Replies

1. 
   BossHog | Jun 08, 2004 10:15pm | #1

   Well, I'll tell you what I know in 30 seconds or less. (-:

   I've been in several houses with floor trusses 2' OC where 3/4" T&G was used. (Including the spec house from hell) I can't tell where the trusses are by walking around on the floor.

   OTOH - I've heard that absolutely no way in hell should you EVER use anything wider than 16" OC for tile floors. I know virtually nothing about tile floors, so I don't really know why that is.

   We add extra floor loading for floors that have tile. You might want to mention it to the truss company you're using.

   Around here, there are a couple of places that carry 7/8" T&G plywood. I might think about using that if I ever built another house.

   BTW - Have you read the thread on floor vibration?

   Gun control? It's the best thing you can do for crooks and gangsters. I want you to have nothing. If I'm a bad guy, I'm always gonna have a gun.
   Safety locks? You will pull the trigger with a lock on, and I'll pull the trigger. We'll see who wins. [Mafia informant Sammy "the Bull" Gravano]

1. 
   AXE | Jun 08, 2004 10:54pm | #2

   Well, I'll tell you what I know in 30 seconds or less. (-:

   I thought you WERE the truss expert... ?

   I've been in several houses with floor trusses 2' OC where 3/4" T&G was used. (Including the spec house from hell) I can't tell where the trusses are by walking around on the floor.

   That's a good testament.  I am putting a truss under partition walls that run parallel to the other floor systems, so I wouldn't have a wall riding on a 3/4" T&G span.

   OTOH - I've heard that absolutely no way in hell should you EVER use anything wider than 16" OC for tile floors. I know virtually nothing about tile floors, so I don't really know why that is.

   I believe this would all have to do with deflection of the floor.  I seriously doubt that tile can't be made to work as long as the subfloor is beefed up to account for it.  In any case, I could easily put tighter spans in the bathroom area.

   We add extra floor loading for floors that have tile. You might want to mention it to the truss company you're using.

   Yes, I will mention that and probably spec out l/600 for the floor.

   Around here, there are a couple of places that carry 7/8" T&G plywood. I might think about using that if I ever built another house.

   I can get TopNotch and Advantech in 1" and 1 1/4" via special order (the framers are surely going to love me for this...)

   BTW - Have you read the thread on floor vibration?

   Yes, and that is why I'm going to stick to 20" deep floor trusses even though they span no more than 16'. I've actually posted several threads about my floor system.  The original design had them spanning 28' and some of them carried 2k lb point loads.  Several of you (including you BossHog) suggested that maybe the floor needed to be redesigned, which I did.  I inserted a couple of big pieces of steel and cut the spans in half.  However, I kept the floor trusses at 20" deep which should make for a good performing floor.

   The other choice is to keep the 16" oc spacing and drop the depth of the truss to something like 16".  But that starts falling into the trap of the floor vibration theory.

   If anyone is interested, here's a pdf of the floor system.

1. 
   BossHog | Jun 09, 2004 12:59am | #3

   I recall those old threads now, but didn't associate them with your name.

   You canm't expect me to be this good looking *AND* have a good memory, can you ???

   I'm at home now, and can't view your PDF file in a large enough format to read anything. I may try printing it up tomorrow at work.

   BTW - I may or may not be ab expert on trusses, but I'm not an expert on plywood. I was hoping that others would chime in with some opinions/experiences.Spend the afternoon. You can't take it with you.

1. 
   htra | Jun 09, 2004 05:22pm | #4

   I have a similar problem, and would like a comment from you guys about it. I have read the paper on floor frequency, and some of the earlier threads.

   I have a house with 16" deep floor truss spans of 22'-0" @ 16"o.c. under mixed use, i.e. kitchen, living room, bedrooms, bathrooms, etc. There is also a bedroom with 26'-0" @ 16"o.c. spans. These are "TrimJoist" trusses.

   There are no loads on the floor trusses other than normal floor design loads.

   According to the TrimJoist span tables, they are showing around L/500+ for these spans. 2x6 strongbacks @ 10'-0" o.c. will be used. Subfloor is 3/4" APA plywood glued with 5/8" Bamboo flooring as finish.

