As a material or combination of materials, insulation of the building envelope helps keep cold air out and heat in during the winter, while keeping warm air out and cool air in during the summer.
Insulation is widely considered the most effective way to improve comfort and the energy efficiency of a building, and can save significantly on heating and cooling costs. However, any time the insulating layer is interrupted, the effective R-value, or efficiency of the insulation, decreases.
In view of this, national energy codes have moved beyond cavity insulation, encouraging the use of continuous insulation (CI) systems, which provide an uninterrupted insulation layer over an entire wall, not just in the wall cavities. This article takes a closer look at continuous insulation, including types of wall systems, the R-values, differences, and costs.
Changing Design Tactics
Faced with code compliance and the pressing need to design for green building goals and save on energy costs, architects are turning to CI as an effective approach to eliminating segmented insulation with open gaps, blocking thermal bridging, and helping to improve thermal performance of the wall assembly.
In addition to continuous thermal insulation, an effective wall assembly will provide moisture vapor control, water-resistive barrier and air barrier, and be resistant to fire and extreme wind conditions. Insulation can play a role in all these characteristics. From interior furring and insulated cavities to foamed panel systems and next-generation insulated concrete masonry block systems, masonry construction offers diverse insulation options for energy-efficient wall systems. The relative performance of each insulation system should be examined not only in terms of its R-value, but in relation to the aforementioned goals of efficient wall assemblies as well as its potential for aesthetic effect, and the specific needs of the project.
Single Wythe Walls
A single wythe wall is a stone, brick, or concrete wall that is one masonry unit thick. Considered the most economical wall type, the single layer provides the structure, exterior surface finish, and, in some designs, interior surface finish. Single wythe walls are durable and inherently fire proof with fire ratings up to 4 hours. Although the thermal mass and inherent R-values may be sufficient to meet code requirements, particularly in warmer climates, additional insulation may still be required. Rigid insulation inserts, foamed-in place or loose-fill insulation can be applied to the interior or exterior of the unit. Furring strips can be added to the interior and allow for the addition of a finishing material such as drywall and accommodate additional insulation.
Alternatively, an exterior insulation and finishing system (EIFS) can be added to the exterior. According to the definitions of the International Building Code and ASTM International, an EIFS is a non-load-bearing, exterior wall cladding system that consists of an insulation board attached either adhesively or mechanically, or both, to the substrate; an integrally reinforced base coat; and a textured protective finish coat. According to Building Science Digests BSD-146: EIFS, EIFS became very popular in the 1980s and experienced a significant number of serious failures, almost all related to rain penetration.
Early EIFS used a face-sealed approach. Drained EIFS are significantly different from face-sealed systems in that, by definition, they have a provision for drainage. Unlike face-sealed perfect barrier systems, such systems can be successfully used as an exterior cladding system in essentially all climates and exposures. Drainable EIFS are not subject to the same limitations of use as face-sealed or barrier systems. In fact, drainable EIFS are among the most robust and advanced moisture control assemblies available. EIFs comply with building codes that reference energy conservation through the CI.
In single wythe walls, R-values will depend on the density of the concrete, the number and height of the of webs, the depth of CMU as well as the type of insulation calculation method used. With the variety of concrete masonry units and insulation types and thicknesses, R-values from 5 to over 20 are possible. Rigid foam inserts will yield an R-value of 3 to 10, and injected foam or loose fill will boost the R-value from 4 to 20.
While single wythe walls can be a cost-effective solution when building goals include permanence and economy, it is important to note that single wythe walls do not have the redundancy of a traditional cavity wall, and water penetration is sometimes a concern. To achieve the weather resistance of a cavity wall, the single wythe wall must be very carefully detailed and built, with particular attention paid to flashing, base condition, joints, and coatings.
Foam Panel Systems
Far preferable in a number of respects are foam panel wall systems. Rigid foam has been a key driver of energy-efficient construction over the last few decades as it gives a significant boost to R-values of walls and roofs with minimal increases in thickness. Further, it covers the framing elements, decreasing and sometimes eliminating the thermal bridging that is characteristic of cavity insulation. Rigid foam insulation can be airtight if properly sealed and taped at seams; air can go around but not through this insulation.
