Collar Ties???

 
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Old 03-07-2006, 08:24 PM   #1
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Collar Ties???


Is there a way to get around using them at all?

I am curious if it is structurally possible to even build without them. It has been several years since I framed full time and when I did we only had one or two houses that we didn't use prebuilt trusses.

Would it be possible to use an over sized ridge board and tie the rafters into it so as to support a vertical load?

In my mind I can see it and I have even drawn out a vector diagram to show load forces and my best estimation of their direction.

Curious as to what you more experienced framers have done.

thanks
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Old 03-07-2006, 10:39 PM   #2
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Re: Collar Ties???


If i ask my engineer to design a roof without collar ties that's what I get. Where I live every roof has to have an PE's stamp and he designs from the IRC. If you had a roof design program, I think you would find that any roof can be designed without them.

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Old 03-07-2006, 10:54 PM   #3
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Re: Collar Ties???


Ridge poles?
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Old 03-07-2006, 11:21 PM   #4
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Re: Collar Ties???


Quote:
Originally Posted by old27
Ridge poles?
There are a bunch of different ways. Most of the guys I know call me "old school" (actually they call me "Stone age framer") but I think anyone who thinks collar ties are necessary is more old school than me.

I got pulled over today and the cop asked for dob. I said 9-19-53. He asked if that was 1953???... or what 1853????? I asked him if he knew when the Civil War was fought. He said He'd have my ticket ready in a few minutes.
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Old 03-08-2006, 02:37 PM   #5
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Re: Collar Ties???


Quote:
Originally Posted by Rob 53
If i ask my engineer to design a roof without collar ties that's what I get. Where I live every roof has to have an PE's stamp and he designs from the IRC. If you had a roof design program, I think you would find that any roof can be designed without them.
I think that's a pretty standard thing everywhere (almost). I'm building a log cabin that was dismantled 4 years ago (originally built in the early 40's we think) and am planning to use ties but something inside me was saying to figure out a way around them.

I also knew I could hire a PE to design it for me but also wondered if there was any industry standard as far as the method of actually building it like that.

Thanks
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Old 03-08-2006, 02:53 PM   #6
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Re: Collar Ties???


Ridge beam, buttressed walls, or steel frame holding top of wall, of course designed by an engineer.
 
Old 03-08-2006, 03:13 PM   #7
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Re: Collar Ties???


Due to the fact no one else mentioned it, it's called post and beam pwr.

Bob
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Old 03-08-2006, 03:21 PM   #8
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Re: Collar Ties???


Quote:
Originally Posted by pwrbildr
I think that's a pretty standard thing everywhere (almost). I'm building a log cabin that was dismantled 4 years ago (originally built in the early 40's we think) and am planning to use ties but something inside me was saying to figure out a way around them.

I also knew I could hire a PE to design it for me but also wondered if there was any industry standard as far as the method of actually building it like that.

Thanks
I would go to the span charts and size a rafter adequate for your span. I would also get approval from the building official because where I live the officials overrule any written codes.
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Old 03-10-2006, 12:38 PM   #9
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Re: Collar Ties???


It is possible to frame a full cathedral ceiling without collar ties with an engineered ridge beam. The ridge beam{usually a parallam or lvl} is sized strong enough to prevent sag, and the rafters are secured on the top verses the conventional method of a plumb cut against the ridge. This prevents any outward thrust that would blow out the side walls. This was done on my house in the master bedroom. Trust Joist Co. can spec the beam for you, they have excellent support to help you. Good luck with your project.
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Old 03-10-2006, 02:41 PM   #10
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Re: Collar Ties???


Quote:
Originally Posted by surf6524
It is possible to frame a full cathedral ceiling without collar ties with an engineered ridge beam. The ridge beam{usually a parallam or lvl} is sized strong enough to prevent sag, and the rafters are secured on the top verses the conventional method of a plumb cut against the ridge. This prevents any outward thrust that would blow out the side walls. This was done on my house in the master bedroom. Trust Joist Co. can spec the beam for you, they have excellent support to help you. Good luck with your project.
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Old 03-10-2006, 06:46 PM   #11
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Re: Collar Ties???


I'm very uncomfortable without at least some collarties.

The engineering principals are simple and easily demonstrated. Build a mockup about 3' high and sit on it. Notice the motions involved. Without a collar tie, the rafters will tend to spread at the base. Add a collartie, it goes into tension and the thrust is downward.
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Old 03-10-2006, 11:00 PM   #12
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Re: Collar Ties???


