Can attic crossties be removed? <!—-><!—-> <!—->
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Have a gable roof 5/12 pitch with 2×6 rafters leading to a 2×8 ridge board at the peak. In the attic are crossties about ¾ of the way off the floor. They are spaced at every other rafter. I am doing work and would like to take them down (I am tired of bending and the occasional knock on the head). Are they structural at this point for the roof, can they be removed with out jeopardizing the roofs’ structural integrity? I think originally they may have been put in place to hold the rafters until the roof decking was on, does this sound right? <!—-><!—->
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Thanks for the help BDV
Replies
Collar ties like yours are designed to keep the roof from opening up like a clamshell in high wind situations. So IMHO opinion they should not be removed.
You might be able to take them off, cut them diown, and reinstall them a little higher to gain headroom...
What are the dimensions of the space under that area of the roof? How long is the ridge? Is the ridge one single 2X8? Is the ridge supported? If so, where?
Edit: What I'm trying to determine is what the framers had in mind when they put in those ties. It could be simply to protect against wind loads, as Boss Hogg said, or it could be a concern about static overloads which would tend to spread the rafters and walls.
Edited 6/8/2007 11:35 am ET by Hudson Valley Carpenter
In the location described, these would do almost nothing to prevent wall spread. They are collar ties, not rafter ties
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In the location described, these would do almost nothing to prevent wall spread. They are collar ties, not rafter ties
All he said was that he had to duck under them. Without actual dimensions, you're guessing that they're collar ties. While I'm trying to help the guy make an informed decision, you're passing judgement without nearly enough evidence.
>All he said was that he had to duck under them. Without actual dimensions, you're guessing that they're collar ties.
The OP also said they're about 3/4 of the way off the floor, which puts it 1/4 of the way down from the top. Sounds like a collar tie to me, unless he's got a really strange attic design.
Don
Don,
It's all speculation until the OP comes back with some real dimensions and a more complete description of the situation.
It's comical how a group of grown men can get all wrapped up in speculating and arguing with each other over a question like this. It's competitive nonsense. Almost as if we're all back in high school and a nicely packaged new girl arrives one morning. Those who see themselves as the BMOC all jump in, trying to help her find her freekin' locker. Geeze guys, at least wait until she smiles, see if she's got all her teeth.
;-)
<Almost as if we're all back in high school and a nicely packaged new girl arrives one morning>
LOL!
True maturity is realizing that it is ALWAYS the new girl.
We're not more mature; just taller
Forrest - knowin' the truth
Some posts refer to the collar tie as being part of a triangle and therefor good. Roof without collar ties is a perfect triangle, Very strong. Roof with collar ties means you have a triangle on top with a trapazoid underneath. Not as strong. Collar ties every other rafter doesn't make any sense . Load has to be trasferred down through bearing walls,columns to the footings. A collar tie maybe holding up one rafter but it's wanting to push out the rafter on the opposing side and not transferring the pressures down. Spreading load and trying to dissapate it over a larger area is not what engineering is all about. It's about making the load go where you want it to go and that is to the footings.
Having said all that I'm sure putting them in or taking them out isn't going to be noticeable to anyone or be structurally catastrophic.
roger
r
Roger,Adding a collar tie does not make a small triangle and a big trapesoid. It makes a big traingle, a small triangle and a big trapesoid. Stronger, not weaker.SaturdayNight and others,A collar tie is placed in the upper third of the rafters' length to prevent the roof opening up at the ridge in high winds. If the rafters need central support because they are too long, one should use a purlin from a wall up to the rafter. If a collar tie is used as a ceiling joist in an attic room, then it is called a collar beam.Attic floor joists, or lower floor ceiling joists are the usual substitute for rafter ties. The term rafter tie really has no use except when only speaking of the structural effect of preventing the sperading of the rafters, and in an open ceiling with all structural members exposed. In that case the rafter tie must be placed in the lower third of the rafters length from ridger to wall plate.Both collar ties and rafter ties are in tension, so a collar tie would be trying to pull the rafter down, not brace it up, but it only has a tensile force operating on it during windy periods. One can wrap a strap over the ridge from rafter to rafter or from rafter to rafter just under the ridge to replace collar ties. One can also replace wooden collar ties with lightly pretensioned cable or light chain. A ridge to rafter hanger that is designed to keep the rafter from moving upwards as well as downwards can be used in place of a collar ties in those cases where a collar tie is needed.SamT
Praise the Corporation, for the Corporations' highest concern is the well being of the public.
WE agree to disagree.
roger
You have the right to be wrong.SamT
Praise the Corporation, for the Corporations' highest concern is the well being of the public.
The tie between the two legs of the triangle can function to keep the sides of the triangle from flexing, and starting into buckling under high wind loads from the side.
The need to have them could be eliminated if stouter members were used, but it is an economic trade off. 2X6s with few extra 2X4s, or a bunch of 2X10s instead.
I know what you are saying and as I said before I'm sure it doesn't matter whether it has collars or not. If the tie between the legs of the triangle(in this case) is so crutial where does it say how that connection is to be made? I keep coming back to my original position that if collar ties are "structural" and not one of those things that we put up "just to be safe", there should be specific sizing on an individual basis set out in some schedule/table. I have never seen a rafter table say that you must upgrade the rafter size if collar ties are not used or the reverse. Maybe they're out there, I don't know.
roger
Roger,A collar tie is structural the same way an anchor bolt is, not the way a stud or bearing column is.SamT
Praise the Corporation, for the Corporations' highest concern is the well being of the public.
"I'm sure it doesn't matter whether it has collars or not."That would make you surely wrong.As Matt has quoted, they are required to be at least 1x6 or 2x4.You seem to be defining structural as that which holds something up, but sturctural members are what resists any sort of load. There are more loads than just gravity and mass.
