# Adding Collar Ties to make a ceiling



## Gary in WA (Mar 11, 2009)

Page 39-40: http://books.google.com/books?id=iw...um=3#v=onepage&q=cutting floor joists&f=false

On heel and toe bearing rafters: http://books.google.com/books?id=iw...age&q=heel or toe bearing with rafter&f=false

Page 257 on struts and purlins: http://books.google.com/books?id=1f...sult&resnum=1#v=onepage&q=collar ties&f=false

Rafter ties: http://myconco.com/ComEngProb.html

The fasteners at the rafter/tie joint are critical: http://www.engineersedge.com/civil_engineering/rafter-ceiing-connections.htm


Gary


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## Joe1. (Jul 24, 2010)

Hi Gary,

Thanks for the information, I appreciate it. I found some of those links, but others I didn't, so they were helpful.

I guess what I have to figure out is at what point on the roof rafters will the ceiling joists/collar ties serve to prevent spreading/lift somewhat without increasing the load on the rafters. I think if I put it at 8', as a framer suggested, I'd be getting too close to the center span. Just to note, the inside is about a 12' ceiling (pointed) right now, but the whole gable roof side, ridge to the gutter, is about 18'. So maybe 8' is not too low. I think I'd rather have the height at 9', though.

Maybe what I'll do is make it at 9', which shouldn't increase the load at that point. As far as spreading, then I'll maybe double the studs all along the knee wall that's there. The I-beam in the garage doesn't fall directly below, but the floor joists are 2x12, so it should be able to take the indirect load. What do you think? If this can take the bearing, I could also add some struts inside the wall, and then I don't have to worry about trying to do much tying with the ceiling joists.

Also, regarding the ceiling joist connections, would you recommend adding a few screws in addition to the nails?

Thanks,

Joe


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## Gary in WA (Mar 11, 2009)

Collar ties *lower than the upper 1/3* of the roof height will not help with wall spreading. (They only keep the ridge together).
Here is the info from: http://myconco.com/ComEngProb.html
"Rafter ties *above the lower 1/3* will not stop the walls from spreading and add extra weight to the rafters.
Many builders confuse collar ties with rafter ties. Both are horizontal framing members that connect rafters, but that's where the similarities end. Collar ties (which are required by the Southern Building Code and no other) function to resist the pressures of wind uplift on a roof by holding the rafters together where they meet the ridge. As high up as they are, collar ties have no leverage to prevent the rafters and walls from spreading outward. That job is best done by the ceiling joists. The wrong and the rights of rafter tiesTo prevent roof loads from spreading the walls outward, rafter ties (or ceiling joists) *must be i*n the lower third of the roof pitch. Collar ties are too high to keep walls from spreading and instead *serve to resist uplift* by holding the rafter together at the ridge.
If there are no ceiling joists or if the joists run perpendicular to the rafters, then the code requires rafter ties. Similar to a ceiling joist, a rafter tie is typically a 2x4 that runs parallel to the rafters, from outside wall to outside wall, and ties the rafters together as* close to the top plate as possible*. Rafter ties need to be installed every 4 ft. down the length of the roof.
Rafter ties do not have to be at ceiling height to be effective, but they must *not be placed any higher than the lower thi*rd of the roof pitch. In other words: Measure vertically from the outside wall's top plate to the bottom of the ridge, and place the rafter ties within the lower third of that measurement. Once they get above that point, they lose their most effective leverage.
I've seen builders compound their mistakes when they try to use rafter ties as ceiling joists in semivaulted ceilings. For maximum headroom or aesthetic balance, they place the rafter ties halfway up the roof pitch, near the center of the rafter span where they're too high to be an effective tie. Applying the insulation and the drywall greatly increases the load on the rafters at their most critical point: midspan (what engineers call the maximum bending moment). This added load can cause the rafters to sag, pulling the ridge down and also pushing the exterior walls outward.
To avoid this problem, you'd need to engineer the rafters to carry the point load created by the additional weight being placed on them. You'd also need to design a ridge beam capable of supporting the roof load, just as you would if it were a cathedral ceiling, which essentially it is."


