[GBlist] RE: OSB

["Hernando Miranda" <hmiranda@cox.net>]

I have never seen OSB that has been left wet for a period of time. I am
familiar with the remaining darkened mush left behind.

A building has to very well waterproofed to avoid major problems and
potentially nasty lawsuits. I was involved in on the plaintiff's side of
a forensic case involving a coed dorm at the University of California at
Los Angeles. OSB was used as throughout the building including bathrooms
and shear walls. 

The owner learned the OSB had disintegrated after a student fell through
the shower wall and into the adjacent coed room! I never learned if it
was a male or female student who accidentally discovered the problem,
but since the rooms were laid out male-female it was most likely a very
embarrassing situation.

The showers were one problem, but the OSB shear wall water damage forced
the University to relocate the students to other buildings at great
expense. The University was just not willing to jeopardize the safety of
students by leaving them in a structure that could collapse during an
earthquake.

The problem was finally solved by re-skinning the entire building and
suing the designer and builders involved. I do know that some of the
faculty who teach in the architecture department at the University will
not go anywhere near OSB for their design projects. They saw the
results, learned of the financial risks and made an informed decision.

I know OSB has held up well in many applications but specifying it in
wet and structural applications has huge potential risk.

Hernando Miranda
Soltierra

-----Original Message-----
Date: Tue, 29 Oct 2002 15:36:35 -0600
To: "Alan Courtright" <acourtri@krl.org>, <greenbuilding@crest.org>
From: "Ralph Bicknese" <ralph.bicknese@christnerinc.com>
Subject: RE: [GBlist] OSB 
Message-ID:
<AIEEIJAOAMLJKJFGLAAJKEMJCFAA.ralph.bicknese@christnerinc.com>

OSB is about as water tolerant as CDX plywood.  Both will swell a little
if wet for a while and will swell more the more often they are wet and
the longer they are kept wet.  I am not sure which performs better in
wet weather.  Both CDX and OSB use glues that do not contain added
formaldehyde and therefore any surfaces exposed inside do not create a
voc problem.

For even wetter applications there is marine grade plywood.  Another
option for other outdoor uses is called MDO (Medium Density Overlay)
plywood.  It has a paper based face to create a smooth surface for
painting.  It must be painted to preserve the face in wet weather but
once painted lasts a long time.  It is frequently used for painted
signs.

Cheers,
Ralph Bicknese

-----Original Message-----
From: Alan Courtright [mailto:acourtri@krl.org]
Sent: Tuesday, October 29, 2002 2:16 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

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

Date: Tue, 29 Oct 2002 14:17:48 -0800
To: Alan Courtright <acourtri@krl.org>, greenbuilding@crest.org
From: JOHN SALMEN <terrain@shaw.ca>
Subject: RE: [GBlist] OSB
Message-id: <PDELILGGEGALIFCGCEMPIEIGCBAA.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

______________________________________________________________________
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
______________________________________________________________________

------------------------------

Date: Wed, 30 Oct 2002 08:28:54 EST
To: acourtri@krl.org, greenbuilding@crest.org
From: BillArchtx@aol.com
Subject: Re: [GBlist] OSB 
Message-ID: <2b.2feb021d.2af13896@aol.com>

Alan - 

OSB, and virtually all composite materials - plywood too - are
manufactured 
with waterproof resins and adhesives.  The problem is that there isn't
100 % 
saturation and encapsulation of the fibers, so if continually exposed to

moisture - or as Joe Ltsebruck says," If the rate of wetting exceeds the
rate 
of drying," then the cellulose fibers will become food for bacteria and
we 
have "mush" - the first stage of rot.

Provided the material is allowed to dry well between wettings - as is
the 
case on most construction sites, many months of weathering will safely
be 
endured.

OSB comes in structural grades equal in performance to plywood of the
same 
thickness - such as "Structural 1."  The CDX label tells us: one side is
"C" 
grade veneer, the other side "D" grade veneer and the "x" is for
exterior 
glue.  With lower grade interior veneers that have open knot holes,
splits, 
checks and other voids, the problem is that water gets into those spaces
to 
cause rot or freezes and causes the veneers to separate.

Best,
Bill

Bill Chaleff, R.A.

Chaleff & Rogers, Architects
1514 Montauk Highway  P.O.Box 990
Water Mill, NY   11976

phone: 631-726-4477
    fax: 631-726-4478

BillArchtx@aol.com

------------------------------

Date: Wed, 30 Oct 2002 10:16:11 -0800
To: BillArchtx@aol.com, acourtri@krl.org, greenbuilding@crest.org
From: JOHN SALMEN <terrain@shaw.ca>
Subject: RE: [GBlist] OSB
Message-id: <PDELILGGEGALIFCGCEMPEEIMCBAA.terrain@shaw.ca>

Here is some more information on OSB.

the drying of osb versus plywood was looked at in few CMHC studies. Here
is a link to one
http://www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/01-139_e.html that
looked at envelope drying rates and the performance of different
materials in a test application. One of the results was "Panels with
plywood sheathing dried faster than comparable panels with OSB
sheathing". Another CMHC study for which I don't have an url looked at
the drying of walls with ventilated stucco cladding. In this study after
a 5 month evaluation period both the sheathing AND the framing in the
plywood sheathed wall was drier than the comparable OSB wall. I thought
this was significant as it was looking at an affectively rainscreened
wall. The caveat was given that this result may vary depending on the
specific product used.

John Salmen

TERRAIN E.D.S.
4465 Uphill Rd.
Duncan BC
CAN  79L 6M7
250-748-7684
terrain@shaw.ca


______________________________________________________________________
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
______________________________________________________________________