I have an addition that is to be built for a homeowner who wants I-joists. I’ve gotten MUCH conflicting info between my Lumberyard and the Big box stores as to the right size joist.
The big boxes are spec’ing Boise Cascade I-joists. The homeowner says they want to feel the floor as solid as possible with as little hint of deflection as possible.
The structure in question here is 20ft 6″ long x 28ft wide. I plan to space I-joists 12 o.c across the width of 28ft for a total of 26 I-joists. I’m using 11 7/8″ I josits. The span that they must span is of course 26ft 6″ (this span includes the foundation wall, outside to outside).
The owner plans for carpet on the floor, maybe wood. A possible large typical aquarium, typical furniture and chairs (this is a Sunroom). The upstairs floor, which mirrrors the first, will be a master BR consisting of typical BR furnishings like a nice heavy bed set.
I’ve been told I can get away with a BCI 90 which is a 3.5″ top/bot cord of the joist. I also been told I can do it with a BCI 4500 MINIMALLY, or that I can use a BCI 5000. One places says I’m told by the others wrongly. One place says I MUST use a 3.5″ cord. Other places say I must use web stiffeners.
Any opinions out there on who is right? One place claims the mfgr says I must use 3.5″. I don’t know who to believe. The price difference is almost double between BCI 5000 and BCI 90.
Replies
Your post is a little confusing. You said: "The structure in question here is 20ft 6" long x 28ft wide." But you also say "...they must span is of course 26ft 6" (this span includes the foundation wall, outside to outside)". Those numbers don't make sense.
Any time you're designing a floor and they tell you that you can "get away with" something that tells me the floor is too thin. If you have to space the I-joists 12" O.C. to get the system to work that's also a red flag.
They're trying to take an 11 7/8" I-joist and make it do something that it won't do well.
I know I've beat this floor vibration thread to death here on BT, but have you read it?
http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=21010.1
My rule of thumb for floor design is a minimum of one inch of depth for every foot of span. i.e. an 11 7/8" I-joist shouldn't span over about 18'. If you're spanning 26' 6" and want a stiff floor, your floor members need to be 18" deep.
Using 11 7/8" I-joists at that span is ludicrous. I don't care what series they are or what their span charts say - They're too freakin' shallow.
If that wasn't clear enough let me know and I'll REALLY tell ya what I think.
(-:
>> Your post is a little confusing..... Those numbers don't make sense.>> one inch of depth for every foot of span. i.e. an 11 7/8" I-joist shouldn't span over about 18'.Uh, wanna try that again?
why not span the 20'6 instead of the 28
I was thinking about the rule of thumb for headers. Sorry 'bout that.A floor member (I-joist, floor truss, or 2x lumber) should have a minimum of one inch of depth for every 18" that it clear spans. That was how I got the 11 7/8" I-joists (rounded off to 12" deep) shouldn't span over about 18'..BTW - That's my own rule of thumb. It does not reflect the views of the management, or any I-joist manufacturer, or even some of the people I work with. But it's based on a lot of experience. Some of that experience was dealing with unhappy people who had bouncy floors.
Get the facts first. You can distort them later.
I respect your opinion. It makes good sense to me.You probably don't remember it, but your advice helped me decide what I-joists I was going to use when we built five years ago. Thanks again!
I don't remember helping you specifically. But I'm awfully glad to hear that I was able to help someone. I don't feel like I get to do that as much as I'd like.
Men were the material he worked with, and he did not forget a face, even one seen briefly and in unfavorable circumstances [R.P. Lister, regarding Genghis Khan]
It's your nature. I'd bet that you help others more than you give yourself credit for.
You've helped me loads and loads. Just never directly.
I think I have trusses sorta figured out because of you.
Thanks
That was a typo. It's about a 20'6" span but that is outside to outside, meaning the span includes the bearing area of the joists. I am told 11 7/8" at 16 o.c will work. It is I who am deciding to use 12" o.c. to ensure additional strength of the floor. Plus I'm glueing down the subfloor then.If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time. -ME
A 20' 6" span is quite a bit different. Still, I don't like it for 11 7/8" I-joists. Making the spacing closer will make very little difference in the vibration characteristics of the floor. I wouldn't recommend anything less than 14" deep.
You are only young once, but you can stay immature indefinitely.
When you say "vibration" characteristics I"m not sure what they're talking about. I read that thread some you pointed me to. The owner here is more concerned about the strength of the floor, wanting to be able to use it as normal as possible yet maintain the clear span in the basement below. In terms of "feeling" anything other than bounce, I'm not sure they'd care????If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time. -ME
When you say "vibration" characteristics I"m not sure what they're talking about. I read that thread some you pointed me to. The owner here is more concerned about the strength of the floor, wanting to be able to use it as normal as possible yet maintain the clear span in the basement below. In terms of "feeling" anything other than bounce, I'm not sure they'd care????