The InsulTech™ insulated concrete masonry system by Oldcastle APG, A CRH Company, offers high thermal efficiency while simplifying the installation process that a contractor would experience with a traditional brick-and-mortar wall.
Types of Foam
Code- and ASTM-compliant foam plastic CI sheathing materials are available with various characteristics and profiles, to meet specific project requirements, the main types being expanded polystyrene, extruded polystyrene, and polyisocyanurate foam, all produced under various trade names. Each type of product has different thermal properties and associated influence on required thickness and costs. Below we explain what each type of foam is.
- Expanded polystyrene (EPS) ASTM C578 is the most economical type of rigid foam and has an R-value of about R-4.0 per inch. Similar to the foam used for impact protective packaging, soil subgrade load-bearing blocks, and floation augmentation for boating and floating, EPS is one of the most widely used types of rigid foam. In successful use for many years in areas where moisture is a concern, EPS “breathes” so that moisture is diffused. It has been found to resist the growth of fungi and bacteria, and to maintain performance properties when exposed to moisture and/or water. EPS insulation is available in a variety of densities to suit project needs, and is frequently used in commercial buildings for roof and wall panel insulation. ASTM C578 provides performance properties on this type of foam insulation.
- Extruded polystyrene (XPS) rigid foam is usually blue or pink in color, with a smooth plastic surface, and available in a wide range of thicknesses and edge profiles. The R-value is about 5 per inch. Used widely in residential construction, this type of rigid foam will not absorb water like polyiso and is stronger and more durable than expanded polystyrene, making it a versatile type of rigid foam. XPS falls between polyiso and expanded polystyrene in price.
- Polyisocyanurate, or polyiso, foam has the highest R-value per inch (R-6.5 to R-6.8) of any rigid insulation, and is the most expensive. This type of rigid foam usually comes with a reflective foil facing on both sides, so it can also serve as a radiant barrier in some applications. It is used widely in commercial applications and increasingly in residential structures.
Foams themselves can be one of two types: open- or closed-cell. In general, the key difference between the two types is density, which has implications when used in insulation. As closed-cell foam is the denser of the two materials, it offers increased R-value per volume, increased resistance of water vapor transmission, and increased rigidity, providing superior structural integrity. A 1-inch layer of closed-cell foam provides roughly the equivalent insulation factor as a 2-inch layer of open-cell foam, making the former particularly advantageous in tight spaces as thinner layers of insulation can be used.
Closed-cell foams are superior insulators: They are strong and act as structural reinforcement for the insulated surface whereas open-cell foams have little structural strength. Open-cell foams typically have R-values of 3 to 4 per inch vs. closed-cell foams’ R-values of 5 to 8 per inch. Another key difference is porosity. Open-cell foam is porous, which means moisture, both water vapor and liquid water, can penetrate the insulation. Closed-cell foam, on the other hand, is non-porous, and thus not moisture-penetrable.
Foam Masonry Panel System
Relatively new to the market, foam masonry panel systems provide continuous insulation and can consist of foam panels, stainless steel screws or anchors, masonry units, and mortar. Type S mortar can be used, which has the advantage of additives to achieve easier pumping, better bonding, flexibility, and dimensional stability. A variety of masonry units are available including durable stone, clay, and concrete brick with others under development. Masonry units are friction fit in the foam, with different types of units having different foam panels.
The foam is the key to the efficacy of the unit, adding good water management with drainage on both sides to take away any water that may infiltrate the wall and protect the structure from damage over its service life of high moisture exposure. R-values are high as well—9.1 Steady State and 13.6 including Thermal Mass. An STC of 51 and an NCMA TEK 13-1B sound transmission rating for concrete masonry walls means loud sounds are only faintly heard and occupants can enjoy their space in peace and quiet.
Some foam systems have been proven to resist wind speeds of more than 110 mph according to ASTM E330 with no lasting deformation, which essentially eliminates the structural risk of damage experienced with lighter-weight veneers. Fire resistance criteria notably NFPA 285 and ASTM E119 assures that tested foam walls have successfully withstood one hour of exposure to temperatures of more than 1,700°F. Foam panel systems should meet the aforementioned criteria.
Download our comprehensive guide to learn more. We give you a breakdown on one of the most important topics in design today—design codes and continuous insulation.
A special thanks to Oldcastle APG, Echelon Masonry, and Architectural Record for supplying us with this article.