Is installing insulation from the inside worthwhile? What insulation materials are used (rock wool, polystyrene, multipor…), and which ones offer the best solution? Is the lower installation cost per square meter the only advantage of this solution?
The best way to insulate a building is by installing insulation on the exterior side of the walls. Installing insulation from the inside always requires a specific reason, and there are many. For instance, if the apartment is on the 15th floor of a building, or if you live in a smaller building where not all residents agree to insulate the entire structure.
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Additionally, insulating walls from the inside is the only solution if obtaining approval for exterior insulation is not feasible, such as for buildings of special significance or in certain locations.
Installing insulation from the inside is significantly more cost-effective, but it’s always a compromise that may not be the best solution. Various experiences can be found on internet forums, from those highly satisfied because their apartment is finally warmer, with reduced heating costs, to those who encountered mold on the walls after installing interior insulation.
There’s no definitive and universal formula that can be applied to every building, guaranteeing that everything will be fine. Much depends on the building itself—its walls, the presence of thermal bridges, whether the walls can attract moisture, and more. Only an experienced craftsman can solve all these problems on-site.
However, there are some guidelines to follow. The first is the choice of insulation. One option is to glue five-centimeter-thick (aprox. two inch) polystyrene boards, over which a reinforcing mesh is applied, followed by plaster. This is an excellent insulation method, but the problem is that polystyrene is not vapor-permeable, meaning it doesn’t allow the wall to “breathe,” which can lead to condensation.
Sometimes, this solution can be excellent, while in other cases, it may not be. Another option is to install rock wool, vapor-permeable foil, and cover this insulation with plasterboard. This solution is better because rock wool allows moisture to pass through much better than polystyrene, reducing the risk of mold.
Additionally, plasterboard panels are sturdier than polystyrene covered with mesh and plaster, reducing the risk of wall damage. Also, they can support the weight of small nails for hanging pictures without damaging the wall. However, this solution is more expensive. Yet another option is to glue Multipor boards, which are also excellent insulators and do not create a barrier to moisture.
Most experienced insulators agree that polystyrene is a much better solution for exterior insulation, while materials that allow moisture passage are better for interior use.
Installing insulation on the interior side of walls will certainly improve the thermal insulation of the rooms, and if done correctly, moisture and mold should not be an issue. However, some undesired effects should be considered.
Walls covered with insulation are not suitable for attaching shelves; special longer anchors must be used. Secondly, when installing thermal insulation, if you want everything to look aesthetically pleasing, electrical junction boxes need to be repositioned, and the visual solution for insulating around radiators needs to be considered, as radiators cannot be moved.
Additionally, new skirting boards need to be installed if the floor is parquet or laminate. It’s also worth noting that installing insulation on the interior side of walls reduces the usable space, which may be negligible in some cases but can significantly impact others.
There are other reasons why exterior insulation may be a better solution. One of them is thermal stability in the room. When insulation is on the exterior side, the walls inside remain warm. A large mass of walls accumulates a significant amount of thermal energy, so the temperature in the room is much more stable. Even after the heating is turned off, the room remains warm for a long time because the walls continue to emit heat.
If the insulation is on the interior side, once the air in the room cools down, the entire room practically cools down, so a constant source of heat energy is needed to keep the room warm. Achieving this can be difficult, so it may be hard to maintain an ideal temperature; the room may end up being either too warm or too cold.
Interior wall insulation can be a good solution for rooms that are only occasionally used. For example, conference rooms in office buildings, which are only occasionally used, can heat up much faster if the walls are insulated from the inside because the walls don’t need to be heated.
With exterior insulation, those cold walls would continue to emit unpleasant coldness for a long time after the heating is turned on. The same may apply to private weekend cottages that are visited, for example, only one or two days a week.
Foto: Freepik