Replies

1. 
   calvin | Mar 13, 2014 07:51pm | #1

   that it is a ridge BEAM says it all.  If it was designed as such, then yes-you need it.

   What reason do you think not?  Does anything tie those walls the rafters sit on, together?  Vaulted ceilings are the usual reason for spec'ing a ridge beam.

2. 
   Mike_Mahan | Mar 13, 2014 09:07pm | #2

   Are there ceiling joists or collar ties? If the answer is no then the ridge carries 1/2 the roof load.

3. 
   nkhandyman | Mar 14, 2014 07:06am | #3

   ridge beam clarification

   I think I need to clarify my original post.  I know what  ridge beam is; I did not mean that a ridge beam on this job was not needed.  I was trying to ask why such a beam of that size is needed,  I have seen many homes built of similar size that 2 2x12 were used as a ridge.   2 x12 rafters will be used across the beam at 2' OC.  these beams will be fastened to the ridge and then the plywood will be supported by the rafters.

   In my mind I see the ridge to be used as a place to fasten the rafters and the area over the rige will be vented.  The prints provide no info on how the ridge should be installed and supported.  My main interest in asking this question is this:  

   What criteria would be needed to design such a large ridgebeam in such a small house? 

   thank you

1. 
   DanH | Mar 14, 2014 07:27am | #4

   But are there joists or collar ties (positioned at least halfway down the rafters)?  If you just put up rafters with no ridge beam and no joists, the forces on the roof push the walls out and you get a "swayback" roof (if the roof doesn't fail completely).

   With a standard standard stick-built roof you have the joists holding it all together and all you need up top is a ridge board (if that).

   And the strength of the ridge beam would be dictated by the roof geometry and the maximum weight on the roof.  A lower slope needs a stiffer beam, and (obviously), a heavier roof needs a stiffer beam.  The fact that they're using 2x12 rafters suggests that significant loads are anticipated.  Tile, perhaps?

2. 
   Mike_Mahan | Mar 14, 2014 11:06am | #5

   This ridge spans 24'. The tributary area is 1/2 the roof span = 19'. With normal roof loads that's close to 500 # per foot on the ridge. With a little heavier roof that could easily be close to 600 # per foot on the ridge. 24' is a considerable span. Calculated out a 2 x1.75 x 24 lvl beam is not excessive. But the beam carries over 6000# at each end, so support should have been detailed. The pitch of the roof makes no difference.

3. 
   LarryG01 | Mar 16, 2014 02:06pm | #8

   Ridge Beam

   ..........for what is worth, I had an elderly cousin that owned a house built around the 1900's.  When she passed and we were cleaning out the house, I was very surprised to see there was no ridge beam.  Basically all that beam does is give you a straight ridge line - there is no downward load on it.  There were collar ties but I read recently that is for uplift forces.  And there was no solid roof decking - justy 1" boards spaced at intervals - and that house went thru the hurricane of 1938.

1. 
   Mike_Mahan | Mar 16, 2014 03:27pm | #9

   Collar ties and/or ceiling joists.

   Collar ties and/or ceiling joists have nothing to do with uplift. They counter the outward thrust created by the rafters. Without them the walls would want to spread. In the 1800s when framing went from timber to stick frame many carpenters did not understand this. They would sometimes put ceiling joists perpendicuar to the rafters. The ceiling itself can hold the walls together, but cutting it in a remodel can lead to catastrophic failure. The collar ties kept your cousin's house from collapsing. Skip sheathing was the norm back then before plywood came into general use. 3 1/2 inches was often the spacing. This was the width of the blade of a framing axe, so it could be used to space the sheathing. With a ridge beam, the rafters press downward on the beam and the walls; there is no outward thrust, so collar ties are not needed.

2. 
   DanH | Mar 16, 2014 04:04pm | #10

   So long as there are ceiling joists, or the collar ties are low enough, a ridge beam is not needed.  It's quite common to see a stick-built roof with no ridge beam/board.

4. 
   DoRight | Mar 18, 2014 10:35pm | #11

   That is a small beam

   Accually an LVL of only 1.75 thickness almost makes it a ridege board.  A ridge board is not structural, but serves only to nail the rafters to it.  Now, since it is 24 inches deep it would appear to be considered a ridge beam and also since it is not just a 1 by.  But  it is still a pretty small beam.

