by Elaina Adams | January 1, 2012 3:16 pm
By Paul Nutcher, CSI, CDT
As sustainable building has become the preferred (or, occasionally, required) construction method throughout North America, design professionals are turning to insulating concrete forms (ICFs). When comprising the building envelope, these materials provide occupants with a safe, clean, healthy, and comfortable environment in which to live and work. Whether residential multi-family, commercial new construction, school, theatre, healthcare, or retail, ICF structures also help reduce a building’s carbon footprint—their insulation can mean less energy to heat and cool than is needed in structures built with conventional materials.
The building envelope efficiencies of ICFs have long been known to insiders. Until recently, however, the structural engineering data for multi-storey ICF construction has been neither widely shared nor accepted by the construction industry in general.
Across the continent, new standards and codes, along with an overhaul of the Leadership in Energy and Environmental Design (LEED) program, will greatly assist project teams in understanding the structural performance capabilities of ICFs as well as the enhanced energy and environmental attributes of these materials versus other building envelope options. To help design professionals in writing improved specifications, it is therefore worth identifying and reviewing the relevant North American standards, coming building codes, and green building rating systems as they relate to ICF construction.
About insulating concrete forms
Insulating concrete forms are a ‘stay-in-place’ wall system made of three primary components:
As a structural material, ICFs usually exceed Canadian code requirements for high wind and seismic resistance. They provide superior sound attenuation and thermal performance equivalent to R-50 thermal mass. This wall system can help lower HVAC requirements and help a project earn LEED points. Benefits to contractors range from reduced cycle time to fewer subtrades onsite to ease of use (the material is lightweight). (For more on ICFs, see the following articles in Construction Canada: “Building with Insulating Concrete Forms” (July 2010), “ICFs, Flooring and Frost” (May 2010), and “Integrating IFAs and ICFs” (July 2009). Visit www.constructioncanada.net and select “Archives.”)
ICFs were invented in the 1940s, evolving as plastic foam and moulding technology improved. These forms became widely commercially available in North America during the 80s, but even then only a handful of Canadian and U.S. companies were experimenting with this new method of forming a wall with stay-in-place foam forms. However, there are nearly 40 companies engaged in the manufacturing and distribution of ICF systems.
While there are numerous manufacturers, there are only three basic product types:
The flat wall system is favoured by most contractors because it is considered to be the strongest, most efficient, and user-friendly ICF block. Some believe the costs of the waffle- and screen-grid are less expensive because they require less concrete, but the increased labor cost to place steel reinforcement and consolidate the concrete elevates the overall price of non-flat wall ICFs. Therefore, the flat wall is an ‘evolved’ form of the screen (i.e. ‘post and beam’) and waffle-grid styles.
Fixed-web forms are the most common; they consist of two expanded polystyrene (EPS) panels held together by plastic ties (i.e. ‘webs’) that are moulded into the foam during the manufacturing process. These blocks are usually 305 or 406 mm (12 or 16 in.) tall with varying widths depending on the thickness of the panels and the width of the core cavity. Each manufacturer has a different design, web ties, connection system, and foam thickness, so forms from different suppliers are generally not interchangeable.
The other flat-wall type is the ‘panel’ system, sometimes referred to as ‘knock-down’ or ‘assemble-on-site.’ They work much the same way as fixed-web blocks except the ties are not moulded into the product, but are inserted into slots in the panels onsite or in an assembly plant before use. The block width depends on the width of the tie used and generally ranges from 102 to 305 mm (4 to 12 in.).
The majority of ICF systems use EPS—the material found in the white foam coffee cups and coolers. The same insulating properties that keep coffee warm and ice frozen are what give ICFs their exceptional R-value performance when used to build the exterior walls of a structure.
ASTM and ULC
As ICFs have not previously fit under one specific code section (i.e. they fall under sections dealing with insulation and R-value, as well as structural sections for walls), the new ASTM E 2634, Standard Specification for Flat Wall Insulating Concrete Form Systems, seeks to provide language suitable for adoption within building codes. (ICFs are classified under Division 03–Concrete within MasterFormat as 03 11 19.)
The scope contained in ASTM E 2634 defines ICFs as systems “that will act as permanent formwork for cast-in-place reinforced concrete beams,” among other building elements such as lintels and below-grade walls for both load-bearing and non-load-bearing walls, foundations, and retaining walls. The ICF manufacturer provides two moulded EPS insulation panels held in parallel axis to each other by moulded plastic or stamped metal with cross ties that typically vary depending on which company produces them, but all offer the same or very similar Work Results.
ASTM E 2634 consists of many other ASTM standards that each establish the required minimum compliance criteria for each attribute required for the ICF components. It does not cover the manufacturing procedures and only a few companies have applied and have become certified under the standard. Most reputable manufacturers have gained International Code Council (ICC) Evaluation Reports, which shows their compliance with the earlier ASTM standards now part of the combined new one. Specifiers can look for both types of documentation in manufacturer’s guide specifications, and either is a legitimate compliance path until several years from now when the new standard starts to become incorporated into building codes.
