Deck Beam Spans and Joist Cantilevers
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- เผยแพร่เมื่อ 1 ต.ค. 2024
- The 2021 IRC provides a pre-engineered span table for sizing deck beams, but it offers a lot more design flexibility than may appear. This video is a quick-talking clip made just for TH-cam, but it comes from comprehensive building code education at BuildingCodeCollege.com
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Such a helpful video! One Question- I need to calculate the "joist span factor" on a 9' wide freestanding deck with only 2 beams, and joists cantilevering 18" beyond beams at both ends. To determine the "actual joist cantilever", do you add both cantilevers together (making it 36") or use 18"?
I'm a newbie to deck building and am just reading through the code book and a Black and Decker book designing decks. I just came to this exact issue and was puzzled, until I found this video. I guessed it worked as you said, but thanks for confirming it, as I'm hesitant to think I am correct as I have had no formal training. You're awesome dude!
You’re welcome! I have a comprehensive series of On-Demand Courses that cover (in depth) all the latest IRC codes for decks. I send a free copy of my ICC deck code book with every enrollment. DeckCodes.com for details.
@@GlennMathewson yes I may take you up on that offer in the near future. Thanks!
Thanks for this! Question re "joist BACK span" which is confusing me At 1:05, in the "maximum cantilever" portion of Table R507.6, it refers to "joist back span" in feet, in 2' increments, from 4' up to the number that is just below the max. "allowable joist span." What is a a "joist BACK span?" It's not defined. Is that the actual ledger-to-beam distance for your joists? If so, isn't that what "joist span" already means?
Thanks Glen, I'd love to see this expanded info in the 2024 IRC.
your videos are great. i’m building a 14x20’ deck that cantilevers; my beam needs to be 20’ but i’m confused on the tables, should i just use 4 beams made up of double 2x10 that are all 5’ long to equal the 20’ span? and insight would be appreciated
would love to find an online calculator that could do this. probably is one somewhere ??
Loved this! Thank you!
If you play this video at .75 speed, it is more comprehensible.
There's no way an average person can keep up and get a good understanding he talks much too fast and move through the lesson too fast.
You know I’m right here, right? You don’t have to refer to me in third person. I’m a real live human and all…. Thanks for the feedback. This video was an experiment.
I’m an average person and followed it just fine. Besides, it’s a TH-cam video and you can adjust playback speeds in the settings, or watch it again.
@@GlennMathewson it's a great vid. pausing video is a helpful tool. some people are just big complainers
@@christopherstafford227
Please keep up these excellent videos. They are very very helpful. Thank you!
Building a low-level 32’x26’ deck and this helped a ton! Thank you
Thanks Glenn, great explanation of the 2021 and the proposed 2024. Makes sense. Question though, using the allowable beam span can the beam also have a cantilever on the beam beyond the post, like 1/4 the beam length?
Yes, a beam sized under the IRC table can cantilever one fourth the adjacent beam span.
Glen, I’m currently extending my deck (original 12x12, but 16’ in one side due to stair landing. I’m extending the 16’ side 8 more feet. So I had to extend the current beam which is around 10’ from the house, but then added a second beam supporting the landing and the new extension around 13.5’ from the house, which left me me with a 2’-6” cantilever. Is this cantilever ok? All I see in the tables is “back span” but doesn’t take in consideration if you have a second beam/support.
Without taking the second beam in consideration, if I only go with the first back span at 10’, I’m allow 2-6” cantilever correct?
Joist are 2x8s and beams are double 2x12s.
Hopefully my confusion and question make sense to you. Thanks in advance.
Honestly not sure if I am picturing this correctly. The backspan length needs to be one single member, the same as the cantilevered one. If it is continuous over the mid span beam, "technically" that mid span beam is now also likely holding down the joist. So that puts all the stress on the wood fibers supporting the cantilever in the area between the midspan beam and cantilever supporting beam. So in that case, yes, the midspan beam would cause you to measure 'backspan" to it. Now... with all that said, personally speaking, I'm not really worried about that. But that's an informal final opinion from a code guy trying to understanding engineering principles.
Is this for 4x4 posts on these beam spans or we talking 6x6 or does it matter?
The post size doesn’t really matter much in this discussion. it’s about the connection.
I have been building 10x12 decks, I use 2x10s, usually have a two foot canterlever, could I get by with using 2x8 joists instead?
Use the table in the IRC before you build sonething you might have to rebuild.
I would rather overbuild than under build. especially raised 6-8’ off the ground with 10 people on it. stick with 10’s and 12’s
What joist spacing? I use 2x8 for 12'. It's fine.
You talk too fast. Thanks. Ill check someone else
Thanks for the feedback.
@@GlennMathewson I really liked your pace!
TH-cam has playback controls, including speed.
Geez what did you say ,,,,slow down or get off the coffee
This video was an experiment. Thanks for commenting. I’m not quitting my coffee.
Me either love the French vanilla
No matter what you build always try to keep it simple. Lots of builders and architects are trying to show off their pretty skills and then a bunch of errors are made when their plans are more complicated than they need to be. Same with cars and trucks.
I have no idea what I'm seeing. I cannot decipher your plans.
skill issue