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Srollins
Member
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# Posted: 6 Jun 2018 18:24
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Hello all,
I need some quick advice, cabin is 24feet wide I'm starting the roof framing as soon as this coming weekend and Understand the difference between a ridgeboard and ridgebeam with that said my plan was to use a 1x12 board 2x8 x16 rafters and 2x6 double collar ties . 2 questions
1. Obviously 8 can't but a 1x12x 32' which is the cabin length so I'm assuming it's ok to piece the board and support temporarily until all the rafters are in, or should I use a 2x ?
2. If my sizing of members seems off please say so, I'm using T&G 3/4" on the roof all is exposed inside . Is it ok to install every 2 feet? Every other rafter to receive a collar tie? Or every one? I think every 16" would hide a lot of the boards and create a crowded look?
Am I missing anything?
Thanks Scott
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Borrego
Member
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# Posted: 6 Jun 2018 18:49
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Why collar ties? Are you trying to get a more open feel with a higher ceiling? There is some difference of opinion on the value of collar ties at all.....
I assume you are not going to have typical ceiling joists?
If you are indeed going for the 'vaulted ceiling' look, you could alternatively support the ridge BEAM
In your mind, if the ties are there to prevent the two sides of the roof from spreading, then they will be in 'tension'...but you can correct this by using straps at every rafter meeting.....if they are there to prevent rafter sag, they will be in a state of compression....
(If you do use them for some reason, remember they must go in the top 1/3rd of the rafter)
But my question is again..why do you want to use collar ties?
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Srollins
Member
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# Posted: 6 Jun 2018 19:19
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I always thought using a ridge board instead of a ridge beam collar ties are required to help tie the opposing rafters together and also help carry the load? I like the look of them as well , sounds like my idea would work right? Every two feet sound right?
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DaveBell
Moderator
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# Posted: 6 Jun 2018 20:09
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Collar ties are not code approved.
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DaveBell
Moderator
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# Posted: 6 Jun 2018 20:17 - Edited by: DaveBell
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A ridge board is used with rafter ties.
A ridge beam with post does not need ties.
Or you can use a truss.
Rafter Ties can only be used about 1/3 the way up the rafter rise.
http://www.small-cabin.com/forum/2_7980_0.html
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ICC
Member
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# Posted: 6 Jun 2018 21:52
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There seems to be some misperception about what a collar tie is and what it does.
There is also sometimes confusion between rafter ties and collar ties.
A rafter tie is located either at the top of the wall, going across between the rafter tails where the rafters sit on the wall. Rafter ties may be located higher, but must be in the lower 1/3 of the rafter/wall top triangle. Rafter ties prevent the horizontal component of the rafter load from pushing the tops of the side walls apart. Rafter ties are necessary when a ridgeboard is used but may be skipped when a structural ridge BEAM is used.
A collar tie is completely different. Collar ties are located in the upper 1/3 of the rafter triangle. Most often they are located fairly close to the peak. A collar tie is intended to resist rafter separation from the ridge beam or ridge board that may be caused by wind uplift. The idea is to keep the roof peak together. Collar ties may be replaced by running metal strapping over the peak with the straps nailed over top of the sheathing. I believe metal straps are superior to conventional collar ties as they are applied over the sheet sheathing. The real peak separation danger occurs when gable ends or windows in the gable ends blow out in high winds. If the wind can get inside, under the roof, the peak may separate and bye-bye goes the roof.
So collar ties and rafter ties have different jobs. If the roof uses a ridgeboard it needs rafter ties; if the ridge is a BEAM, rafter ties are not needed. However, the peak should have collar ties or metal straps with both ridgeboards or ridge beams. Factory made trusses are a different matter.
There are tables in the IRC that specify how many nails and what size should be used to connect the rafter tie to the rafter tail. This is known as the heel joint. When the heel joint is moved up into the rafter triangle adjustments must be made in the number of nails. More nails as the rafter tie moves up to the maximum 1/3 point.
Adjustments in load carrying for the rafters also must be made as the rafter ties move up into the lower 1/3 of the rafter triangle. That is also in the footnotes to the IRC rafter tables.
The 2x8 rafters mentioned should be good on 16" center rafters to about 45PSI ground snow load.
Quoting: DaveBell Collar ties are not code approved.
