To Sister? or Forget it?

[WalterIV]

I've got a detached garage with a gambrel roof and loft space that I'd like to fix up a bit.  Here' the problem:

The floor joists on the loft are 2 x 8s on 16" centers spanning 16 feet, and very bouncy!  What would be the best way to shore this up?  Putting in a beam underneath really isn't an option, unfortunately...I'm curious if I could sister these joists?  Any ideas?

Appreciate any suggestions, thanks, W

[PEG688]

How long is the building ?? A beam , a gluelam may only require one post .


You could sister TJI /BCI  maybe , is there a plywood floor above yet?? Plumbing pipes , wires etc ??

 You could cut the joist and flush mount the beam , maybe ??  Again maybe one post . if your in the neighborhood of 40 ' or less.






 So why no beam ??

   

[WalterIV]

Okay, I've gone back to add some detail. Thanks for the help!

To answer your questions:

The building is approx. 18' W x 20' D

There is thin plywood sheathing laid down on the joists above (1/2"? it'll be replaced with 3/4"T/G if I can get these joists shored up), and wires all over in and out of the joists.

I didn't think a beam would work unless I wanted to take out all the joists to cut them (big pain with the electric all over, and then the roof rafters tied in...) ...maybe I'm wrong about that, if so, please let me know.  As you may guess, I'm pretty green when it comes to this type of work...so any help & suggestions offered will be greatly appreciated.  

I've attached a rough sketch of the layout.

Thanks again! W

[WalterIV]

Oops, that didn't work.  Here it is:

[PEG688]

Put the  beam under the joist , a GLB should be able to be caculated / made large enought at 20' of span to require no post in the field , you will need post under it at each end .



The beam in the background spans  14' or so and it's not that big a beam.

Would that work?? It would cut your joist span in 1/2 .  

 

[WalterIV]

Yeah, I think that would work.  

Another question, or two:

Where do I get a GLB/equivalent beam?

...and what's the best way to fix posts to a poured concrete foundation?

Thanks, W

[PEG688]

Where do I get a GLB/equivalent beam?

...and what's the best way to fix posts to a poured concrete foundation?

Thanks, W

A good lumber yard , not H/D , Blowes , or other big box.


Depends , you MTL will , or should , beef up the existing slab by ,

#1 Under mining your existing slab from the outside then filling that space up with concrete so you have a 8" x 16"x16" thickened area under the post .

#2: If you have a wall plate existing just nail the post to the plate and add a Simpson strap , like a MST 16 to it .

#3: If the under mining deal won't work you could maybe put a header like a 1x10 on the plate cut out a few studs and slip it in so you spread that load out over 4' instead of 6" , (point load).

All those MTL will not pass inspection , you may have to cut the concrete floor dig out for a thickened area . post pad , and add a Simpson post bracket set in the concrete.

And as you are  a newbie most of what I typed you MTL have no clue what the hell I'm  talking about . I have no photo to express what I'm saying.    

 

[desdawg]

If the ceiling is open and you can get into it a row or two of solid blocking or some bridging would help you gain some rigidity I would think. Overlaying the existing plywood with another layer at a 90 degree angle to what is there would be another option to ripping out the existing. Just some thoughts.

[OldDog]

How about placing a 2x4 along the bottom edge of joist to create a T joist?

It will strengthen the joist a lot.  You can glue the entire length and use screws.

Maybe try it on 1 joist and see what happens?

You would lose 1 1/2" overhead which may not be a problem.

Just a "Kentucky Idea"

[glenn kangiser]

DIY TJI.  Sounds like it could work.

[WalterIV]

Thanks for all the ideas, folks.  I think I'll start small ("DIY TJI"...) and go from there.  Hopefully, I can avoid blasting into the foundation to set some posts...

Here's something that's bothering me, though.  This garage was built about 8 years ago by a previous owner of my house.  The second floor loft has a skylight, electric, and even a phone jack... so, apparently, somebody planned on using it for something!  So I can't figure out why it was built with such flimsy joists--any ideas here?  Makes no sense to me...  

Thanks for all your help, I'll keep you posted on my progress.  

[PEG688]

Here's something that's bothering me, though.  This garage was built about [highlight]8 years ago by a previous owner of my house.[/highlight]

   The second floor loft has a skylight, electric, and even a phone jack... so, apparently, somebody planned on using it for something!

  So I can't figure out why it was built with such flimsy joists--any ideas here?  Makes no sense to me...  

