What type of ci works best?
Several kinds of insulation, sometimes employed in combination with other building materials, can be used to achieve the desired ci performance. One is sprayed polyurethane foam (SPF). Four kinds of rigid or semi-rigid products are more commonly employed (noted with their R-value per inch):
- semi-rigid mineral fibre—R-4.0;
- expanded polystyrene (EPS)—minimum R-3.6, typical R-3.85;
- XPS—R-5.0; and
- foil-faced polyisocyanurate (polyiso)—R-6.5. Design professionals can refer to CAN/ULC S704.1-2017, Standard for Thermal Insulation, Polyurethane, and Polyisocyanurate Boards, Faced, for long-term thermal resistance values.
In high-performance buildings with better insulation, 100 mm (4 in.) or more of these rigid materials might be incorporated into the enclosure. However, a benefit of walls with ci is the elimination of thermal bridging, enabling them to be thinner than equivalently insulated walls without ci.
The aforementioned insulation types can meet these goals, and all are relatively inexpensive building materials. They also offer good long-term thermal resistance and the ability to reduce operating costs.
Mineral fibre
Also called ‘mineral wool’ and ‘stone wool’ insulation, mineral fibre is noncombustible and fire-resistant due to its high melting temperature, allowing fire ratings of one to two hours. It is resistant to water and moisture, which helps it retain R-value when wet. Chemically inert, this UV-stable insulation does not rot, cause corrosion, or support microbiological growth. Most products made with mineral fibre for building applications are derived from natural and recycled feedstocks, and do not require fluorocarbons in manufacturing. In typical applications, mineral wool allows for draining water and absorbing sound for acoustical properties in the envelope.
For nonresidential projects, this insulation is a medium- or high-density semi-rigid board. It can be foil-faced, and works in cavity wall and rainscreen applications. Its fire and moisture performance make mineral fibre a good choice for wet cavity walls, as well as metal cladding systems or open-joint rainscreens.
Polyisocyanurate
Polyiso has the highest recorded R-value per inch compared to other rigid-foam-board insulation materials, according to Polyisocyanurate Insulation Manufacturers Association (PIMA); its R-value increases with board thickness. However, as per CAN/ULC S704.1 2017, there is some thermal drift in long-term resistance over time, in cold temperatures, or both.
Some polyiso products have a higher level of inherent fire resistance, and the material has been used in various assemblies passing fire tests, particularly CAN/ULC S134. One must consult the manufacturer for additional information.
Polyiso’s foam core is moisture-resistant with some water absorption potential, and the boards are stable and compatible with most construction sealants and adhesives.
Foil-faced polyiso insulation is commonly used in masonry and rainscreen cavity walls, where its high R-value per inch tends to reduce the cavity depth needed. Polyiso experiences some change in R-value in cold weather, which may be considered when calculating ci performance.
Expanded polystyrene
Known for high R-value per unit cost, EPS is cost-effective, dimensionally stable, and commonly used for ground contact and below-grade uses, as it does not retain water. Faced boards also function as a vapour retarder. However, when used as sheathing, EPS should be laminated or used with an air- and moisture-barrier layer. A versatile rigid insulation, EPS is useful in foundation applications and is typical in EIFS façades, as well as integrated assemblies such as insulating concrete forms (ICFs) and structural insulated panels (SIPs).
Extruded polystyrene
The use of XPS takes advantage of its closed-cell structure and water resistance, offering a cost-effective choice for good R-value. It is also recyclable—another benefit for green building projects. Specifiers often use plastic-faced versions, which can serve as vapour retarders. Like EPS, XPS is combustible, and its performance may be affected over time by UV light. It may also absorb more moisture over time than other insulation boards.
For these three reasons, XPS is generally unsuitable for open-joint applications such as metal panels, terra cotta, or high-pressure laminates. Instead, it works well for barrier walls and closed-joint rainscreens, as well as most cavity-wall drainage systems.
Conclusion
As shown, there are benefits and drawbacks to each insulating material. For an EIFS project, EPS is ideally compatible. For brick veneer, the higher R-values of polyiso and XPS allow for thinner wall sections, meaning smaller shelf angles and lintels that help reduce thermal bridging.
While rigid-foam insulation boards offer varying performance capacities, they all have excellent R-values per unit cost. All the materials noted can meet the core goals of a ci layer, and all are relatively inexpensive. Looking at initial investment alone, insulation is a valuable performance element. In a CMU masonry wall with an installed cost of $475/m2 ($44.10/sf), the ci layer accounts for only about seven per cent of that total. For a steel-frame assembly, the first cost is just over eight per cent. By comparing their functional characteristics, specifiers can determine which insulation works best for a given ci application.
Specifying the right materials is one step in the complex yet critical process of wrapping a building in a blanket of ci. By adding to this process such variables as cladding choice, fire-safety rules, building operations, and life-cycle needs, the specifier team can make the best choice possible to meet the highest building-efficiency standards.
Andreas Lueth serves as architectural and national accounts representative for Sto Canada. Based in the Greater Toronto Area (GTA), Lueth has lengthy experience in the building materials business, spending many years as both a business owner and agency representative. He has extensive knowledge of exterior cladding systems. Lueth currently represents Sto Canada as a board member of the EIFS Council of Canada and is a member of the Toronto Chapter of CSC. He can be reached at alueth@stocanada.com.