There is wind - up, down, and lateral.
There is Siesmic loading
There is Hydraulic loadingAll of these must be resisted with structural ma=embers designed to counteract the forces applied.Wind uplift is an occasional load while gravity is a permanent load, but both need to be accounted for - which is why collar ties are used
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I'm wrong so often that I could be wrong thinking I'm wrong so often. Actually I don't mind being proven I'm wrong because not only have I learned something new but it replaces faulty knowledge.
Back when I was an apprentice draftsman I think the definition of structural was anything that affected the integrity of a structure. I know, pretty vague, but about 4 decades ago.
For the last 2-3 hours I have been trying to copy a page out of the BC Building Code (almost identical to the Canadian Building Code)and I can't make it work. I'll type out a little
9.23.13.7
1 Ceiling joists and collar ties of not less than 38mm by 89mm (2x4) lumber are permitted to be assumed to provide intermediate support to reduce span for rafters and joists where roof slop is 1 in 3 or greater.
2 Collar ties referred to in Sentence (1) more than 2.4m long shallbe laterally supported near the centers by not less than 19mm my 89mm continuous members at right angles to the collar ties.
"are permitted to be assumed" means if you want to use them you can with conditions. Throughout the code when they want you to do something they use the word "shall" or "will be". The only phrases in the entire code that I can find (though I might have missed some) are the two above. Shall or will be ,are not in there.
The rafter table in the code tells you the size of rafters needed for certain applications and spans. Now according to sentence 1 with collar ties you can reduce the rafter span. By what and how much? That would have to be figured out by someone with a stamp which what I said much further back in the discussion. I'm sure an inspector would want to see some sort of calculation if my rafters didn't match the rafter table.
So in effect I'm saying that IF you use collar ties then you are obliged to do certain things, moreso if have reduced the rafter span by using collar ties but I've yet to see anything written (at least up here) where you must use collar ties.
If your codes are different and you "must" use collar ties then I can see we are both right.
Waiting with trembling anticipation.......roger
I can see that as a diff in regional codes. In Canada you primary concern is snow loads. In Texas and Florida, the greater concern is tornadoes and hurricanes.Even the language in your code is presupposing down loads when it adresses the subject, and it seems to permit it without requiring it.
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What is hydraulic loading?
the load pressure from the weight of the roof structure?
I don't think hydraulic loading pertains to this situation. He was just using that as an illustration of how many types of loading there is. I think hydraulic is like the pressure against your basement wall by water saturated backfill. If I'm wrong, I'm sure someone will correct me :-)
BTW - the weight of the roof structure is dead load.
"I don't think hydraulic loading pertains to this situation"That's what I thought too, but figured there might be something to learn by asking about itThanks
Matt had it.When clay soils get saturated, they expand - some as much as three times their volumn but normally 50% is extreme. That is enough to damage foundation walls.Basement slabs can find themselves lifted to crown or crack as well
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Water - usually in foundations or crawlspaces
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Got it :)I had to ask cause it sounded peculiar in regards to this topicthanks
I was trying to list multiple examples of the many kinds of loads a building must be structured to resist because too often we think in terms of only gravity induced loads
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"Without actual dimensions, you're guessing that they're collar ties."I was guessing at absolutely nothing nor passing judgment. I was dealing with simple facts that apparently went right over your head.He clearly stated that these members were 3/4 of the way up off the attic floor.
A collar tie by definition is placed in the upper 1/3 of the rafter and its purpose if to prevent unhinging at the ridge in high wind uplift situations.
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They are called "collar ties" and they are structural.
No, you should not remove them.
You can develop a detail to re-frame the interior of the roof, to raise the ties , or do a hung roof and eliminate the ties. Any decent framing carpenter should be able to point you in the right direction.
Thgose are called collar ties and they are normally structural and in some places required by code.
There arre other ways of perofrmning the same structural need that could be evaluated by an engineer
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3/4 of the way up the pitch? Those are not collar ties, they're ceiling joists. Collar ties occur at the bottom of the rafter. If there is a structural ridge beam, then you should be able to remove them. If they're really 3/4 up you will probably be able to remove them anyway, because they're doing more harm than good. But if you don't have a structural ridge beam then they might be holding the roof together in a "collection of scantling" kind of way. Amazing the way some structures hold themselves together.
I believe you have your terminology exactly reversed--collar ties are near the tops of rafters, celing joists at or very close to the bottoms of rafters. Ceiling joists are what you attach your ceiling to. And as Piffen (or someone early on) said, ties prevent opening of the tops of the rafters where they attach to the ridge from wind creating low pressure there. Don't know about the poster who said they prevent rafter upthrust or whatever--sounds plausible.
Edited 6/9/2007 10:51 am ET by Danno
Thanks.
I use collar and rafter tie interchangably, probably incorrectly. By suggesting that they were ceiling joists I was suggesting attic ceiling with my tongue in cheek.
If we want to discourage uplift separation at the ridge, we could accomplish that with A34 hangers or similar into the ridge board.
I suspect that BDV's collar ties, or whatever we elect to call them, under analysis, are doing exactly nothing. But since everything else about his assembly is undersized, I would hesitate to remove them before addressing other elements. Buildings that are underbuilt have a remakable talent for holding themselves up beyond reason. You never know what is doing what in a "scantling assembly"
Do some googling. It will help you get your terminilogy straight. Granted you may find some incorrect info, but at least 90% of what you find about collar ties will put them in the upper third.
