Weatherproofing ICF Walls: Lessons in resiliency from B.C. field testing

by Katie Daniel | April 20, 2017 10:25 am

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By Douglas Bennion
Successful independent field-testing and code compliance analysis in British Columbia has resulted in the compilation of the first comprehensive set of residential construction details for insulating concrete forms (ICFs) in North America.  From footings to trusses, the ICF details presented in the provincial Homeowner Protection Office’s (HPO’s) upcoming release, “Building Envelope Guide for Houses,” offer a concise and cost-effective path to best practices and B.C. code compliance. Ongoing efforts indicate a strong potential for expanded adoption of these details in jurisdictions across Canada.

Many different methods—and even more opinions—exist on weatherproofing ICF walls. Only recently has the industry had scientific evidence upon which to base best practices for installation of window and door openings in such walls. “ICF Field Testing Report,”[2] a research report issued by HPO, provides a range of solutions compliant with building codes such as the B.C. Building Code, Part 9 (which is modelled after the 2015 National Building Code of Canada [NBC]). These solutions address the widest-possible range of building types, from single-family homes to high-rise commercial buildings.

To convey the report’s findings and make them easily applicable to individual projects, it is best to start at the core of the issue—how to permanently prevent air and water leakage at window and door openings in ICF walls. The answer begins with the following two basic code-compliant paths to water resistance in building shells.

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Moisture protection plane
Mainly concerned with wood-framed walls, building codes typically call for a primary weather barrier (such as siding or stucco) with a secondary weather barrier (such as building paper or another synthetic membrane) behind it. This is because framed walls must be kept dry to protect against moisture damage to both framing members and the insulation within.

Both codes, however, contain exemptions from the secondary weather barrier requirement in the case of above-grade masonry or concrete walls, which are recognized as watertight planes and shed water adequately on their own. As a result of the research summarized later in this article, ICF walls are now characterized as a complete assembly under B.C. residential code, without the benefit of added building paper or air gap (i.e. rainscreen) behind exterior cladding. This means ICF walls will not be subject to the same requirements for added weather protection as wood-framed walls, but the same exemptions as other concrete and masonry walls, which are recognized as able to resist water penetration on their own, without added layers of protection.

Exterior insulation
The expanded polystyrene (EPS) used in the manufacture of ICFs will not permit the passage of water or water vapour, but the horizontal and vertical joints between ICF units can allow penetration of water driven either by wind or gravity. This is an apparent conflict with building codes, which typically require the exterior building shell to be able to shed water to the outermost plane of the wall, where it cannot harm wood framing. Unable to view concrete behind the ICF outer insulation, building officials often default to more familiar wood-framed construction requirements and expect a membrane between the building sheathing and the exterior cladding. This has not only proven to be unnecessary, but is also unpopular among ICF proponents who object to the added costs.

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Testing ICF walls for water intrusion
In 2013, a number of North American ICF manufacturers teamed up to provide code-compliant, tested construction details for window and door penetrations in ICF walls. HPO agreed to partner in this targeted research project, recognizing the value of the research to support its goals of energy reduction and resiliency in B.C. housing stock.

Phases 1 and 2 of the testing began in 2014. Several 2 x 2-m (6 x 6-ft) wall samples were constructed using 152-mm (6-in.) core ICFs, and each employed a different buckout method common at the time. These included various wooden bucks—some spanning the full width of the ICF wall, others recessed into the ICF cavity—as well as vinyl block-outs designed specifically for the ICF industry. The assemblies were laboratory-tested at the Vancouver headquarters of a B.C. window manufacturer, using its air/water intrusion testing equipment. Simulated wind-driven rain was pitted against a typical fixed-pane vinyl window sample in compliance with ASTM E331, Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference, in conditions representing a range of building types.

The results were more instructional than encouraging. Most examples allowed water and air penetration past the assembly at relatively low levels of pressure and water flow. Some held to mid-range pressures, but all failed at
the high-pressure criteria levels. With those results, the ICF technical representatives and building science experts at RDH Building Science set about designing six additional test samples implementing modified features or untested techniques for a second round of tests. These all yielded much-improved results, with one displaying quite unexpected and extraordinary performance.

