> Certain building materials need to breath. As explained in the linked video, they actually need to dry. This does not need to happen to the outside environme

> Certain building materials need to breath. As explained in the linked video, they actually need to dry. This does not need to happen to the outside environment. IMHO, using the two terms (dry/breathe) interchangeably is causing confusion, as each has certain connotations in many people's minds. The person in that video lives in Austin, Texas, and when he builds or renovates structures he has a stand-alone, whole-house dehumidifier designed into the HVAC system (the client can of course reject the suggestion): * https://www.youtube.com/watch?v=OKJnP_6uxcg https://www.youtube.com/watch?v=OKJnP_6uxcg > If the there are discontinuities it is possible to get condensation when the temperature / dew point align just wrong. Which, as explained in the first link (BSI-001), is why you want external insulation (if possible); some portion of the insulation being continuous is code in many places nowadays. That way the condensation occurs on the outside of the water/vapour control layer. Joe Lstiburek: * https://www.youtube.com/watch?v=rkfAcWpOYAA&t=25m26s https://www.youtube.com/watch?v=rkfAcWpOYAA&t=25m26s This is harder to do with renovations, but is code in most places. In Ontario, Canada the code (IIRC) also specifics what minimum portion of the insulation that should be on the 'outside' of the vapour control layer: the colder the region the more has to be external, so that condensation happens on the outside of the structure. Having it 100% external is ideal, but would cause trade-offs in other aspects of the building, which may not be desirable. An example of such a structure: * During construction: https://www.youtube.com/watch?v=d8i-93ABo3I https://www.youtube.com/watch?v=d8i-93ABo3I * Finished: https://www.youtube.com/watch?v=hTwq-qUnr9I https://www.youtube.com/watch?v=hTwq-qUnr9I Sadly, last time I checked, there was still no mandatory air tightness test for new builds in Ontario.