by Andy Lennox
In the construction industry, ‘innovation’ can be viewed as speed or efficiency of construction, increased durability, sustainable, new materials, systems, or processes. While innovation can also translate into safety and other aspects, it is generally spurred by economic benefit—for example, the speed of construction is a major driver, as its achievement offers cost advantages from labor, financing, and occupancy perspectives. Such is the case with insulating concrete forms (ICFs).
The ICF technology has been in the North American market for almost a half-century. It has recently made great strides over the past 25 years in the residential realm as market forces—such as lumber’s fluctuating price—have put the industry in the position of looking for other material solutions. However, over the last decade, there has been a move to use ICFs in commercial and high-rise residential applications. ASTM E2634, Standard Specification for Flat Wall Insulating Concrete Systems, describes the requirements for the manufacture of units for walls with uniform cross-sections. The respective concrete standard is American Concrete Institute (ACI) 318, Building Code Requirements for Structural Concrete.
ICFs are a permanent formwork system for reinforced concrete construction. The interlocking modular units are dry-stacked into position and filled with concrete. They can be used for almost any concrete wall—interior or exterior, below-grade or above-grade, short or tall. The concept can be seen as the marriage of two proven technologies: concrete mass sandwiched between two layers of expanded polystyrene (EPS) foam insulation.
A traditional exterior concrete wall contains six building components:
● reinforcement bar;
● air barrier;
● vapour barrier; and
ICFs combine these six components into a single building system installed by one crew at the same time. The thermal mass effect of the concrete enhances the insulation’s energy efficiency and the forming system’s airtightness, creating an opportunity for owner/developers to realize savings through the operation of the building.
ICFs can also minimize drywalling and electrical work onsite, but care must be taken with the placing of concrete in any form. Vibration is the key to proper consolidation, specifically around windows and doors. Specially designed door and window bucks are used for ICF systems—some are proprietary and some are site-manufactured.
With innovation, there sometimes are unexpected discoveries with the use of new technology in an application. For example, innovative contractors who used the ICF system in a non-residential application found there were significant constructability advantages with the speed of construction in addition to the high-performance attributes of the ICF wall. In Canada, one Ontario builder saw a significant uptake for the construction of high-rise residential student residences. The speed of construction recognized by the owner/developers provided them with completion dates that not only saved them money, but also achieved the early occupancy they required.
This article highlights growing use of ICFs in four sectors in North America—hotels, mid-rise, schools, and tall walls—to show how the building technology significantly enhanced the speed of construction.
Hotels on the horizon
Hotel builders are seeing the benefits ICF construction can offer in various areas. The faster a hotel can open, the sooner its owners start generating revenue. With insulating concrete formwork, construction typically progresses much faster than traditional concrete masonry unit (CMU) block construction—this factors in ICFs being insulation, forming, and attachment surfaces all in one, whereas the block is but one component. In other words, ICFs combine formwork, structure, interior and exterior strapping, and air and vapor barriers, resulting in more efficient construction with less sub-trade congestion onsite. On average, installers are able to complete a floor a week, depending on the project size. The various manufacturers provide specialized training for the application of their proprietary system.
Another contributing factor to getting the hotels open sooner is the ability to build in differing climates. Weather can play a key role in any construction project; winter can often halt a job entirely. The versatility with ICFs offers builders the advantage of building year-round. This is because the curing process offered by the forms means concrete can be poured on the coldest days. The EPS foam containing the concrete actually serves to store the natural heat produced inside the concrete core during the hydration or curing process. Studies have proven concrete installed in this condition can be placed and maintained at temperatures as low as −20 C (−10 F), even sustained for as long as three days.1 In such conditions, the process of hydration has been proven to increase to levels as high as 27 C (80 F) within the formwork, based on a concrete core of 160 mm [6 ¼ in.] thick.
National model energy codes, such as the International Energy Conservation Code (IECC), are advancing the way in which commercial and residential exterior wall construction is approached by emphasizing the use of continuous insulation (ci) systems. As the name suggests, these assemblies provide a continuous insulation layer over an entire wall, rather than just in the wall cavities. With other traditional building systems on the market, this ci layer has to be applied, but it is an integral part of ICFs.
In addition to energy performance benefits, ICFs are non-combustible and can offer fire protection ratings of up to four hours. As an added advantage for hotels, the assemblies also provide greater sound attenuation, offering sound transmission class (STC) ratings of up to 55—the material provides a further break than traditional concrete, thanks to the addition of the insulation changing the material density. EPS, the key component of ICF products, is also resistant to mold growth, lowering long-term maintenance costs for owners compared to wood-frame hotel construction.