   I have not had experience with spans like this. I understand many factors come into play with floor frequency, so personal experience really becomes important. Can anyone give me an opinion about how these spans will perform as far as customer satisfaction?

   Thanks

1. 
   BossHog | Jun 09, 2004 06:04pm | #5

   A 22' clear span floor truss 16" deep is within my comfort zone.

   But no way am I O.K. with a 16" floor truss spanning 26'. (Assuming you mean a clear span)

   I don't personally have any experience with trimjoist brand. But that length/depth ratio is bad. No way would I go for that.During the mid-1980s dairy farmers decided there was too much cheap milk at the supermarket. So the government bought and slaughtered 1.6 million dairy cows.How come the government never does anything like this with lawyers? [P.J. O'Rourke]

2. 
   htra | Jun 09, 2004 08:02pm | #6

   Yes, these are clear spans. If we must we could go to a deeper truss on the 26 foot span, but I think a mid-point bearing would be easier in this case. There are only 11 trusses with this 26' distance.

   The Trim Joist span chart says a 16" will go 28 feet @ 16"o.c. I expect it would, but one wonders about the feel even at L/500.

   The truss plant guys and even the Trim Joist manufacturer both say everything's fine. Of course. This is why I'm trying to get some real-world comments from this forum.

3. 
   BossHog | Jun 09, 2004 09:26pm | #7

   The manufacturer you're dealing with may not have any frame of reference to work with other than span charts. Guess you could ask them if they have a way to figure the vibration frequency on the floor.

   I stuck your 26' truss in the spreadsheet I have, and came up with 11.5 cycles per second. Anything over 15 is considered acceptable, 12 to 15 marginal, and under 12 is unacceptable. So yours won't fly.

   Trouble is, using vibration frequency isn't part of any building code I know of. So they just use span charts.

   I'm speculating here, but I'd almost bet that they told you you HAVE to set them eithr 12" or 16" OC to make those spans. That's a pretty common thing to do. But they're trying to do the wrong thing, IMHO.

   If you want to break up the 26' span, you might use an offset beam instead of a center beam. Like where the floor plan gets wider, continue that on with a beam. That way you keep your basement as open as possible.I am the bad thing that happens to good people.

4. 
   AXE | Jun 09, 2004 09:46pm | #9

   "I stuck your 26' truss in the spreadsheet I have"

   Can you stick some numbers in for me?  I'd like to see six numbers, which would be real world for me, but also give us some idea how span and truss depth affects frequency.  All spans are 16'.

               oc spacing    16"      24"

   truss depth

   16"

   18"

   20"

   Thanks MERC

5. 
   BossHog | Jun 09, 2004 10:02pm | #10

   There's nothing secret about the spreadsheet. I'll email it to anyone who wants to play with it.

   Honestly, with a 16' span any of those scenarios are going to be in the acceptable range.We are all born naked and screaming.If you're lucky that sort of thing won't stop there.

6. 
   jonblakemore | Jun 10, 2004 04:25am | #11

   Could you post as an attachment?  I'm interested (I'm a sucker for a spreadsheet). 

   Jon Blakemore

7. 
   BossHog | Jun 10, 2004 01:56pm | #13

   Here ya go.

   It's pretty self explanatory. Just enter the span, spacing, and depth. You can also change the modulus of elasticity, weight of the truss, and weight of the plywood if you want to.

   The "F" number at the bottom is the frequency in cycles per second.

   Most of the other cells are locked so you don't accidentally mess them up.Two wrongs don't make a right.But three rights make a left.

8. 
   htra | Jun 10, 2004 04:23pm | #14

   Thanks for sharing that formula, Boss Hog. Very neat.

9. 
   BossHog | Jun 10, 2004 04:43pm | #15

   No problem.

   Keep in mind that this formula isn't my work - The math is a little over my head.

   All I did was put it in a spreadsheet.What does it mean if you break a mirror with a rabbit's foot?

10. 
    v8trike1 | Jun 11, 2004 04:38am | #18

    I would love to have that spreadsheet!!