Edited 6/10/2007 8:23 pm ET by Matt
Okay. Yes, hangers would probably work to replace the collar ties, if all they are doing is preventing them opening like a clamshell. But like another poster suggested, they may be assisting the rafters to resist wind or snow loading on only one side.
Concerning "scantling assembly"--I was taking down some wall cabinets in my kitchen in an old house. The previous owner had put them in. [Among other crazy things he'd done was to build a five foot tall by five foot wide brick wall dividing the kitchen and the living room (used cement for mortar) with nothing under the floor in the crawl space to support this wall (or the refrigerator next to it).] I'd removed just about every nail holding the cabinets--many of which had missed studs and still the cabinets wouldn't come down. I finally saw one 16 penney nail that was sticking through the living room side of the drywall (not into any stud). I drove it back and the whole 8 foot length of cabinets came down! One 16 penney into drywall was holding that weight! I was impressed!
The engineer I use wants to write a coffee table book that is a collection of scantling assemblies. The things you find when you tear into existing structures are amazing. When I tear apart a rotten wood foundation to expose that one whole corner of a house has no support, and the owner asks what is holding up the house, I reply "inertia" or as Newton observed, "A body at rests remains at rest until something comes along to change its mind. The house simply has no idea that it's not supposed to stay up. Neither, it seems, did your cabinets.
I recently renovated my old home. An original side porch had been enclosed and converted to living space back in the 1970s. When my contractor pulled down the ceiling he was amazed to find that the ends of the Ceiling joists (with 2nd floor above) were cut short and not bearing on anything, resulting in a 6' cantilever past the bearing wall. My contractor could not explain it.
Yes, hardware can be used to perform many of the functions of the collar ties, but should be designed or reviewed by an engineer
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"I suspect that BDV's collar ties, or whatever we elect to call them, under analysis, are doing exactly nothing"I suspect you are 100% wrong. To back up your theory, you need to explain why many local codes require them in high wind areas, and why they were placed there in the first place.
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You're absolutely right. Great discussion by all.
LOL, and you are now absolved of all your past structural sins, my son!;)
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Not trying to perpetuate this argument ...err, I mean, discussion, but my house is built in a very similar way to the OP's and there's been a lot of good information in this post, but I have a question.My ceiling joists are not continuous and overlap atop a center bearing wall. I have 2' overhangs on my eaves so the rafters rest on the top plate of the 2nd floor walls and are nailed to the plate as well as the joists.My collar ties are ~1/4 of the way down from the ridge as well, but are 2x4's spaced at every fourth rafter and very poorly nailed.If in fact, collar ties are to resist uplift at the ridge, wouldn't they be more effective as they moved closer to the ridge? Does the code specify *within* the top 1/4, meaning that 1/4 the distance from the ridge is the *maximum* distance?I have thought about replacing my ties with 3/4" plywood gussets, glued and nailed right up at the ridge. It seems to me I would get the most headroom and improve tremendously on the current design.Comments?Jerry
>> My ceiling joists are not continuous and overlap atop a center bearing wall. I have 2' overhangs on my eaves so the rafters rest on the top plate of the 2nd floor walls and are nailed to the plate as well as the joists. << Having the ceiling joists spliced is a very common way to do it, especially since 2x8-28' (or however wide your house is) are expensive and special order.
>> My collar ties are ~1/4 of the way down from the ridge as well, but are 2x4's spaced at every fourth rafter and very poorly nailed.
If in fact, collar ties are to resist uplift at the ridge, wouldn't they be more effective as they moved closer to the ridge? Does the code specify *within* the top 1/4, meaning that 1/4 the distance from the ridge is the *maximum* distance? <<
Here in NC, code requires the collar ties be 48" OC and be in the upper third. Sometimes you see them pushed all the way up., but it might simply have to do with weather a carpenter would have needed a ladder in the attic to do it. Just as a bit of trivia, our code calls them "collar beams".
>> I have thought about replacing my ties with 3/4" plywood gussets, glued and nailed right up at the ridge. It seems to me I would get the most headroom and improve tremendously on the current design. <<
You asked for an opinion... :-) It would be a waste of time unless you consider it likely that you would be hit by a severe hurricane, earthquake, or tornado. I'd throw a few more nails in what you have and if you want to strengthen things a bit put in some more 2x4 ties. If you want more head room, push them all the way up.
Yeah, I should have mentioned the need for increased headroom for light storage, otherwise I wouldn't bother messing with them; although,one side of the roof is covered with solar panels which could contribute to uplift. Being on Long Island, we do see the occasional hurricane ...hmmm. Thanks,
Jerry
Edited 6/11/2007 7:46 am ET by Jerry18
Within the top third means anywhere in that upper third of the rafter. When hardware is used instead, it is immediately at the top
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I had thought about whether hardware or wood gussets would be easier and I'm still not sure. Gussets would require fabrication but be easy to install (w/nailgun); hardware requires no fab but has to be hand nailed (for me). Done right it seem either way would be adequate.Jerry
What do you call the joists that are nailed and sitting on the top plate and also nailed to the rafter that's sitting on the top plate?Joe Carola
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Security thingies!Joe Carola
Edited 6/9/2007 12:14 pm ET by Framer
I call those collar ties, although I probably have my terminology screwed up. I have an obscure theatre degree, and am a self-taught remodelor. In my mind, the only succesful collar tie, or rafter tie is the equivelent of the attic floor joist, that is, the hypotenuse of the roof triangle. As the other postings state, when you move the tie up from the base of the rafter, the tie's ability to resist outward stress is dramatically reduced, and actually ends up compounding the load on the rafter.