The knee wall should be supported below on a wall or beam to transfer the rafter dormer loads down to the earth. 


Could you post a picture please? 


Just measure the height of the rafters, vertically, from top plate to peak, not on the slope.



Gary


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## creamaster (May 11, 2008)

Like GBR said make sure the rafter ties are in the lower third.. take a look at my garage. It was sagging badly, the ridge beam was 2 pieces and was separating and the rafters were being pulled out of the ridge beam and the walls were separating. Not pictured was a partial loft that was built that was attached to the roof near the ridge beam then tied into 2 walls in the corner, the loft almost extended halfway out to the garage, BUT, there was no support to ground so it was pulling mostly at the center of the roof. 

You can see the labeled pieces in the pic

#1 there were 3 of these up there before I took 2 down, basically collar ties, I guess were added after the loft by prvious owner to try and stop the separation

#2 I added these 16 ft 2x4's in the lower third as rafter ties to help stop the walls from separating

#3 The original "rafter ties" built with he house in '64. They are halfway up, NOT in he lower third, and thus didn't help as much to stop the separating

#4 A cable I installed to help pull the walls together before I installed my rafter ties.

Before I jacked up the roof and cabled the walls I bet there was almost 3/4" inch separation at the 2 ridge beam pieces. After adding my rafter ties and cable its holding well for past 2 years.


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## Joe1. (Jul 24, 2010)

Thanks for the responses, guys. Yeah, Gary I read that information on the site. I understand what they're saying about the important differnce in funciton between the collar and rafter ties. I can't install rafter ties here, because it's a finished room I'm dealing with. Plus it shouldn't call for it; they were built without them to begin with. The floor joists here are parallel to the rafters, and are 2x12s, so I think the walls should be okay in terms of not separating. I'm just trying to make up for some poor work here and there (such as the smaller birdsmouthes) by stiffening things up a bit. I'm not evevn sure it's really necessary to do so, but I'd like to to play it safe, while I have the room taken apart.

As far as the vertical height, I believe it is about 13 or so feet from top plate to bottom of the ridge. 

Maybe I can take some pictures and post them later.

Regarding the knee wall, yeah I know it should be going straight down to bearing and to the ground, but the I-beam below is a few feet away across a finished floor, so I can't do it. I was just wondering if it would serve some purpose to reinforce the knee wall here and there, since the floor joists are pretty large.

Joe


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## Gary in WA (Mar 11, 2009)

The collar ties are not required if the ridge is structural, unless locally. Different types of connections with shear hangers better than any for lateral shear forces: http://books.google.com/books?id=E5...epage&q=structural ridge roof framing&f=false

So, 36', is that wide or long? Rafter span? Beam size and span? 



Gary


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## Joe1. (Jul 24, 2010)

No, the ridge is not structural. Sorry, the _length_ of the whole room inside is about 36-37', and the outside length (wall thickness and eave overhang) is about 39'. The rafter span is about 23-24', which makes the height about 14', given the 14/12 roof pitch I have. From inside, the floor to ceiling height is about 13). And again the rafters themselves are about 18 feet long.

The wall distance between the rafters, if the collar ties are placed at 9' high, is about 6' 4". The ties I plan to use are 8' long; they'll lap the sides of the existing rafters about a foot. So I guess that makes the span roughly 8' And I plan on using 2x6's, 16 OC. But the existing ties are 2x10s, so there will be 6 2x10's among the other 2x6's. 

Joe


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## Gary in WA (Mar 11, 2009)

The knee wall is not structural. The collar ties may be required as your ridge is non-structural. 

The rafter ties are required and should be in the bottom 1/3 above the top plates rafter bearing. Any higher up and you should consult a Structural Engineer for safety. I really want to see a picture of this.......

Gary


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## Joe1. (Jul 24, 2010)

Okay Gary, I'm sending my photographer (brother) out now, ha.

