To use a vapor barrier or not? Organic insulation or mineral wool? Since opinions are so divided, it would be good to thoroughly highlight this subject once and for all, as fully as possible. Many physical theories cast doubt on those faced with insulating correctly or not. Many older houses have been insulated with wood shavings in various forms, from shavings to sawdust, without any vapor barrier and have functioned well for several generations without the construction being damaged. Unfortunately, this insulation method hasn’t been optimal in terms of lambda and a tendency to sink over the years, thereby creating voids lacking insulation. Also, a good deal of construction malpractice has occurred and is evident in this construction form where many sections lack insulation. This construction has consisted of tongue-and-groove wooden exterior paneling directly on wind paper directly against a wooden frame containing sawdust and from the frame inward clad with tongue-and-groove boards covered with Tretex boards, which have been painted and wallpapered. In terms of cost, there is a significant difference between organic and mineral insulation. When is organic needed versus inorganic? The big difference is that mineral insulation cannot buffer moisture, meaning it doesn’t absorb moisture but leaves all the moisture for the construction to handle, whereas organic insulation absorbs a lot of moisture and buffers it so that the construction does not need to handle it. This leads to a drier construction with moisture problems. Convection and diffusion are two ways to drive moisture into the construction, which can be addressed with a vapor barrier like construction plastic. Which is always normally recommended when using mineral wool. All air contains moisture; the higher the temperature, the more moisture the air contains. But the big problem is where the warm air meets the cold air and condenses into water. This is not desired inside the wall construction but as far out as possible. Based on this reasoning, it wouldn't matter much what type of insulation is used in a wall construction, provided the dew point is outside the construction and in materials that can handle this moisture, such as a coastal board consisting of mineral wool and then an air gap outside this and further with outer paneling. It could be considered that with such a construction, no vapor barrier would be needed since mineral wool also has good diffusion properties and easily ventilates moisture but is not hygroscopic and thus does not relieve the wooden construction in the same way as organic. So I urge everyone who understands this subject to provide some input on this matter, including roof insulation without an air gap but then with a diffusion-open underlay versus not diffusion-open. When can inorganic versus mineral be used, or not? Vapor barrier or not? + Today there are vapor barriers that are more or less diffusion-open, and it is easy to make mistakes that are left to the next generation.
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