If you're going to utilize open space in your attic, sensibly three conditions need to be met: The floor joists should be sufficient to support the load, the outward thrust of the rafters needs to be addressed either by a ridge beam or by your floor joists being tied to the base of the rafters, and finally the rafters need to be adequate to span the distance between the ridge and the base, and support the load of the roof. To make changes to the structure without consulting an engineer would be unwise, but be prepared to find that some or all of the other three conditions are not currently being met by today's standards.
And before you insulate, check out the unvented attic assembly that has been adopted by the IRBC. May we never settle for fiberglass insulation again, my brothers!
You need to check your definitions first. The ceiling joists are commonly rafter ties and are probably what he is walking on when he bumps his head on the collar ties. Codes that require collar ties require that they be placed in the upper one third of the rafter. That makes it pretty hard for them to be ceiling joists in that location.It is a common error to confuse the terms collar tie and rafter tie, so don't feel too bad
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A gable roof is dependent for its structural integrity upon a closed triangle to balance all the forces. If the base of the triangle (in many cases, the floor of the attic) isn't closed by joists that tie the two halfs of the roof together, the collar ties or rafter ties (not quite the same thing, as Piffin pointed out) should be presumed to be structural and should not be removed.
If I remember my terminology correctly, collar ties are placed higher on the rafters, and thus do not provide the same degree of resistance to spreading at the rafter ends as do rafter ties, which are placed lower. This is because the rafters themselves bend outwards below where the ties are attached; so where you place that 'pivot' point is structurally important. (Someone please correct me on that if my memory has played tricks on me.)
The dead load of a gable roof without a structural ridge beam (such as yours) can be sufficient to cause the walls it is sitting on to spread outwards. (This you can prove to yourself by mocking up a cardboard model without any ties or joists, and then pushing down on the ridge with your finger to see what happens.) It does not necessarily take wind load, snow load or anything but the weight of the roof itself for this to happen over time. Unless those walls are held together by a structural member working in tension across the space between them, spread will eventually occur to a greater or lesser extent.
Rafter ties, collar ties, and joists which run perpendicular to the ridge of the roof are in tension with respect to the two opposing building walls upon which the roof sits. Joists which run parallel to the ridge are not. Partition wall top plates running perpendicular to the ridge are in tension for those two walls, too, but to prevent spread they must be spaced along the length of the building walls at sufficiently close intervals. This is not usually practical.
IMO it would be extremely foolhardy of you to remove this framing without having an engineer or a qualified framer look at it first and render an opinion.
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foolish men call Justice....
I guess this will stir a hornets nest. I read an interesting letter from an engineer, in Breaktime, who stated that collar ties do nothing structurally to the building in fact hurts it. It was an older article but it made me look up some books regarding collar ties. What I found out that if the collar ties were in fact structurally needed they would have to be put in very specific locations just like the webs in a truss and at no time did I find any reference to specific locations in fact most publications I had never even mentioned collar ties. One stated that the collar tie be placed 2/3 up and put in every other rafter. If it is so structural why not every rafter? No mention as to how it was to be fastened or even the sizing of the collar tie. Truss construction is very specific about the location of everything and the sizes of everything.
I started at 16 as a structural steel draftsman apprentice and had to learn ( long since forgotten) all about where loads are being transferred to and to be honest what that engineer said made sense. It's the ceiling joists that stop the roof from spreading not the collar ties. Now if an engineer designed a roof with collar ties and adjusted the rafter and joist tables to accomodate the collar ties that would be different. I have never seen a collar tie table. They may be around but I haven't seen it.
Okay guys, run with it.
roger
The short answer is: Yes, you can remove almost any part of the atiic structure you want to--it's probably been done before at least once on at least one other building.
The catch, though, is that no one here can tell you what will happen if that stick, or that board, or whatever you hammer loose, will "do" afterwards.
Our methods of wood frame construction have phenominal amounts of "excess" structural capacity in them (generally). Good for our houses; bad for our "pratices" in that there are all sorts of people who have done one thing or another and "nothin bad happened (yet)."
Really, what you need is a competent person in your specific attic.
Some one who can see not only the memeber, but its connection, too.
A number of the responce already in this thread would change if those "crossties" were 1x6's; or if they had either only one, or a gazillion sinkers toenailed in the ends. One of "us" might have a different answer if we saw the stub ends of former trusses up there, too. Just too many questions possible looking at this empty white text-filled screen.
Lots of ways to "triangulate" a roof that do not whack a person in the forehead--some more elegant than others. Other times, one just has to "lump" it while banging around in attics (amazing how even a mediocre hard hat can be as handy as hindering, too).
According to the modified 2000 IRC we use in NC, collar ties must be installed at a minimum, of every 48" in the upper 1/3 of the roof framing unless the ridge is designed as a beam and so supported to the foundation.
Do not remove the collar ties unless you plan the redesign/reframe the roof by installing a beam under the original 2x8 ridge or removing the 2x8 ridge and installing an LVL ridge. In either case the collar ties are an integral part of the roof rafter support and a resisting member designed to prevent a phenomenon call "rafter thrust".
In other words, these collar ties work in conjunction with the ceiling joist, so long as the ceiling joist run parallel with the rafters and are securely fastened to the rafters, by preventing the roof from "pancaking flat" under the applied dead & live loads.
"According to the modified 2000 IRC we use in NC, collar ties must be installed at a minimum, of every 48" in the upper 1/3 of the roof framing unless the ridge is designed as a beam and so supported to the foundation."It doesn't sound like there is anything in that statement that would preclude him from moving them up higher. Is there any reason they couldn't tie the rafters together just below the ridge beam? They'd still be in the upper 1/3 of the roof...
Correct. Our code, modified 2000 IRC, states that collar ties simply must be in the upper 1/3 of the roof framing. Nothing would prevent moving the ties closer to the bottom of the ridge board to gain additional head room under the ridge.
