Joist framing 12″oc to 16″oc – overlap?
Hello again,
One floor in my house is enginered for 40 PSF live load, 10 PSF dead load, 360 deflection, where:
- one side of a floor (over 2×4 bearing wall) is 2×10 12″oc (17’span) and
- the other side is 2×10 16″ oc (10′ span)
The question is:
- since the joists won’t overlap (often) do you just have varying length blocking between the joists where they bear on the wall? or is there another way of doing this?
Joists down South here are usually southern yellow pine. I also thought of going to 2×12’s 16″ oc (notched at both ends) and just having the ceiling below a couple of inches lower. The main reason for trying to keep with 16″ oc is that everything else is 16″ oc and it all lines up better. Also, since that bearing wall is 2×4, I’d need to have a tripple top plate since some joists would not bear within 5″ of a stud. Aditionally, it seems like the whole process would be easier (framing, slooring, plumbing, electric, sheetrock,…) would be easier if I kept to 16″ oc.
Any thoughts would be appreciated.
Thanks,
Roger <><
Replies
Sounds like a good situation for I joists. Boise Cascade's AJS-25's will easily span your 17' at 16" oc and are only 9 1/2" deep with a 3 1/2" flange. In the areas with the shorter span you could drop down to AJS-20's to save a few bucks (9 1/2" w/ a 2 1/2" flange).
Might be worth a looksee. A few extra bucks will give you a better floor and solve your layout issues.
Use varying length blocks where the 2 different floor sections meet over the 2x4 bearing wall if you want to stay with the proposed config.
2x10 - 17' span - that's pushing it. I doubt that you are gonna be happy with the performance of the floor. The 12" O.C. helps a little but not a lot. The SYP helps a little, but again not that much. Even though that would meet code minimums, or at least it would where I live, when using span tables, it's always best to be very conservative.
L/360 will allow more than a 1/2" defelection but more important would the ammount of vibration that would be generated by the floor. For longer spans, go with a better performance spec than the code min L/360 - go with at least L/480 or, even better, L/600.
I'd check to see if you can get an I-joist that would perform better. Around here, I-joist suppliers will engineer their floor systems for free so you would not have to worry about paying another engineering fee.
BCI I-joists:
http://boise.bc.com/ewp/east_spec_guide/sec_2_pg4-15.pdf
http://boise.bc.com/ewp/spec_east_south.jsp
http://www.gp.com/build/product.aspx?pname=Wood+I+Beam%e2%84%a2+Joists&pid=1390&hierarchy=pc
Edited 4/14/2005 7:01 am ET by DIRISHINME
since the joists won't overlap (often) do you just have varying length blocking between the joists where they bear on the wall? or is there another way of doing this?
If you can't use I-joists as Dieselpig and Dirishinme has suggested then yes,just put blocking in between and that's all you need. This happens all the time.
I also thought of going to 2x12's 16" oc (notched at both ends) and just having the ceiling below a couple of inches lower.
Forget that idea. You can't notch the bottom of the 2x12's and it makes no sense to do that and have different ceiling heights when you have a normal situation here. If your saying that you thought about doing this with 2x12's than ask the Engineer to use I-joists and everything will be 16" centers.
Also, since that bearing wall is 2x4, I'd need to have a tripple top plate since some joists would not bear within 5" of a stud.
Where did you get that from? I've never heard that before. As far as I'm concerned that's not true, I've never seen it or done it.What you have is a normal situation as I've said and there's no problem with what your doing and yes going from 16" centers on one side to 12" centers on the other side is a pain but it's nothing new.
If you don't like it go for the I-joists and be done with it, other than that if you keep what you have , it's just different size blocking and that's it.
Edited 4/14/2005 8:07 am ET by Framer
Don't know if you've read enough here to know, but I'm the resident fanatic about floor performance.
No way should 2X10s span 17'. That's a length/depth ratio of about 22. I like to see that ratio limited to about 18.
Th means 2X10s shouldn't span more than about 14', regardless of the spacing.
There's a thread about Floor Vibration that explains why I think that way.
I'd strongly recommend a change in your floor design by either adjusting your bearing points or using a deeper floor system.
