Replies

1. 
   Riversong | Mar 14, 2008 07:48pm | #1

   I am trying to determine the size of a ridge bean

   I would suggest something in between a kidney bean and a fava bean.

   Oh, you must mean ridge beam.

   You call it a shed, but I'm assuming this is not a shed roof but a gable roof with equal pitches on each side, and that it's a free-standing building.

   Are you trying to build a structural ridge without any ceiling joists (rafter ties)?

   If not, then the size of the ridge is immaterial, other than it's usually one size deeper than the rafters.  So it could be 2x8 or 1x8 or even no ridge at all (with rafters nailed together in pairs).  It's only purpose is to align the rafters - nothing structural at all. 

    

   Riversong HouseWright

   Design *  * Build *  * Renovate *  * Consult
   Solar & Super-Insulated Healthy Homes
1. 
   Ragnar17 | Mar 14, 2008 09:22pm | #4

   I would suggest something in between a kidney bean and a fava bean.

   And people around here say you don't know beans.   ;)

1. 
   Riversong | Mar 14, 2008 09:40pm | #5

   Ha!

   I know my ridge beans:

   View Image

2. 
   hotwheels | Mar 15, 2008 01:53am | #6

   Ah yes, I can only blame myslef for lack of agility on the keyboard!Yes, the idea is a beaM for a gable roof on a free standing building (8x12 feet).I do plan to make a cathedral ceiling without ceiling joists. However, I would like to store some lumber in the upper part of the building, so I thought that using rafter ties (maybe collar ties) would offer a platform for that storage and also add some extra strength to keep the roof from sagging and the walls from spreading?After reading yours and other posts it seems that a 2x8 or maybe an LVL would work?Thanks
   JR

1. 
   Tomrocks21212 | Mar 15, 2008 03:28am | #7

   If you're building this with a true ridge beam, one that is sufficiently sized to carry half of the roof load, and assuming you're correctly attaching the rafters to it, the walls won't spread. They can't. There are no horizontal forces imparted to the walls by this construction, all loads are vertical.

    

2. 
   cargin | Mar 15, 2008 05:05am | #8

   hotwheels

   I do plan to make a cathedral ceiling without ceiling joists. However, I would like to store some lumber in the upper part of the building,

   If your gable end is 8' your run is 4' and your rise is 5". 5" x 4 = 20" If you install 2x6 ceiling joists then you only have 14 1/2" or less. Probably 13" with the birdsmouth taken into consideration.

   If your gable end is 12' then you will end up with 23". Not alot of space for lumber storage.

   rafter ties (maybe collar ties) would offer a platform for that storage

   I think you should plan on using ceiling joists to maximize your storage.

   But if you are storing Blue Ridge Beans then the collar ties should be fine.

   Rich

    

3. 
   Ragnar17 | Mar 15, 2008 08:36am | #9

   After reading yours and other posts it seems that a 2x8 or maybe an LVL would work?

   A 2x8 sounds very undersized -- even for a small outbuilding.

   The reason you're not finding a "rule of thumb" for sizing a structural ridge beam is that it is highly dependent on the individual structure.

   As Tomrocks correctly said, the beam has to be sized to bear one half of the total roof load (the other half is shared by the eave walls).

   The first assumption you have to make is how much load your roof will carry.  Are you in snow country?  Is the beam going to be spanning the 8-foot or 12-foot dimension of your shed?

   Once you assume a roof load (in pounds per square foot), you'll be able to calculate the total anticipated load (when adding in the dead load), and then size the beam for shear and deflection.

    

1. 
   hotwheels | Mar 15, 2008 06:50pm | #10

   Thanks for the response.About the roof load and its relation to the ridge beam size:1) I live below the snow line, although once every 10 years or so we get an inch that will stick. So, I am not sure what load there is on the roof other than the weight of the roof material itself and any forces generated by wind. How is the load calculated for this type of situation?2) I plan for the ridge beam to span the 12' length of the building. I will support it at each end.3) I can always pay an engineer to tell me the size of a 12-14' beam for an 8x12 building with x pitch roof and no snow load, but it seems as if I can over-engineer the beam and skip that engineering consultation. An LVL might then be my best solution.