In Canada, the new Underwriters Laboratories of Canada (CAN/ULC) S717.1, Standard for Flat Wall Insulating Concrete Form Units, is nearly identical to the U.S. version because there is a lot of overlapping of the performance and quality auditing requirements of the ICF systems. However, in respect of Canadian code-specified references, the ancillary standards are understandably different. The new standard will help specifiers ensure projects are receiving ICF products of a high level of consistency and quality.
CAN/ULC S717.1 was approved for publication by the ULC Standards Committee on Thermal Insulation Materials and Systems during their November 2011 meeting. The committee provided the task group with a mandate to address the concerns of four committee members before ULC publishes the standard, which is expected in February 2012.
While the industry task group members were closely involved in the development of ASTM E 2634 and made significant efforts to match requirements between the two documents, there are some variations between them.
The scope is the same in the ULC and ASTM standards, as the Canadian one used the American version as a starting point, according to Keven Rector, a member of the CAN/ULC S717 committee and a technical expert with an ICF manufacturer. There are a few differences, of course—for example, quality control and product certification portions or administrative requirements within the ASTM standard were moved to ULC’s informational annex sections in the Canadian version. Overall, the same standards referenced in ASTM were only changed in Canada when an equivalent domestic standard existed, such as those for thermal barrier protection and flame spread.
Concrete construction offers environmental benefits in an array of areas, including energy conservation. ICF construction has a direct impact on LEED certification for the following reasons:
The new U.S. LEED rating program for 2012 includes stricter requirements for gaining certification in an ongoing process of producing environmentally neutral, or even restorative, architecture. The goal is to eventually ensure the lowest certification level produces buildings with an environmentally neutral impact, with the higher certification levels potentially returning resources to the environment through net-zero-energy buildings. In the proposed LEED 2012 standards, several organizational changes to the rating system are worth noting when it comes to ICFs.
In the past, CaGBC has adapted its American counterpart’s LEED rating systems once they are released. The process of adaptation has allowed the Canadian council to recognize differences in codes, standards, regulations, and guidelines. Currently, CaGBC is working with USGBC and other Green Building Councils from around the world to develop a framework for adapting LEED for use internationally. CaGBC is hopeful this can be done in a way that meets the requirements of the Canadian market; such a framework should allow Canadians to benefit from the new rating systems as soon as they are launched (currently planned for November 2012).
This situation makes it important to understand the current LEED framework in the United States. A second public comment period ended in September for a draft of LEED 2012 for Building, Design, and Construction (BD+C), which will cover these programs:
Preceding the new version, USGBC released the “LEED Pilot Credit Library,” which is already available to project teams under the current LEED 2009—many of these credits will become permanent in the new rating systems.
Right now, trial versions of the credits to be added to the new LEED 2012 are available to project teams looking for Innovation in Design (ID) credits by selecting one from the library of ‘pilots,’ two in particular of which the ICF industry will be watching to see how well they fare under the new rating system. Both share similar language to the verbiage in the new credits in the rating system’s second public comment draft.
The first of these is Pilot Credit 1, Lifecycle Assessment of Building Assemblies and Materials, which is available to project teams working on LEED NC and Healthcare projects. The credit relies on the Athena EcoCalculator (offered by the Athena Institute, out of Merrickville, Ont.) for calculating and comparing the various material assemblies from a lifecycle assessment (LCA) perspective.
LEED treats an ICF as a portion of the building envelope system or assembly. The LCA practitioner produces an impact score sheet for the assemblies assessed and those results are plugged into the LEED LCA Calculator to generate the documentation a project team needs to continue with the building design process. How the Athena Calculator will be brought into LEED 2012 is expected to be clarified in the final version.
The other credit relevant to ICFs is Pilot Credit 43, Certified Products, in which building materials can either be certified to approved standards, or manufacturers can offer product data in approved formats. Either way, the proposed credit would reward project teams with one point for a green product with a label verifying the product has been third-party-certified for at least a single sustainable product attribute, while the credit leaves product performance to be captured somewhere else in LEED. This pilot credit also refers to another USGBC document under development—“LEED Standard for Standards.”
The energy efficiency of ICF walls are well-documented in studies and research by the Portland Cement Association (PCA) and CTL Group consultants, (For an example, see the article, “Concrete’s Mass Appeal for Energy: A Look at LEED EA Credit 1 Across Five Climates,” by Martha G. VanGeem, PE, ASHRAE, LEED AP, and Medgar L. Marceau, PR, CSI, ASHRAE, LEED AP, in the November 2008 issue of The Construction Specifier. Visit www.constructionspecifier.com and select “Archives.”) as well as in ongoing research projects by the U.S. National Association of Home Builders (NAHB) under the Program for Advanced Technology in Housing (PATH) and the Oak Ridge National Laboratory (ORNL).
The baseline building performance measurement is calculated with Appendix G of American National Standards Institute (ANSI)/ASHRAE/IESNA 90.1-2010, Energy Standard for Buildings Except Low-rise Residential Buildings, using a computer simulation model for the whole building project. Further details of the requirements for this calculation are listed in the prerequisite within LEED’s Energy and Atmosphere (EA) category.
