Read Byggmax's latest newsletter on how to construct an insulated interior wall for soundproofing purposes. I was quite surprised because they suggest using age-resistant plastic in interior walls. I googled this and didn't find many hits except for the below info from a site called husvillaguiden.se. What do you think about this, should you really use plastic in interior walls..??? Using plastic in exterior walls is logical since warm air meets cold, leading to moisture precipitation. An interior wall that takes in moisture should logically also be able to release moisture, in principle, breathe. Besides, the insulation you put in interior walls should already be saturated by the air's relative humidity, i.e., it already contains a certain amount of moisture.
Interior Walls
On the inside, sheet material is nailed, usually drywall. Between the drywall and the insulation, there should be a moisture barrier. This usually consists of plastic. The moisture barrier is important. Warm air transports large amounts of moisture. If the moisture is allowed to penetrate the insulation, the wall will be ruined by moisture, usually resulting in mold. Old houses with almost no insulation allowed air to circulate through the wall. The wall remained dry. The more insulation and windproofing there is in the wall, the greater the problem with moisture in the walls. The moisture that makes its way in does not come out. Perfect for mold. It is controversial among people in general to put plastic in the walls. Some argue that the plastic causes moisture problems. The truth is both. An intact moisture barrier poses no problems. A moisture barrier that is installed incorrectly and is not tight allows moisture in but not out. Drilling into a wall, or when nails are hammered in to hang pictures, can cause holes in the moisture barrier, possibly resulting in moisture damage. You can never escape that the more insulation there is, the greater the risk of mold. Thickly insulated walls must be completely tight and not allow moisture to penetrate.
Interior Walls
On the inside, sheet material is nailed, usually drywall. Between the drywall and the insulation, there should be a moisture barrier. This usually consists of plastic. The moisture barrier is important. Warm air transports large amounts of moisture. If the moisture is allowed to penetrate the insulation, the wall will be ruined by moisture, usually resulting in mold. Old houses with almost no insulation allowed air to circulate through the wall. The wall remained dry. The more insulation and windproofing there is in the wall, the greater the problem with moisture in the walls. The moisture that makes its way in does not come out. Perfect for mold. It is controversial among people in general to put plastic in the walls. Some argue that the plastic causes moisture problems. The truth is both. An intact moisture barrier poses no problems. A moisture barrier that is installed incorrectly and is not tight allows moisture in but not out. Drilling into a wall, or when nails are hammered in to hang pictures, can cause holes in the moisture barrier, possibly resulting in moisture damage. You can never escape that the more insulation there is, the greater the risk of mold. Thickly insulated walls must be completely tight and not allow moisture to penetrate.
Skip the plastic in the interior walls. 
If it's a warm room adjacent to a significantly colder one, e.g., some kind of cold storage or garage (which is built onto the house), then the plastic might have its place.
If it's a warm room adjacent to a significantly colder one, e.g., some kind of cold storage or garage (which is built onto the house), then the plastic might have its place.
Member
· Norrbotten
· 3 390 posts
Well, have the laws of physics changed according to Byggmax then? No, what would be the purpose, not a vapor barrier but sound insulation? A plastic film might have a certain soundproofing effect when combined with insulation, so it's perhaps not entirely unreasonable. But it can hardly be called "standard practice."copello2 said: