Deflecto Calculator Q's [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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Racer X
03-01-2007, 05:35 PM
Hey gang,

Neat Deflecto calculator. I want to double check to see if a bathroom of mine is suitable for porcelain tile. so I listed below the what's needed to determine deflection... I'll just place my questions after each one.

Joist Material= I have I-Joist but don't see it as a choice- do I pick SYP? and what does SYP stand for?
Joist Height= I have 12's -so where good here.
Joist Width= I have 1.75 at the top and bottom caps of the I-joist. Only 1.5 is listed as a choice. I go with 1.5w. correct?
Joist Spacing= I believe that I have 16" oc. I suppose I can look at the nail pattern. So I'm ok here.
Joist Length= How do I measure the joist length? Do I take the measurement based on the length of the bathroom only? or the entire length as it runs thru the bath, thru the hall and ends under a bedroom at the front of the house?

Also, what does the "L" stand for? (eg. L/360) ...and the higher the number= more deflection or less?


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03-01-2007, 07:44 PM
The Deflectometer does not work for engineered wood. You must get deflection information from the manufacturer.

Joist length matters not, nor do any of the other parameters you mentioned. The necessary length is the unsupported span of the joist under the area to be tiled.

Joist can be a hunnert feet long, sitting over support walls spaced every ten feet and the unsupported span is ten feet (less the width of a wall).

Room over these really long joists can be a hunnert feet wide or five feet wide, unsupported span is still ten feet.

L = Length. Usually expressed in inches for our purposes. L/360 is the length of the unsupported span divided by 360. Allowable deflection for the ten-foot span above (uncorrected for wall width) would be 0.33 inches.

Racer X
03-02-2007, 08:21 AM
Great, that makes perfect sense. My bathroom has to be near 10 feet but I will check this weekend. I will also see if I can find the manufacturers specs. I believe I saw some markings on the I-joist in the basement.

I'm almost sure a little bathroom is ok for porcelain tile -I just wanna do this to better understand deflection and the structural makeup of my home as well as know what I'm reading when I'm in here.

Thanks for the schoolin