I think I am forgetting to note one factor, which is probably important. The 39' or so roof length is only on one side, the other gable side has a large other gable section running into it perpendicularly. So one side is a full 39' length, where as the other side only has gable ends of about 10' on either end. The short gable sections there have no knee walls, and only go directly to the floors the wall. The middle section where the other part of the house runs into has what seems to be a large header carrying the load down to the I-beam in the garage.

I'll get those pictures right now, though.

Joe


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## Joe1. (Jul 24, 2010)

Okay, here are the pictures under a photo album. There are some of the outside of the gable section of the house, from underneath in the garage (of the I-beam, etc.), of the dormers, and the whole room itself.

I appreciate any advice. 

Thanks,

Joe


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## Joe1. (Jul 24, 2010)

photos 1


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## Joe1. (Jul 24, 2010)

photos 2


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## Joe1. (Jul 24, 2010)

photos 3


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## Joe1. (Jul 24, 2010)

photos 4


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## Gary in WA (Mar 11, 2009)

Looks good other than one hanger too high on the center rafter above the dormer opening, but it will pass inspection.

Do you know the ridge is separating? 

Notice in this article about the proper connection of ceiling/floor joists to rafters: http://www.finehomebuilding.com/how-to/qa/removing-collar-ties.aspx

Make sure there is no short wall from the floor joists to the rafters: http://www.unified-eng.com/ch/thrust.html

Make sure the rafter/joist connection is well nailed: http://www.engineersedge.com/civil_engineering/rafter-ceiing-connections.htm

As you already had an Inspection by your local Building Department for the room over the garage at main house building and recently the dormer additions, why are you concerned with the ridge? 

Gary


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## Joe1. (Jul 24, 2010)

Hi Gary,

Thanks for the response. Yeah, I know the hangers are a little off. That's not my work, or else they wouldn't be off:no:. They're plenty of other things off on those dormers also. The dormers were inspected already though anyway, and there were no issues.

Anyway, I started yesterday on the ceiling, and I'm about 2/3 done. I'm using all new 2x6's set at 9 1/2' (the height I believe of the first tie you see--as they were all off as much as half a foot), and I have them all at 16 OC. I've fastened them all with 10d nails, and I've tried to go as far in with the ties and nails as I could--I have about 6-8 nails on each side of the ties. I think it should be pretty strong, even without the bolts, etc. I may add a few screws here and there to help a bit. I'm counting the 16 OC helping a lot here--it seems like a lot of wood!

I got rid of the old ties, because they were fairly cracked here and there, and it didn't pay to try to keep them after I removed them (to reset the height). 

The height is within the 1/3 from top. Not great for any spreading issues, but good for collar ties. The ceiling therefore is 3 feet above center, so that should be enough to avoid the extra dead load on the existing rafters. 

As far as the short wall, I'm not really understanding what you mean. Do you mean the knee wall I have? 

The reason why I have the concern for spreading would be more obvious if you saw how things on this house were constructed. Firstly, the birdsmouthes are too small (by a fair amount), and secondly there seems to be some spacing on the ridge to rafter connection. I can't tell if they messed up the cuts, which considering the way other things are built is very possible, or if there is indeed a little of a spreading issue. Perhaps the ridge is just set crookedly, I don't know.

I just wanted to stiffen things up a little. The way I have it now, it should help as far as collar ties goes, without effecting the rafters (being off centered as they are). 

I might get some more strapping and add them to the existing rafter to top plate connection, if I can get in there with them. 

Joe


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## Gary in WA (Mar 11, 2009)

"As far as the short wall, I'm not really understanding what you mean. Do you mean the knee wall I have?" ----- No, the article was showing short wall failure because of missing rafter ties. 

Remember to add an access for the new attic, if over 30sq.ft. and 30" high......

Gary


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## Joe1. (Jul 24, 2010)

Hi Gary,

Okay, that's what you meant. Yeah, I have some access already to the new attic. The attic from the other roof section deads into it and I've broken out the sheetrock in that area in order to get the collar ties in place.

Anyway, everything else seem good to you? Maybe I'll get some pictures up of the framing before sheetrocking.

Thanks for the help.

Joe


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