Replies

1. 
   Guest_ | Mar 08, 2000 06:41pm | #1

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   j.c.

   You can certainly use a ridge beam/rafters, which is what I would do. With scissor trusses and a 4/5-12 roof pitch you wouldn't get much of a cathedral ceiling inside. If you have a draftsman draw up plans, he will be able to size your ridge beam and rafters to handle the roof loads in your area. Or your lumber yard can do it. Make sure there is adequate support for each end of the beam, going down to the foundation.

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   Guest_ | Mar 09, 2000 12:41am | #2

   *j.c.A beefy ridge will do it. 16' isn't that long a span, hence the ridge beam won't need to be too humongous. The architect will be able to size it for you. JimL gave you some good advice.Red dog

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   Guest_ | Mar 12, 2000 02:38pm | #3

   *Being in the truss business, I'm supposed to say that trusses are the answer to all your problems..........But, in this case,Jiml and Red Dog are right on. A scissor truss would look ricidulous. You would only have about 15" of rise in the center, unless you could go with a steeper pitch on the roof.

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   John_Coelho | Mar 26, 2000 09:22pm | #4

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   J..

   I agree with everyone so far, a structural ridge beam sounds like the right thing to do for your roof design. A scissors truss used on a roof with a pitch of only 4/12 or 5/12 doesn't allow for much of a cathedral ceiling below.

   You will have to have the structural ridge properly sized for your area considering live and dead loads. Don't put too much faith in having a draftsman or the lumber yard size this for you. You really should have a qualified engineer perform this service for you to ensure you have adequate support for your roof. It's a simple design that should take less than an hour and won't cost you much money. It would be money well spent to know you are using the proper framing components for an investment as important as your home.

   I am a registered engineer and would be happy to size this ridge beam for you if you contact me with a little more information regarding your proposed addition. Good luck with your project!

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   Guest_ | Mar 27, 2000 09:01am | #5

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   The truss manufacturers in my area say to cut your roof pitch in half to get yor celing pitch on sissors. That would be a 2/12 or 2-1/2/12 on the ceiling. Real shallow. go with the Rafters and ridge.

   This will give you a goodlook on gable windows from the otside as the lines will all be parralel.

   My 2 cents.

   AE

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   Guest_ | Mar 27, 2000 12:44pm | #6

   *David - You're certainly right in saying that the bottom chord pitch should be roughly half of the top chord pitch. But that's only a rule of thumb. On a scissor truss that's only 16' long, you could get 5/12 over 3/12 with no problem, or maybe 8/12 over 6/12. (Unless you had one hell of a snow load) On larger trusses - say 40' or so - This becomes more of a problem. Then it might become more economical to do 6/12 over 2.5/12, or something like that. The angle of the top chord slope minus the angle of the bottom chord slope should be 9 degrees or more typically. That can be squeezed down a bit below 9 degrees, but then it' hard for the saws to cut.

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   Guest_ | Mar 27, 2000 07:30pm | #7

   *J.C.A structural ridge could certainly accomplish what you need. It needs to be supported at each end in a way that transfers loads to the foundation. (I am wondering if your ridge is perpendicular to an existing house wall- if so does the end that will fall inside the existing wall occur over an opening?)A simple line drawing done on graph paper (one square equals one foot) should provide enough info to get a microlamm or similar product sized. Lumber yards send your drawings out to be reviewed by the folks who produce the engineered products, they determine the loads and reccomend the proper size beam. Since they want you to use their product, they provide this service free of charge.Make sure your rafters are sized for all live and dead loads and provide ample depth for full insulation w/air flow.

4. 
   Jon_Jordan | Mar 28, 2000 12:40am | #8

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   Just curious why no one mentioned anything about wind-bracing, we call'em collar ties down here but how are you going to stop the down and out forces on the perimeter walls without some sort of wind brace? Doug hubbard asked about the attachment to the house, and I agree that if the ridge is securely attached to the house over transferred loads, then the gable picks up the other end of ridge load. If scissors are not used, which have built in bracing, then how were the rest of yall handling this problem. Or maybe I missed something.

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   Guest_ | Mar 28, 2000 01:25am | #9

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   Jon-

   A structural ridge counteracts the down and out force you are talking about. That is why the sizing of the ridge beam is critical.

   In a typical stick frame roof the rafters transfer loads down at the ridge and walls. This force pushes the ridge down and causes the rafters to exert force out against the walls. Collar ties counter the outward thrust by not allowing the rafters to spread.
   No spread- no place for the ridge to go.

   The same thing can be accomplished with a ridge beam sized to carry the roof loads. If the ridge beam is sized properly it will counteract the downward loads imposed on it.

   Does that make sense? I'm not great at explaining either.

   hubcap

6. 
   Jon_Jordan | Mar 28, 2000 01:55am | #10

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   Yep, Doug, your right about the ridge bieng beefed up to compensate for the need for bracing, missed that part. The idea of an oversized microlam or flitch beam wasn't connecting in my tired mind because of the relatively small size of the addition. but your correct, that would stiffen it up considerably. I did miss something imagine that!

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   j.c._lexxus | Mar 28, 2000 01:55am | #11

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   I want a 16'x16' addition with a cathedral cieling but no tie rods. Is it possible to accomplish this with a ridge beam and rafters or do I need to use scissor trusses? The roof pitch will be a 4-12 or 5-12. The 3 new perimeter walls are to be brick veneer. If I can use a ridge beam what are my options with dimensions of the beam and the rafters? I appreciate any advice.