The 2011 North American Fenestration Standard (NAFS) has 18 levels of pressure criteria, increased from three under the original CAN/CSA A440, Specification for Windows, Doors, and Skylights. The levels tested here fall within the pressures given in NAFS, but conform generally to the older standard.

Tested levels were:

• 150 Pa (3.13 psf);
• 300 Pa (6.26 psf); and
• 700 Pa (15 psf).

These levels generally correlate to low-rise, mid-rise, and high-rise building types. Lab testing was successful up to 5000 Pa (104 psf), in one module’s case—seven times the average pressure criteria for high-rise building enclosures under NAFS. Even more surprising was the fact the most successful ICF buckout method was also one of the simplest and least expensive to install.

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Field testing
Data extracted from laboratory testing was used to ‘shortlist’ four additional test assemblies for a more realistic and accurate field test under ASTM E1105, Standard Test Method for Field Determination of Water Penetration of Installed Exterior Windows, Skylights, Doors, and Curtain Walls, by Uniform or Cyclic Static Air Pressure Difference. While the most successful results came from ICF wall samples featuring non-flanged (i.e. boxed or equal-leg) window frames, the ICF industry made it clear a flanged window option, mounted to the exterior face of the wall, was a necessity. Widespread use of this option made it critical to provide it, rather than attempting to force a change.

A technical subcommittee was formed to design a cost-effective buckout option able to both accommodate a flanged window installation and demonstrate adequate moisture and air resistance. Brian Hubbs, the lead engineer for the project at RDH, provided input.

Hubbs suggested a reglet be cut in the EPS just above the flanged window opening, allowing the head-flashing from the window to be sealed directly to the concrete core. Thus, the core’s watertight plane could be preserved and extended to the exterior of the flush-mounted window, and the opportunity for water to pass around the extended window buckout minimized. This method proved to be successful at the first two pressure levels tested, with minor leaks detected at the highest levels. Even though it was not fully successful in testing, this method’s effective performance at tested levels exceeds requirements for nearly all residential building types in all regions.

Phase 3 involved field-testing. A site in Surrey, B.C., was selected and the four assemblies were constructed onsite according to designs developed, critiqued, and accepted by technical professionals from the ICF industry, along with building envelope engineers who oversaw the entire project. Again, ASTM E1105 was implemented at varying wind-pressure and water-flow levels meant to reflect conditions expected on a range of building types.

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Module 1: Recessed (internal) wood buckout
This sample used a recessed wood buckout left in place after pouring of concrete—a method commonly used in ICF projects across North America. The installation was completed with a box-framed window, which was mounted at the outside edge of the concrete core via clips fastened to the wood buck. A reglet was cut into the EPS above the window, back to the concrete core. Window flashing mandated by NBC and Part 9 of the B.C. Building Code was applied to all sides of the window in ‘shingled’ fashion, with the head flashing sealed back to concrete inside the top reglet. Both the interior and exterior face of the window were sealed with foam backer-rod and silicone sealant.

The module was successful in resisting air and water infiltration up to pressures of 300 Pa (6.26 psf), which is equivalent to moderate to severe conditions expected on low- to mid-rise construction.

Module 2: EIFS basecoat
The second wall section also used an internal wood buck, but an exterior insulation and finish system (EIFS) basecoat layer was wrapped from the exterior face of the building back into the window opening, past the position of the window. This method is common in commercial and multi-family residential buildings finished with face-sealed EIFS or stucco systems. A box-framed window was also positioned at the exterior face of the concrete core, and again, the interior and exterior faces of the window were sealed with foam backer-rod and silicone sealant.

The module was successful in resisting twice the air and water infiltration of the first sample at 700 Pa (14.62 psf), equivalent to the most severe conditions expected on high-rise construction in any building use category. This module was likely more successful because of the direct connection of the window frame to a fully sealed exterior wall coating wrapped back into the window opening.

