# How do you measure a floor systems deflection ratio?



## ohiohomedoctor (Dec 26, 2010)

I have a suspect sub floor and a customer who is at ends with a builder. We are installing 18 inch porcelain tile and uncovered a bouncy 8 year old subfloor. I know its sub par but how do you put a value to how sub par it actually is? Thanks for your time! :thumbsup:


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## angus242 (Oct 20, 2007)

http://www.contractortalk.com/f73/joist-deflection-110786/

Need:
joist unsupported length
joist dimension
joist spacing
joist species
subfloor type & thickness


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## ohiohomedoctor (Dec 26, 2010)

I get the equation, I have a cut joist which was scabbed. I was wondering if there was a way to measure actual conditions so they could go back to the builder.


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## ohiohomedoctor (Dec 26, 2010)

angus242 said:


> http://www.contractortalk.com/f73/joist-deflection-110786/
> 
> Need:
> joist unsupported length
> ...


Thanks


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## Rob1954 (Jun 22, 2010)

Kind of difficult to do, but if you have joists which have been modified, there is only one way that I know of. 

Measure the static and unloaded position of the floor with a taught wire stretched from end to end of the joist on top of the subfloor.

Load the floor with a known load at mid-span or uniformly along the joist. Measure the deflection using your measuring tape.

Have an engineer or someone who can calculate the predicted deflection using the load, span, joist size, species, etc. noted in the post above. Compare the predicted deflection against the actual from your load test, and you will have your answer.

Not easy to do, dangerous if your not careful, and not the most accurate. Best thing to do is hire a structural engineer who can evaluate the framing, recommend a solution, and take the liability out of your business.


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