Thermal bridging: The ASHRAE estimates traditionally framed houses have a framing factor of 25% or greater. This means you take your insulation R-value and reduce it by your framing factor to get a more true wall value. Ouch! New building energy codes try and address this by adding a continuous layer of insulation on the outside of the sheathing R20+5 or R-15+10. We almost whole heartingly disagree with this approach. While this strategy could help if a vaper permeable insulation is used (roxel,hemp,wood fiber ect) all we usually see is XPS (extruded polystyrene). Same stuff we use below grade for its water resistance. Now we have a house basically wrapped in plastic, with a large amount of heating days. Often vapor drive is inside out and is trapped by this plastic, cold plastic, and what does it do? It condenses, leaving us with wet walls, NOT GOOD! We could add a moisture barrier on the inside, problem is, that thin plastic is punctured so many times by nails and screws it become very ineffective, also creating a cavity that will get wet eventually with no opportunity to dry either direction, even worse. 

     If only there was a smart material that could allow drying but also slow down vapor transmission. Plywood and osb, hiding right in front of us. These sheet goods, when properly air sealed, slow down moisture migration. The higher the humidity, the less moisture they allow through. The large volume of eco-friendly cellulose not only aids in thermal transmission but also disperses moisture rapidly allowing the best opportunity of drying in either direction thanks to the plywood. The staggered and spaced framing members ensure the only wood touching the inside and outside are the top/bottom plates and window/door bucks.  With everything taped and sealed the opportunity for air leakage, carrying not only cold air but moisture laden air as well.

Also aiding in the control of the crawly critters, I for one don't enjoy.