I can't believe you guys are still at it.
I think the OP has already sold that house.
That was good. Very good.:)
roger
While adding a dormer to our home, the architect specified metal strapping over the ridge in lieu of collar ties. (I skipped the ridge vent too, the 2/12pitch wouldn't allow it) Since I was only removing half the roof, I didn't want to have to strip off the relatively new roofing off the "unaffected" or undormered side. I was told by both the inspector and the architect that I could avoid the strapping by adding the collar ties, despite the fact that the ceiling joist of the new room were tied from the roof rafters to the top plate (and the tails of the roof rafters. The after the thing was about 75% framed, the inspector had a change of heart and allowed me to skip the ties, but suggested that I tie the ceiling joist on the long side (right side) to the roof rafters.
yours was a pretty unique situation, but I can see that.
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"unique". That describes this house very kindly.
How about this: Take them down while working, then put them back up again when you are done. Easiest way to do this is to number them so you know exactly where each one goes, then drill a couple of bolt holes on each rafter to remount them exactly where the were before. After drilling, pull the nails and set the board aside. When your project is done, throw some 3" bolts through those holes to reattach the ties.
Rebuilding my home in Cypress, CA
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Give us the length of the rafters and tell us about the attic floor framing including the size and length of the lumber, and how it is attached to the rafters and if it is spliced in the center of the house. Is there a load bearing wall down the center of the house?
The collar ties can possibly be pushed up all the way to the ridge but without more more information, it's just speculation.
Breaker Breaker 1-9 BDV- You got yer ears on there captain?
Could you provide a little more detail on your attic construction?
Thanks
Sorry for the delay, I had to do some more measuring. Here is what I have:
Starting at the top the ridge board is a 2x8 28’ long board, with no splices. It runs the length of the attic with no other support then the roof-rafters (i.e. no support columns)
The cross-ties/collar ties, are 1x6 about ¼ the way down from the peak (3/4 way up from the floor) they are located on every other rafter.
The 2x6 roof rafters at the top are attached to the 2x8 28’ long ridge board.
At the bottom of the 2x6, roof rafters are the 2x8 28’ long bottom plates on either end of the floor-joists (ceiling- joist if you are on the second floor looking up).
These 2x8 plates lay flat and run perpendicular across the top of each end of the floor-joists (ceiling- joist if you are on the second floor looking up).
The floor-joists (ceiling-joist if you are on the second floor looking up), which are 2x6 26’ long joists running perpendicular to the ridge. There is a load-bearing wall in the middle of the 2x6 26’ long joists floor-joists span, but NO splice in the floor-joist (ceiling-joist if you are on the second floor looking up).
Each roof rafter is sitting on top of the 2x8 bottom plate and in line with each floor-joist (ceiling- joist if you are on the second floor looking up) below it.
Thus an isosceles triangle is formed with the 2x6 floor-joists on the bottom (the unequal side) and 2x6 (equal sides) rafters on each side joining at the ridge plate.
It would be my conclusion that the 1x6 cross-ties/collar ties, (¼ the way down from the peak ¾ way up from the floor) do not add any structural support to the isosceles triangle.
The load is being carried from the roof down the roof rafters, which are in turn then trying to force the walls out/away from the house. This force is being held in check not by the cross-ties/collar ties (which are mounted to far up the roof rafters) but by each floor-joist (ceiling- joist if you are on the second floor looking up). Which is running with no splices from one end of the house to the other holding the bottom cord if you will of the isosceles triangle.
Hence keeping the wall from being pushed out is not the cross-ties/collar ties but the floor-joist (ceiling- joist if you are on the second floor looking up). Therefore, they (cross-ties/collar ties) can be removed with out affecting the structural integrity of the isosceles triangle.
Does this sound right? BDV
May I just say, "Wow". Now that's a complete description.
Except for loads...do you get any unusual loads on that roof? Heavy snow, high winds?
Edit: One other question, out of curiousity mostly...are the ridge and rafters rough sawn lumber?
Edited 6/9/2007 12:58 pm ET by Hudson Valley Carpenter
BDV,
Great description of what you have. Your basic analysis of the triangulation is correct...However, collar ties can be serving several other issues not addressed by the Joists (base of triangle). As noted by others in posts earlier they act to tie the upper 1/3 of the rafter together so that one side of the roof cannot lift up due to unbalanced wind loads. They can act as a compression member for slightly undersized rafters and allow for longer length rafters of a given size member.( Think of how a truss works) As others have stated, best route is a competent analysis by someone who can crunch the numbers that apply in your area. To dismiss them as simply unneeded may not be correct.
"Poor is not the person who has too little, but the person who craves more."...Seneca
So, it sounds like the rafters are about 14' long. Are they on 16" or 24" centers? What state do you live in and in what part - trying to get an idea if there is significant snow load...
Edited 6/9/2007 3:13 pm ET by Matt
You are right regarding the down load stresses. The collar ties contribute nothing to resisting that spread.But they do resist the up-load from wind and that is why they are required in many locations. You need to know what your local requirements are and whether you experience high winds to determine whether they can safely be removed.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Let's take your points one at a time.
Starting at the top the ridge board is a 2x8 28’ long board, with no splices. It runs the length of the attic with no other support then the roof-rafters (i.e. no support columns)
A ridge board is not the same thing as a ridge beam, a heavy, structural member the purpose of which is to hold up the rafters at a uniform height and keep them there. Scantlings for ridge beams are taken from code tables, or calculated by an engineer. They are frequently built up from multiple pieces of 2x framing lumber (as many as 4 or even 5 thick). A ridge beam may be supported by posts (vertical columns) at several places along its length to reduce unsupported span and thus allow for the beam itself to be smaller in section. These posts must transfer the load straight down to a footing via load-bearing walls or columns.
