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Old 02-14-2012, 08:37 PM   #16
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Is this joist combo sufficent?


Sorry Jet, you're wrong. Underlayments also goes perpendicular to the joists. Of course you off-set the underlayment from the subfloor. Ply & OSB is stiffest when oriented with the facegrain perpendicular to the joists.

We like pics.

Jaz

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Old 02-14-2012, 08:48 PM   #17
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Is this joist combo sufficent?


Quote:
Originally Posted by JazMan
Sorry Jet, you're wrong. Underlayments also goes perpendicular to the joists. Of course you off-set the underlayment from the subfloor. Ply & OSB is stiffest when oriented with the facegrain perpendicular to the joists.

We like pics.

Jaz
You will always keep grain direction the same when staggering your ply. I should of stated of using ply on ply then my method is correct but doesn't matter with backerboard I guess.

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Last edited by JetSwet; 02-14-2012 at 08:53 PM.
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Old 02-14-2012, 09:18 PM   #18
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Is this joist combo sufficent?


No. The facegrain should always go perpendicular to the joists, that is where you need the stiffness. Backer boards or membranes have nothing to do with this.

* Beginning in 2007, the TCA Handbook for Ceramic Tile Installation listed in bold print the following requirement for two-layer wood sheathing installation methods:
face grain of plywood shall run perpendicular to joists for maximum stiffness

Plywood underlayment direction
Knowing that the subfloor must be installed with the strength axis perpendicular to the joists for code compliance is important. But the tile contractor must also understand the importance of running the plywood underlayment perpendicular to the joists if he or she is to maximize potential for a successful installation. In fact, engineering science for the two-underlayment orientations reveals that both the subfloor and underlayment should run perpendicular to the joists (without exception).

*from an article titled; Impact of plywood underlayment direction
By Frank Woeste and Peter Nielsen


Frank Woeste, Ph.D., P.E. , is professor emeritus at Virginia Tech University, Blacksburg, VA, and a wood construction and engineering consultant.
Peter Nielsen is general manager and technical director for Schluter Systems L.P. (www.schluter.com) in Plattsburgh, New
York

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Old 02-15-2012, 06:16 AM   #19
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Is this joist combo sufficent?


Quote:
Originally Posted by JazMan
No. The facegrain should always go perpendicular to the joists, that is where you need the stiffness. Backer boards or membranes have nothing to do with this.

* Beginning in 2007, the TCA Handbook for Ceramic Tile Installation listed in bold print the following requirement for two-layer wood sheathing installation methods:
 face grain of plywood shall run perpendicular to joists for maximum stiffness

Plywood underlayment direction
Knowing that the subfloor must be installed with the strength axis perpendicular to the joists for code compliance is important. But the tile contractor must also understand the importance of running the plywood underlayment perpendicular to the joists if he or she is to maximize potential for a successful installation. In fact, engineering science for the two-underlayment orientations reveals that both the subfloor and underlayment should run perpendicular to the joists (without exception).


Jaz
I've never had issues doing it this way with running the other way with 2nd layer of ply.
I can not imagine running both layers of ply the same way it would serve no purposes of the 2nd layer of ply.

The grain direction stays the same way as your ply direction meaning you shouldn't go parallel and perpendicular in the ply layer you are putting down.

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Last edited by JetSwet; 02-15-2012 at 06:30 AM.
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Old 02-15-2012, 07:52 PM   #20
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Is this joist combo sufficent?


Hi,

Quote:
I've never had issues doing it this way with running the other way with 2nd layer of ply.
What kind of "issues" did you expect? Luckily that is why we have people whose work it is to do the testing for such issues.

Quote:
I can not imagine running both layers of ply the same way it would serve no purposes of the 2nd layer of ply.
Well......sorry you're not grasping.

Quote:
The grain direction stays the same way as your ply direction meaning you shouldn't go parallel and perpendicular in the ply layer you are putting down.
I have no idea what you're trying to say here.

Jaz
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Old 02-15-2012, 08:27 PM   #21
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Is this joist combo sufficent?


Makes sense to me. Its kind of the same concept as sistering a floor joist with plywood. You would never run it perpendicular in that situation. So this is like sistering the plank subfloor. Maybe im oversimplifying the structural dynamics. Im an accountant not an engineer.

