Continuous insulation: Rethinking the correlation between density and compressive strength

Air leakage resistance

Mineral wool can be installed using various hanging systems without compromising the integrity of the air and water barrier.

Vapor permeability

Mineral wool will not trap liquid moisture in the wall cavity where it can contribute to situations affecting air quality.

Sustainability

Since it is comprised from up to 75 percent recycled contents, the material can be removed from post-industrial processes and re-used. Like all insulations, mineral wool can reduce greenhouse gas (GHG) emissions by reducing the energy needed to heat and cool buildings and contributes to sustainable building practices.

While the features described above are widely recognized for making mineral wool a good option for interior insulation applications, the material is not always top-of-mind for ci, where insulating materials like expanded polystyrene (EPS), XPS, and sprayfoam are widely used. Foam plastics continue to be a valid choice in many situations with noncombustible claddings, and with advances in production technologies, mineral wool may now be considered not only a viable option for ci with combustible claddings, but also the preferred ci material for buildings. For example, mineral wool is particularly advantageous when working with claddings made of plastic and laminate where a noncombustible ci material is required to pass National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components.

The case for higher strength at lower density

The change in mindset to higher strength at lower density is similar to the way people had to change their thinking about lightbulbs a few years ago with the shift to light-emitting diodes (LEDs). Most people were used to speaking about the brightness of bulbs in terms of watts, and it was hard to imagine we could achieve the desired level of light with fewer watts. However, when comparing the measure that really mattered—lumens—it was easy to see with the new technology, a 5-watt bulb could indeed produce as much light at a 60-watt lamp. Separating strength and density requires a similar shift in thinking, and can be a game-changer in design.

Less weight on cladding

Today’s variety of lightweight, attractive cladding options can help designers maximize the creative aesthetics and functionality of buildings. However, given the traditional density-to-strength equation for specifying exterior-grade insulations, designers have to weigh ci options (quite literally) against available cladding choices, always accounting for weight per square foot, deflection concerns, fasteners, and necessary cantilever capabilities.

By delivering a high compressive strength to comparatively lower weight and density, mineral wool insulation presents designers and specifiers with a greater range of options in pairing a building’s cladding with ci. Mineral wool is a practical ci option with traditional heavy cladding choices, such as masonry, as well as light materials, such as newer plastic and laminate claddings. The product can be used with brick, metal, stone, masonry, terra cotta, concrete, and architectural cladding options, including phenolic panels and high-pressure laminates. Other insulation options simply do not offer this level of flexibility under varying claddings.

With its noncombustible properties, mineral wool also helps designers and specifiers meet NFPA 285 and otherfire standards when working with new, lighter cladding materials that are more combustible than traditional veneers.

The ability to use a lighter weight cladding with mineral wool also provides some options in the construction process itself. Lighter cladding can reduce the need for additional workers and expensive equipment like overhead cranes. Handling lighter material is also less fatiguing and cumbersome for installers transporting the material and working on the jobsite. Additionally, an easy to handle building material can help support the number one priority on every job: worker safety.

More than compressive strength

While compressive strength always ranks near the top of the list when it comes to specifying materials, a product’s dimensional stability must also be considered. New, lighter, and stronger mineral wool ci options reduce risks of façade deflection under pressure and over time. Since the cladding is attached through the mineral wool insulation, a cantilever is established that helps to prevent this unwanted movement.

Not to worry, though, because even with higher dimensional stability than some other mineral wool products, these advanced mineral wool ci still have the ability to accommodate irregular surfaces and fit together tightly compared to many of their foam plastic counterparts.

Uncompromised thermal performance

While the density of this product is reduced, designers may be concerned about a reduction in thermal performance. Fortunately, reducing density does not sacrifice thermal performance of the material. These products are tested to exhibit a minimum R-value of 4.2 per inch thickness just like other mineral wool ci counterparts. Therefore, installing these materials into exterior walls does not require compromising thermal comfort or energy efficiency for the mechanical and weight benefits.

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