Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Carpentry

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 05-21-2013, 08:52 AM   #1
Member
 
Join Date: Mar 2013
Location: Chicago suburbs
Posts: 214
Share |
Default

Floor joist deflection


In planning for a ceiling, I've measured that on our longest span, we have about 3/8" of joist deflection in the center. Span is 12'. I don't think this is a problem, if you take an L/360 structure, 12*12/360 is .4" allowable sag, which means I'm under that and perfectly fine structurally. However, I'd like my floors to be level since it has made a couple doors on upper floors hard to latch (you have to lift up on them).

What's the best way? Would pushing up on the existing joists then sistering in additional joists be good? Or is a joist that's sagged ruined so as to take that shape forever, so that it would be best to replace the existing ones one by one, doubling those up? The key issue there being the nails thru the floor cannot easily be redone.

Any suggestions?

SquishyBall is offline   Reply With Quote
Old 05-21-2013, 09:00 AM   #2
AHH, SPANS!!!
 
Join Date: Apr 2012
Location: Durham NC
Posts: 1,663
Default

Floor joist deflection


Quote:
Originally Posted by SquishyBall View Post
In planning for a ceiling, I've measured that on our longest span, we have about 3/8" of joist deflection in the center. Span is 12'. I don't think this is a problem, if you take an L/360 structure, 12*12/360 is .4" allowable sag, which means I'm under that and perfectly fine structurally. However, I'd like my floors to be level since it has made a couple doors on upper floors hard to latch (you have to lift up on them).

What's the best way? Would pushing up on the existing joists then sistering in additional joists be good? Or is a joist that's sagged ruined so as to take that shape forever, so that it would be best to replace the existing ones one by one, doubling those up? The key issue there being the nails thru the floor cannot easily be redone.

Any suggestions?

while working from the room below,level existing joists and add sistered joists to them nailed really good is the best way, imo. if you plan to remove existing joists then plan to pull entire upstairs flooring out...

hand drive is offline   Reply With Quote
Old 05-21-2013, 09:32 AM   #3
Member
 
Join Date: Mar 2013
Location: Chicago suburbs
Posts: 214
Default

Floor joist deflection


Quote:
Originally Posted by hand drive View Post
while working from the room below,level existing joists and add sistered joists to them nailed really good is the best way, imo. if you plan to remove existing joists then plan to pull entire upstairs flooring out...
Thanks -- Have you any experience w replacing an interior floor then? The tile above this floor is going to be replaced later eventually -- so I'd have no issue taking up all the tile and full mortar bed... (digging out the mortar bed alone would remove 1-1/2" of concrete weight).

But where the plywood goes under existing walls and especially the exterior wall would be impossible to replace... also we have an extra 2x4 board building up each wall at the bottom since it is a 1-1/2" mortar bed in this room. The joists in this section were set that much lower (and notched at the wall and beam), so to replace them full height would mean taking out that lower board under each wall and tucking new flooring in under the walls. Is that even possible?

To be clear, here's our cross section:



Ideally I'd like to do away w the mortar bed altogether. But that means removing that additional plate under the walls that make this room.
SquishyBall is offline   Reply With Quote
Old 05-21-2013, 09:45 AM   #4
Roofmaster
 
Join Date: Oct 2012
Location: Maryland
Posts: 3,606
Default

Floor joist deflection


It may be me, (And it often is) but this post does not make any sense. Doors are in walls, walls are usually supported by a double joist below. Why are your doors sagging, and what exactly are you trying to do??? It sounds like you are going through a heck of a lot for very little gain.
__________________
" A lot of men build things, and a lot of things fall down "

jagans is online now   Reply With Quote
Old 05-21-2013, 09:56 AM   #5
AHH, SPANS!!!
 
Join Date: Apr 2012
Location: Durham NC
Posts: 1,663
Default

Floor joist deflection


it would be best to cut the flooring free from the wall and build the new floor at the height you want and butt new floor to the wall. if you've got a single joist under the exterior wall like in the pic you might need to re enforce the joist under the exterior wall before you cut the plywood free from wall, flooring does help to lock in the whole floor system some but a good framed joist system should be all that is needed. so, tear out old system- put in new system with no 1 1/2" notch which raises new system 1 1/2" to take up for the thickness of tile and mortar.
hand drive is offline   Reply With Quote
Old 05-21-2013, 10:00 AM   #6
Member
 
Join Date: Mar 2013
Location: Chicago suburbs
Posts: 214
Default

Floor joist deflection


@Jagans... Okay, Backing up...