OTOH, a ridge board such as you have is essentially non-structural, so it doesn't matter if it has splices or columns. Once the roof is finished, the rafters hold up the ridge board, not vice versa. As such, it is often sized according to the length of the plumb cut on the rafters which will be nailed to it. While the roof is being framed, it is common for temporary posts to be used to hold the ridge board up and keep it from sagging; these are removed later (or not, if they don't bother anything).
The purpose of a ridge board is to aid the framer in assembling the roof; it gives him something to which he can nail a rafter before he has raised its mate into place. Otherwise he'd have to nail the two rafters together at the ridge joint, gusset that joint, and then raise the set as a unit.
The cross-ties/collar ties, are 1x6 about ¼ the way down from the peak (3/4 way up from the floor) they are located on every other rafter
If these collar ties (and their height above baseline indicates they are) are really 1x6 and that is not a typo, they can only be acting in tension as they would flex way too much if put in compression. That fits with Piffin's mention that they could be there to prevent unbalanced wind loads from pulling one side of the roof off the ridge board. But I find that unusual, unless there is a single 1x6 on each side of every other rafter set (in other words, a pair of 1x's making up each collar tie). Usually, 2x lumber is used, and as there is no advantage to using lumber with a deep section when it is in tension or compression only, it would be 2x4.
...(ceiling- joist if you are on the second floor looking up).
Floor joists and ceiling joists are not the same thing. The joist does not take its name from your point of view in looking at it but rather from its function. If it is there to hold up only a ceiling which does not have a 'live' floor above it (as is the case in an unoccupied attic space), it is a ceiling joist. If the joist must hold up a floor upon which live loads will be placed, it is a floor joist, and its scantling will be much greater than that of a ceiling joist for the same unsupported span. A ceiling may be nailed up underneath floor joists as they are rated to support one; flooring (except for walk-boards in attics) may not be nailed on top of ceiling joists.
At the bottom of the 2x6, roof rafters are the 2x8 28’ long bottom plates on either end of the floor-joists .... These 2x8 plates lay flat and run perpendicular across the top of each end of the floor-joists
'Plates' do not run on the flat across the tops of joists. A plate is either the bottom (sole plate) or the top (top plate) member of a stud wall. Joists sit on top of the top plates of load-bearing walls, and are toe-nailed to them. When a piece of lumber the same size as the joist is face-nailed to the ends of the joists to 'close the box', it is known as a rim joist.
What you are describing didn't make sense till I read a bit further and saw Each roof rafter is sitting on top of the 2x8 bottom plate and in line with each floor-joist (ceiling- joist... at which point it appears that this roof dies directly into the second story ceiling with no eaves overhang at all. I don't quite know what to call this 2x8; my inclination would be to call it an eaves board, as it seems to serve the same function as the ridge board. But I have never heard that term before.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Edited 6/10/2007 9:48 pm ET by Dinosaur
The floor-joists (ceiling-joist if you are on the second floor looking up), which are 2x6 26’ long joists running perpendicular to the ridge. There is a load-bearing wall in the middle of the 2x6 26’ long joists floor-joists span,
This indicates these are ceiling joists; a 13' span is about 4 feet too long for 2x6 floor joists.
It would be my conclusion that the 1x6 cross-ties/collar ties... do not add any structural support to the isosceles triangle.
Yes, but.
Structural support is not all there is to it. There is also structural integrity, which means what keeps it all from flying apart under certain non-gravity loads.
I can't quite tell from the way you use the two terms if you're completely clear about that: Hence keeping the wall from being pushed out is not the cross-ties/collar ties but the...ceiling-joists.... Therefore, they (cross-ties/collar ties) can be removed with out affecting the structural integrity of the isosceles triangle.<!----><!---->
Does this sound right?
If I take what you wrote at its proper meaning, the answer is "No."
When you remove anything from a structure, you necessary affect its structural integrity. You have to understand that. The effect the removal will have might be detrimental, benefical, catastrophic, or inconsequential...but there will be a calculable, if not immediately visible, effect.
Roof framing is what separates real framers from ordinary nail pounders. It is a specialised application of geometry and force mechanics in the real, 3-dimensional world, and if it is badly done the consequences can be anything from embarrassing to deadly. Before you start yanking parts out of your roof structure, you need to get someone in there to look at it who is qualified to calculate what the result on the roof's structural integrity will be.
There are many here who are qualified to do that...but, unfortunately, not over the internet. You need eyes-on-site for this one.
Hope this was helpful.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Our code allows the use of 1x6 or 2x4 for collar ties. In modern homes you just never see 1x6 used as 1x6 isn't something that is used very much (if at all) in a standard framing situation.
Our code allows the use of 1x6 or 2x4 for collar ties.
That's interesting; I don't think I've ever seen 1x rated as framing material except for diagonal anti-racking strapping on a sheer wall. Thanks. I like learning new stuff.
Does your code require paired one-by- or single planks?
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Now you made me have to go and look it up... :-) Our code is based on IRC2000 and the collar tie (collar beams as they call them) is a NC state addition to the code. The 1x6s do not have to be paired. I wonder what other states who use IRC have there - if anything. It's in section R802.3.1. BTW - does anywhere in canada use IRC?
Also BTW - Sorry I can't come to your fest... I'm guessing it would be about a 14 hr drive and plane tickets to anywhere just aren't in the budget... Heck... with gas prices the way they are a 28 hr rd trip in a pickup might be the same $ as a plane ticket...