One great success story in mid-rise ICF construction is the La Concha Pearl condominium project in La Paz, Mexico. ICF installation on this seven-story, 33-unit luxury beachfront development took place over an eight-month period, putting the building into service far ahead of the expected norm in the region. The sales team reported the reduction in the ‘pre-construction’ sales phase, where potential customers had no real building to see, was a huge benefit in persuading would-be residents to buy. If this holds true for other projects, there may be more developers and owners actively requesting ICFs.
In this particular case, the developers, having already made a commitment to minimize the impact on the local community, undertook some re-design of the building to optimize it for ICF, minimizing wasted materials and time onsite. The design phase was also shortened because the ‘flat-wall’ ICF design meant the project engineer could confidently rely on known, published design parameters for poured-in-place concrete structures via American Concrete Institute (ACI) 318, Building Code Requirements for Structural Concrete. Though a departure from the more common masonry block building found in the region, the project engineer and local building officials were well within their comfort zone, meeting no unfamiliar challenges posed by ICFs.
The general contractor, despite starting with only a few experienced ICF hands, was able to offer great training and oversight. His efforts resulted in a doubling of average production over the course of the 240-day installation, cutting the average time-per-floor in half. Crews quickly and eagerly accepted the new technology, taking great pride in learning a new craft.
The La Concha Pearl project is ICF-intensive—the assemblies were employed for both walls and floors, more than doubling the usual amount of concrete forms found on the typical project. Only 43 per cent of the total ICF area was a wall system; the majority was used for the floors.
The general contractor reported that, once shoring was in place, his crew would lay an entire 557-m2 (6000-sf) floor in about three hours, using the ICF T-beam floor forms. Since ICF floor forms replace about half of conventional suspended floor forms, post-pour removal of only primary shoring frames and beams was easily and quickly completed. Resumption of construction on the succeeding upper floors was never delayed, as each floor was fitted with a minimal amount of re-shoring (temporary posts) to carry construction loads through to the ground-floor level.
As an additional note, the La Concha project is situated in an extreme seismic zone. This led the project engineer to an extreme reinforcing bar specification. On lower floors, a double mat of steel, pre-tied into place, was specified. The knock-down design of the ICF wall system allowed the crews to fit ICF components through the pre-tied rebar mats, row by row, without disturbing pre-positioned reinforcing.
In Pincher Creek, Alberta, a 930-m2 (10,000-sf) private school was built utilizing ICFs. The school board and designers decided on this route for a faster build as well as improved energy, long-term resiliency, and sound efficiency. The contractor was pleased, noted the recorded time spent building with ICF was about half the time of that of a typical wood build, while providing the best in insulation and sound barrier—this latter criterion was especially important given the often-powerful, noisy southern Alberta winds.
The ICF walls included the standard 1.2-m (4-ft) frost wall and 2.7-m (9-ft) walls, with 3.7-m (12-ft) walls for the gymnasium. No other form of insulation or vapour barrier was required by using the forms. The gymnasium walls provided an especially strong barrier for sporting activities with no need for plywood, which would have otherwise been required behind the gypsum in wood builds. The solidness and strength of rebar-reinforced ICF blocks was a definite factor in the choice to employ this construction methodology.
During construction and concrete pouring, use of ICF bracing made it easy to straighten walls while providing solid, safe scaffolding for construction workers. The design of the block makes it a quick and efficient to attach the upright channels for bracing utilizing simple screws. Workers have a safe platform to work from, with a built-in hand rail and no need for tie-offs that would normally be used with other construction scaffolds.
The school board was satisfied with the decision to choose ICFs in the construction of the school. In the few years since completion, there have been no complaints or issues. The fewer labor-hours in the building of the school continues to be a deciding factor for the contractor and architect as they have since used ICFs in other construction business and plans design.
Richardsville Elementary (Warren County, Kentucky) is the first net-zero ICF school in the United States. Designed by Sherman-Carter-Barnhart Architects and engineered by CMTA, this building was constructed to be a two-story, energy-efficient structure that incorporates renewable materials and insulated concrete forms for its superior building envelope.
Generating its own energy, the 6715-m2 (72,285-sf) Richardsville is the next generation of educational building standards, and a valuable tool to educate students on energy and water conservation as well as the value of recycling. The project is designed to use only 18 kBtu/sf annually—75 percent less than the nation average standard set out by American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings.