I've noticed some doors do not shut perfectly. Just recently working on the basement, I checked all the joists for level. I noticed 3/8" max deflection at the center of 12' spans. While not structural, this sag does confirm why the doors on the floor above it are not shutting properly. The hinge side has sagged, tweaking the door down, thus you have to pull up on the door to shut and latch one particular closet door.

There are a lot of things I want to accomplish:
1) A level floor. Just because. It is not a risk and not necessary, but I want it to be done well, and I want level floors. The only cost is materials so why not.
2) A level ceiling.
3) Redo the tile (eventually) in the room above, removing the mortar bed, and putting in instead hardwood floors at a floor height that matches the rest of the house instead of this being recessed 1-1/2".

So what started as drywalling a ceiling naturally develops into should I jack the rafters and sister in new ones, or should I go thru all the effort to pull out the mortar bed, put in new un-notched full height joists that will bring the plywood up to the level of the rest of the house... and how feasible is doing so... or should I just leave it and move on, as it's perfectly "fine" but not as good as I'd like.

I can do all or none of it, and am just looking for ideas from ppl who have done this before - how feasible it is to fit new flooring under existing walls. Doing it little by little, not compromising structure, etc.

In the end, it would be perfect... full height extra joists, higher floor, level floor, level ceiling.

If it is not feasible at all to pull out the mortar bed then the best solution is just to jack the joists and sister in new ones to level it out as best I can and then if and when we redo the floor above later, we'll just have to build it up w 1-1/2" of OSB.

You can say it's a lot for a little, but I want it right. Details like that matter to me. Brainstorming it in a forum to hear pros and cons is the place to start, before spending money.

Edit: Reload the page since I updated the image above to show the transition to the "normal" floor of the rest of the house.

Last edited by SquishyBall; 05-21-2013 at 10:24 AM.
SquishyBall is offline   Reply With Quote
Old 05-21-2013, 10:20 AM   #7
AHH, SPANS!!!
 
Join Date: Apr 2012
Location: Durham NC
Posts: 1,663
Default

Floor joist deflection


easiest now would be to level old floor joists and sister them. when you are ready to re do the flooring above add 2 layers of subfloor 3/4" thick to get your 1 1/2" spacing. the best part of sistering is the strength gained from having a double floor joist, to get that strength/span capability with a new single joist floor would require an upsized joist to be used...
hand drive is offline   Reply With Quote
Old 05-21-2013, 12:14 PM   #8
Member
 
GBrackins's Avatar
 
Join Date: Apr 2012
Location: Fairhaven, Massachusetts
Posts: 2,854
Default

Floor joist deflection


Squish,

for your reading pleasure .... http://www.tileusa.com/Articles/Defl...Samulski07.pdf
__________________
Gary

"You get what you pay for, and sometimes free costs more!"
GBrackins is online now   Reply With Quote
Old 05-21-2013, 03:52 PM   #9
Member
 
Join Date: Apr 2012
Location: UK
Posts: 713
Default

Floor joist deflection


Quote:
Originally Posted by SquishyBall View Post
I want level floors.
You will never get level timber floors. The floor will deflect under its own weight, it will deflect under the applied (live) load, and there will be long-term creep of the timber joists.
Wouldn't it be easier just to plane the sticking doors?
tony.g is offline   Reply With Quote
Old 05-22-2013, 12:47 PM   #10
Member
 
Join Date: Mar 2013
Location: Chicago suburbs
Posts: 214
Default

Floor joist deflection


The fix wouldn't be to plane the doors, it would be to move the strike plates. But still that's just a Band-Aid fix. After more thought, I may sister in 3 LVL beams. They're on sale at Menards right now, so for $40 x 3 I'm done for $120, and at that point I'm pretty sure the sag issue will be resolved. Doesn't require demolishing my first floor and it's stronger than the rest of the house.

SquishyBall is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
strengthening floor joist jpaz Building & Construction 26 12-08-2012 04:14 AM
deflection in 8" Steel I Beam? BlueBSH Building & Construction 22 07-08-2011 03:14 PM
Maximum absolute deflection value benjamincall Building & Construction 3 04-02-2011 02:21 PM
2x9 deflection and tile former33t Flooring 8 10-13-2009 06:49 AM
Travertine - subfloor deflection issue Saint Flooring 4 02-24-2008 06:36 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.