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rakuz66 06-17-2008 03:44 PM

ridge beam
 
Is it ok to build a ridge beam under the collar ties? In other words, I have 2x8 rafters that have collar ties about 1ft down from the ridge. It's a cabin in snow country and I would like to beef up the ridge by installing a ridge beam. Can I build it under the collar ties? or does this defeat the purpose of the collar ties?

Termite 06-17-2008 04:28 PM

The collar ties really serve the same purpose as a ridge, provided they're low enough. The higher they are in the roof, the less benefit they have. The closer to the walls they are, the more effective they are. The collar ties help prevent the bearing walls and rafter tails from thrusting outward when the roof is loaded. A ridge does the same thing, except it transfers the load from the rafters downward, and is in a fixed position, thereby preventing the walls and rafter tails from thrusting outward.

A ridge, or technically a beam, could be located under the collar ties, although there would need to be a connective means to the top of each rafter to transfer loading to the ridge. Collar ties are in tension, not in span (compressive loads and resulting deflection), so bearing them on the beam would accomplish very little. The connection of the collar ties to the rafters would then be in shear if they were bearing the roof load on the beam, and the reaction would likely be way too much for the shear connection to be able to withstand. It would be very unconventional, and would require some engineering.

The beam should be situated at the top of the rafters to be effective, which would enable the rafters to bear on the beam. The existing collar ties could be removed to accomodate the beam. I'd still recommend installing collar ties as low as reasonably possible, unless the beam is beefy enough to do all the work.

rakuz66 06-17-2008 08:37 PM

Hi Kctermite, Here's my plan. To fill in the gap between the collar tie( which is 1 ft down from the ridge) and which is attached to the matching rafters with a 2x12 cut like a triangle to equal the bottom of the collar tie. Then install a ridge beam under that. This way the load will transfer from the rafters to the ridge beam without placing the collar tie in unwanted tension.
By the way, this span is 15 ft long by 22 ft wide. So the rafter span is 11ft. I already have 4 doubled 2x12's every 4 ft at plate level holding the walls from spreading. I am only thinking of putting in this ridge beam as an extra precaution. Hope this all makes sense.Snow oad is heavy.

47_47 06-18-2008 08:56 AM

Do you have an adequete footing for the beam supports?

rakuz66 06-18-2008 08:59 AM

I plan on it.

47_47 06-18-2008 03:25 PM

Even though this beam is being added to an existing structure, 15' is a long span, I suggest you get an engineer involved and have him spec the beam and supports. Think of all the work of footings, posts, beam and attaching to the existing structure. If designed or done improperly you will not get a stronger roof.

rakuz66 06-30-2008 10:37 AM

If my rafters are undersized, will the addition of a ridge beam underneath them help? In other words, will the ridge beam help reduce the live loads on the rafters in a cathedral ceiling?

Termite 06-30-2008 12:19 PM

Quote:

Originally Posted by rakuz66 (Post 134766)
If my rafters are undersized, will the addition of a ridge beam underneath them help? In other words, will the ridge beam help reduce the live loads on the rafters in a cathedral ceiling?

Not really. If your rafters are undersized/overspanned, the only real benefit would be to reduce the span. That's usually accomplished with a purlin.

feralfreak 07-29-2008 01:01 AM

Quote:

Originally Posted by thekctermite (Post 131199)
The collar ties really serve the same purpose as a ridge, provided they're low enough.

:confused1: does that mean that a person doesnt have to have a ridge beam?! how do you manage to get the lookouts on the ends?! i thought the only way to get around a ridgebeam was with trusses


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