[Strawbale] OSB in detail

RT ArchiLogic at yahoo...
Wed Dec 8 19:53:32 CET 2010

On Tue, 07 Dec 2010 16:12:55 -0500, Derek Roff <derek at unm...> wrote:

<snipped,mangled & pasted>
( for full text of message, see:

http://amper.ped.muni.cz/pipermail/strawbale/2010-December/002230.html  )

> --On Tuesday, December 7, 2010 8:06 PM +0100 asbn <asbn at baubiologie...>
> wrote:

>> I would like to have a completely natural structural board instead of
>> OSB, but we didn't find a board with the same advantages and a
>> similar price.

> This described sequence of motivation, analysis, and product selection
> is at the root of so many of our problems in the world.

> I don't think it is possible to be active in the world ofgreen building,  
> and also be free of compromises with companies andproducts

Which brings us back to the original point which started the thread that  
started this thread:

         "OSB or Not ?"

It is entirely possible to build SB walls that are structurally sound and  
air-tight without utilising OSB.

In fact, SB walls built using wet-applied plaster instead of OSB can be  
better structurally, will almost always have a significantly better  
thermal resistance value (see note below), are less difficult to make  
air-tight and depending upon the type and thickness of the plaster used,  
will be clad in a skin that is more vapour permeable.

OTOH, most plasters will not have any traces of noxious chemicals like  
phenols, formaldehydes, diphenylmethanes, diisocyanates etc. that are  
commonly found in OSB.

(For those who aren't already aware, "Material Safety Data Sheets" (MSDS)  
are available for all manufactured products (ie simply Google "MSDS  
Oriented Strand Board" in this instance) and they list & describe all of  
the potential health hazards associated with that product.)

It seems that including OSB in a SB wall creates more problems than it  

This is the Note Below

I don't know if EuroBaleHeads are aware of the first set of thermal  
resistance tests that were performed on SB wall panels at the Oak Ridge  
National Laboratory (ORNL) back in the previous millennium which resulted  
in alarmingly low thermal resistance values for the SB walls tested.

I forget what the actual test results were (something like R-10  
ft^2*hr*degF/Btu (or RSI -1.76 m^2*degC/W in metric units) or less if I  
recall correctly ? (Hoping someone will correct me with the actual number)  
... but I do recall that it was lower than the thermal resistance of a  
conventional wood-framed/fibre batt-insulated wall using skinny 2x4 (38 x  
89 mm) studs.

I also remember that the reason for the disgustingly low thermal  
resistance value of those first SB test wall panels was attributed to  
their being clad with gypsum board sheathing rather than wet-applied  
plaster and that since the board sheathing could not conform to the  
irregular surface of the SB, allowed air movement to occur at the  
cladding/SB interface so that thermal resistance-lowering convection  
currents occurred within the SB wall.

I suspect that the identical process would occur when OSB is substituted  
for gypsum board sheathing.

=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at  Y a h o o  dot  c a >
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