Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Building & Construction

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

Reply
 
Thread Tools Search this Thread Display Modes
Old 09-28-2009, 02:59 AM   #1
Newbie
 
jjneedshvac's Avatar
 
Join Date: Sep 2009
Location: philadelphia pa
Posts: 6
Share |
Question

Stiffen joists


I am looking to stiffen up my floor joists under a new kitchen and bath. My old house has true 2x8 joists (not 1.5x 7.5) over a 12 ft span sitting on a new glulam beam spanning 14 ft. I thought I might glue and screw 3/4 plywood to each joist to stiffen them up to accept porcelain or perhaps stone tile. I would also use 2x8s to make blocking between the studs afterwards to add stability. I was going to cut the plywood in 8 ft and 4 ft pieces to cover the 12 ft span, alternating the 4ft section on each joist.

Will this give me the stiffness and deflection factor I need to tile?

I hope this made sense.


Last edited by jjneedshvac; 09-28-2009 at 03:00 AM. Reason: spelling
jjneedshvac is offline   Reply With Quote
Old 09-28-2009, 05:49 AM   #2
Master General ReEngineer
 
Bondo's Avatar
 
Join Date: Dec 2007
Location: Chaumont River, Ny.
Posts: 3,670
Default

Stiffen joists


Ayuh,.. It might,.. Or you could add uprights at the center of the span...

Bondo is offline   Reply With Quote
Old 09-28-2009, 07:43 AM   #3
Mold!! Let's kill it!
 
Join Date: Feb 2008
Location: Central Pennsylvania
Posts: 2,830
Default

Stiffen joists


You didn't say what centers your existing joists are set at. If they are on 12" centers you may want to sister new joists to old. If they are on 16", you might be better off to add joists in between.
Maintenance 6 is offline   Reply With Quote
Old 09-28-2009, 08:07 AM   #4
I have gas!
 
Clutchcargo's Avatar
 
Join Date: Mar 2007
Location: Massachusetts
Posts: 1,765
Default

Stiffen joists


I'm doing the same thing for my kitchen to stiffen up the floor getting ready for tile. I'm ripping 2x10s down to get the width of the old stock and sistering with glue and nails.
GL
__________________
I tear things down and build them up.
Clutchcargo is offline   Reply With Quote
Old 09-28-2009, 08:55 AM   #5
Civil Engineer
 
Join Date: Mar 2009
Location: Boston
Posts: 4,119
Default

Stiffen joists


By my computations, true 2x8 joists centered 16 inches OC spanning 12 feet with a live floor load of 40 psf (typical for a bathroom) and a dead load of 10 psf would have a maximum deflection of approximately 0.2 inches at the center, for a d/L ratio of about 1:600. This is OK for most tile, maybe not for large format porcelain, but remember you need to add two layers of subfloor, which will stiffen the joists somewhat. Unless you are planning on putting a very heavy tub (i.e. cast iron) full of water on the bathroom, you should be OK without doing anything. However, you may want to hire a structural engineer to check these calcs, as your load may be different than I assumed, the joists may be made of a species of wood that is not as stiff as normal, or there could be an unusual geometry situation that affects the loading on your joists. Or my calcs could be wrong.
Daniel Holzman is offline   Reply With Quote
Old 09-28-2009, 09:52 AM   #6
Member
 
Join Date: Jan 2009
Location: South of Boston, MA
Posts: 17,248
Default

Stiffen joists


Hmmmmm...something I had not considered
I thought my 2nd floor (new) bath (shower) 2x6 floor joist spanned 8'
They don't - they span closer to 11'
The bathroom wall ends at 8'...but the joists span to the next wall at 11'

When you say new kitchen & bath - just remodeling the area?
If totally remodeling why not add some joists?
Scuba_Dave is offline   Reply With Quote
Old 09-28-2009, 02:45 PM   #7
Registered User
 
Join Date: Mar 2009
Posts: 9,968
Default

Stiffen joists


How many layers of plywood would you need? Have you tried Googling "strengthening floors"? As others have said: http://www.finehomebuilding.com/PDF/Free/021184090.pdf
Be safe, Gary

Gary in WA 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
OSB Stronger than Plywood? Weathermaker01 Flooring 15 12-22-2012 09:06 AM
Sister or Replace Floor Joists brando1118 Carpentry 25 10-26-2008 08:43 PM
help with 2nd floor joists g heil Building & Construction 5 09-12-2008 06:41 PM
Best subfloor and material thickness nugentcn Flooring 7 09-07-2008 12:48 PM
3/4" hardwood, same direction as joists? zel Flooring 13 05-15-2007 08:50 PM




Top of Page | View New Posts

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