What Is Mineral Wool Insulation Good For?
What Is Mineral Wool Insulation Good For?
If you are comparing insulation materials for your home, you may have come across Mineral Wool alongside options such as EPS, Wood Fibre and phenolic insulation. But what is Mineral Wool insulation good for, and when should you choose it?
Mineral Wool is a fibrous insulation material commonly used as part of external wall insulation systems. It provides thermal insulation while also offering useful properties relating to fire performance, sound reduction and vapour permeability.
This combination can make Mineral Wool particularly useful for projects where the requirements go beyond simply achieving a certain level of thermal insulation.
However, that does not mean Mineral Wool is automatically the best insulation for every property. The right choice depends on the building, the performance required and the complete external wall insulation system being installed.
What Is Mineral Wool Insulation?
Mineral Wool is an insulation material made from mineral fibres.
For external wall insulation, it is commonly supplied as rigid or semi-rigid slabs that can be fixed to the outside of the existing walls before being covered with a reinforced render system.
The Rockwool External Wall Dual Density Slabs available from EWI Store are specifically designed for external wall insulation. They use a dual-density construction, with a firmer outer surface designed to receive the render system and a more flexible inner layer that can accommodate slight variations in the substrate.
Once installed, Mineral Wool forms the main thermal layer within the EWI system.
Mineral Wool can be particularly useful where a project needs a combination of:
- Thermal insulation
- Strong reaction-to-fire performance
- Vapour permeability
- Acoustic performance
- A robust external wall insulation build-up
These characteristics mean Mineral Wool is often chosen for projects where there are specific performance requirements rather than simply selecting the lowest-cost insulation board.
Let’s look at these benefits individually.
Is Mineral Wool Good for Thermal Insulation?
Yes. Mineral Wool is designed to reduce heat transfer through the building fabric.
The Rockwool External Wall Dual Density Slabs available from EWI Store have a stated thermal conductivity of 0.036 W/mK.
In simple terms, adding Mineral Wool to an external wall increases its resistance to heat loss.
During colder weather, this can help the property retain more of the warmth produced inside rather than allowing it to pass as readily through the external walls.
The amount of Mineral Wool required will depend on the existing wall and the thermal performance the finished wall needs to achieve.
EWI Pro’s example calculations show that the required thickness can change depending on the wall construction, which is why there is no single Mineral Wool thickness suitable for every property.
Is Mineral Wool Good for Fire Performance?
Fire performance is one of the reasons Mineral Wool may be selected instead of another insulation material.
The Rockwool External Wall Dual Density Slabs available from EWI Store achieve a Euroclass A1 reaction-to-fire classification.
This makes Mineral Wool particularly worth considering where fire performance is an important part of the project specification.
However, the insulation board is only one component of an external wall insulation system.
The performance requirements for the complete façade still need to be considered, including the building type, system specification and all of the other materials being installed.
Is Mineral Wool Insulation Breathable?
Mineral Wool is highly vapour permeable.This means water vapour can move through the insulation relatively easily rather than being strongly restricted within the material.
The Rockwool External Wall Dual Density Slab currently lists a water vapour resistance factor of typically below 1.
For homeowners, the important point is that Mineral Wool can form part of a vapour-permeable external wall insulation system.This can be particularly useful where moisture movement through the wall needs to be considered carefully.
However, breathability depends on the whole wall build-up.
Choosing a vapour-permeable insulation board does not automatically make the complete wall breathable. The basecoat, reinforcement and final finish also need to be appropriate for the intended system.
Is Mineral Wool Good for Sound Insulation?
Mineral Wool can also provide acoustic benefits.
Its fibrous structure can help absorb sound, which can reduce the amount of external noise passing through the wall construction.
This can make Mineral Wool particularly worth considering for homes near:
- Busy roads
- Railway lines
- Commercial areas
- Schools
- Other regular sources of external noise
Sound performance will depend on the whole wall construction rather than the insulation board alone, but acoustic performance can be an additional advantage when Mineral Wool is compared with other external wall insulation options.
Is Mineral Wool Good for Older Houses?
Potentially, yes.
One reason Mineral Wool can be considered for older properties is its vapour permeability.
Traditional and solid-wall buildings can behave differently from modern cavity-wall homes when it comes to moisture movement. Using a more vapour-open insulation system may therefore be appropriate for certain properties.
However, the age of the house alone is not enough to decide which insulation should be installed.
Before choosing Mineral Wool, it is important to consider:
- What the existing wall is made from
- Its current condition
- Whether there are existing moisture problems
- How the wall currently manages moisture
- The required thermal performance
- The complete EWI system being proposed
For some traditional properties, Wood Fibre or another specialist breathable system may also be considered.
