Hello, so here is the scenario
I have a 20×40 building Im trying to design, the space is fully open no interior walls. I was thinking of building a ridge beam out of 2×12 material but it would have to span 42′ (that’s from eave to eave). I was thinking maybe (3) 2×12 sistered and staggered all the way down. The first question is would that be enough to support the load. And second, would I need a support such as a column in the middle of the building to help support it? Its my first time building such long beam so need input please. Thank you very much!!!
Replies
Take your specs to a real lumberyard and ask them to submit your “design” to a structural beam supplier.
Here, Here!
The funny thing about a ridge board on a symmetrical gable roof is that it doesn’t really support a load. That’s why some old buildings have 1x ridges or even no ridge board at all. On a gable roof the rafters support each other by pushing on one another. The ridge is really just a convenient nailer and makes layout easier and keeps things straight. A doubled staggered ridge would be fine as would a splice between two rafters with a mending plate in my opinion.
Have an old house where they didn’t put in either a ridge beam or rafter ties for 24’… the result is the walls being pushed out not as much as it would have if they didn’t push some bracing in attic (the 1/3 done from peak)…. U either need ridge beam or roof rafter ties…. Definitely talk with structural engineer….
Are you going to have a ceiling? No ceiling means no way to keep walls from spreading unless the ridge beam carries half the roof load. Better run this by a structural engineer.
no ceiling as in drywall, but will still have ceiling joists throughout.
If you are ok with the exposed joists, a clear span may be more economical with a 20 ft span engineered roof joist framing, instead of rafters and a 40 ft beam capable of supporting rafters.
Include transportation to the site and placing on the structure as you compare options.
we want the rafter style because we will be using the attic space in the future for storage. truss style does not give me that option
Attic truss.
I'm building a house soon here with similar dimensions.
So if you want to avoid heavy beams and a crane (maybe), you can just order one LVL ridge board that is deep enough for the plumb cut of the rafters to attach to it without hanging down. Then for half the 20' span which is only 10', you could use 2x8 rafters, and install collar ties 1/3 the height down from the ridge, and ceiling joists that are 20' long out of day 2x12 or if your paranoid about deflection you could order LVL ceiling joists but only if budget allows. That's it, it doesn't need to be engineered, it is all in the IRC the roof span tables, just make sure you use the correct table with your regions snow and other applicable loads (ie dead load).
Have fun!
Prescriptive design is for a roof board, and ceiling joists that hold the walls from being pushed away by the rafter and roof loads.
Many of the responses here were based on an understanding (perhaps misunderstanding) that the question was about a ridge beam, and no joists at the top of the walls.
I think earlier he said no drywall but he would have ceiling joists throughout? I actually don't know if the ceiling joists need to be sheared off with drywall though, I'd have to take a peek at that section if it specifies the way trusses specs do. And since he said ceiling joists throughout, I figured a ridge board would be more cost effective, eliminate need for engineer and easier to stack himself since I assumed he would be doing the work. If he truly wants a beam yeah you're right he's gonna need an engineer we can't give him any real advice without calculating beams ourselves, which has to also be done by the engineer anyway so no real point in helping with that.
so this is a rough design so far. i am still missing the ceiling joist we will be installing. No drywall on the ceiling joists.
The joists are not an add-on, they are critical for the strength of the structure.
https://codes.iccsafe.org/content/IRC2018P7/chapter-8-roof-ceiling-construction
Light reading. helpful figures closer to the end. footnotes are important to read and understand.
This is fine, you've got plenty of shearwall area to work with. Throw in the ceiling joists, nail em off with enough nails per IRC as well as the collar ties and you're good to build. Other here seem to think you can't frame a roof. Do you know how to cut a birds mouth or how to frame the barge rafter shown in your diagram? If so, great. If not, no need to hire a carpenter, buy the roof cutters secrets book. It will teach you all aspects of room framing is an easy but excellent level of understanding. I wouldn't venture too far in the book at one time, as it takes years to fully understand some of the types of roof framing. Anywho, if you really want the official code book with spans on rafters, ceiling joists (and their allowable live loads) just buy the 2018 IRC book on Amazon for $200.00. The book tells you everything you will need to know about the code if you care to read the one little section about roof framing. I say all this because I wish someone had helped me with answers when I was learning, only to realize you're really alone and no one is going to help you with any meaningful information. Most folks will want to impose their set of opinions on you to make themselves feel superior. There's not much to it really, break it down into small simple steps and attack them one at a time and ask all questions along the way. Hope this helps along your project!
I never said I wasnt installing joists. I said I didnt put them in the drawing yet as Im still working on it.
Thanks Andy, made perfect sense and I was confusing my naming which you and others helped me figure that out. I am not going for a ridge beam but a ridge board. Im good to continue now and I think I should be good. Either I sister a few boards together the length needed or Ill find out how much an engineered LVL that length will cost.
https://www.finehomebuilding.com/forum/tying-2-ridge-boards-together
You should hit google or grab a book on residential framing, it will probably answer most of the questions you have about building a one story gable roof structure. You have some homework to do if you plan to build this yourself and you are on a forum asking about ridge beams.
I am concerned your proposed design might push the walls out. Have you considered using scissor trusses combined with a high pitch roof to give you more interior space. With scissor trusses you can totally eliminate the ridge beam.I used scissor trusses on my 20 foot wide workshop and found them easy to put up with one helper. Suggest you talk to a truss manufacturer to see what they can come up with for you.
I do not want a truss system. I want an open attic concept. Truss system is not meant for storage and does not allow space for things. But thank you for the suggestion.
Attic truss.
http://design.medeek.com/resources/truss/trussgallery.html
Like Calvin has been pointing out, you have options.
Whatever you do, first step would be to understand what the load capabilities you need, both in terms of roof rafter snow and other loads, and a a good understanding of what you plan to put in that attic space.
attic floors designed for a couple plastic christmas trees may not be good for boxes full of books, or keeping your engine block collection.
Also, do not be afraid to contact your local building codes department for information and assistance.
With joists installed to hold the wall end of the rafters from moving away from each other, the structural member at the peak where the roof rafters meet is not going to carry much load, and does not need to be a beam.
In these cases, it is more properly called a ridge board.
https://www.techsupport.weyerhaeuser.com/hc/en-us/articles/207291947-Ridge-Beam-vs-Ridge-Board-
Link is to more helpful information.
Thank you this was very helpful!
Using (3) 2x12s sistered and staggered should work, but check with an engineer for heavy load considerations. You might need a support column in the middle depending on the weight.