Energy inefficient Japanese walls – am I missing something?
I am from Connecticut but am about to build a house in a climate zone 4A section of Japan. I have talked with several Japanese builders and am concerned about the energy efficiency of their building envelope design. Before abandoning local practices, I would like to read GBA readers’ opinions to help decide if my concerns are well-founded.
Here is an overview of what I have learned of walls in Japan. The standard Japanese 2×4 wall from outside to inside consists of panels of artificial siding, a 1/2″ vented rain screen, house wrap, 1/3″ plywood sheathing, a 17″ OC 2×4 stud bay insulated with 2″ fiberglass batts, polyethylene vapor barrier sheet, and 1/2″ sheet rock. Windows are aluminum frame and single pane. Also the amount of wood in the walls make them the polar opposite of advanced framing. 2 photos are attached.
I originally planned to build according to local custom as I assumed the builders would know what was best for the area. However, I later learned that the life expectancy of a newly built Japanese home is 35 years and know first-hand how cold in the winter and hot in the summer they are (most homes are heated with one or several unvented kerosene heaters and there is an air conditioner in each room). I would rather build one house and build it right so my family can live in comfort without exorbitant energy costs. It seems to me that local building practices have too little insulation and I am worried about the interior vapor barrier with air conditioning on during the hot and humid summers. I have raised these concerns with local builders but they have tried to assure me that their methods are correct. Are my concerns well-founded? Would it be advisable to abandon local practices for a more efficient building envelope?