They are code approved for the task they are meant for(noted above). You might want to reference IRC section R802.3.1 where collar ties are mentioned by name. 1x4 is the minimum size and should be no more than every 4 feet... if rafters on 24"centers are used that means every other rafter pair. Closer spaced is okay.
Srollins, yes you may use a 1x12 for a ridge board. You can scab two or more pieces together between rafters. A ridge board is not structural. All it does is keep the rafter tips properly spaced until the roof sheathing is in place. You specifically mentioned using a 1x ridgeboard. I assume that means you will also be using a rafter tie on each rafter tail end. At 24 feet wide I would guess you are splicing the rafter ties. Lap splices must be 3" or more in length or be positioned over a bearing partition, wall or beam and properly toenailed to the bearing member.
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Borrego
Member
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# Posted: 6 Jun 2018 21:59
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Quoting: Srollins I like the look of them as well
Are the collar ties mainly for looks? Other wise they can be worked around.....I don't see the point, but i haven't seen the drawings.....
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toyota_mdt_tech
Member
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# Posted: 6 Jun 2018 23:12
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Quoting: DaveBell Collar ties are not code approved.
They were required on mine. Of course, I had rafter ties on every one and I was required to have a collar tie every 4feet.
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toyota_mdt_tech
Member
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# Posted: 6 Jun 2018 23:16
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Srollins, if your building is square, make all your rafters ahead of time. All identical. Now set the end 2 gable end rafters in place, no ridge board yet, let the rafters come together and find center. Do the same at the other gable end. Now build your ridge board, splice it etc and get a buddy and lift it in between those rafters you butted up, spread rafters apart, set them in place and screw it in place, then square it all up and remove screws and nail it in place. I think a rafter, maybe consider 16". 3/4" sheeting is going to be stout. 
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Borrego
Member
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# Posted: 6 Jun 2018 23:58
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Quoting: toyota_mdt_tech make all your rafters ahead of time. All identical. Now set the end 2 gable end rafters in place, no ridge board yet, let the rafters come together and find center. Do the same at the other gable end. Now build your ridge board, splice it etc and get a buddy and lift it in between those rafters you butted up, spread rafters apart, set them in place and screw it in place,
This is good advice! ^^^^
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DaveBell
Moderator
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# Posted: 7 Jun 2018 03:51
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He appeared to be using only collar ties. I thought everyone could see that. No mention of 22 ft rafter ties. Maybe I should have said collar ties without rafter ties is not code approved.
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DaveBell
Moderator
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# Posted: 7 Jun 2018 03:53
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For the 24' span, he might need to do trusses so the roof doesn't fall on his head.
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Srollins
Member
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# Posted: 7 Jun 2018 06:30
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I think I understand, my goal is to NOT have any rafter ties or some call ceiling joist , I want the cathedral look but like the appearance of collar ties which are near the peakcorrect? So it sounds like I need to use a ridge beam not board correct? If that's the case I need to figure out a way to support the beam due to the building length 32 feet . Does this configuration sound about right 2x12 for ridge beam supported on both ends by some sort of post, rafters 10/12 pitch using 2x8, then coller ties at 2x6 question is if you guys think this design is good my only other question is 16" on center or 24? Thanks guys
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toyota_mdt_tech
Member
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# Posted: 7 Jun 2018 09:01
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Yes, ridge board, make sure its load goes down to footers, a laminated beam, I wouldnt splice it, tough deal. I would have some drawings engineered to get it right.
Maybe consider engineered scissor trusses to give it a someone open affect but no ridge beam/board needed.
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Srollins
Member
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# Posted: 7 Jun 2018 09:12
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I think trusses is the way to go, thanks for the advice guys I really appreciate it.
Scott
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ICC
Member
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# Posted: 7 Jun 2018 09:58
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Quoting: Srollins Does this configuration sound about right 2x12 for ridge beam supported on both ends by some sort of post,
No. Not good. You need an engineer if you want a cathedral ceiling that wide and that long. Or have a truss company (engineer) design a scissors truss to span the width and simulate a cathedral ceiling.
What about roof insulation?
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Borrego
Member
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# Posted: 7 Jun 2018 11:26
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Quoting: ICC What about roof insulation?
