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Floor Joist Deflection Help

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#22 ·
To me, it really doesn't matter what the expected or actual rating of the floor is.
Get the Owner to waive any deficiencies or warranty work based on his design. Especially without a stamped drawing. Save yourself a headache down the road.
 
#23 · (Edited)
Assuming that your existing joists are Doug Fir# 2 or better, the spacing is 16" oc, a span of 15' using 2x10s this should do the trick for you.

2 plys total. I don't think you need to glue but it can't hurt.

And this is with a deck of just about 3/4" ply.

Andy.
 

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#25 ·
Andy, there's some info the poster didn't give, so Here's what I read between the lines.

There is limited acces, only from above, and not for the full length of the joists.

He'll be sliding whatever he puts in into place. He can't use full depth material, and whatever dimension material he uses has to be capable if that.

The ends will wind up a couple feet from bearing.

The original floor system is underdesigned by current standards, he's only concerned about deflection for the tiled part of the floor.

If he could go bearing to bearing, he could just slide in a couple SPF joists that have been ripped to allow them to be stood up in place, then nailed together for full length sistering, or shim at the top plate to share load. That isn't happening here.
 
#26 ·
So, take this to a LPE, and he'll tell you you can laminate to get the deflection on the specific area you're looking at. He'll also look at the existing l/318, realize he's effectively concentrating loads at the ends of the laminations. He isn't going to give you a design without beefing up the rest of the floor system, since it doesn't meet current code and the modifications make that worse.

BRG walked through one of these pain in the butt situations years ago. He went conventional - there's a reason conventional is conventional.
 
#28 · (Edited)
OK, serious response. You can take a big chunk of wood out if the middle of a joist, and only have to derate by 15%. You're taking 1/3 from each side, so 10% derating compared to a triple laminated.

On to laminating. Laminating actually increases the rating. The worse (imperfections) the laminating members, the higher % the rating increase. That's for high quality laminating. Really low quality laminating, you'll just end up with something better than a single joist.

Getting a high quality lamination in areas with limited access is just really difficult. So, a 25% boost in strength due to triple laminating (This is a realistic assumption, but still an assumption) can be more than offset by poor quality of gluing under the circumstances.

To be conservative, I took it to be reduced by the total increase due to lamination, plus 50% of one of the added members (top and bottom members).

Personally, I wouldn't glue lam in a situation like this, you Can't really tell if you have full contact. A slight gap is a disaster. Nail lam isn't as sensitive to small gaps, but I doubt you can get full strength with 2X4s without splitting.
 
#29 ·
Convince them to go with porcelain! L/360 You could get that with a sheet of ply. Add Detra Heat, everyboy wins!:clap: Marble can bite you in other ways, wrong thinset, bad coverage, flash, grout, sealer, yada yada, and 2X THE STRUCTURE!! sometimes its just not worth it. Porcelain is better! IMO
 
#30 ·
Don't do hokem pokem. There's no reference for gluing up stuff on the sides of joists.

Chewing the cud on "possibles and might be's" is all well and good, but its no way to conduct business.

The archys and engineers can give ratings when the floor is treated as a diaphragm. Plywood applied to top surface AND bottom surface.

A fee for an approved floor system is nothing compared to warranty down the road.

And remember - the customer pays this fee.
 
#31 ·
SmallTownGuy said:
Don't do hokem pokem. There's no reference for gluing up stuff on the sides of joists.
Click to expand...
There are no prescriptive solutions, if that's what you mean. There are plenty of references for nail lam and glue lam and combination of nail and glue lam, and these are what an engineer would use to come up with an engineered solution.

It's worthwhile thinking through how you want to approach a problem before you go get stamped plans, especially on a remodel. The usual prescriptive solution would probably be to pull siding, sheathing, and rim board if you can't slide full length joists into place from inside. Maybe he can get it from the inside if he pulls ceilings, no way for me to tell.
 
#32 ·
hdavis said:
So, take this to a LPE, and he'll tell you you can laminate to get the deflection on the specific area you're looking at. He'll also look at the existing l/318, realize he's effectively concentrating loads at the ends of the laminations. He isn't going to give you a design without beefing up the rest of the floor system, since it doesn't meet current code and the modifications make that worse.

BRG walked through one of these pain in the butt situations years ago. He went conventional - there's a reason conventional is conventional.
Click to expand...
Years ago....