I hope they do not have a kitchen over this floor, because I would guess
walking thru it the dishes in the cabinets would rattle....
regards
What I ment by "vibration characteristics" was the frequency the floor would vibrate at. Changing the depth of the floor members changes the frequency a LOT. Changing the spacing doesn't change it nearly as much.
Creativity is great, but plagiarism is faster.
A 20' 6" span is quite a bit different.
Still, I don't like it for 11 7/8" I-joists. Making the spacing closer will make very little difference in the vibration characteristics of the floor.
I wouldn't recommend anything less than 14" deep.
I am just a carpenter, but I agree...
regards
"That was a typo. It's about a 20'6" span but that is outside to outside, meaning the span includes the bearing area of the joists."
I guess I should not post without reading the other replies.
Nevertheless, I still would not span 20'6" with 11-7/8" joists, regardless of the flange width or joist spacing.
I have 60 series 11-7/8" joists @ 16"OC (2-5/16" LVL flanges) spanning 18'6" in my home and I wish I would have gone with 14" joists.
With an aquarium, especially if you have no partitions in the rooms, you run a strong risk of feeling like you're walking on a trampoline. I have several sections of my house that have an 18.5' span, but the section that feels the worst is the one that is wide open. It seems that an interior partition breaks up the dynamics of the bounce.
I would consider 14" joists at 16" OC, or for what I would bet would be a great floor would be 16" joists at 19.2" or 24" OC.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
I recal once spanning 20' with a 2-1/2" flange TJI at 12" OC. It had been speced out already and I questioned it, but it has performed well for an open room above it. We used strapping below at 16" OC and did an immaculate job of seating hangers in spite of the fact that there was almost no room to nail them in a 9-`1/2" spaceI suspect the reason he is constrained to that depth is that he is having to match floor and ceiling heights of the existing structure, but this HO may be expecting too much out of I joists. if he wants clear span and rock solid in that depth, he better get ready to pay for using LVLs as joists or at least the very haeviest I joists available - then there is only 8" space to swing a hammer in
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The HO started building this addition and got called away due to work. The foundatin is already made out of cinder block. Thus the footprint is established. The HO drew up his own plans. He claims that he was told 9.5" I joists would do the span but I corrected him and told him no way. The HO wants to have this as a clear span to avoid having obstructions in the way in the basement as they want to pull in their Bobcat for storage. Earlier this year as I planned this project out I was told 11 7/8" Ijoists would work and that if I placed them 12"oc I would have a much stronger floor, especially if I glued it. We had to reconstruct a portion of the foundation due to it failing. When we did so we set the height to allow for the 11 7/8" joist plus 1.5" for the sill it rests upon. If I have to go deeper than 11 7/8" that's going to hurt. From what I was told 11 7/8 is fine but the when I actually went to order them this week THEN people started questioning me and the selection made. Go figure.If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time. -ME
"If I have to go deeper than 11 7/8" that's going to hurt."
You can get wood webbed floor trusses as deep as you need, and get them with a mid chord bearing that's 11 7/8" tall. The extra height will hang down below the sill plate inside the foundation.
Doctor: I'm not sure what exctly your problem is, but I think it's related to drinking.
Patient: Maybe I should come back when you're sober.
Like I said, the HO needs to know ahead of time that a rock solid floor cannot be done with I joists. Gotta be his choice.it can meet code, but it will have vibrations/bounce.So if he wants rock solid,he wants LVLs instead of I joists. Show him the cost comparison and let him make up his own mind to confirm in your mind whether you have a fool for a client.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
You should be consulting an architect or engineer.
mike
I did, sorta, the manufacturer.If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time. -ME
I don't think a ~19.5' clear span will be very stiff for 12" I joists, even they are the heavy ones 12" OC. In addition to the vibration thing consider this:
Although vibration is what causes complaints, also consider what your design spec is for total deflection:
If it is L/360 the floor can deflect up to .65" and be in spec! (A trampoline)L/360 is a commonly used spec.
L/480 = .49"
L/960 = .24" (acceptable)
Boss may correct me (again) and say that I'm not stating it in exactly the correct technical terms, but the data still holds...
"If it is L/360 the floor can deflect up to .65" and be in spec!"
True, but - That's not the whole story.
Keep in mind when you see span charts that say L/360 they're only talking about LIVE load - Not total load. The total load deflection is typically restricted to L/240 when L/360 is used for a live load.
That same floor has a deflection limit is .89" under total load at L/240.
I poured Spot remover on my dog. Now he's gone.
