I'm not sure exactly why because I'm not from there, I've just seen the practice in a bunch of YouTube videos. I think historically houses there have always bee

I'm not sure exactly why because I'm not from there, I've just seen the practice in a bunch of YouTube videos. I think historically houses there have always been very built very lightweight without exterior sheathing, and maybe it's just inertia that resists the increased cost that exterior sheathing would bring. They also build with 2x4 exterior stud walls and nearly all homes are single-storey slab-on-grade structures, whereas most of North America has moved to 2x6 exterior walls as standard (partly because it allows for more insulation) and multi-storey houses are common. I don't know what to think about it, to be honest. Here in Canada I've started to see a lot of houses built with fibreboard sheathing with an integrated 1/2" or 3/4" outer foam insulation layer. The stuff is very flimsy and turns into oatmeal when it gets wet, but apparently it's sufficient. Builders use it because it's cheap and increases insulation and decreases thermal bridging, but I think I would prefer regular OSB sheathing with building paper, or Zip sheathing with taped seams if I could get it (I've never seen it used here before).