Always a good point 
Quoting: toyota_mdt_tech Maybe consider engineered scissor trusses to give it a someone open affect but no ridge beam/board needed.
Good idea, you will have room for insulation and create the open space you want...
Quoting: Srollins Does this configuration sound about right 2x12 for ridge beam supported on both ends by some sort of post
No! Not a 2 x 12 ridge beam....and they don't make them at 32 ft. 32 ft is probably too long for even an engineered wood beam, you may need to go to a metal one...Or put a post in the middle
Or use trusses, but they'll run you about $4k....
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snobdds
Member
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# Posted: 7 Jun 2018 11:29
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My engineer designed my cabin by using I joist for the loft and as double purpose for the rafter ties. It required framing the walls to be 12 feet high, all continuous and the I joist at the 8 foot mark. Then we also had to use collar ties every 16 inches. The loft designed to be 3/4 of the overall space, so that means the final 1/4 of space is cathedral space and no rafter ties. We had 11 feet of snow up there this winter and she held up just fine.
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KinAlberta
Member
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# Posted: 7 Jun 2018 15:11 - Edited by: KinAlberta
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In the pic below, It appears to be: a large expanse, exposed collar ties, no rafter ties, ridge board...
CH+D mag's Fall 2012 Best Of Photos / Charleston Home + Design Mag
https://s-media-cache-ak0.pinimg.com/originals/ee/b9/81/eeb98164cc2349db68572250cbd4f 9ae.jpg
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snobdds
Member
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# Posted: 7 Jun 2018 16:42
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That's a hip roof, not a gable end roof. The hip portion of the roof acts like rater ties.
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DaveBell
Moderator
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# Posted: 7 Jun 2018 17:39
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Quoting: Srollins I think trusses is the way to go, thanks for the advice guys I really appreciate it.
I was designing for the ridge beam. 24' span also. I decided it would be just easier to do trusses on 10' walls.
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KinAlberta
Member
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# Posted: 7 Jun 2018 20:16
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Quoting: snobdds That's a hip roof, not a gable end roof. The hip portion of the roof acts like rater ties.
I’m a bit surprised that that would provide enough resistance against the centre span sagging and spreading the walls.
It looks like there’s the distance of 4 or 5 rafters going up to the ridge board plus a few on each end that tie in to the diagonal rafters near the peak (though to a diagonal support).
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ICC
Member
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# Posted: 7 Jun 2018 21:26
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A hip roof is a very sturdy roof. FWIW, it is well suited for areas with high winds, hurricanes. A gable roof is worse because the gable ends can let wind in and under the roof.... poof! The steeper the pitch with a hip roof, the stronger it is. Strength depends a lot on the care the carpenters took cutting the rfaters and in nailing. A hip roof is more difficult to frame properly. Uses more materials than a gable roof too.
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NorthwoodsGuy
Member
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# Posted: 7 Jun 2018 21:28
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Where do you live? Do you know what your snow load is? You use collar ties if you have a vaulted ceiling and no attic. Their purpose is to keep the outward force from the roof and its load from pushing the walls outward. If you have floor joists for your attic, they do this for you. If you are using a ridge board, your rafters need to be rated for the entire 24' span- even with no snow load, the most you can go with a 2x8 is about 15'. Truss is definately the cheapest option.
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ICC
Member
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# Posted: 7 Jun 2018 21:47 - Edited by: ICC
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Quoting: NorthwoodsGuy If you are using a ridge board, your rafters need to be rated for the entire 24' span-
Rafter span is the horizontal distance measured from the plumb line of the inside face of the ridge board to the inside face of the side wall top plate. That is more or less one half the entire width of the building. In this case, the 24 foot building width produces a rafter span of about 12 feet. If you have been sizing rafters using the full width span you have very sturdy rafters.
Tutorial can be found here. Scroll down to bottom to see drawing of rafter span.
Quoting: NorthwoodsGuy If you have floor joists for your attic, they do this for you.
YES, absolutely true!!
Yes, ground snow loads need to be factored in. If no snow we still use a live load of 20 PSF to take account of winds, rains, etc.
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Quoting: NorthwoodsGuy You use collar ties if you have a vaulted ceiling and no attic. Their purpose is to keep the outward force from the roof and its load from pushing the walls outward.
No. Rafter ties do that, not collar ties. That was covered above in previous comments. ----- Collar ties are too far up in the gable roof triangle to prevent wall spread.
