I have read how to install tile over plywood flooring at various
websites.

They say the maximum floor joist should be 16" on center with 'a
maximum deflection of 1/360 of the span, at midpoint.'

What does this mean? 1/360th of an inch movement (up & down) between
joist?

I saw this at Super-Tek.com

Thanks,
Dave

DaddyMonkey wrote:

....
...with maximum deflection of 1/360 of the span, at midpoint.'

What does this mean? ...

What it says...max (vertical) deflection (inches) = Span (in inches)/360

Span is unsupported length of the joist.

"DaddyMonkey" wrote in message
...
I have read how to install tile over plywood flooring at various
websites.

They say the maximum floor joist should be 16" on center with 'a
maximum deflection of 1/360 of the span, at midpoint.'

What does this mean? 1/360th of an inch movement (up & down) between
joist?

I saw this at Super-Tek.com

Thanks,
Dave


If the span is 20' that is 180". If you divide that into 360 segments, you
get 1/2"

Edwin Pawlowski wrote:
"DaddyMonkey" wrote in message
...

I have read how to install tile over plywood flooring at various
websites.

They say the maximum floor joist should be 16" on center with 'a
maximum deflection of 1/360 of the span, at midpoint.'

What does this mean? 1/360th of an inch movement (up & down) between
joist?

I saw this at Super-Tek.com

Thanks,
Dave



If the span is 20' that is 180". If you divide that into 360 segments, you
get 1/2"


It means the floor joist is not suppose to bend more than 1 degree at
the mid point. The industry claims greater deflection will cause the
tiles/joints to crack if more than that. This can be true when you get
into larger tiles.

"DaddyMonkey" wrote in message
...
I have read how to install tile over plywood flooring at various
websites.

They say the maximum floor joist should be 16" on center with 'a
maximum deflection of 1/360 of the span, at midpoint.'

What does this mean? 1/360th of an inch movement (up & down) between
joist?

Nope...

Length of the joist divided by 360.

So, if the joist is 240 inches (20 feet), you are allowed to have up to 2/3
inch (.666666") of movent at the center point of the joist.
240/360=.6666...

DaddyMonkey wrote:
I have read how to install tile over plywood flooring at various
websites.

They say the maximum floor joist should be 16" on center with 'a
maximum deflection of 1/360 of the span, at midpoint.'

What does this mean? 1/360th of an inch movement (up & down) between
joist?

I saw this at Super-Tek.com

Thanks,
Dave


What it means is that the allowable deflection of your floor is
1/360 of the span.

Example: span = 360"

360 / 360 = 1"

allowable deflection at the center of the span is 1"

--
Robert Allison
Rimshot, Inc.
Georgetown, TX

I think they mean 1/360th of the span of the floor joist, length-wise. Tom
Work at your leisure!

If deflection is the vertical movement of the floor joist span measured
at midpoint, there needs to be a set (known) weight to obtain this
measurement.

A small child standing on the center of the joist will give a different
reading than an elephant.

"DaddyMonkey" wrote in message
...
If deflection is the vertical movement of the floor joist span measured
at midpoint, there needs to be a set (known) weight to obtain this
measurement.

A small child standing on the center of the joist will give a different
reading than an elephant.


I am sure not an expert on these matters. From what I can read in my
reference books the deflection factor is based on live load (as in a floor)
or dead load (as in a roof).

Children are permitted in residential construction. Elephants are not
likely.

I'm lazy or I would get the book and quote the "load per square foot"
factor.


Colbyt

Flooring -- what is 1/360 deflection?

allowable deflection is the span/360

example a 15ft span would have 1/2" alloable deflection

In article ,
DaddyMonkey wrote:
If deflection is the vertical movement of the floor joist span measured
at midpoint, there needs to be a set (known) weight to obtain this
measurement.

A small child standing on the center of the joist will give a different
reading than an elephant.


Most building codes have the following limits for residental construction.
Total deflection 1/240 (for both dead and live load)
Live load deflection 1/360

The dead load is the mass of the floor and fixed structure.
The live load is what can come and go such as people, furniture, etc.

A typical building code is 40 lbs/sq ft under live load for residental
construction. For some other types of construction the live load requirement
can increase quite a bit. For example a library under current codes has a
maximum deflection of 1/360 with a live load of 150 lbs/sq ft..

I thought that this might boil-down to the usual fire code/building code
type of mumbo-jumbo...
So many people within so many square feet of space... bla,bla,bla

But still.... a 120 inch span (10') of a single floor joist would be
about 1/3rd inch up-and-down play... that seems (to me) like a heck of a
lot of movement... tile fooling or not!

But, I guess, that's withOUT adding the strength of the subflooring
that will tie the joist together.

Am I right or wrong?
David

But still.... a 120 inch span (10') of a single floor joist would be
about 1/3rd inch up-and-down play... that seems (to me) like a heck of a
lot of movement... tile fooling or not!

Although what they're talking about is deflection, not bounce, it's
still a lot of movement. But that's why many builders work to
L/480 or higher. Like most of the rest of the code, L/360 is a
MINIMUM standard. If you build to just barely meet code is all
respects, you should end up with a crappy house that's livable,
and not excessively dangerous to you or your community.

In article ,
DaddyMonkey wrote:
I thought that this might boil-down to the usual fire code/building code
type of mumbo-jumbo...
So many people within so many square feet of space... bla,bla,bla

But still.... a 120 inch span (10') of a single floor joist would be
about 1/3rd inch up-and-down play... that seems (to me) like a heck of a
lot of movement... tile fooling or not!

But, I guess, that's withOUT adding the strength of the subflooring
that will tie the joist together.

Am I right or wrong?

Slightly wrong. the 1/360 deflection is for the floor as a whole.
But with that said, the live load is *everything* that is not part of the
structure itself. This includes such items as entertainment centers, furniture,
bookshelves, and of course people and animals. It is highly doubtful that
you'll ever encounter a floor that's moving 1/360 every day as people walk
about on it. But like another poster stated, the 1/360 is a minimum requirement
and a lot of builders build to 1/480 or even stiffer.