Mineral wool or polystyrene: which is better for insulating a house facade?

What is the best way to insulate a house facade?

To approach the selection process in a well-considered manner, it is necessary to familiarize yourself with the basic characteristics and features of both materials.

Mineral wool

Its key properties include good vapor permeability, minimal heat loss, and non-combustibility (fire safety). Stone wool simultaneously addresses several issues: it raises the surface temperature of interior walls, eliminates thermal bridges, and reduces external noise. Furthermore, it is a budget-friendly material, which is a crucial factor for most clients. Lightweight basalt wool boards are typically selected for "wet" facade systems designed for plastering.

Styrofoam (expanded polystyrene)

The main advantages of this material lie in the combination of high energy efficiency, favorable thermal conductivity, low weight, durability, and ease of installation. It is easily cut with a knife and absorbs virtually no water. Heat retention is achieved thanks to its composition, which consists of 98% air trapped within its cells. The cost of insulation using this foam is significantly lower compared to alternative insulation materials. When installed, the panels do not impose an additional load on the walls or foundation. For facade systems, the PSB-S-25 grade is most commonly used, as it provides the optimal density for wall insulation.

Facade insulation: what to choose – mineral wool or polystyrene?

Material efficiency and cost are not the only factors considered when selecting the right material. The specifics of the installation process also play a significant role in choosing between expanded polystyrene (foam) and mineral wool for a facade.

Insulating walls with facade mineral wool involves using a specific system of components, where each element works in conjunction with the others. The installation requires the mineral wool itself (in the appropriate thickness), an adhesive mixture, thermal insulation anchors (dowels), reinforcing mesh, primer, and facade plaster.

Preparatory work involves cleaning and drying the wall. Highly absorbent surfaces must be primed. The subsequent process follows this sequence:

• Installation of the starter profile – it is positioned precisely using a level, following the geometry of the facade.
• Application of insulation adhesive – it is spread over the surface in a thin layer using a notched trowel, working it into the fibers.
• Adhering the insulation boards – the first row rests on the starter profile, with the boards laid out so that vertical joints are staggered.
• Additional securing with insulation anchors – these are installed only after the adhesive has dried.
• Surface reinforcement – ​​the boards are coated with a layer of adhesive into which the reinforcing mesh is embedded, and additional profiles are installed at the corners.

Facade finishing – the reinforced layer is primed once fully dry, followed by the application of decorative facade plaster. Installing facade polystyrene foam requires a base profile, specialized adhesive, anchors with plastic cores, fiberglass mesh, and decorative plaster. The installation process follows much the same procedure as that for mineral wool:

• Surface preparation – old plaster, paint, and dirt are removed from the walls. The surface is then primed.
• Installation of the base profile – this ensures the first row is aligned correctly and protects the bottom edge against rodents, condensation, and moisture.
• Adhering the polystyrene – the panels are installed using either a continuous or spot-application method for the adhesive.
• Mechanical fastening – this is carried out a few days later, once the adhesive has fully dried. Anchors are installed at a rate of 5–6 per square meter.
• Mesh reinforcement – ​​the mesh is embedded into a layer of adhesive spread over the entire surface of the polystyrene panels.
• Finishing work – applying the decorative plaster finish to the facade.

If you are unsure whether to choose mineral wool or polystyrene foam for your facade insulation, it is best to consult with specialists from a construction company.