subfloor deflection when floating eng hardwood

Old 07-10-06, 08:48 AM
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subfloor deflection when floating eng hardwood

I have a tri-level townhome (built in 2001) and i would like to install a floating eng. hardwood floor on the top 2 levels. From the best i can tell the joists are TJIs that are 9 1/2" deep and 24" oc...and my subfloor is 3/4" OSB....however, I'm concerned about potential subfloor deflection and how it will effect the floating floor.

I notice that just about every floating eng. hardwood floor has a subfloor requirement that joist be no more than 19.2" oc. But then they say you "might" be able to add more subfloor to help with the support. I called two of the eng. floating floor manufactures help lines and they said I "should" be okay with my joist spacing as long as there is no bounce in the floor...but they didn't sound to convincing to me.

1) Do I need more subfloor support to make sure i don't damage the floating floor seams, etc?

2) If answer to question 1 is yes, then if I put down another layer of subfloor ( I was thinking either 3/8" or 1/2" plywood) would this give me sufficient enough strength to somewhat minimize the deflection between the 24"oc joist? After reading other posts it seems i need to run the additional subfloor perpendicular to the joist, offset from the existing subfloor seams, and prevent screwing the additional subfloor to the joist - only screw it down to existing subfloor.

3) I really want to use floating method if possible since I am a DIYer installing floor for the first time; however, would I be better off with a glue or nail down floor with 24"oc joist or would I have the same deflection issues?

Thanks in advance for any help or suggestions!
Old 07-13-06, 06:24 AM
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I have a similar situation... I have some old style engineered joints 24" OC. I know the floormoves some, because we have a projector mounted to the ceiling downstairs and everytime someone walks upstairs, it shakes the picture on the screen. My house is 3/4" OSB as well... Looking forward to any suggestions as well!
Old 07-15-06, 12:43 PM
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As a rule I don't use OSB in my jobs anywhere. Used it once as 3/4" tongue and grooved subflooring and had a lot of problems. With your 24" OC floor framing I would install a layer of 1/2 " CDX or underlayment plywood, screwed and glued. The new 1 1/4" subfloor should be stiff enough to support your floating floor adequately.

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