- Sorry I can't come to your fest... I'm guessing it would be about a 14 hr drive and plane tickets to anywhere just aren't in the budget... Heck... with gas prices the way they are a 28 hr rd trip in a pickup might be the same $ as a plane ticket...
Norfolk is about 14 hours; I used to drive a tugboat for a company down on the Southern Branch and did the commute by car (bought a new one just for that, too, then quit after four months, LOL). One month when I got there, the port captain told me the boat was in Greensboro, handed me the keys to the company Suburban and told me to drive down to meet it. This was at 11pm, as I arrived after a 14 hour drive. Ooooooooh, that was a long night....
There's a tradition of carpooling for these fests. It helps to share the gas costs and the driving too. A drive which would take 18 hours solo can be done in 15 hours if you have a fresh driver to take over when you start losing it.
You might be able to hook up with Grant (SeeYou) who's coming outta Lexington in the 'MommyVan'. There is also Shep who's leaving from New Jersey; and a bunch of guys coming up from NY/PA. Start a 'CARPOOL!' thread in the Fest folder.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
I can see why a one by would be okay since as a collar tie, it's stress would be in tension rather than compression so it's not going to deflect.
ceiling joists
I suspect that OP was (originally) trying to suggest the percieved height of the members by relating it to a 'finished' attic space.
(Which forced recollection of discovering collar ties dragooned into being ceiling joists without reguard to structural niceties in common stud framing <shudder,shudder>.)
I'll also guess that these members were installed "by eyeball," in that some one decided it didn't "look right." That person then used what was near to hand (or cheapest), which is how this attic (might have) one-sided 1x6.
I still have a mental image of 5-half dozen sinkers whacked into the ends of these, best a person could 'tween rafter bays with a too-small hammer.
But, that could also be a left over from my very first impression, that OP was asking about railroad "sleepers" (aka crossties) in the roof framing--and that image of creosoted 8x10's spiked in has had a had time getting unstuck from mind's eye . . . )Occupational hazard of my occupation not being around (sorry Bubba)
Since I am considering doing exactly the same thing in the top floor of the new house I have to ask. Y'all say have someone competent come out and look at it. Who exactly would this competent person be? I'm guessing a structural engineer?
thanks,
Daniel Neumansky
Restoring our second Victorian home this time in Alamdea CA. Check out the blog http://www.chezneumansky.blogspot.com/
Oakland CA
Crazy Homeowner-Victorian Restorer
Yes.A good framer who knows his stuff can figure it too, but the problem with that is - How do you, an HO, know whether you are talking to a framer who knows beans from potatoes. For every one who can think, there are 10-20 who have bashed the brains out of framing nails and splintered up trusses all their working lives without really thinking about structural stresses
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Who exactly would this competent person be? I'm guessing a structural engineer?
I would describe that as an excellent guess.
You could vet/winnow the names in the yellow pages by asking about the firm's experience with residential framing, and/or have they done consulting remodel work (it's middling easy to apply "book" skills to unbuilt plans; working with "as built" can take experience and deftness).
Good in the initial phone call process to ask about familiarity with local code requiements, too (which means it's often worth your while to scan your city's web page to find what code is in effect).
Attic conversions can be fascinating. Getting the floor joists sized correctly, then with good load paths back to the foundation is fun. Integrating new insulation into the new envelope is also interesting. Sizing the various mechanicals properly is yet another bit of fun as well. It can be a heck of a way to find out how smart a passle of folk are <g>.Occupational hazard of my occupation not being around (sorry Bubba)
Or ask the Building Inspector if he has any recommendations.
Thanks those questions will be helpful in that I seem to have bad luck 'picking' an engineer I can work with.
Lucky for this situation the attic was built originally as finished space and they did pretty well considering. The floor joist are full 2by8's 16"oc with a max span of 12' The roof rafters are a bit weird not exactly 2by4's on 24" centers. Its a 2by4 with a thin strip of wood to get a total depth of a 2by6???
We demo'd the chimney over the weekend and now have a huge chase to run the plumbing-wiring-heating up to the third floor.
If I can remove the collar ties I plan on doing cathedral ceilings with a corbond spray foam hot roof.
Daniel Neumansky
Restoring our second Victorian home this time in Alamdea CA. Check out the blog http://www.chezneumansky.blogspot.com/
Oakland CA
Crazy Homeowner-Victorian Restorer
Yes, quite. Nothing like finding flooring that looks like seconds from the finish floor up in the attic, to finish out a "trunk room" that has been additional living space for a few decades. With walls tipped up under the roof that just bear on the ceiling joists, which are 2x4 @ 16" . . . and all the client want is to make the closets a couple feet deeper into the "used" part of the attic . . . <sigh>
ties I plan on doing cathedral ceilings with a corbond spray foam hot roof.
I like it. Think the Decorating Committee would let you put a "flat" across the cathedral? Not just collars, but other utilities will run in that "borrowed" space (and a "flat" makes it a lot easier to get that ceiling fan installed).
Going to foam all the roof, or just in the new space? If only in the new, you have to watch the detailing where the verticals meet the existing ceiling insulation. Not the bridging so much (it's somewhat unavoidable) but the infiltration.Occupational hazard of my occupation not being around (sorry Bubba)
I like it. Think the Decorating Committee would let you put a "flat" across the cathedral? Not just collars, but other utilities will run in that "borrowed" space (and a "flat" makes it a lot easier to get that ceiling fan installed).
That's a good idea that flat space would be helpfull for running utilities. I'll also have 4' knee walls to run stuff behind. I'll have to check the measurements of how high the ridge board (not beam for heavens sake) is off the floor and how high up the flat would be...don't like the idea of a fan 6" above my head-what if I jump for joy or something?
