I had specified new "underlayment" to be put over the old 3/4" pine
board subfloor in a new 2nd story addition. What our contractors
installed in our absence is regular 1/2" OSB sheathing material, not
specifically rated as underlayment. They screwed and glued it down very
well. After two weeks I already see swollen areas and chips coming
loose due to water being dragged in and left due to the construction.
Is OSB sheathing considered a reasonable underlayment for a carpet? I
expected plywood rated underlayment, with the top side sanded, not this
chunky stuff which is not even particularly smooth to begin with.
Regards, Wolfgang in VT
water is no friend to plywood either.
to save things maybe complete drying with additional fans, Bin primer
to seal the floor, top coats of paint that matches the primer type, and
a thicker carpet pad.
what you bought for the job may vary:
there are different finishes on the OSB according to this quoted
"Special Features of OSB and Waferboard Panels
Panels 15.5mm (5/8") and thicker are manufactured either with a
square-edge or tongue and groove on the long edges.
Panels may be sanded smooth on one or both sides for particular end
uses such as floor underlayment or interior finish, or they may be spot
sanded to meet the required thickness tolerances.
Manufacturers may alter the surface of some of their OSB or waferboard
panels to make them more suitable for a particular end-use."
it says at: http://www.cwc.ca/products/osb/uses.php
Thanks for the replies. I will talk to the contractor tomorrow. What
they put down in my house is regular "APA rated sheathing", not sanded,
no tongue and groove. I specifically excluded OSB from all other areas
of construction (wall and roof sheathing, bathroom subfloor), but did
not do this for the carpet underlayment since I had never even seen OSB
rated "underlayment", so am a little frustrated that they went cheap on
me there. Just tells me that one should never "assume" anything in a
On 14 Jan 2006 21:26:59 -0800, email@example.com scribbled this
I wouldn't recommend 7/16" OSB for flooring. Any moisture for any
length of time will cause it to swell.
Plywood can last a long, long time. I just worked on a floor that has
5/8" plywood sheathing. Based on the design of the kitchen, I estimate
it is the original flooring material which means it is about fifty
years old. Most of this floor was in good shape and only a small
amount needed to be replaced, despite years of moisture (what with it
being in a kitchen and having those 12" vinyl tiles on it.) In similar
circumstances, OSB would have failed completely in a very short period
Your remedy? It wouldn't be too expensive to laminate (glue and screw)
1/4" plywood on top of that OSB. That would be far easier than trying
to tear out all that OSB and install new plywood.
I'm sure OSB is fine for some applications. I'm not sure what they
are, but I'm sure there is something it is good for. I know many here
think OSB is a fine material, and this has been discussed many times,
but the only real reason to use OSB is to save a little money up
front, although, in my considered opinion, it will likely cost you
more in the long run...
(Remove the Primes before e-mailing me)
If it is a '*new* 2nd story addition' how can there be anything
*old* in the *new* addition? :-)
'Underlayment' is an ambiguous term. I have seen; 1/4" luan
plywood, 7/16" OSB, 1 1/2" light weight concrete, 2 x 6 T&G SYP,
3/4" T&G exposure I plywood, and ... 'underlayment'.
Underlayment and sheathing refer to the use of a material not the
type/size/physical-properties of a material.
Millions of yards of carpet have been laid directly on OSB.
The second story is new. The subfloor however was preexisting in the
former attic, since we did not change the footprint of the space, only
the ceiling height...
I specified "underlayment suitable for carpet application" in the
contract. What I found so far is that APA does not recommend "rated
sheathing" material as underlayment for any floor, only "Sturd-I-Floor"
OSB is recommended for carpeting. But I am not saying that what we have
now won't work, just wanted to educate myself before talking to the
business owner. Do you know if the OSB you have seen is the
Thanks for your input.
Per the APA website, OSB APA Rated Sturd-I-Floor is an OSB panel
intended for *single-layer* flooring.
"underlayment suitable for carpet application" does not
require/equal 'OSB APA Rated Sturd-I-Floor'.
Some of the OSB I have seen is APA Rated 'Sturd-I-Floor', most was
APA Rated Stud-I-Floor is an OSB panel designed for a specific use.
OSB Rated Sheathing is more than strong enough when used as carpet
underlayment because the strength of the floor is in the subfloor.
I think the real issues are ....
Does the underlayment need to be repaired or replaced?
Which specific locations need to be repaired or replaced.
Who pays for the repair/replacement.
Was the subfloor adequate?
Thanks to Mike and all for the replies. We'll just have to see how it
holds up over time. It would not have been my choice to save 100 bucks
or less in material (we are talking 240 square feet here) over proper
plywood, but it does not seem to make sense to rip it out at this
Regards, Wolfgang in VT
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