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Srollins
Member
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# Posted: 8 Jun 2018 06:24
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Good info here but I'm getting lost, last question I promise will this work? Cabin is 24' wide 32' long 1x12 pieced together as the Ridge board all the way 32' , not supported because it does nothing anyway but provide a place to nail the rafter to correct? Thalf half the cabin has a loft so the loft floor can serve as rafter ties, after the rafters are in add collar ties close to ridge, the other half is what is kicking my butt I would like to run the rafters and simply add collar ties possibly drop them a bit maybe use 16' material for this? Pitch will be 8/12 min depends on the appearance, head room in the loft etc. at this point thinking 2x6 rafters or 2x8 ? 3/4" T&G on roof, cabin is in West Virginia not a whole lot of snow but it does see some. Starting to frame this weekend unless I use trusses then my whole plan changes, I would prefer to stick frame this not a big fan of trusses any help on this as quickly as possible would be greatly appreciated.
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ICC
Member
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# Posted: 8 Jun 2018 10:30 - Edited by: ICC
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Quoting: Srollins Cabin is 24' wide 32' long 1x12 pieced together as the Ridge board all the way 32' , not supported because it does nothing anyway but provide a place to nail the rafter to correct?
Correct
Quoting: Srollins Thalf half the cabin has a loft so the loft floor can serve as rafter ties, after the rafters are in add collar ties close to ridge,
IF the rafter ties are located at the wall tops to form a nice triangle that is perfect.
Question? What are you planning to use for these rafter ties which are really floor joists if there is to be a loft built on them? Is there a center support wall or beam?
Quoting: Srollins I would like to run the rafters and simply add collar ties possibly drop them a bit maybe use 16' material for this? Pitch will be 8/12 min
IF you span the width with a 16 foot long member that will end up in the lower 1/3 of the gable triangle. That makes that 16 foot member a rafter tie, NOT a collar tie. So in effect you would be raising the rafter tie from the wall tops to approx 1/3 the vertical distance between wall top and roof ridge. That means the strength rating of the rafter must be de-rated by about a third. The rafter calculator indicates you should use something like grade #2 S-P-F for the rafters on 16" centers. Because the raising of the rafter ties derates the rafter you should use a minimum size of a 2x8. Just what works also varies a little with wood species. What is available where you are?
Those rafter ties would be on every rafter pair. Theoretically, you could double up the ties with two on a rafter pair and then do every other rafter. But that is theory and not necessarily sound engineering advice.
Quoting: Srollins 3/4" T&G on roof,
And how will that roof be insulated? Better to figure that out now before you nail something together than to try and figure it out, make do, later.
I hope you don't mind me saying, but I think you are rushing this build process. Think out and plan all the details before cutting and nailing.
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Borrego
Member
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# Posted: 8 Jun 2018 10:35
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Srollins, not wanting to hurt your feelings but you need some help with this....no one here has seen your project and are offering educated guesses (although there are some smart folks on here)
What you are suggesting sounds sketchy.....wouldn't take you a couple hours to run this past an engineer and get it right......
You'll waste a lot of time and money to do this wrong. I would rather build it once and build it right..... Just my $.02...
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ICC
Member
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# Posted: 8 Jun 2018 10:54
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My way of looking at this is that all the aspects of the build should be drawn, either on paper or using software. Moving away from the conventional in one part affects other parts. EG: Moving the rfater ties up into the rafter triangle derates the rafter size. It also changes the number or size of nails used to connect the rafter tie to the rafter. We are guessing, assuming a lot and that can be a bad thing. Thanks for reminding us of that Borrego.
I never knew there was to be a loft floor over part of the length until this morning. That is a very wide span, 24 feet. That would usually have an intermediate bearing wall or a beam. Or would be a floor truss. Can the main floor support that? Is the main floor supported centrally or just at the outside walls?
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NorthwoodsGuy
Member
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# Posted: 8 Jun 2018 11:27
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Quoting: ICC No. Rafter ties do that, not collar ties. That was covered above in previous comments. ----- Collar ties are too far up in the gable roof triangle to prevent wall spread.
Yes, absolutely right. Sorry about that. And thanks for clearing up the span issue. I am NOT an engineer or code expert.... 
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