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I had a friend rebuild a roof on a cabin I own and after reading your story of collar ties I am concerned. The roof was built spanning a distance of about 26 feet wide. It is cathedral in design- thus no rafters to hold the walls in. The center board is supported on both ends and there is a beam that runs parallel to the center board about 8 foot off the ground- not at the top of the ceiling. To prevent the walls from being pulled out the builder used collar ties to hold the top together and the beam keeps the end wall from going out. My concern is without the rafters is the support of the center board enough to keep the roof up and the outside walls from being pushed out during heavy snow loads??
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How big is the "center board", only 1x6? How long?
Making a truss out of the center board and the 8' off ground beam will fix it, or is it already a truss?
*I am a little confused (it' been happening alot latly)by rafters do you mean ceiling joists"collar ties"? and by center board do you mean ridge?I am not sure if it is a hip roof or a gable roof? how long is the span of the center beam that runs parallel to the ridge? Is it possible to put extra posts from the center beam to the ridge? When you said collar ties did you mean collar ties? one of The functions of a collar ties is to keep your exterior walls from spreading. A little more info would be helpful. Email me at [email protected] D.G.B
*You mentioned he used collar ties to keep the walls from kicking out. If he installed these properly you should have no problem. 2/3 down from ridge, at least every other rafter, would have been ideal. Also its good to bolt threw ,rather than just nail them, but I have seen many nailed and hold up for a 100 yrs.
*John- Are the rafters sufficiently tied to the floor joists? If so- and if the joists are continuous across the span- they should resist any thrust a snow load can impose. If the rafters are sitting on walls that's another story..I'm a bit confused about the configuration of your framing. Sounds kind of like your friend used what I'd call "purlins" to break the span of the rafters. If these are sized adequately (?) they will have a substantial effect resisting thrust as well. There are several things that would need to be known to make any kind of determination about your framing: the span from ridge to eve; the distance from gable to gable (assuming it's a gable roof..); the size of the purlins (if this is indeed what they are..); the size of the rafters; the pitch of the roof; the snow load in your area; and if there are other tying elements in the framing. Perhaps you could do a sketch and attach it.Just read an article- think it was in JLC- which said most collar ties installed are useless, as they are not far enough down the rafter to resist thrust adequately, and are often redundant, as the rafters are tied by joists. I've heard some guys say collar ties function more like joist bridging- passing a wind load to the opposing rafter. I'd be interested in hearing what an engineer has to say about this.
*John:Center board?? Roof with no rafters??My suggestion is that you go to a library or something, get out a book on basic carpentry, and learn a few of the basic terms with respect to roof framing. This will allow you to communicate your question in more of an effective manner.
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I had a friend rebuild a roof on a cabin I own and after reading your story of collar ties I am concerned. The roof was built spanning a distance of about 26 feet wide. It is cathedral in design- thus no rafters to hold the walls in. The center board is supported on both ends and there is a beam that runs parallel to the center board about 8 foot off the ground- not at the top of the ceiling. To prevent the walls from being pulled out the builder used collar ties to hold the top together and the beam keeps the end wall from going out. My concern is without the rafters is the support of the center board enough to keep the roof up and the outside walls from being pushed out during heavy snow loads??