Vapor Flow in Light Frame Construction
I would like to hear comments from Scientists and “Others”
I am an Other, an Architect…not a Scientist
I am very interested in designing Low Energy Homes.
I am fascinated with Passivhaus and European Construction.
I have noticed the “Euros” usually do not use foam (spray, sheets or blocks)
They tend NOT to use membranes, peel and stick etc.
Here is an example wall mock up.
The most common type wall has an OSB type air barrier on the interior side of the structural wall
The “OSB” is air barrier (they call it air-tightness layer)and racking board (shear panel)combined
The gypsum board is always furred out about 2 inches inside of the racking board.
This creates a “service space” for all the wiring and avoids penetrations in the air barrier.
It also protects the air barrier from the occupants (hanging pictures etc)
Sometimes they insulate the “service space” sometimes not.
The outer skin of the structural wall they call sarking board.
It is a panel usually with tongue and groove or lap joints all around.
Many times the joint is not taped … but it appears to be reasonably airtight.
I assume that the outer face of the panel may be coated with a water shedding coating.
The panels seem to be very vapor open.
The panels seem to have High R-value.
Sometimes the outer skin looks to be gypsum board.
They do NOT usually use house wrap or felt.
They always use furring strips before attaching siding.
The siding seems to be always REAL wood not fiber-cement or vinyl or waswood.
The walls are very Thick with high R-value
The cavity insulation appears to be cellulose or rock-wool
At first glance this all seems very complicated and labor intensive.
The walls are very airtight yet rather vapor open.
My current thinking is that these guys are “ahead of us” and are on a better track.
Most of our(North America) “High Performance” Walls rely on foam products and are not as vapor open as these Euro-walls.
Our walls are starting to be just as complex and labor intensive as the Euro-walls yet less forgiving.
One thing the Euros seem to do to offset some of this complication is that they panelize offsite.
Here is a short video with a lot of fascinating details that they do in a different way.
One thing I noticed is they do not always “break” their sheet goods over the studs or rafters.
I have also noticed that when the “Euros” use Foam it looks to be always a vapor open foam.
Is it really important for Vapor to flow thru?
Or is it enough for it to flow in both directions?