    I am going 32 feet with 24 inch trusses spaced 16CL...

    your thoughts??

    thanks

    Scaffold guy

    [email protected]

11. 
    AXE | Jun 11, 2004 04:44am | #19

    F = 12.6 ... I don't think BH is going to like that....

    MERC

12. 
    v8trike1 | Jun 11, 2004 04:57am | #22

    BH??

13. 
    AXE | Jun 11, 2004 05:06am | #24

    Sorry 'bout that, I'm usually careful about acronyms.  That's "Boss Hog", the resident truss frequency monitor.

14. 
    BossHog | Jun 11, 2004 04:44am | #20

    http://forums.taunton.com/tp-breaktime/messages?msg=44168.15

    I've done 32' floor trusses 24" deep before. That's pushing the limits a bit, but can work. Sure makes a nice basement.

    Absolutely under no circumstances leave out the 2X6 strongbacks. I'd put them on every vertical.The greatness of a man can nearly always be measured by his willingness to be kind.

15. 
    v8trike1 | Jun 11, 2004 04:55am | #21

    Thanks for the input---  ever use2x10 or 12 strongbacks?

    will do---

16. 
    BossHog | Jun 11, 2004 02:08pm | #27

    "ever use2x10 or 12 strongbacks?"

    Nope. I've known a guy who used 2X8, but I've never seen anything larger.

    Get 'em too big and they get in the way of your mechanicals.

    BTW - Speaking of mechanicals - If you're planning on running your ductwork through the trusses, talk to your HVAC guy and the truss company about it.

    Can't tell you how many times I've had guys come back after the house was framed wanting to cut out a bunch of webs so they could run their ductwork somewhere it wasn't planned for.

    It works great if it's planned ahead. But it can be extraordinarily frustrating if it isn't.I love cats...they taste like chicken.

17. 
    AXE | Jun 11, 2004 03:54pm | #28

    The HVAC chase is definitely in my mind, however with all those point loads I have it makes it difficult to find a place to put the chase at all.  Maybe you can take a look at my truss plan and pick out where it looks like I could put a chase.  I just don't know how close to point loads and how close to exterior walls I can go.  I also have a stairwell and some flush steel beams that almost cut the house in half making a large chase from the east side (right on the drawings) to the west side difficult.  I had sort of resigned myself to not having a wonderful HVAC trunk in the floor, but if I can get it in there, I'd be happy.

    MERC

18. 
    BossHog | Jun 11, 2004 05:14pm | #29

    With point load you don't have a lot of hope of getting a rectangular chase to work out.

    The general rule of thumb is that a duct has to be halfway between bearings, puus or minus a foot. But throw in cantilevers and point loads, and that goes out the window.

    But you don't necessarilly need a chase to have ducts in the floor. If the truss company will line up the webs where you want your ducts, that should do it just fine - If your trusses are deep anough.

    As a general rule of thumb, I tell people that trusses need to be about 18" deep before you can get all your ducts in them.Never go to bed mad — stay up and fight.

19. 
    AXE | Jun 11, 2004 05:32pm | #30

    Man, I can't thank you enough for all your input on this.

    I think I am using either 16 or 18" trusses, probably 18" since I have a w16x45 flush beam in the floor.  I might be able to get away with 16's, but 18's sure would make life easier.  I will have the truss manufacturer line up the webs correctly so I can get some good straight duct runs.  I don't want to be snaking flexduct through it, I'd like to use metal ducts.

    MERC

20. 
    BossHog | Jun 11, 2004 05:58pm | #31

    Hey - No problem. Folks here have helped me with tons of things. I can't always repay a kindness, but I can generally pass it on.

    It might be helpful to have your HVAC guy meet with your truss guy. (I've done that several times) That way they can discuss options for where to run stuff.Love is the delusion that one woman differs from another.

21. 
    AXE | Jun 11, 2004 06:23pm | #32

    Outstanding:

    "Love is the delusion that one woman differs from another."

     

    HVAC guy = me, so that simplifies things some.

    MERC

22. 
    jonblakemore | Jun 11, 2004 05:00am | #23

    Boss,

    Were you the one who said that a family member used the mechanical chase for access, using a skateboard? 

