Achieving continuous advantages with EIFS insulation

by Katie Daniel | February 28, 2018 3:38 pm

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By Andreas Lueth
Continuous insulation (ci) has been a part of some Canadian code requirements since 2011, but the concept can still be confusing for design and construction professionals. In American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) 90.1-2013, Energy Standard for Buildings Except Low-rise Residential Buildings, ci is defined as being “uncompressed and continuous across all structural members without thermal bridges other than fasteners and service openings.” (This article has been adapted from an earlier piece bylined by Brian Chang, which appeared in the June 2017 issue of The Construction Specifier, the official publication of CSI. Visit www.constructionspecifier.com[2].)

The insulation can be installed on the enclosure’s exterior or interior, or be integral to opaque envelope materials. Wherever it is located, the ci layer must span across or through thermally conductive elements such as steel columns, metal studs, and concrete masonry units (CMUs). Otherwise, thermal bridging through high-conductivity structural components can result in reduced insulation performance by up to 40 to 60 per cent in metal-framed buildings, and up to 20 per cent in wood-framed enclosures, according to studies by the U.S. Oak Ridge National Laboratories (ORNL). (For more, see “A Review of High R-value Wood-framed and Composite Wood Wall Technologies Using Advanced Insulation Techniques,” by Jan Kosny, Andi Asiz, Ian Smith, Som Shrestha, and Ali Fallahi. It appeared in Energy and Buildings [72], published in 2014 by Elsevier.)

Thermal bridges have other detrimental effects, including condensation and moisture accumulation in the enclosure, as well as occupant discomfort in localized interior spaces. Traditional non-continuous insulation—for decades, simple layers located neatly between steel columns or light-gauge studs—is insufficient in this regard. An exterior insulation and finish system (EIFS), which offers ci by design, offers an effective alternative.

Codes and certifications
Specifying ci can be essential to meeting key energy codes, as well as achieving certification under Passive House, Leadership in Energy and Environmental Design (LEED), or various net-zero-energy or reduced carbon footprint and greenhouse gas (GHG) programs. (Continuous insulation [ci] is found in National Energy Code of Canada for Buildings [NECB] Part 3–Building Envelope and the National Building Code of Canada’s [NBC’s] Article 9.36.2.5, “Continuity of Insulation.” ASHRAE 90.1-2013 is not referenced in NBC, but is applicable in Supplementary Bulletin 10 [SB–10] of the Ontario Building Code [OBC], British Columbia’s Building Code, and the City of Vancouver’s Building Bylaw.)

Some of these benchmarks offer prescriptive solutions. Using the project’s climate zone, the space’s conditioning category, and maximum allowable U-factor (i.e. rate of heat loss), ASHRAE 90.1 offers guidance on applying ci to achieve required performance levels. Using an example from Supplementary Bulletin 10 (SB-10) of the Ontario Building Code (OBC), a nonresidential building in Climate Zone 5 would see a minimum of R-12 ci, in combination with R-13 batt-type insulation in above-grade steel-framed walls.

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Occupant safety requirements affect use of ci. Most relevant for Canadian building teams are those dealing with the use of combustible components in exterior walls and the protection of combustible insulation. This subject area is deserving of its own article, but suffice it to say here, if use of the proposed wall assembly is not described in the code’s provisions (i.e. as it relates to combustible or noncombustible construction allowances), the design team should seek conformity assurance through the successful completion of code-referenced fire assessment standards. (Within the code there are a number of referenced standards allowing for the use of combustible components in a building, or a part of building required to be of noncombustible construction. Proponents undergoing fire assessment usually, though not always, conduct the testing under a certification program through Underwriters Laboratories of Canada [ULC], Intertek, or Quality Assurance International [QAI]. These certification bodies then publish directories listing the subject materials and/or assemblies. Design or certification listings serve as conformity assurance the given material meets the code-referenced standard and related pass/fail criteria.) For example, protection from adjacent space—as described in OBC Article 3.1.5.12, “Combustible Insulation and its Protection”—lists a number of thermal barriers that may be employed for the protection of combustible insulation. If the assembly does not include one of the code’s acceptable material solutions, a product shown to meet the code’s thermal barrier requirements through Underwriters Laboratories of Canada (CAN/ULC) S101, Fire Endurance Tests of Building Construction and Materials, may be used. From an exterior protection standpoint, wall assemblies containing any combustible components such as combustible exterior insulation may require testing under CAN/ULC S134, Fire Test of Exterior Wall Assemblies, as per National Building Code of Canada (NBC) Article 3.1.5.5, “Combustible Components for Exterior Walls.” A proactive policy of ensuring the proposed wall assembly meets any and all applicable code criteria, above and beyond those relating to energy efficiency, is best.

With the rise in use of ci and air barriers, National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-loadbearing Wall Assemblies Containing Combustible Components, has become a vital and ubiquitous requirement for building projects. Specifiers often check to ensure their proposed assemblies have already been subjected to the costly test, in which an impressive full-scale multistorey mockup is subjected to a fire intended to simulate a blaze originating from an interior room. In the 2015 International Building Code (IBC), six sections (including 1403.5 for weather-resistive barriers [WRBs] and 2603.5.5 for foam plastic insulation) reference NFPA 285.

