Thread: Ridge beam and rafters

Does the addition of a ridge beam help reduce the live loads on rafters in a cathedral ceiling?

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Originally Posted by Robert A. Kuzmick

Does the addition of a ridge beam help reduce the live loads on rafters in a cathedral ceiling?

No, it only transfers the load elsewhere.

If you have rafters and a regular ridge board (non-load bearing), the load is all transferred to the bearing walls the rafters bear on.

If you have rafters and a ridge beam (structural ridge which is load bearing), the load is transferred to the bearing walls the rafters bear on and to the bearing the structural ridge (ridge beam) bears on.

The live load on the rafters themselves does not change.

Hello again Jerry and thanks for your reply. My situation is that I have an 11 ft rafter span (building width is 22ft) with a 70# snow load. I have a cathedral ceiling in half of this width (11ft), and the other half is a regular ceiling height. The rafters are tied together at the ridge with collar ties and gusset plates. I actually used your idea ( if you remember me) and ran doubled 2x10's every 4 ft at plate level to tie walls together. My idea was to put in a ridge beam to help redude the snow load on these rafters???? Make any sense???

Originally Posted by Robert A. Kuzmick

My idea was to put in a ridge beam to help redude the snow load on these rafters???? Make any sense???

Robert,

You could install purlins with supports to the load bearing wall in the center (if it is a load bearing wall), with the supports not more than 45 degrees off the vertical, to effectively reduce the span of the rafters.

If the span is 11 feet and the height above the center wall is 11 feet, then 45 degrees would put the purlin at the center of the rafters, reducing the rafter span by 1/2. Of course, though, the purlin load would be going to that load bearing all in the center.

With less height above the center wall, the purlin would move upward toward the top of the rafters, being as you would need to keep their supports within 45 degrees of vertical. Still, though, that would offer some reduction in rafter span.

I really appreciate all your assistance Jerry. Unfortuneately, I have no center bearing wall. I have a bearing wall and beam, but it's off center, so the purlins would be less than 45 degrees. The only way I could help with rafter span and snow load is to either
A) Put a knee wall in place on top of the 2x10 beams out from the outside wall about 1 ft or so.
B) Put in a ridge beam.
C) Do nothing. My present rafters are short about 18 inches to 2 feet. The engineer who came out to inspect camp said it's fine, and signed off on it. Unfortuneately, I'm still concerned. It's a small area( 11x15 ).

Robert,

How about this:

You have two load bearing end walls, right?

If so, instead of putting in a "structural ridge" (ridge beam) which would be supported to each end wall, and which would do nothing to address the loading on the rafters nor the span of the rafters, why not install a "structural purlin" (new term I just coined meaning you take the structural ridge and move it down from the ridge to serve as a purlin), reducing the effective span of the rafters from wall-to-purlin and purlin-to-ridge.

Not sure I follow you??? When you say down, do you mean straight down from the ridge??? As in a straight 2 ft drop?? and then run purlins to rafters??
Or do you mean down the length of the rafter??? In other words, place a ridge beam 2 ft off from center, and run the beam underneath raters 2 ft from ridge center????

Maybe this will help to clear some of the confussion on terms.

Another option I thought might help would be to place a "semi" ridge beam, maybe 2 lvls, at about the midpoint of the rafter span . I would place them underneath the rafters, and carry the supporting posts down to the foundation. Does that seem practical????

Robert,

This:

Originally Posted by Robert A. Kuzmick

Another option I thought might help would be to place a "semi" ridge beam, maybe 2 lvls, at about the midpoint of the rafter span . I would place them underneath the rafters, and carry the supporting posts down to the foundation. Does that seem practical????

Is the same as this:

Originally Posted by Jerry Peck

Robert,

How about this:

You have two load bearing end walls, right?

If so, instead of putting in a "structural ridge" (ridge beam) which would be supported to each end wall, and which would do nothing to address the loading on the rafters nor the span of the rafters, why not install a "structural purlin" (new term I just coined meaning you take the structural ridge and move it down from the ridge to serve as a purlin), reducing the effective span of the rafters from wall-to-purlin and purlin-to-ridge.

"Structural purlin" .... "semi ridge beam" ....

It's just a plain old beam. Adding a beam to support the rafters mid-span, and posts to support the beam and carry the load down to the foundation, is a typical method for doing what you are trying to do --reduce the rafter span -- when you don't have an interior bearing wall to carry the load.

Thank you! Sometimes when I get so involved in something I lose sight of what's going on. That's my plan then.