 

It does to me he , prev. owner, was MTL a DIY type guy who did know $hit from shine ola , and thought he could "get away " with lighter joist than where needed , he could even have taken some advise from other DIY types who also didn't know Jack Shick about shine ola.  

The  "I" joist idea is some of the same as is the blocking and sudo blocking /  "box beam" floor system , put the beam in , reduce the span by 1/2 or "put up with " a bouncing floor system .

Of course YMMV , what the hell do I know

G/L PEG  

[glenn kangiser]

Structurally, the 2x4 on the bottom does make sense.  It will become a tension member if properly glued and screwed.  It will stiffen it.  Not much compression member on the top though to stop the bouncing.

Of course, your way would be the right way, Peg.

The homemade T wouldn't pass any loading charts, codes or be something that is predictable though.

[PEG688]

Sure it would stiffen it some  BUT not enought. All those hoops for a still bouncey floor . Sorry to be so up front but the beam is the easist , surest way to take that bounce out .

[glenn kangiser]

Oh -- there you are.

[PEG688]

Another issue would be the existing joists , MTL, have a belly / sag/ reverse crown  to them by now . Adding more weight / mass to the bottom would tend to exacerbate that situation as would a row of blocking and sheathing the floor , again more weight to a under sized structural member.  

 Possible resulting a castrophic failure / collapse.

[glenn kangiser]

You got that right.  Gluing and screwing a member to the bottom would definitely lock in the sag and possibly add to the other problems you mention.  Its too early for you to make me think right now, PEG. :-?

[PEG688]

It ain't that early Glenn look at yer watch or your computer clock

[glenn kangiser]

I suppose you are right, but I had a rough week.  Had to work all week.  I'm not Paris Hilton you know.

Since all work was out of town I had to get up between 4:30 and 5 or so each day.  That may not be bad if I went to bed before 12 or 1.

[PEG688]

  I'm not Paris Hilton you know.

You sure !! :-/ :-? I thought all you Califorinactors  was movie stars   Maybe yer Jed Clampit!! Where Elly May :-/ :-/

[tc-vt]

Are the I-joists large enough to handle a floor intended for living space?  If they aren't undersized and the problem is that you don't like the deflection of the floor, these may be helpful.

Check out these APA publications on retrofitting I-Joists:

The index page:
http://www.apawood.org/level_c.cfm?content=pub_joi_libmain

Like everything else on the internet, you need to register.

Data File: Construction Practices for Wood I-Joist Floor Vibration Retrofit
http://www.apawood.org/pdfs/download_pdf.cfm?PDFFilename=managed/D720.pdf

Tom

[PEG688]

Are the I-joists large enough to handle a floor intended for living space?  If they aren't undersized and the problem is that you don't like the deflection of the floor, these may be helpful.

Ah Tom the joist are 2x8,

[highlight]The floor joists on the loft are 2 x 8s on 16" centers spanning 16 feet[/highlight], and very bouncy!  
Appreciate any suggestions, thanks, W

What wood , we don't know , could be Pine , could be D.Fir , Spruce???  :-? :-/

But either way they ain't currently manf. "I" joist. The "design team " was suggesting   DIY sudo "I" joist   :'(  Which really would have been or would be upside down "T" joist  

[tc-vt]

I noticed that they were 2x's right after I wrote.  I thought I sent a response to that effect but somehow it didn't make it to the internet.

The 2x8's are too small.  For a dead load of 10 psf and a live load of 40 psf and a deflection of L/360, the longest span for 2x8  douglas fir select grade is 13-7.  Spruce pine fir #2, closer to what might be in there, would be 12-3.

Look at this article:
http://www.hammerzone.com/archives/framecarp/supplement/floor/joist1/sister.htm

Tom

[PEG688]

I noticed that they were 2x's right after I wrote.  I thought I sent a response to that effect but somehow it didn't make it to the internet.

The 2x8's are too small.  For a dead load of 10 psf and a live load of 40 psf and a deflection of L/360, the longest span for 2x8  douglas fir select grade is 13-7.  Spruce pine fir #2, closer to what might be in there, would be 12-3.

Look at this article:
http://www.hammerzone.com/archives/framecarp/supplement/floor/joist1/sister.htm

Tom

Huumm interesting concept  ,  they should a put in a flush beam  ,



Some things should be done right . Convoluted hoop jumping , adding more weight by sistering with the same demention lumber and ponying  load onto walls over head are all BAD ideas .  

But hey they sell lumber and labor .

Over and out on this one , G/L what ever you do , you'll need it