In general, project teams must focus on NFPA 285 early in the design phase as the market may not offer enough compliant assemblies for walls of greater than 12 m (40 ft) above grade. Additionally, some rainscreens and other cladding types have yet to be tested with foam plastic insulations. In these cases, the design team can choose to employ a tested combination of products or have the proposed assembly tested.

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Expectations with performance
One primary benefit of ci is it maintains the enclosure and framing elements at temperatures closer to those of the building interior. With the additional R-value at the exterior, the dewpoint moves toward the outside and, in some cases, exterior to the insulation in the framing cavity. This effect can eliminate or reduce condensation in the enclosure that may otherwise prematurely degrade structural materials.

Further, ci protects against the thermal bridges where structural components, substructure, anchors, and other penetrations reach through to the exterior. For example, uninsulated steel-stud framing in contact with exterior sheathing is an efficient conduit for heat, regardless of how much insulation is packed between the studs. Adding ci across all the steel frame members dramatically cuts heat and cold bridges, boosting overall R-value and reducing U-factor.

Other penetrations through the façade can cause thermal bridging and compromise the ci layer as a result of inadequate detailing or misalignment of the thermal control layer. If the structure includes steel shelf angles without stand-offs, it will transfer heat. Exposed concrete floor slabs and steel penetrations for balconies or canopies can also cause problems.

Windows and doors with thermal breaks not coinciding with the opaque wall’s thermal control location, or where structural members hold off their lintels, can also result in bridging challenges. Sometimes, parapet walls are incorrectly detailed, becoming a building-wide perimeter heat sink. The enclosure design team must track all possible thermal bridging paths. Properly designed, the ci layer cuts U-factor considerably.

Use of ci can also reduce moisture accumulation due to transport of water vapour through envelope materials such as brick or CMU. This mitigation is especially effective when a properly specified and installed WRB is used. Attention to climate zone, the type of wall system employed, and the building’s intended use help ensure proper enclosure function.

Further, the ci layer can serve as part of an air barrier system and moisture barrier protections—an efficient ‘double use’ of a material. For example, extruded polystyrene (XPS) insulation boards can be an effective air barrier material, typically with taped joints and sealed penetrations using silicone- or latex-based sealants compatible with XPS. To determine whether the ci systems employed will perform as a code-compliant air barrier assembly, specifiers can refer to manufacturer data per CAN/ULC S742-11, Standard for Air Barrier Assemblies–Specification, and CAN/ULC S741-08, Standard for Air Barrier Materials–Specification, or ASTM E2357, Standard Test Method for Determining Air Leakage of Air Barrier Assemblies. (Specifications sometimes also refer to ASTM E2178, Standard Test Method for Air Permeance of Building Materials, or ASTM E1677, Standard Specification for Air Barrier Material or System for Low-rise Framed Building Walls.)

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Choice of cladding and ci implications
Before choosing the ci solution, building teams generally select or recommend their cladding system. Esthetics, performance needs, and suitability to the application are among the considerations when choosing a cladding. Construction type, climate zone, and the intended building use help determine where the ci layer is placed in the enclosure assembly. Its location affects construction sequencing and cost, meaning construction preferences may drive the choice of cladding so the ci layer is easy to apply, inspect, and in some cases, repair. When the ci insulation layer is outboard of the structural framing, the detailing and construction tends to be much less complex than when it is interior to the structure, obviating such interruptions as floor slabs.

This usually leaves two options for ci location: behind the cladding or integral to it. Cladding options typically falling outboard of the ci layer include masonry and brick exteriors, as well as panelized metal systems (e.g. aluminum composites), often with mineral wool as the ci layer. Since the ci materials must be supported, the façade attachment hardware can serve in some cases to secure both the cladding and the insulation—examples include clips, horizontal girts, and screws with sealing washers. Other types, such as impaling fasteners, are designed to support insulation alone.

Also exterior to the ci layer are built-up façade cladding systems requiring no penetrating fasteners to attach the insulation, further minimizing thermal bridging. For example, EIFS assemblies can use fully adhered insulation boards to offer good wind load resistance and protect against cracking caused by thermal expansion and contraction.

For cladding systems such as precast or tilt-up concrete panels and masonry cavity walls (e.g. brick veneer), the ci layer is integral. XPS can be employed under various masonry veneer exterior finishes or over steel-stud framing, concrete, or masonry wall structures. Similarly, ci is a feature of rainscreens and rain barrier cladding designs made with metal or aluminum composite panels, fibre-cement board, glass-fibre-reinforced concrete, or other materials. In these assemblies, the chosen insulation must meet minimums for compressive strength and any relevant code requirements.

With many metal cladding systems/rainscreens, joint detailing can influence the selection of the ci material. Rainscreens with masonry veneer or open-joint panels are designed to admit moisture, which is then drained and/or dried through ventilation in the assembly’s cavity or air gap. If exposed to moisture, the ci material should be water-repellent. In some cases, the open joints may also allow ultraviolet (UV) light from the sun past the cladding. Therefore, exposed insulation and barrier materials should be rated for UV degradation. For buildings or parts of a building required to follow noncombustible construction provisions, metal cladding systems incorporating a combustible insulation are required to undergo CAN/ULC S134 assessment to ensure the assembly satisfies the code’s life-safety objectives.

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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.

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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[8].

Source URL: https://www.constructioncanada.net/achieving-continuous-advantages-eifs-insulation/

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