Hello,
I’m about to try and level out my first floor. Someone ran the main girder of my house way off middle and left me with 2×10’s to span 15′. then poured a 6″ mud floor in the bathroom. With the mud removed I am set to repair the 1″ plus sag in the joists. Originally I was going to sister the 2×10’s then a friend suggested that I laminate on 3/4″ ply to one side of each joist with plenty of PL and screws! This would make my installation much easier and give me the ability to install the plywood after my crib wall is in place for jacking rather than having to place 2×10’s in each joist bay before installing my jacking wall. What do you think? Suggestions are sorely needed!
Eman
Replies
This topic gets covered about once a month.... run a search and you'll learn lots.
FWIW.... you're buddy needs to keep his day job IMHO. Sister the joists or add a mid-span beam w/ posts and footings. I also wouldn't build that wall you're thinking about.... too awkward to work around. I'd build a temp beam and jack that instead. Less lumber wasted and easier to work around. Just my two cents.
Personally, I'd go with the midspam beam as long as headroom wasn't an issue and you didn't mind a few extra lallys in your basement. Knock the beam together, stick it up in the air, jack it all up level, cut your lallys and you're done. Don't let the footings scare you, it's easier than you think to do. Less material, no waste, less aggravation.
Many ways to skin this cat. Pick one and have fun!!
Thanks, some of the archives seem to support the plywood sandwiching and some do not? To me it seems to make sense ...afterall isn't a TJI joist just a 1/2" web of OSB in the center? Wouldn't 3/4" plys of CDX on a joist be sufficient if the joints were staggered? Isn't that the purpose of CDX in the first place - to resist racking such as used in sheer placements for diaphram support? I have no way of leaving my temporary beam in place as I need the space in its entirety. Just wondering aloud here...any other feedback is greatly considered!
Eman
Like I said.... just my two cents.
heres my 2 bits worth.
if a beam can go under it a beam can go in it.
if the room isnt too wide, you could put 2 temp beams perpendicular underneath and jack post them level.
half way along your 15 ft span i would slice out enough space to let in a engineered beam. psl or lvl. have an engineer spec it.
then you can hang the floor joists off it.
no posts in the room downstairs and you can do it all from below.
i have done it a few times and it makes your floor bomb proof
if ya want a sketch of what im gabbin about lete me know.
cheers
Tmaxxx
Urban Workshop Ltd
Vancouver B.C.
Putting 3/4" plywood on one side of each joist will give you less than half as much additional stiffness as sistering on another 2x10, for two reasons. One, because it's not continuous, and two, because the cross grain plies add much less tensile strength than the longitudinal plies.
You could make the plywood continuous by gluing and screwing a generous gusset or splice plate over each joint, and you could put plywood on both sides of each joist. At that point you would have invested a lot more in materials, time, and effort, and still not added as much stiffness as another 2x10. Is not having to pre-place the sisters really worth all that extra cost?
Yes, that too is a good point! There is always a time consideration. Cost wise they work out to be reasonably close...maybe 20% more for the plywood. I did come across a couple things atht interested me though...in Rob Thallon's framing framing book there is a header that he describes which was developed by the NAHB that uses 1/2" ply to stiffen between the top plate of a wall and a single board on flat to construct a header usable and adaptable to 8'. The other was a reference in 'Renovation' 2nd ed., Litchfield - that describes scabbing on plys to both faces as you described with adhesive and screws to sister joists. Thanks for your input!
Eman
E, sounds like you're gonna add the ply regardless of what we tell you here. Too bad, because for all the reasons Diesel and Uncle Dunc said it's a bad idea. Extra work, extra material, less strength, more fasteners.
The OSB in I-joists is there to hold the LVL flanges apart; all the strength is in the LVL flanges, not in the OSB web. That's why you can cut all those big holes out of the OSB without losing any strength.
That's my 2 cents. Hey, you're already up to 6 cents worth of free advice!
Mike
I have to disagree...those LVL flanges wouldn't hold themselves straight without the web....it's an engineered system, with enough tolerance for those big holes in the webs....
JR, I might have oversimplified a bit, but what I said was "The OSB in I-joists is there to hold the LVL flanges apart" which I believe is the same thing you said. The poster was saying he would sister plywood to the joists because I-joists have osb webs, and I was just trying to explain the basics of why that wasn't the best solution. It's hard to sum up four years of engineering school in one post.
Mike
Yeah, OSB in particular has lousy strength under tension. It does OK in compression, though, which is why it works well for I-joists.