4. 
   oops | Mar 14, 2014 11:31am | #6

   Granted, the ridge beam you describe seems excessive for average residential construction. The only way to size a ridge beam is to know the span of the beam and the load that it will be carring. 

   You might condider taking the plans to your LVL supplier and have them ask their LVL suppliers engineers look at it. This a service that they normally provide.

5. 
   sapwood | Mar 14, 2014 12:04pm | #7

   Your question is impossible to answer with any accuracy whatsoever unless you list all the design criteria. Any opinion offered without that basis is simply WAG.

6. 
   DanH | Mar 19, 2014 07:22am | #12

   Actually, 2 LVLs, 24 inches deep, is a pretty substantial ridge beam.

7. 
   davidhopes | Mar 21, 2014 10:16am | #13

   Ridge Beam

   Beam has to be sized to carry the load,  If you get any deflection in the ridge beam, you will automatically get spreading of the 16' long walls. It may take a while, but it will happen. The pitch of the roof will have a lot to do with it.

   The stiffer, the ridge beam, the less the deflection and the less the spreading.

   Transition Roofing

1. 
   DanH | Mar 21, 2014 05:46pm | #14

   But Mike Mahan claims the pitfch of the roof is irrelevant.

1. 
   Mike_Mahan | Mar 21, 2014 08:28pm | #15

   Roof pitch.

   The pitch of the roof makes no difference in the load on a ridge beam.  The load that a ridge beam must support is vertical. Imagine the ridge as a wall with two shed roof on each side. The ridge beam is just that wall with a very large opening. When the ridge beam is undersized it will act as a ridge board in failure without collar ties or ceiling joists to resist outward thrust. Roof pitch is relevant to that thrust. Collar ties need not be very large to resist thrust, but without them the  pitch affects the thrust. If the pitch were infinite (the roof would be a wall) there would be no thrust. If the pitch were zero the roof would sag in the middle and the walls would be pulled in. 

1. 
   BossHog | Apr 04, 2014 07:10pm | #18

   "The pitch of the roof makes

   "The pitch of the roof makes no difference in the load on a ridge beam."

   Actually - I think they do now.

   Depends on how new the codes are and what's versions have been adopted where you're at.  Live loads are still the same.  But dead loads sometimes vary with the pitch.

1. 
   Mike_Mahan | Apr 05, 2014 10:15am | #19

   Thanks for pointing this out. Dead load will indeed increase as the pitch increases because the rafter-length/unit-span will increase. Also, steeper roofs often are required to support less live load. I was simply looking at the geometry for any given load, not the prescribed requirements.

8. 
   MYBuilder | Apr 04, 2014 06:10am | #16

   Every stick in your frame carries load from something, or it shouldn't be wasted. A ridge BEAM always transfers roof load. Some need a POST to transfer the load through the gable wall to the wall or walls below to the footing. As stated in earlier posts, these beams hold the peak up and the walls parallel to it in. If there is an attic floor or collar ties, the beam trnasfers a smaller load. If you choose to eliminate the beam by nailing the rafters to each other, like a truss, the nails transfer the load from one side of the roof to the other. The sheathing also helps transfer this load from palne to plane and rafter to rafter. A single ply beam of small depth still keeps the ridge staight and level by transfering the load in three dimensions. Trusses only transfer load in two dimensions, the sheathing transfers the third.

   Someone stated that roof pitch doesn't matter, but it does. The more flat the roof, the more force the ridge beam carries. That is why a steeper pitched roof can be framed from smaller dimesion lumber.

9. 
   DanH | Apr 04, 2014 07:12am | #17

   A ridge beam carries load, by definition.  A ridge board doesn't.  Two different things.

10. 
    DanH | Apr 11, 2014 06:47am | #20

    I simply meant that there are roofs built with neither a ridge beam or a ridge board. 

    In cases where a ridge beam is unnecessary the ridge board is mainly a convenience -- a way to provide for simultaneously connecting rafters together and also bracing them laterally.  The same effect can be accomplished (as I suggested) by somehow fastening the rafter ends together and applying separate lateral bracing of some sort.