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Old 02-15-2012, 08:30 PM   #22
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Is this joist combo sufficent?


Jaz, you stated before that the 2nd layer of ply goes the same way as the 1st which is incorrect.

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Old 02-15-2012, 08:52 PM   #23
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Is this joist combo sufficent?


Jet,

Please do some research, check it out before continuing this discussion. It's really very simple. Ply & OSB is stiffest in the direction of the face grain. You have 3 plies in that direction and 2 the other. There is a good reason subfloor goes perpendicular to the joists, same reason applies with underlayments. Try it yourself, test a piece of ply. This is elementary, underlayment 101.

Some people reading this might get confused and later install underlayment the way you described. I could probably send you the entire article if I thought it might do some good.

Jaz
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Old 02-15-2012, 08:53 PM   #24
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Is this joist combo sufficent?


Quote:
Originally Posted by JetSwet
Jaz, you stated before that the 2nd layer of ply goes the same way as the 1st which is incorrect.

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Its not Jaz saying it. A gentleman with a PhD in engineering specializing in building materials conducted labratory expeirments on this topic. His final conclusion was that all ply, underlayments, etc. Have to run perpendicular to the joists for maximum rigidity.

Google him. It will give you the full article.
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Old 02-15-2012, 09:41 PM   #25
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Is this joist combo sufficent?


Lol I can't tell you how many pros do it the way I do this has been a Discussion for so many years jaz how many times have you heard this done or had to correct some one who has brought it up to you?
Have you ever tryed it that way jaz?

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Old 02-15-2012, 09:59 PM   #26
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Is this joist combo sufficent?


There are many so-called pros who never learned to do things the right way and simply "don't know & don't know that they don't know.

That is one reason we here at this fine forum ask new contributors to give a short bio of their experience and also list ways they may be contacted such as websites and other public forms. It's very simple to show up and give info even when the info is wrong. People come here cuz they're DIY's, they think that if they get an answer here, it must be correct. That of course is not the case.

Jaz
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Old 02-16-2012, 11:23 AM   #27
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Is this joist combo sufficent?


Better to just move on from this topic.

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Old 02-17-2012, 02:57 PM   #28
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Is this joist combo sufficent?


Not to confuse anyone, the plywood - sub-flooring or underlayment always runs perpendicular to the joist direction for greatest strength.

Compare the load ratings with deflection and spans: http://www.trioforest.com/pdf/Load-Span_Tables.pdf

Just as JazMan said: http://www.apa-europe.org/Languages/.../PDF/R340G.pdf

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Old 02-17-2012, 04:59 PM   #29
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Is this joist combo sufficent?


The reason to put 2nd layer of ply opposite of the 1st is to cover your seams 2 ft really doesn't have much to do with the joists your taking the weekness out of the seams from the 1st layer of ply which already exceeds wait limit as the chart you have posted if you use 3/4" ply.

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Old 02-17-2012, 09:32 PM   #30
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Is this joist combo sufficent?


BTW Jet, what do you do for a living? If it has nothing to do with floors, or installing underlayments I might simply let you continue to do it wrong since it would only be in your own home.

You are not grasping the theory of deflection and how proper orientation of the plywood panels reduces in-between-joists deflection which is responsible for more failures in a floor composite than the in-joists deflection.

You are confusing yourself thinking that the subfloor + underlayment unit is independent from the whole system which includes the joists. In other words, your theory would make sense if you were simply laminating the sub & the underlayment, making a single unit, (like the sheet itself), but never installing it to a floor/joists system. The orientation to the joists makes all the difference. Placing the panel with its stiffest axis perpendicular to the joists has proven to reduce deflection over this span.

In a typical assembly of two 5 ply panels, you would therefore have a total of 10 plies, 6 would be oriented perpendicular to, while 4 would run parallel to the joists. Since we know the perpendicular oriented axis is stiffer, that is the way it should be installed.

The second panel is of course off-set from the seams of the subfloor. I could go into the recommendation of starting the end of the underlayment 1/4 way of the distance of the joists spacing from a joists, but then that would be difficult to describe without photos and sketches. So, I won't. However you are free to learn on your own.

Jaz

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