I recently built a house and spanned the 2x10 joists out at max, 12" oc, solid blocking, two rows. and strapped with 1 x 4's. It worked ok but I won't do it again, what I will use is 2 x 12's @ 12 oc. with solid blocking, this works better for longer spans. What I am saying is if you can include blocking and strapping in your 'fix' it might help.
I don't see anything wrong with well glued, nailed/screwed 3/4" plywood on both sides, plus the above, plywood is easier to handle. But jack your joist back into shape as much as possible before scabbing on.
Thanks David...the bridging, blocking and strapping sounds like a good addition. It is sound advice from my point of someone working alone. Not everyone has a lot of hands around afterall. I set up the cribbing and temp beam today. It is leveled out and the damage done by the 5" mud floor someone poured into the bathroom is so obvious with the beam there now. Thanks again!Mike...let's remember this is a forum for discussion and sharing ideas. Everyone of the replies I got I appreciate greatly and take them into consideration....all the details cannot be considered by someone on a computer however. Thank you to all for your help and positive feedback! Eric
"I set up the cribbing and temp beam today. It is leveled out and the damage done by the 5" mud floor someone poured into the bathroom is so obvious with the beam there now."
EMan, a few questions to help me picture your situation:
This damage you speak of, is it crushing damage where the existing joists bear onto the original beam (the one that's not quite at mid-span). What's crushed: the joists, the beam, or both?
Is this crushing affecting both sides of the beam? In other words, do the floors above - supported by joists bearing on both sides of the original beam - each need to be levelled?
Is there crushing where the joists bear onto the sill plate? If not, why not?
Has the sag telegraphed to upper levels, such at a ceiling/floor above, or to the roof structure?
EMan, a few questions to help me picture your situation:"This damage you speak of, is it crushing damage where the existing joists bear onto the original beam (the one that's not quite at mid-span). What's crushed: the joists, the beam, or both?"Hey Pierre1 ...no there is no literal 'crushing' going on. The original support girder is intact and straight almost to the 1/8" in supporting the floor joists. The problem is only on the side of the house where the support girder is off centered leaving a 15' span for the 16oc 2x10's. This section is roughly 21' long from the rear of the home and stops at the chimney from where on the other side of the chimney the original builders continued the main girder in the middle of the house. "Is this crushing affecting both sides of the beam? In other words, do the floors above - supported by joists bearing on both sides of the original beam - each need to be levelled?" No, it doesn't appear that way at all. I used a laser level to take readings all over the sills, girder and joists. Everything else is within tolerances for an old home."Is there crushing where the joists bear onto the sill plate? If not, why not?
Has the sag telegraphed to upper levels, such at a ceiling/floor above, or to the roof structure?"
There is some telegraphing onto the upper floor directly above where my problem lays out in the joists below. As I mentioned before the really bad joists are supporting the bathroom. There was no sistering under the tub, the evidence of rot tells me the floor abutting the tub was not sealed effectively and one joist even split fromthe weight of the combined 5-6" mud floor, tile and 1" plaster and metal lathe on the walls. When I removed all that the house seemed to let out a sigh of relief. Thanks for your questions...sounds like you have experienced something like this??Eman
Where you at?
There's a couple of us BT'ers that work together/meet when we can...myself, and Aaron Rosenthal....
I think he's Irish, but that's okay. G,D,& R."If 'tis to be,'twil be done by me."
You're far too generous. So then, I gather all you want to do is to take the sag out of these overspanned joists and prevent reoccurence. You didn't mention what use your basement is put to, so I'll presume preserving headspace down there is not an issue.
Incidentally, per my Canadian span tables, the max span for 16" o.c. 2x10 No.1&2 SPF with a 5/8" subfloor is 13' - note that this is for new materials.
The solutions presented to you by dieselpig, tmaxxx and Uncle Dunc are all valid in your circumstances: simply halve the problematic 15' joist spans with a new built-up or engineered beam.
A built-up beam supporting a single floor, for a supported length of 7.5 feet (15'/2), is sized as follows per my Canadian span tables:
Allowable built-up beam clear spans, for SPF, No.1&2:
if 2x8 3-ply: 10'7" ; if 2x8 4-ply: 12'2" ; if 2x8 5-ply: 13'8".
if 2x10 3-ply: 12'11" ; if 2x10 4-ply: 14'11" ; if 2x10 5-ply: 16'8".
if 2x12 3-ply: 15' ; if 2x12 4-ply: 17'4" ; if 2x12 5-ply: 19'4".
Note that allowable spans vary according to species/grade used. Adding mid-span Lally columns on proper footings can help should you want to preserve headspace by using a 2x8 built-up.
You should have your final solution approved by your local buiding dept. official before proceeding.