Going to foam all the roof, or just in the new space? If only in the new, you have to watch the detailing where the verticals meet the existing ceiling insulation. Not the bridging so much (it's somewhat unavoidable) but the infiltration.
I'm going to foam the entire underside of the roof deck from ridge board to the soffits. I want to completely seal the entire roof structure. There is no existing ceiling insulation to deal with.
Daniel Neumansky
Restoring our second Victorian home this time in Alamdea CA. Check out the blog http://www.chezneumansky.blogspot.com/
Oakland CA
Crazy Homeowner-Victorian Restorer
and how high up the flat would be...don't like the idea of a fan 6" above my head-what if I jump for joy or something?
Yeah, setting a 2x4 5 1/2" down leaves you a space for all sorts of things (like a smurf tube from here to there--never know, might need a plasma EPS conduit 25 years from now<g>).
Ever see one of those 33" or 36" ceiling fans and wonder who'd ever need one? Folks with a 6/12 cathedral ceiling at the top of a convective column <g> . . .
If your budget & AHJ allow, cover the rafters, too, with an inch or so of foam. The house just over the Brazos from here that has 4" on the deck, and 1.25-1.5" over all roof framing maxed out last summer at 87º in the attic. We added a 2" flex T at the end of the hvac trunk and put a sheetmetal damper on it half open. That attic has yet to break 80º and we're solid into out third week of mid 90s and Heat Indices this week over 100.Occupational hazard of my occupation not being around (sorry Bubba)
could also be a left over from my very first impression, that OP was asking about railroad "sleepers" (aka crossties) in the roof framing--and that image of creosoted 8x10's spiked in has had a had time getting unstuck from mind's eye
LOL. Yep, that would be a difficult image to get shet of....
OTOH, what BVD said that really blew me away was that his framing "would appear to be quarter saw[n]. Type of wood is a mix of Douglas Fur and Oak."
Ohhhh boy. Quarter-sawn old-growth oak framing. Maybe the real reason he wants to pull those collar ties is to sell 'em....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Ohhhh boy. Quarter-sawn old-growth oak framing. Maybe the real reason he wants to pull those collar ties is to sell 'em....
Old "construction grade" framing like could command some price even in s/w let alone h/w.
The construction "Douglas fur" sticks me with a memory of the taste of wet coniferous bark with a hint of chain oil and two-troke exhaust, though . . . <g;koff,koff,sppt--rrr!rrr!rrr!>
Shoot, my 1951 house is all (then) No 2 Sugar Pine; all of the sheathing is 1x6 T&G (subfloor, walls inside & out, ceilings, roof deck, the works--no adding a j-box with a keyhole saw here, nosiree). Iffin I win the lotto, then the place gets taken apart for the boards.Occupational hazard of my occupation not being around (sorry Bubba)
I took some interior walls out of a turn of the century house and this one stud was 2 1/4"x 4" of heart something that was so dense it takes two hands to lift it.
be yep, kept all them babies:o)
I built the chimney after my hoeing in the fall, before a fire became necessary for warmth, doing my cooking in the meanwhile out of doors on the ground, early in the morning: which mode I still think is in some respects more convenient and agreeable than the usual one. -Thoreau's Walden
Edited 6/12/2007 12:02 am ET by rez
was 2 1/4"x 4" of heart something that was
Back when I used to pull down barns for their barnboard for the tres chic out on the left coast, I'd see those too; usually half rotted, ro with 75 generations of owl nest in a giant whopping knothole . . . Occupational hazard of my occupation not being around (sorry Bubba)
From back before I knew what it was and what the value of it, I used some 9x9 posts and a 8x16 beam salvaged from a job for my shop.Turns out they are pure clear vertical grain heart pine
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
rez,
Two story house with attic.
k
be duhAt length, in the beginning of May, with the help of some of my acquaintances, rather to improve so good an occasion for neighborliness than from any necessity, I set up the frame of my house. No man was ever more honored in the character of his raisers than I. They are destined, I trust, to assist at the raising of loftier structures one day. -Thoreau's Walden
I notice that you didn't answer my Q - are the rafters 16" or 24" OC. The reason I ask that, is that I'm trying to ascertain if the roof structures is constructed reasonably soundly, so that if it is, I could say, replace them with 2x4s pushed all the way up. If not, I wouldn't mess with it.
All I can say is Wow! Thanks for all the information. Here I will try to answers some of the additional questioned posted for me:
The roof rafters and ceiling joists are on 15.75” or 14” centers.
The house is located in Chicago built circa 1930.
As to type and condition of wood. There is no bark on rafters or joists. Looking at small section of some exposed ends it would appear to be quarter saw. Type of wood is a mix of Douglas Fur and Oak. The actual dimension on the cross-ties/collier-ties is 1” x 5.75”. The actual dimensions on the 2 x 6 rafters and joists is 1.75” x 5.75”.
Thanks again for help. BDV
Thanks for the additional information.
IMO, you can move them up under the ridge. If replacing the 1X6 with 2X4 will help the headroom, you could do that.
Sounds like it is built fairly sturdy for a house of that age. I deal with new homes so I'm not an expert on old houses though. And it's just a simple gable roof - right? Anyway, as Hudsonvalleycarp said, I think you can replace them with regular 2x4s and push them all the way up. Probably nail in the new ones and then remove old. Maybe 4 nails on each end of each collar tie. Gonna be fun nailing into that old wood. :-) For extra strength, put one on every rafter pair.
That, with one caveat: I really don't know what the snow loading is like in Chicago.
All those posts just to get here... :-) The thing is that most everyone here is pretty gun shy about making structural type recommendations with limited information and the "I'm not there so I can't see it" type a thing... Actually, I might get blasted shortly :-) Thanks for your patients.