The choice of insulation for the facade is a key moment in building a structure, not only because it affects the maintenance of optimal temperatures inside the building but also because it can have an impact on your budget, both at the time of purchase and in the long run. The right choice can save you significant amounts on heating costs in winter and cooling costs in summer.
Today, there are various solutions available in this field, and we will focus on the most popular ones to help you assess which option best suits your needs. If you're wondering whether to use mineral wool, EPS (expanded polystyrene, commonly known as Styrofoam), or XPS (extruded polystyrene) for exterior insulation, you'll find a list of the most important factors to consider below.
Thermal Conductivity Coefficient
This coefficient describes the insulation material's ability to conduct heat. The smaller its value, the better it will insulate your home because it will allow less heat to pass through. In this regard, XPS stands out with thermal conductivity coefficient values (lambda) ranging from 0.030 to 0.034, depending on the thickness.
Following closely is mineral wool with values ranging from 0.034 to 0.035. Styrofoam has a thermal insulation capability of 0.038, putting it in a slightly less favorable position compared to its competitors in the group. While not significant, differences are noticeable.
|
Insulation Material |
Thickness (mm) |
Minimum Thermal Conductivity Coefficient |
|
XPS |
50 |
0.033 |
|
Mineral Wool |
50 |
0.034 |
|
EPS F |
50 |
0.038 |
Fire Resistance Rating
In addition to the energy efficiency that facade insulation can provide for your home, safety regarding fires and their spread should not be neglected. What you should pay attention to in this case is the fire reaction class. Mineral wool has the best ratings in this regard. It's a non-combustible material with a fire reaction class of A1.
In case of a fire, its behavior is safe. Mineral wool prevents the spread of fire without emitting toxic substances or flaming particles.
Styrofoam and XPS, on the other hand, are combustible materials with a fire reaction class of E.
Ecological Impact
Given the ecological crisis the world is facing, environmentally friendly building materials are of utmost importance. In this context, stone mineral wool is the future of insulation because its origin is entirely natural. It is produced from volcanic rocks without toxic substances and is 100% recyclable.
On the other hand, EPS and XPS boards are made from polystyrene, a polymer derived from petroleum, making them pollutants. While manufacturers emphasize that their production process is highly eco-friendly and environmentally responsible, once they become waste, they can cause significant harm to nature, the climate, and oceans.
Vapor Permeability
The "breathing" ability of facade insulation refers to the material's capacity to allow water vapor to pass through it, which is known as vapor permeability. Vapor-permeable insulation is crucial for preventing residual moisture from being trapped in the walls and building. Comparing wool, Styrofoam, and XPS in this regard reveals significant differences.
Mineral wool ranks first in this aspect, freely allowing residual moisture to escape from the walls and building and falling under the category of "breathable" materials. Second is Styrofoam (EPS), which is also a "breathable" material, albeit weaker than wool. Third is extruded polystyrene (XPS), which is water-resistant and characterized by virtually zero water absorption, making it "non-breathable."
When constructing the facade, it's important to consider all elements of the insulation system, including insulation, primer, paint, and plaster. This is why acrylic plasters, which are non-vapor-permeable, should not be applied to facades insulated with "breathable" materials like mineral wool. As a rule, only vapor-permeable exterior plasters are recommended for mineral wool and EPS.
It's interesting that on "non-breathable" thermal insulation materials like XPS, both types of plasters – vapor-permeable and non-vapor-permeable – can be applied. (For more information, see Which Exterior Plaster to Choose?)
Mineral wool is odorless, doesn't decay, doesn't support pest, fungal, mold, or bacterial growth. It contains a water-repellent additive to ensure that water cannot pass through the board and reach the existing masonry.
Thickness
Here, the main rule is that the greater the thickness of the insulation material, the better it will insulate the building.
Placement Location
Exterior insulation is more effective and contributes more to energy savings. When insulation is on the outside, the room warms up slowly, but once the heat accumulates in the walls, the insulation significantly reduces heat loss, thereby reducing energy bills. When you stop heating, and the insulation is on the outside, the room cools down much more slowly.
With interior insulation, the room heats up much faster since the insulation does not allow the heat to accumulate in the building's walls. However, when heating is turned off, the room cools down much faster. Therefore, interior insulation is justified only in cases where it's not possible to insulate from the outside.
Compressive Strength
Here, there is an absolute leader, and that is XPS with compressive strength ranging from 200 to 300 kPa (kilopascals), which is equivalent to 20 to 30 tons/m2. It is especially suitable for floor insulation over which a cement screed will be applied, as well as for underfloor heating. Of course, there are good options with mineral wool, but it has much lower compressive strength.
Price
Price, although not a technical characteristic related to the insulation properties of materials, is a factor of interest to all of us. Styrofoam is the least expensive option, being significantly cheaper (almost half the price) compared to facade wool and XPS, which are approximately at the same price level. The price also depends on the chosen thickness of the insulation – the thicker it is, the more expensive it becomes.