RE: [GBlist] OSB

[JOHN SALMEN <terrain@shaw.ca>]

It is not that it turns to mush but that it has poor drying characteristics
compared to plywood and this can have implications (including mushy type
stuff). For example in a wall section you can safely assume that all parts
of the wall will to varying degrees get wet. When I say varying degrees I
mean that the outside siding will be a barrier to most of the moisture, then
the building wrap will deal with a significant amount of the balance and
then the sheathing, etc. Since plywood has good drying characteristics and
is exposed to generally small amounts of moisture it can deal with them
without remaining moist and transmitting any moisture further into the
assembly (framing plates, etc.) OSB on the other hand is slow drying and so
tends to transmit more moisture and to also break down more rapidly if not
given a chance to dry. A west coast environment is especially difficult as
there is often little opportunity for a material to dry.

Mould and fungas and decay are the results as it takes about 20% moisture
over time to produce growth but then once established it can re-establish
with less moisture present (16-18%). The poor drying characteristics of OSB
can lend themselves to creating moist enough conditions over a long enough
time period to begin fungal growth - and then there is more potential for it
to sustain that growth.

-----Original Message-----
From: Alan Courtright [mailto:acourtri@krl.org]
Sent: October 29, 2002 12:16 PM
To: greenbuilding@crest.org
Subject: [GBlist] OSB


Lately there's been an opinion expressed that if OSB gets wet, it'll turn
to mush.

But here on the we(s)t side of Washington (which actually gets less rain
than New York City) people build all the time using OSB, including for
roof underlayment, and seem to feel no need to cover the stuff up if it's
raining during the construction process.

Is there no equivalent to CDX in OSB?  I'd think mfrs would make some of
the stuff with exterior glues?  And is there an equivalent to the smoother
grades of plywood also, for other uses?

                         -|//*Alan Courtright*\\|=
                                Poulsbo, WA
                             acourtri@krl.org




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This greenbuilding dialogue is sponsored by REPP/CREST, creator of
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______________________________________________________________________


______________________________________________________________________
This greenbuilding dialogue is sponsored by REPP/CREST, creator of
Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
Environmental Building News and GreenSpec http://www.BuildingGreen.com
______________________________________________________________________