In the new LEED 2012 EA category, available credits will be reduced, with some being shifted to the new Performance (PF) category. This is a change reflecting an emphasis on measuring energy efficiency after initial certification. The EA credits moved to Performance are concerned with measurement, performance, and verification over the project’s life. Contained in the changes to Energy and Atmosphere, as well as the new Performance category, are opportunities for projects using ICFs to retain and even expand possible credits toward LEED certification.
Additionally, research has shown the thermal mass of an ICF building envelope would fare better during the energy modelling portion of the commissioning for an easier time in passing testing and verification benchmarks details in ASHRAE 90.1, especially compared to wood or steel construction.3
Concrete and ICFs
In LEED 2012, the Materials and Resources (MR) category will be overhauled from a building materials and products manufacturer’s perspective. Design professionals will have to relearn the compliance pathways for gaining points through the MR category, and manufacturers will need to update their documentation to reflect the changes.
Several credits are new and others have been eliminated in an attempt to reward LEED project teams for specifying materials on a lifecycle basis, rather than just single sustainable attributes. In fact, products that once contributed to multiple LEED credits—such as recycled or regional content—can now only contribute additional points if they have third-party certification or can document their product’s reduced environmental impact through an LCA.
Relevant to ICF systems, instead of LEED 2009’s MR Credit 1, Building Reuse–Maintain Existing Walls, Floors, and Roof, USGBC has developed a new MR Credit 1, Environmentally Preferable Structure and Enclosure. It gives project teams various options, among which is the exclusion of fly ash in concrete as a substitute for cement and as recycled content (but only for healthcare projects). It also requires an LCA of any major structural elements reused in new construction projects, as well as any exterior portions of the building dividing the conditioned space from the outside.
A forthcoming BD+C LEED 2012 Reference Guide will further explain the specifics, including the design parameter methodology for the LCA. Additionally, the new LEED will require reuse of structural enclosure materials to be “better than average” when compared to the USGBC’s stated “highest value impact categories” within an LCA, including Climate Change, Human Health, and Water (consumption and pollution). Further, waste from municipal solid waste cannot qualify as recycled content if the project team seeks to earn this credit. ICFs will be better than many comparable structural systems due to their lower global warming potential (GWP) over 60 years, as discussed later in this article.
In cases where the building will be reused, much remains the same as the LEED 2009 MR Credit 1, except the threshold is higher for three points as 90 per cent reuse is now the new benchmark. The remainder of the new MR Credit 1 asks project teams to source materials locally when possible. There are also guidelines for reuse of historic buildings or abandoned structures in typically blighted areas; ICF durability can play a role here, too.
Since ICF walls are a major portion of the building envelope, the system can be considered part of the calculation for reuse credits in LEED for MR Credit 1, as it can be a load-bearing portion of the supporting building systems.
USGBC has indicated it believes LCA has its limits. Therefore, the council has introduced additional criteria relevant to ICF walls such as MR Credit 5, Responsible Sourcing of Raw Materials, which looks for a commitment by manufacturers mining raw materials to support programs such as the Framework for Responsible Mining. This credit has relevance for the ICF industry since one of the main ingredients of the system is concrete.
Lifecycle analysis of concrete
While much is made of ICF benefits to conserve energy consumed by buildings, the LCA of concrete buildings published by the Massachusetts Institute of Technology (MIT) Concrete Sustainability Hub, in its 2011 report, “Methods, Impacts, and Opportunities in the Concrete Building Lifecycle” showed ICF homes can reduce a structure’s GWP compared to light-wood-framed single-family homes. Visit www.think-harder.org/MITResearch.aspx This report is perhaps the best indicator of how insulating concrete forms for commercial new construction and renovations can have a positive impact.
The research was undertaken because the manufacturing of portland cement is very energy-intensive, and the report helped dispel some myths about concrete’s sustainability. It also showed buildings generally consume the most energy while occupied; therefore, this stage of the lifecycle is responsible for 88 to 98 per cent of the GWP emissions. Initially, all building types in the report had very similar emissions over a 60-year lifecycle when concrete construction was compared to steel and wood construction in different U.S. climates. The addition of fly ash then further helped reduce concrete’s environmental impact. The authors concluded:
Although the concrete homes have higher initial embodied emissions than light-frame wood construction, the lower annual operating emissions means that the emissions of concrete houses are lower over a 60-year period… The cumulative emissions of the ICF houses are 4.7 per cent lower in Chicago and eight per cent lower in Phoenix than the equivalent light-frame wood house.
Energy loss impacts finite resources. Insulating concrete forms have a high resistance to heat flow and, when correctly specified and installed, reduce energy usage. Lowering energy consumption reduces not only the owner/tenant’s utility bill, but also the built environment’s carbon footprint.
As these aspects of ICFs become more salient (due to codes, standards, and increased awareness), they will become better documented candidates for the building envelope on a rising number of construction projects.
Paul Nutcher, CSI, CDT, is president of Green Apple Group, LLC. He has nine years of building industry experience as a marketing and sustainability consultant. Nutcher can be contacted at email@example.com.
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