Turned the wall into a truss and sistered new x8's onto old oak joists (half span).

All that travertine, and the entire bathroom still looks like the day I put it in.
(even the one nail pop where I overdrove the screws to mount a cup on the ceiling to accept my glass stabilizing rod......still pisses me off :laughing:)



That said.....I just had to call in my Engineer for a list of modifications and upgrades on a 150 year old one I'm into now.

I try to design it first, tell him my plan, and await his confirmation.

He only bounced me on one thing. Not encasing a steel column base in concrete.
He let me go because I had a three pack of studs flanking it on both sides.

Money well spent. :thumbsup:
 
#33 ·
My recollection is you covered using an LVL, but had some big drawbacks. Then mulled over a built in place box beam, but again drawbacks. Then the trussed walls, which could be done in place fairly readily, and wasn't clunky, it just disappears.
 
#34 ·
hdavis said:
My recollection is you covered using an LVL, but had some big drawbacks. Then mulled over a built in place box beam, but again drawbacks. Then the trussed walls, which could be done in place fairly readily, and wasn't clunky, it just disappears.
Click to expand...
You Sir....are like an elephant.

That.....exactly. :thumbsup:
 
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#35 ·
BlueRidgeGreen said:
Years ago....

Turned the wall into a truss and sistered new x8's onto old oak joists (half span).

All that travertine, and the entire bathroom still looks like the day I put it in.
(even the one nail pop where I overdrove the screws to mount a cup on the ceiling to accept my glass stabilizing rod......still pisses me off :laughing:)



That said.....I just had to call in my Engineer for a list of modifications and upgrades on a 150 year old one I'm into now.

I try to design it first, tell him my plan, and await his confirmation.

He only bounced me on one thing. Not encasing a steel column base in concrete.
He let me go because I had a three pack of studs flanking it on both sides.

Money well spent. :thumbsup:
Click to expand...
I forgot to mention that part of the job was a god-forsaken, trampoline, crap bomb of a Master Bath floor system that I had my guys laser and level by sistering x10's (half bearing on each load wall........), and adding extra x 10's to essentially make it 12" on center. (original old joist spacing was all over the map...28"...11"...whateva).
Got lucky. The entrance was the high spot......glory be....

Advantek.

6x40 porcelain plank over Ditra-Heat.

Slam.....dunk!
 
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Discussion starter · #36 ·
hdavis said:
Andy, there's some info the poster didn't give, so Here's what I read between the lines.

There is limited acces, only from above, and not for the full length of the joists.

He'll be sliding whatever he puts in into place. He can't use full depth material, and whatever dimension material he uses has to be capable if that.

The ends will wind up a couple feet from bearing.

The original floor system is underdesigned by current standards, he's only concerned about deflection for the tiled part of the floor.

If he could go bearing to bearing, he could just slide in a couple SPF joists that have been ripped to allow them to be stood up in place, then nailed together for full length sistering, or shim at the top plate to share load. That isn't happening here.
Click to expand...
You're correct on not being able to use full depth material.

With 2x4's we can at least get closer to the bearing point than with doubled 2x10's.
 
Discussion starter · #37 ·
tang said:
Convince them to go with porcelain! L/360 You could get that with a sheet of ply. Add Detra Heat, everyboy wins!:clap: Marble can bite you in other ways, wrong thinset, bad coverage, flash, grout, sealer, yada yada, and 2X THE STRUCTURE!! sometimes its just not worth it. Porcelain is better! IMO
Click to expand...
It would be great wouldn't it? All tile on this job is marble, floors, walls, shower floor, everything.
 
#40 ·
SmallTownGuy said:
Don't do hokem pokem. There's no reference for gluing up stuff on the sides of joists.

Chewing the cud on "possibles and might be's" is all well and good, but its no way to conduct business.

The archys and engineers can give ratings when the floor is treated as a diaphragm. Plywood applied to top surface AND bottom surface.

A fee for an approved floor system is nothing compared to warranty down the road.

And remember - the customer pays this fee.
Click to expand...
Yup, that's what I don't understand about threads like this. Where are they at in the permit process? If I walked into the building department and showed them a set of prints then said "Yeah I'll just glue some 2x4's in there to take the load", they would shake their head. They would most likely tell me to have an engineer stamp it off since it is not an ordinary floor load. Maybe he's doing it illegally? Or maybe he's trying to be his own engineer. But it's something we should really know first before offering advice on an open forum.
 
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