    Jon Blakemore

23. 
    BossHog | Jun 11, 2004 02:01pm | #26

    "Were you the one who said that a family member used the mechanical chase for access, using a skateboard?"

    Yup - But it was a mechanic's creeper.Liberty without learning is always in peril and learning without liberty is always in vain.[John F. Kennedy]

24. 
    SamT | Jun 11, 2004 12:35am | #16

    DJ,

    I had a chance to look over your floor plan and saw some things I would issue an RFI for.

    Joist IDs.gif shows areas where it is ambiguous which joist is named what.

    Layout Change.gif indicates where layout is obviously not on 16"OC but there are no notes explaining. Some of them are extras top the layout due to partitions and point loads but at least two sets of three appear to totally break the 16" layout. I know the framers can look at the second floor plans to determine the extra joist positions, but I would rather see all the required dims on this sheet. It would really help prevent OhShetz.

    Callouts.gif shows several issues; End supports for the load bearing beams, is the bottom left corner typical?; Do the joist sit on or hang from the doubled 2x10s; The left wall is called out identical to the right wall, does the engineer really want 2 sets of paired 2x10s in that wall or is one set ok?; What header goes over the french doors? This section of the drawing looks like an after thought and appears incomplete. No exterior windows? What detail at the top wall?

    Specials.gif has no details for over the wing walls and what type ribbon joist or header is carrying the point loads from above? Is he just depending on the cantilevered joists, one of which is not under the load, to do the job?

    I realize that some of these issues will be addressed in the details that you did not post. I also know thaat I am seeing some things that aren't there.

    SamT

    Arguing with a Breaktimer is like mud-wrestling a pig -- Sooner or later you find out the pig loves it. Andy Engel

25. 
    AXE | Jun 11, 2004 03:46am | #17

    Wow, going over this stuff with a fine tooth comb....

    As you said, most of this is covered in other drawings (my drawings are 11 pages worth). My archy is actually quite good and generally covers all the details.

    As far as setting the joists - I will be here and my brother in law is the framer.  I will get the material here ahead of time and have everything laid out and straight in my mind.  Since the roof is going to be off my house, I plan on doing all kinds of leg work before the roof comes off.  You can bet having the trusses well organized is one of those things.  I agree that he got a little wacky with the 16" oc spacing.  Several of them got off that spacing because he wanted to slide one slightly to pick up a point load so I didn't have to get an extra truss.  But I think I'm going to 24" oc anyway, so I will redo the layout with the truss manufacturer.  I am going to go dead on 24" oc starting from the right side and insert trusses as necessary to pick up point loads.  I want that ply to go down fast, so I don't want to get off correct spacing.

    Callouts.gif -- One thing that probably isn't clear is that you are looking at a screened porch with cathedral ceiling.  There are no floor joists there at all.  The doubled joists are for threaded rod/turnbuckle collar ties.  I've attached a couple elevation pdfs so you can see the roof structure.

    specials.gif - These are all good questions.  Again, it's not clear from the floor plan, but there is only a gable end wall here.  My second story is all a 12/12 roof pitching down to the floor - and just a couple of dormers. See the elevations.  But your points are definitely something I had looked at and have on my list of things to get clarification on.

    Thanks for the eagle eye.  -MERC

26. 
    BossHog | Jun 09, 2004 09:38pm | #8

    I just looked over the trimjoist website. There isn't any mention at all about floor vibration.

    Their 18" deep joists have a lot better charachteristics at a 26' span. If you end up going with the longer spans, that would help some.

    Don't know what the cost difference would be, though.Bumpersticker: It's not my fault I'm the only one in the world who knows how to drive correctly.

2. 
   Scooter1 | Jun 10, 2004 05:29am | #12

   I'd use Inch and an eigth t&g.

   Regards,

   Boris

   "Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934

3. 
   MajorWool | Jun 11, 2004 08:21am | #25

   I lived at 838 Shadylawn while serving time in Chapel Hill. For a small town it certainly had a wide variety of architecture. It was that 40x10 deck overlooking the creek which sold me.