[Greenbuilding] Difference between an Air Barrier Strategy vs. AB materials (was Re: Water Barrier)

[RT]

andOn Mon, 04 Mar 2013 16:34:15 -0500, Eli Talking
<elitalking at rockbridge.net> wrote:

> Does any body see risk for multiple air (non vapor) barriers?  I  
> understand the risk of trapping liquid between multiple vapor barriers.   
> However, my thinking is that just an air barriers will allow drying to  
> the warm side even if one has leaks in the barrier.  Because so much of  
> the performance for tightness hinges on the execution of the air  
> barrier, I tend to want several layers of air barrier, such as sealing  
> osb seams, sealing foam seams, taping foam seams, et.  Chances are all  
> of those may have some execution flaws.

I think that it might be useful to go back to basics.

An "air barrier" is a strategy.

If the strategy is effective, then the building is air-tight.

There are any number of materials that can be utilised in the creation of
an effective air barrier --gypsum board, plywood or aspenite, plastic sheet
membranes (ie Tyvek, poly), sheet metal, glass, caulking, gaskets, spray  
foam etc.

Most typical buildings will some of the above in numerous layers
through a particular component cross section, as Eli proposes.

It is the detailing of the discontinuities between the materials used that  
determines whether or not the strategy is effective.

But I think that a simple example would let Eli answer his question by  
himself.

Take 3 or more plastic bags that each have pinholes or tears in them in  
different spots and then them inside of each other so that you'd get the  
"multiple air barrier (material)s" with non-aligned leaks" situation that  
Eli proposes.

Then fill the multi-layered bag with water and tie it shut.

I think you know the rest.

-- 
=== * ===
Rob Tom					AOD257
Kanata, Ontario, Canada

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