I have an addition that is to be built for a homeowner who wants I-joists.
Why? who hyped them up?
If you want a stiff floor go with floor trusses use all the inner bracing as speced.
Glue and screw the min. 3/4 ply.
You may have the same hight as I Joists, but far easier to run mechanicals.
Vibration as I understand is less of an issue.
I joists floors I have walked on were dissappointing at best. They have to be installed perfectly. I have seen to many people miss filling and blocking.
I haven't read any of the replies yet.
Still, I can assure you that you don't want to span 26'+a with 11-7/8" I joists, unless the top and bottom flanges are 50ksi steel.
Jon Blakemore
RappahannockINC.com Fredericksburg, VA
Would it occur to you to read a span table such as the one shown here, and make your own decision? This one is from Weyerhaeuser's I-Level product group.
The 560 series looks to be what you need. Flanges are 2x4 in size.
The 11-7/8" 560 will deflect about 5/8" at full live load of 40 psf, carrying a dead load of 20 psf. Twenty is a considerable dead load.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
Edited 8/16/2009 5:14 pm ET by Gene_Davis
Hey, Willie, Why not split the span in half with a glulam or microlam flush and hang short 12" joists from both sides?
Hey, Willie, Why not split the span in half with a glulam or microlam flush and hang short 12" joists from both sides?I guess that would work, but can a Glulam span 28ft wide without support in the middle somewhere? I doubt it.If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time. -ME
If you make it about 18" deep or so
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Willie
Turn the LVLs 90 degrees.
Then they would span 20' 6" and then your I joists would span 14'
You would have to run this by BI and make sure the foundation was good for it.
Rich
Theres enough here to make your eys bleed
http://www.bc.com/dms/wood/ewp/europe/europe_uk/uk_tech_12-35.pdf
NAIL IT !!!
No kidding.If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time. -ME
Sorry I just realized that was in metric or something try this one
Check out page 4 for the different options in bounce and stiffness
http://www.bc.com/dms/wood/ewp/3_Guide_Resources/east_south_us/1_alljoist_Spec/2009-alljoist-US-spec-guide.pdf
NAIL IT !!!
Edited 8/16/2009 10:31 pm ET by steven4077
When you use span tables and approach the upper allowed limits of a member, the floor performance suffers - and almost certainly won't produce a "stiff" floor.
Decreasing the spacing, say from 16" OC to 12" OC only helps a little...
To me I-joists aren't that much better than dimensional lumber as far as producing stiff floors. The BIG advantages to I-joists is they come in longer lengths without costing more per linear foot, and they come in deeper depths than dimensional lumber. The depth is what stiffens the floor. 2x18 dimensional lumber floor joist???? 18" I-joist? no problem. It is just more $$$ :-) 38' I-joist? Yes sir - how many do you want?
To me, a 12" I-joist is similar in performance to a 2x12. How stiff would a 2x12 floor at 12" OC be at a 19.5' clear span? I'd say not very. OK - so you are talking the BCI-90s so maybe they are comparable to a 3x12 floor joist. Still may not get you to where you want to go....
From the ilevel.com site I requested their CD with the software that rates a floor for vibration and perception of solidity by average people. Among the things it notes as affecting the feel is the presence of strapping and sheetrock underneath. That apparently makes a large difference.
You can always prop up the floor from below with the bobcat.
View Image
"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
>G<
Had a floor that was 2x10s that maybe spaned 14+', 16" OC. Had a complaint that it wasn't stiff enough. Specifically, the items in the china cabinet (with glass shelves) rattled when someone walked int he room. Getting the idea from here, we strapped the underside of the floor (it was a crawl space) with 2x4s 16" OC. Tacked up with nails and and glue then screwed in place with deck screws. The last think I wanted was some new floor squeeks. Didn't make a difference from what I could tell or from the HO's perception either. That was my actual expierence... Yours may be different, but it is just kiinda hard to shine a turd....
When faced with a similar situation at our house (great room is 19 x 32 or so) we ran flitch plate beams (11 1/4" deep) the shortest direction and flush-framed I-joists the other way to the flitch plates. As a result we were able to drop down to 9 1/2" deep 230 series I joists. Hell of a nice floor - no vibration at all. We chose to express and clad those beams in wood, but of course you could make them disappear as well.
Otherwise from experience you're going to have a bit of vibration and 'live-ness' to deal with.
"In terms of "feeling" anything other than bounce, I'm not sure they'd care????"
Yes, they likely will care, and it won't be good.