As Surf says, if you have a ridge beam (suitably sized for the load) with the rafters sitting on it not beside it, there is no horizontal force on the wall due to loading of rafters. One of the problems with collar ties is that they are in tension, tension joints in wood are tricky and can fail over time. Collar ties toward the top of the roof are very heavily loaded, toward the bottom are less loaded until they touch the plate and are at that point called ceiling joists and doing the best job they can for the least effort. The struc. engs. I speak with don't use collar ties to hold the walls together at all, that must be acheived in some other manner, but they do use them to decrease the span on the rafter and hence allow you to use smaller dimension rafters for the same deflection. Rich.
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Old 03-10-2006, 11:11 PM   #13
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Re: Collar Ties???


In this instance you are using the ridge beam as the major structural component. The unfortunate aspect of this design is that this area is where all of the heat and humidity tend to collect. Over time the ridge will sag and the walls will bow. In the interim it will be patch and paint.

The concept does work but is expensive in todays world.
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Old 03-10-2006, 11:28 PM   #14
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Re: Collar Ties???


Quote:
Originally Posted by reveivl
As Surf says, if you have a ridge beam (suitably sized for the load) with the rafters sitting on it not beside it, there is no horizontal force on the wall due to loading of rafters. One of the problems with collar ties is that they are in tension, tension joints in wood are tricky and can fail over time. Collar ties toward the top of the roof are very heavily loaded, toward the bottom are less loaded until they touch the plate and are at that point called ceiling joists and doing the best job they can for the least effort. The struc. engs. I speak with don't use collar ties to hold the walls together at all, that must be acheived in some other manner, but they do use them to decrease the span on the rafter and hence allow you to use smaller dimension rafters for the same deflection. Rich.
I agree with Rich here and have done many roofs where the floor joists tie the rafters and walls together with no ridge beam or collar ties are required. Critical calculation is where the rafters and floor joists tie together and also how the floor joist are joined, (if there are two). The calc would = # of nails, gang nail, gusset, or gang plate. The rest could come off span charts.

In Teetor's example, build your 3 ft triangle and tie your bottom chord well with some extra nails, then sit on it, for a thousand years or so. No collar tie required.
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Old 03-10-2006, 11:39 PM   #15
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Re: Collar Ties???


This is a great debate.

It really is quite like the "What came first: the chicken(ridge) or the egg(collar tie)?"

Do Ridges sag because they aren't beefy enough? (another thread: are ridges necessary in non-cathedral applications?)<<<<<<<<<<can't wait

OR

Do Ridges sag because common rafters are not tied together to form a cohesive unit, thus enabling the squish weight (technical term) of the roof to thrust downward, hence causing walls to blow/bow out?

-I.M. Pei27
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Old 03-10-2006, 11:52 PM   #16
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Re: Collar Ties???


Done correctly, they will last for centuries with slate roofs. Go to Europe, there are millions of them. Realise too that they were built when big trees were plentiful, carpenters really understood wood and labor was cheap (indentured slaves).

To reproduce that style today will cost you less than a castle but more than your average house. BTW, you have to heat and cool all of that dead airspace.
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Old 03-10-2006, 11:53 PM   #17
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Re: Collar Ties???


Response to Old.
Tied together is critical without a ridge beam. In my experience tied at the floor joist is best.If the rafters have to sit on top of the floor a collar tie won't hold it anyway so there i woud go ridge beam. That's my experience with the roofs and engineers I've worked with. I still own buildings I did 25 years ago and warranty roofs I did 30 to 35 years ago.

Last edited by K2; 03-10-2006 at 11:56 PM.
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Old 03-11-2006, 12:39 AM   #18
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Re: Collar Ties???


Why do I keep thinking of a wishbone? The difference is that, with a roof, nobody wins.
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Old 03-11-2006, 09:21 AM   #19
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Re: Collar Ties???


Quote:
Originally Posted by Teetorbilt
Why do I keep thinking of a wishbone? The difference is that, with a roof, nobody wins.
Wishbone with a bottom chord. Your wishbone with only a collar tie 2/3 of the way up will still spread with 4 feet of wet spring snow. Wishbone tied to a bottom chord, (joists), will hold the snow just fine provided the rafters are sized properly and all connections are adequate.

Practical Engineering 5/96 has a few pages devoted to this subject but I can't find it printed online. I'll keep looking.

Last edited by K2; 03-11-2006 at 09:44 AM.
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Old 03-11-2006, 05:30 PM   #20
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Re: Collar Ties???


Quote:
Originally Posted by Teetorbilt
In this instance you are using the ridge beam as the major structural component. The unfortunate aspect of this design is that this area is where all of the heat and humidity tend to collect. Over time the ridge will sag and the walls will bow. In the interim it will be patch and paint.

The concept does work but is expensive in todays world.

With proper venting would this really be an issue at all? And if so I would be interested to see the cost difference between a big beefy lvl vs. a steel I-beam ridge.

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