Thanks for your input. I'll probably be going with 2x12's 16"oc [this will only raise the materials bill by about 600]. I do appreciate the input, as I lack the experience and don't want to wind up with a floor that I'm unhappy with.
One more quick question if I may: I have a floor downstairs (over basement, blocking not yet in place) that is 16' span with 2x10's 16"oc. Would you recommend
doubling them up ?or
sistering with with 2x12's? or
other option?
Roger <><
To me, adding depth or adding a bearing are the best options. Doubling up an overspanned joist would do very little.
If a case of the clap spreads, is it then considered a case of the applause?
I'm still lost as to why you'd 'notch' 2x12s. As mentioned, I'd go with TJIs.
Just remember, the trades will be boreing and cutting into your already 'pushing the limit' joists. ahh....what was the question ?
My grampa told me that if you notch the bottom of a joist that you end up with an efective joist size the same as the smallest hight. The reasoning is that with a load the notch creates a week spot that cracks away from the joist remaining on the leadger.
I would go with 2x12 on 12oc or Ijoist. In the long run you want a solid floor . You don't want to be writing back in a few years wanting to know how to stiffen the floor. Thet just leads to heated debate here.
Re the 2nd Q, are the 16' spanned 2x10s SYP or SPF?Matt
I re-measured it today. It's actually 15' span 2x10 SYP.
Roger:
I can tell you from experience that a 16" O.C. SYP 2x10 15' span floor will be OK - a little bouncy - but OK. I probably would have gone with 12" centers. If you are worried about it, double up. Bridging (blocking, etc) will make a difference so small that it will be hard to tell the improvement and just introduces the possibility for squeaks. If the 16" OC were SPF, it would more likely fall in the 'sucks' catigory.
You need to get that SYP sheathed quickly though - it likes to "twist up" when left out in the sun.
BTW - you know that when we say "span" we mean "clear span" - which means from the face of the load bearing walls below. So, the "span" will be the same as the ceiling size (usually the width) of the room below. But you probably already knew that...
BTW - I'm in Raleigh. Matt
I have a floor downstairs over basement that is 16ft span with 2X10s 16 inch on center...would you recommend doubling them up, sistering with 2x12s or...
I agree with Boss Hog that adding depth or placing a bearing ( support) wall underneath to shorten the span is the ideal way to go...but sometimes you can't go that route due to various circumstances.
That said... sistering 2x12s to 2x10s is no more advantageous than doubling the 2x10s with another 2x10...the reason is that you will have to notch the ends of the 2x12s so to slip onto the top plates ( if floor has already been sheathed). Hence, the 2x12 just became a 2x10.
Doubling the 2x10s would help; without a doubt. But a more effective approach would be to place 2X10s in between your current joist bays...thus giving you 8 inch centers. This should be more than adequate to stiffen the floor...You may not like this idea cause the bays may no longer be wide enough for heat duct runs, and other misc items...but if the proposed 8 inch OC poses no such problems , then that is one possible solution.
Consult with a rep from one of the (earlier) listed engineered lumber websites...they may have an idea using their products and/or may be able to answer how stiff your floor would become if you chose one of theabove mentioned ideas ( doubling 2x10s..or placing in-between for 8 inch centers).
Good luck.
Davo
> I'll probably be going with 2x12's 16"oc [this will only raise the materials bill by about 600].
I have Doug fir 2x10's, 12" oc, spanning 15 ft at home. With two rows of cross bracing, this is a very solid floor.
> One more quick question if I may: I have a floor downstairs (over basement, blocking not yet in place) that is 16' span with 2x10's 16"oc. Would you recommend ....
For a basement, the most common approach is a girder and posts down the middle to break it up into two 8 ft spans. That makes for an extremely firm first floor.
-- J.S.
Sounds like your question about different size blocks is a mute point now from the rest of this thread, but for futurre reference, when blocking a wall as you mentioned, I cut all the joist on the 12" side to bear 2" on a 2x4 wall then I block all the 16"side as normal with 14.5"blocks shove up to the 12" and nailed thru similar to if the were rim...knowhatImean? I love BCI joists,by the way.... Good luck
That's a really smart idea. A little time consuming to cut all the joists (unless you had to anyway) if you coulda just lapped 'em, but a neat solution none-the-less.