Author Topic: Floor Joist Blocking ( Bridging)  (Read 10749 times)

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Offline Jimmy C.

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Floor Joist Blocking ( Bridging)
« on: May 12, 2005, 05:11:28 AM »
What is the proper way to do floor joist blocking?

I have my joists on 16" centers and I will be placing 1.25 thick T&G plywood on top of that.
With the ply wood running Five  4x8 sheets going across the 20 ft width and Five  4x8 sheets going down my 40 foot length.
How many rows of blocking do I need?
Do I need blocking under every plywood intersection?


« Last Edit: May 12, 2005, 07:00:14 AM by Jimmy_Cason »
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Offline Daddymem

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Re: Floor Joist Blocking
« Reply #1 on: May 12, 2005, 05:18:20 AM »
Jimmy I can't answer your questions but we will be building roughly the same home.  Pardon my ignorance, but why the tongue and groove plywood?  
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Offline Jimmy C.

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Re: Floor Joist Blocking
« Reply #2 on: May 12, 2005, 05:21:46 AM »
Quote
Jimmy I can't answer your questions but we will be building roughly the same home.  Pardon my ignorance, but why the tongue and groove plywood?  


The way I understand it is the T&G would keep the intersections of the plywood flush with each other.

« Last Edit: May 12, 2005, 05:36:19 AM by Jimmy_Cason »
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Offline Daddymem

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Re: Floor Joist Blocking
« Reply #3 on: May 12, 2005, 05:27:39 AM »
Ah, probably important with no basement below and not as important for us with basments?  I was thinking that if the plywood were to be the finished floor, T&G might be nice.....
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Offline Jimmy C.

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Re: Floor Joist Blocking
« Reply #4 on: May 12, 2005, 05:32:09 AM »
We plan on placing a hardwood floor on top of it.

So it must be as smooth as possible.

I have heard that sometimes a leveling agent is poured onto the floor.

Then it is allowed to harden and level out and the hardwood is place on that.  
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Chuck Ardizzone

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Re: Floor Joist Blocking
« Reply #5 on: May 12, 2005, 06:40:31 AM »
Are you talking about bridging?  The cross bracing between floor joists?  You don't need it at every plywood intersection.  In 20' two rows would be plenty.  It will helps eliminate the flexing in the joists by transferring some of the load to the other joists.  Basically it helps stop the squeaks.  This it the same thing that the T&G plywood does.  The T&G helps eliminate the uneveness between sheets and the flexing.


Offline John Raabe

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Re: Floor Joist Blocking ( Bridging)
« Reply #6 on: May 12, 2005, 10:18:31 AM »
If you don't use T&G subflooring then you need to block all the panel joints as the edges will move over each other and squeak and possible show through to the flooring above. Usually 3/4" T&G is plenty for a residential floor load unless the joists are further than 24" o/c.

As you probably already know, you lay out the T&G panels so that the 4' butt joints from two panels land on a joist and the 8' T&G joints span between the joists. You leave a little space in both joints so the panels can expand and contract. Don't glue the panels to each other but do glue them to the joists.

Now for the question of bridging. The easiest bridging to install is the quick metal "X" type. One end bites into the wood and the other takes a nail. They are put in as a pair and are normally installed at the 1/3 points of the joist span. Thus there would be two sets in a normal span.

Bridging is not always done or needed. It can be used it two situations: 1 - when the joists want to twist and turn, and 2- when the span of the joists is approaching the deflection limit. Then the builder/owner wishes to reduce the possibility of bounce by getting the joists to share the loads through the bridging.
« Last Edit: May 12, 2005, 10:27:30 AM by jraabe »
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wingam00

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Re: Floor Joist Blocking ( Bridging)
« Reply #7 on: October 31, 2007, 09:56:19 AM »
Reading old post and have a question.
John you stated about laying out T&G plywood the following;  
Quote
As you probably already know, you lay out the T&G panels so that the 4' butt joints from two panels land on a joist and the 8' T&G joints span between the joists.

Why?  

Just Trying to learn is the reason for the question.


Offline PA-Builder

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Re: Floor Joist Blocking ( Bridging)
« Reply #8 on: October 31, 2007, 11:09:21 AM »
Quote
Reading old post and have a question.
John you stated about laying out T&G plywood the following;  
Quote
As you probably already know, you lay out the T&G panels so that the 4' butt joints from two panels land on a joist and the 8' T&G joints span between the joists.

Why?  

Just Trying to learn is the reason for the question.

 

Wingam,

Since the 8' sides of the panel "lock together" with the tongue & groove, they do not need additional support from below.  The  4' ends of the panels are square, and are designed to just butt together; therefore, they need the support from below that the joists will provide.  Also, I agree with John concerning the 1 1/4" thickness.  Most residential applications are fine with a 3/4" thick panel, even if only carpet is to be used.

Offline JRR

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Re: Floor Joist Blocking ( Bridging)
« Reply #9 on: October 31, 2007, 11:35:45 AM »
In my opinion, bridging is one of those things ... even if not needed, almost never hurts.  

I agree with Chuck, two rows should suffice for 20'.  I think the old rule of thumb was; "every 8 feet or less".

Bridging gives you a chance to really true-up joists, taking the twists out.  I tried the Simpson metal bridging once ... and I guess I'm just to old to learn something new ... ended up removing it and going back to wood.

Unless the tops of the joists are very straight; I would use plenty of glue, but just enough screws (not fully tight) to keep the plywood sheets anchored in place.  Come back in a couple of days to finish the screw pattern.  That is, if you have the time.

wingam00

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Re: Floor Joist Blocking ( Bridging)
« Reply #10 on: October 31, 2007, 12:37:06 PM »
Thanks PA-Builder, for the answer.  It now makes sense.
 :)

So if the 4' side was T&G it would not matter?

Mark

Offline PA-Builder

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Re: Floor Joist Blocking ( Bridging)
« Reply #11 on: October 31, 2007, 05:01:59 PM »
Quote
Thanks PA-Builder, for the answer.  It now makes sense.
 :)

So if the 4' side was T&G it would not matter?

Mark

4x8 sheets are almost always placed so that the long edge (8' side) is perpendicular to the joists (as shown in the diagrams provided by Jimmy C.).
« Last Edit: October 31, 2007, 07:01:09 PM by PA-Builder »

Offline MountainDon

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Re: Floor Joist Blocking ( Bridging)
« Reply #12 on: October 31, 2007, 05:13:11 PM »
Quote
Now for the question of bridging. The easiest bridging to install is the quick metal "X" type.
There are several different models of Simpson bridging.

go see at...

http://www.strongtie.com/products/connectors/nca-tb-ltb.html#gallery

They save time compared to wood bridging. Of course wood bridging gives you a chance to use some of your cut offs.
Just because something has been done and has not failed, doesn’t mean it is good design.

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Offline desdawg

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Re: Floor Joist Blocking ( Bridging)
« Reply #13 on: November 01, 2007, 06:41:24 PM »
I have used solid blocking in the past rather than bridging. If you have 2X10 joists cut 2X10 blocks the right lengths and nail them in. (Speaking of using up scraps.) This will be a lot more time consuming however. We usually did this where joists met over bearing walls.
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