1. 
   Framer | Mar 15, 2008 07:05pm | #11

   Forget about getting any storage with a 4' run. That's to the outside of the plate, it's less when figuring to the inside of the plate and then adding the height of the collar/rafter ties. If you want to put collar/rafter ties unless you make the pitch a 12/12 or 20/12. Your better off with  no ridge beam and using ceiling joists and making the pitch 12/12....... 16/12.......20/12.

    

   What size rafters are you using, 2x4 or 2x6? What pitch are you using?

   What is the wall height? Is there a height requirement to the top of the rafters?

    

   Joe Carola

   Edited 3/15/2008 12:31 pm ET by Framer

4. 
   Riversong | Mar 15, 2008 07:54pm | #12

   so I thought that using rafter ties (maybe collar ties) would offer a platform for that storage and also add some extra strength to keep the roof from sagging and the walls from spreading?

   Collar ties (in the upper third of rafter span) are to prevent uplift and spreading at the ridge.  Rafter ties (often doubling as ceiling joists - in the lower third) are to prevent outward thrust on the bearing walls.

   Though it used to be done, it's a mistake to rely on collar ties to increase the stiffness of a roof or resist out-thrust.  Always size your rafters for the expected load and the design span.

   After reading yours and other posts it seems that a 2x8 or maybe an LVL would work?

   A S-P-F 2x8 ridge beam would carry up to 25 psf of total dead and live load for a 12' span and a 4' rafter run.  It sounds as if that would meet your needs. 

   Riversong HouseWright

   Design *  * Build *  * Renovate *  * ConsultSolar & Super-Insulated Healthy Homes

1. 
   hotwheels | Mar 15, 2008 08:00pm | #13

   Thanks! I think that is what I will do. I am throwing out the idea of storing lumber in the building. I am increasing the pitch to 6/12 to give me a few more inches of head room, since I limited the wall height to 7'. I don't want the structure to be too high mostly because of aesthetic reasons, so going to a 12/12 pitch to get more head room isn't an option.Thanks to all for the roof lessons!

2. 
   Ragnar17 | Mar 14, 2008 09:11pm | #2

   Sounds like you're making a 8x12 shed with a gable roof.

   Are you going for a "vaulted" ceiling, or will you be using ceiling joists / rafter ties?

   A bonafide ridge beam is only required if you are building a vaulted ceiling.  If you have ceiling joists / rafter ties to hold the walls together (against the spreading force of the rafters) then no ridge beam is required at all.  Sometimes, people will put in a 1x6 or 1x8, but that's only to help with construction, and is not a structural element.

3. 
   cargin | Mar 14, 2008 09:19pm | #3

   hotwheels

   I think you want a ridge board for this gable roof. It is not weight bearing as such. It functions to give you anailing for your common rafters. Like riversong said if you are using 2x6 rafters then you should probably use a 2x8  or 1x8 for the ridge board.

   Then you should use collar ties. These function to keep the walls from spreading.

   If you have a large addtion and you want a cathedral ceiling with no collar ties then you would want a ridge bean (sorry I mean beam),  that bears weight on each end of the gable. This is carry the roof weight so the downward thrust of the rafters doesn't cause the walls to bow.

   Attached is a picture of roof framing and terms.

   Rich

4. 
   user-270695 | Jan 22, 2015 08:15pm | #14

   RIVERSONG!!

   I miss you over at GBA!!

   Im building a 10x16 cabin stick framed. I too want a structural ridge. We live in SE Pa. Yes snow. Im thinking a double 2x10 structural ridge and 2x8 rafters for the simple gabled roof with a 8-10 pitch. Sound about right??