Jeff
Edited 8/17/2009 9:38 pm ET by Jeff_Clarke
This is interesting what you say. What is a Flitch plate? If you will picture this. The footprint of this structure is sorta like a tophat. There are two wings on either side of the big span. Each of the wing is a 12x13 room. Then you run into the large sunroom between the two which measures 28ft WIDE x 20'6" long. Knowing this could you reexplain your post to help me see it better? Perhaps you're onto something that may help here???If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time. -ME
A flitch plate beam is a 'sandwich' of steel and wood bolted together in a specific way. A company called BetterHeader (http://www.betterheader.com) makes preassembled flitch plates with recessed fasteners, which makes it easy to place hangers for flush construction (no projected bolt heads). They aren't cheap, but the labor savings over field assembly are significant.
Can you do a simple diagram of you situation? I can't picture it from the 'top hat' description.
Jeff
Jeff, will do diagram tomorrow. Up late tonight and beat tired. I'll draw quick diagram and scan it in and email it to you then or post it here for others to see.If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time. -ME
So, using flitch beams assumes there is enough room below for the beams to hang down...
Hypothetical question for either you or Boss (or anyone else who has actual experience with such a scenario):
A floor system is a 16'x16' square. Maybe using 2x10s as floor joists 16" OC. What would the floor feel like if say every 3rd joist was replaced with a flitch beam? or LVL, for that matter? So, the 'stiffener joists' would be 4' OC. Just to clarify, the flitch beams or LVLs are running the same way as the regular joists and in the same plane as the joists.
It may make some difference - along with solid blocking/bracing which is important. The equivalent method here to what is being discussed above would be to run a flitch plate beam down the center of the room and frame 8' joists to it - you can leave the 2 x 10s OR change to 2 x 8s and strap the ceiling to avoid a beam hanging down.
You could also just run 2 x 12s 12" on center with two rows of blocking - that will give you a pretty firm floor on a 16' span ;o).
Jeff
I guess the hypothetical idea wasn't a good one. Doesn't hurt to ask. OTOH - For the most part I try to avoid blocking or bridging. I have not found it to make an appreciable difference in stiffing the floor and I have found it to cause squeaks. No thanks! It is required by (our) code for long spans though on dimensional lumber.
I doubt a flitch beam would make any appreciable difference. Vibration changes most with changes in depth. Changing the strength or spacing of the members makes less difference.
I can picture in my mind a world without war, a world without hate.
And I can picture us attacking that world, because they'd never expect it.
My own garage is 22 feet wide outside to outside. I did a room above it a few years back with 14 inch I joists , I thought it was okay. Two summers ago I did one same span for my buddy, they speced 16 inchers and it was better. I think the 12 inchers are two small and when you go 12 inch centres it is a pain to run pipes or wires in those smaller cavities.
Have a good day
Cliffy
>> The wall studs are built with three 2x4's making I-Beam studs on 16" centers. <<
What was the purpose of that?
Found this on the web and thought it was interesting based on all the discussion there has been on this thread and others regarding BCI joist spans. This is from BCI and it rates their own system as 3 stsar , 4 star and code approved. note that the tables are for a L/480 live load deflection. What it says is the 117/8 series joist is marginally adequate at this span by their own table. According to these tables for a high quality floor it would require a 14" deep joist for a 20 foot span. Keep in mind this is the 2 5/16 flange width. i did not find the 3.5 flange witdh table.
feel like you should go to a deeper joist? 16 inch deep at 16 " oc?
NOTE: The illustration below is showing several suggested applications for the Boise Cascade products. It is not intended to show an actual house under construction.
NO MIDSPAN BRIDGING IS REQUIRED FOR BCI'S
1 - For load bearing cantilever details, click here.
2 - VERSA-RIM 98 Rim Board will transfer vertical load, see note under floor details.
3 - BCI Rim Joist (where bearing length allows) will support 2000 lbs. per lineal foot of vertical load.
4 - FOR INSTALLATION STABILITY, Temporary strut lines (1x4 min.) 8" on center max. Fasten at each joist with 2-8d mails min.
5 - BCI joist blocking or 2x4 "squash" block on each side required when supporting a load-bearing wall above.
6 - VERSA-LAM header or a BCI joist header.
7 - 1 1/2" knockout holes at approximately 12" o.c. are pre-punched.
8 - See allowable hole sizes and locations.
9 - VERSA-LAM LVL beam.
10 - Endwall blocking may be required.
11 - BCI Joist Blocking is required when BCI Joists are cantilevered.
Residential Floor Span Tables
spacing
12"
16"
19.2"
24"
32"
12"
16"
19.2"
24"
32"
12"
16"
19.2"
24"
32"
Table values assume that sheathing is glued and nailed to the joists.
Yes it says no midspan bracing necessary.
But do it anyway ;o) I always do.
Jeff
Sounds like you have some time on your hands...