[Greenbuilding] air gap in walls

[John Straube]

The poly in the wall assembly is just a vapor barrier and the air barrier is the Icynene
The poly is not needed IF they relative humidity in the home is controlled to safe and healthy levels, like under 40%RH in cold weather (below freezing). 

Stephen Collette wrote:
> Hello everyone,
> 
> I did an inspection on a house this week that had odour issues. This  
> was a new west addition (300 ft2) to the existing farmhouse. It is a  
> sunroom with heaps of windows and half a dozen skylights. A sort of  
> octagon sunroom. Heated with radiant floor, electric baseboard and  
> tied into the homes existing forced air. The house has it's own air  
> con as well, and the addition has a self standing wall mounted unit.   
> The homeowner complained of a sour smell. The homeowner DID request  
> all of those things be installed, as he called himself a britches and  
> belt kind of guy.
> 
> The builder installed window seats around most of the octagon. He  
> spray foamed the walls and cathedral ceilings (3/12 pitch inside and  
> out) with Icynene. 4 inches of it.  For the larger window seats, he  
> left the rest with just air.
> 
> Construction from the outside in-
> Mabec wood siding
> typar
> chipboard
> Icynene and 2X6
> air gap
> poly
> drywall
> 
> The window seats are about 18 inches. It seems odd to have this air  
> gap.  I would have figured filling it with something or put the poly  
> closer to the insulation. I'm concerned about moisture issues with  
> this build up. I would appreciate any thoughts on this one.
> 
> I'm in Lakefield, ON just northeast of Toronto, and considered cold  
> climate, despite the global warming thing going on here.
> 
> Thanks
> 
> Stephen
> 
> Stephen Collette B.B.E.C
> Principal
> 
> Your Healthy House
> Indoor Environmental Inspections & Building Consulting
> www.yourhealthyhouse.ca
> stephen at yourhealthyhouse.ca
> 705.652.5159
> 
> 
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> 

-- 
Dr John Straube, P.Eng.
Associate Professor
Dept of Civil Engineering & School of Architecture
University of Waterloo
Waterloo, ON Canada