple of bolts, which likely wouldn't hold without splitting the wood. As the pitch gets shallower, the forces get larger.

 

Of course, as dshall mentions, they probably won't do any harm.

Love those articles Richard, really help clarify things.

Share this post


Link to post
Share on other sites

Most failures in wood structures are due to either dry-rot or bad connections.  Back when bridges were being built using wood timbers the connections were done using things like "Split Ring" and "Shear Plates".  During the housing boom of the late 1940's on into the mid 1960's a lot of homes were built using just nails.  The failures that occurred due to winds and seismic forces have resulted in a lot of improvements using metal fasteners.  Properly analyzing the lateral forces in wood connections is an important part of residential design. 

 

For very standard construction the prescriptive codes today are adequate.  However, as soon as something is done that is outside of "very standard" it's critical that a competent professional is consulted.  IOW, either an Architect or Engineer who is able to preform the structural analysis to ensure the structure can withstand the expected vertical and lateral forces.

Share this post


Link to post
Share on other sites

I can't believe that Berkley Breathed missed that one. Has anyone else been following the new adventures of Opus, Bill the Cat and the others on Facebook?

Share this post


Link to post
Share on other sites

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now

  • Member Statistics

    28870
    Total Members
    9156
    Most Online
    ChiefJeet
    Newest Member
    ChiefJeet
    Joined