I recently built a cabin using SIPS as a subfloor over concrete piers and 2 x 10 joists. I wanted to lay a floating floor on top of the OSB but the SIP manufacturer wants me to put down another underlayment of plywood before the finish floor. What do people think??

In the past, several SIP manufacturers have told me to use underlayment over their OSB SIPs flooring. I think they wanted to stiffen the floor.

As Alton says, I think stiffness is the issue.
Here, I think the issue would be how you actually built the structure under the SIPS. It sounds like you laid up a 2x10 joist system UNDER the SIPS, rather than using a double 2x spline system (or in additon to). If this is the case, then your floor will probably be stiff enough without the added plywood. However, more detailed information on how your floors are built would be helpful. IE: joist spacing, spline configuration, SIPS thickness, etc.

I'd say "try it" for a small section and see if you find it stiff enough. Or measure the deflection/stiffness.

The additional sheathing isn't for stiffness, it is take care of any height differences between the panels. If you run the underlaymet opposite direction of the panels, you will have a much better surface for your finished floor.

Posted By Douglas Engel on 26 Jul 2010 11:49 PM
I recently built a cabin using SIPS as a subfloor over concrete piers and 2 x 10 joists. I wanted to lay a floating floor on top of the OSB but the SIP manufacturer wants me to put down another underlayment of plywood before the finish floor. What do people think??

floating floor will be fine, any other type use underlay

If your going to use wood you do not need it. If you are going to use a carpet or vinyl I would install an additional layer of underlayment because the flake board skins are not strong enough to take a punching force of say a sofa leg or a bed leg or something really heavy with a small area being dropped on it.

Jeff,
Not trying to start a fight, but:
For someone who promotes themselves as a construction professional,
the use of deregatory slang terms such as 'flake board' seems rather unprofessional.
It just seems to me that your very legitimate point has been lessened by this objectionable terminology.
Those of us here who consider ourselves 'professionals' in some branch of construction, should try to maintain a clear focus on our opinions, and not let our biases get in the way.

BTW- I don't know if you are old enough to remember some of the things 'blandex' or 'aspenite' was called before the engineering was worked out to turn it into true 'oriented strend board', but I sure do.

Best not to jump to conclusions. "flakeboard" is often used in a non-derogatory way. One company even named their company with it.

Sorry, but I have been an advocate of OSB for a very long time. I know that my regional bias is showing, but I have never heard the term 'flakeboard' used in referencing OSB in any manner other than as a derogatory. And I can't conceive of a 'flakeboard' business.

I apologize. I did not mean to be derogatory. Please replace the phrase flake board and insert the word OSB in my prior post.

After some reading I now know flake board is particle board not OSB. Thank you for informing me. Wow, is was almost like i made a racial slur :)

Posted By wes on 31 Jul 2010 05:03 PM
Sorry, but I have been an advocate of OSB for a very long time. I know that my regional bias is showing, but I have never heard the term 'flakeboard' used in referencing OSB in any manner other than as a derogatory. And I can't conceive of a 'flakeboard' business.

There actually is a company called "Flakeboard" that manufactures particle board, MDF and "DuraFlake" .....but no OSB

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr53.pdf