Module 3: Hybrid wood buckout with flanged window
The third sample used a flanged window with a wood substrate flush to the exterior face of the ICF wall. This method is common in low-rise residential buildings finished with face-sealed (i.e. stucco) systems or a variety of cladding options (including lapped siding, panelized cladding, vinyl, and shingle applications), and was deemed critical by the ICF stakeholders. In this module, a flanged window was fastened to the outer face of a permanent wood buckout at the exterior face of the EPS. Code-mandated window flashing was also applied to all sides of the window in shingled fashion, with the head flashing sealed back to concrete inside the top reglet. Only the interior face of the window was sealed with foam backer-rod and silicone sealant.

The module was successful in resisting air and water infiltration up to pressures of 300 Pa—the same as the first sample tested in this phase.

Module 4: Window sealed directly to concrete rough opening
In the fourth sample, the buck was stripped after the pour, leaving the concrete core exposed. This method is common in multi-storey commercial and multi-family buildings of any height. A box-framed window was positioned at the exterior face of the concrete core for this module, and both the interior and exterior faces of the window were sealed directly to the concrete core with foam backer-rod and silicone sealant.

Since the concrete core provides full protection, no exterior window flashing was required.

This assembly was by far the most successful at resisting water and air infiltration—after having resisted pressures up to 5000 Pa (104.42 psf) in laboratory testing, the field-test module was successful in resisting air and water infiltration up to pressures of 700 Pa (14.62 psf).

This extraordinary performance is equivalent to wind-speed conditions of more than 804 km/hr
(500 mph). Such conditions do not naturally exist on this planet, but this ICF wall/window assembly has proven to be fully resistant to them. (The top commonly recognized wind-speed range uses the Enhanced Fujita Scale, [EF] which defines an EF5 tornado as having wind speeds ranging from 419 to 512 km/hr [261 to 318 mph]. For more on the Fujita Scale, visit en.wikipedia.org/wiki/Enhanced_Fujita_scale[7].) In this author’s opinion, it is a game-changer for the ICF industry.

Not only was this fourth module the most effective at preventing air and water intrusion, but because it needs no added flashings, it also represents the least-expensive option for ICF installers.

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Conclusion
The successful results presented in HPO’s “ICF Field Testing Report” have guided the formulation of new best-practice construction details for ICF buildings in the upcoming revision of the organization’s “Building Envelope Guide for Houses,” slated for release this spring. Other provinces will likely be modelling their own future ICF guidelines after the information published in B.C. The author is not aware of any ICF-specific guidelines developed outside the provisions of the 2015 NBC, although these have been adopted by most provinces and other local jurisdictions in Canada.

As building codes concerning ICFs continue to emerge, the ICF industry will continue to offer guidance to the International Code Council (ICC), supported by the ICF construction details developed as a result of this research.  (While the I-codes offered by ICC are available for adoption worldwide, they are the mainstay of U.S. codes. Canada recognizes the I-codes only in a general and advisory fashion.) For instance, it has been suggested code change petitions based on the HPO work be submitted on both a provincial and national level.

From an ICF industry perspective, this third-party research fosters a major step forward in providing proven, cost-effective solutions for code-compliant design demonstrating high performance across a broad range of building types and uses, even in the most extreme conditions. Add to this the structural and fire capacity of reinforced concrete structures, and ICFs’ role in resilience becomes clear.

(An earlier version of this article appeared in the September 2016 issue of ICF Builder.)

[9]Douglas Bennion manages the technical department for Quad-Lock Building Systems, an ICF manufacturer that was one of the industry stakeholders in this project, and was instrumental in all phases of the research project reported above. His work has supported the ICF industry since 1989, and he has directly contributed to developing ICF building code and manufacturing standards in Canada, the United States, and the United Kingdom. Bennion regularly conducts training and continuing education seminars for builders and design professionals around the world. He can be reached via e-mail at douglas.bennion@quadlock.com[10].

Source URL: https://www.constructioncanada.net/weatherproofing-icf-walls-lessons-in-resiliency-from-b-c-field-testing/

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