The insulation should therefore be selected around the building rather than simply assuming Mineral Wool is always the best choice for an older home.
What Does Dual Density Mineral Wool Mean?
You may see the term dual density when looking at Mineral Wool boards for external wall insulation.
This refers to the way the slab is manufactured with two different density layers.
The outer surface is denser, creating a stronger face for the render system and mechanical fixings.
The underside is more resilient, allowing it to accommodate small variations in the surface of the wall.
This makes the board particularly suitable for use as part of an external wall insulation system rather than simply being a general-purpose insulation product.
Can Mineral Wool Be Rendered?
Yes, but Mineral Wool needs to form part of an appropriate render system.
A typical Mineral Wool external wall insulation build-up can include:
- Existing wall
- Suitable adhesive
- Mineral Wool insulation
- Mechanical fixings
- Reinforced basecoat
- Fibreglass mesh
- Primer
- Decorative render
EWI Pro’s current Mineral Wool system guidance includes Rockwool Dual Density Slabs alongside EWI-225 Premium Basecoat, mechanical fixings, reinforcing mesh, primer and a suitable final render.
This is important because Mineral Wool behaves differently from lighter insulation such as EPS and needs compatible products throughout the system.
Does Mineral Wool Need Mechanical Fixings?
Yes, Mineral Wool used within an EWI system needs to be installed according to the specified fixing method.
The Rockwool External Wall Dual Density Slabs are designed to be used with suitable adhesive and mechanical fixings.
The exact fixing type and quantity will depend on the system specification and project.
This is another reason why insulation boards should not be considered separately from the rest of the EWI build-up.
Is Mineral Wool Better Than EPS?
Neither insulation is automatically better.
They simply have different strengths.
Graphite EPS is lightweight, thermally efficient and often more cost-effective, which makes it a practical choice for many standard residential EWI projects.
Mineral Wool may be preferred where factors such as vapour permeability, acoustic performance and fire performance are higher priorities.
EWI Store’s existing insulation guidance makes the same distinction: Mineral Wool should not simply be viewed as an upgrade from EPS. It is a different insulation material suited to different requirements.
The right question is therefore not:
“Is Mineral Wool better than EPS?”
It is:
“Which insulation is more suitable for this property?”
How Thick Should Mineral Wool Insulation Be?
There is no universal Mineral Wool insulation thickness.
The correct thickness depends on the existing wall construction and the thermal performance the finished wall needs to achieve.
As an example, EWI Pro’s certified system calculations show:
- 110mm Mineral Wool on the example 215mm brick wall
- 120mm Mineral Wool on the example 200mm dense blockwork wall
to achieve the example target U-value of 0.30 W/m²K.
These are examples rather than standard specifications for every home.
The difference demonstrates why the existing wall needs to be considered before choosing the insulation thickness.
What Are the Main Advantages of Mineral Wool Insulation?
For external wall insulation, the main reasons to consider Mineral Wool are its combination of properties.
It can provide:
- Good thermal insulation
- A Euroclass A1 reaction-to-fire classification with the Rockwool Dual Density Slab
- High vapour permeability
- Acoustic benefits
- A purpose-designed surface for rendered EWI systems
- A wide choice of insulation thicknesses
This can make it a particularly versatile option for projects where several different performance requirements need to be considered together.
Are There Any Disadvantages to Mineral Wool?
Mineral Wool is not necessarily the most practical option for every property.
Compared with EPS, Mineral Wool is generally heavier and denser. Installation also requires products and fixings appropriate for the board.
It may also cost more than a standard EPS system.
For a straightforward residential project where budget and thermal performance are the main considerations, EPS may therefore still be the more appropriate choice.
The additional characteristics of Mineral Wool are most valuable when they are relevant to the project.
Where Can You Buy Mineral Wool Insulation?
EWI Store supplies Rockwool External Wall Dual Density Slabs for use within suitable external wall insulation systems.
The boards are available in a wide range of thicknesses, allowing the insulation depth to be selected according to the requirements of the project.
You can shop mineral wool insulation at EWI Store alongside the compatible adhesives, fixings, reinforcement and render materials required for the wider EWI system.
Before ordering, make sure the insulation type and thickness are suitable for the property and the complete system being installed.
So, What Is Mineral Wool Insulation Good For?
Mineral Wool is a strong external wall insulation option where thermal performance needs to be combined with vapour permeability, acoustic benefits and strong reaction-to-fire performance.
For a straightforward residential project focused primarily on thermal performance and cost, EPS may still be the more practical choice.
But where the requirements of the property place greater importance on breathability, sound reduction or fire performance, Mineral Wool may be particularly well suited.
The important thing is to choose the insulation around the building and the complete EWI specification rather than selecting it based on one benefit alone.