Richardville was a learned lesson from previous schools built with ICFs elsewhere in the Bluegrass State. During construction onsite, the Warren County School District experienced reduced time in construction schedules. With CMU-constructed schools, running electrical can add to the construction schedule. Tyically, conduit has to be placed and fished through the walls. ICF construction offered this project’s electrical contractors the ability for quick installation times and having the wiring easily accessible on the face of the wall.
Retail chain Cabela’s is one the world’s foremost outfitters of hunting, fishing, and outdoor gear. Looking for energy efficiency and lower long-term operating costs, its architectural firm specified insulating concrete forms for the exterior walls of a new facility in Saskatoon, Saskatchewan. As the project progressed, it became evident ICFs not only delivered high-performance tall walls, but also a faster build.
This Cabela’s store measures about 64 x 64 m (210 x 210 ft) with the exterior tall walls ranging from 8.8 to 9.5 m (29 to 31 ft) in height. The wall’s assembly included six construction steps:
● concrete core;
● steel reinforcement;
● exterior and interior insulation;
● air barrier;
● vapor barrier; and
● stud work/furring strips.
According to 2014 RS Means data, if these walls were built with CMUs and finished to the same degree, the expected labor rate to build a comparable wall assembly would be 0.217 man-hours per square foot. On this particular job, however, the ICF installation crew recorded a labor rate of 0.109 labor hours per square foot. This suggests the walls were completed using half the labor that would have been traditionally required.
Several factors contributed to this speed. For example, the exterior tall walls were designed for maximum efficiency. The 203-mm (8-in.) concrete core provided sufficient room for rebar placement and concrete consolidation. The horizontal rebar was specified at 406 mm (16 in.) on center (oc) to be consistent with the course height of the ICF system.
By specifying the vertical rebar at 20m at 406 mm oc (versus, say, 10m at 203 mm oc), less bar had to be handled and placed, resulting in lower labor costs and easier and quicker concrete consolidation. Further, the designers were mindful of the ICF block dimensions in order to minimize the time spent cutting the blocks to make them fit.
Unassembled (i.e. knockdown) ICF blocks were assembled around the pre-built rebar cages used in the pilasters every 6 m (20 ft) of tall wall. This was much faster than the alternative method of building the rebar cages around the in-situ ICFs. Rugged rebar chairs built into the webs enabled the 6-m lengths of horizontal rebar to be quickly ‘snapped into place’ by a single crew member. Additionally, slide-in end caps quickly terminated wall sections and created vertical seams for expansion control.
Contact lap splices were used in the corners to allow concrete to easily flow through the corner forms. Use of running bonding (as opposed to stack bonding) was also maximized to reduce the installation and removal of temporary form support on both sides of the tall walls. Protecting the interlock during the concrete pours also eliminated any potential delays during subsequent course placement.
Further, the tall-wall scaffolding bracing system (which can be used to brace ICF walls up to 38 m [125 ft] without additional engineering) had many additional time-saving features. For example, it quickly connected directly to the concrete core providing an improved safety factor (required by Occupational Safety and Health Administration [OSHA] standards) and the ability to quickly precision-plum the walls.
As the guardrail was attached, no tie-offs for the crew members were required. The scaffolding’s wind-bays, which also function as 2.1-m (7-ft) work-bays, were located every 10.1 m (35 ft)—this means material was easily available at high heights. With extra scaffolding onsite, sections could be erected while others were being taken down.
Insulating concrete form applications are only limited by the designers. Some applications may require small redesigns to handle the structural loads, but many of these formwork systems have specially designed blocks or sections to deal with any unusual details. Technological advances are also allowing the creation of larger units, which will speed up construction even more.
The recent formation of the Council of ICF Industries (CICFI) is also expected to yield additional resources for building owners and project team members interested in exploring the suitability of this material. The group represents itself as the voice of the North American ICF manufacturing industry, and will serve as the information source for all information about the forms.
1 For more, see the report, “Cold Weather Construction of ICF Walls” by John Gadja (Portland Cement Association [PCA], 2002). (back to top)
Andy Lennox is a vice president of Logix Insulated Concrete Forms Ltd. He has worked in the ICF industry for 17 years in various sales, marketing, and management capacities. Lennox is the inaugural chair of the Council of ICF Industries (CICFI). He can be contacted by e-mail at email@example.com.