Insulating Concrete Form Systems

A subset of CIP is a notable exception that has been gaining acceptance in residential  construction  across  North  America.  Originating  in  Europe  in  the  1960s  and  then  migrating to eastern Canada and the northeastern United States was a variation on  traditional  CIP  that  provided  for  forms  that  were  multipurpose  and  that  stayed  in  place after the walls were poured. Called insulating concrete forms, or ICF, this class  of product was designed as a stay-in-place form for poured concrete that was made  predominantly of expanded polystyrene (EPS), a polymer product derivative of oil  and natural gas refining. In each case, the objective was to combine the insulation  derived  from  thermal  resistance  of  the  EPS  with  the  thermal  mass  and  structural  value of the concrete, and further to minimize infiltration by creating a monolithic  wall system.

The  earliest  ICFs  used  sheet  EPS  connected  by  plastic  or  metal  clips  or  were  molded EPS that imitated the form factor of CMU (concrete masonry units) blocks.  In the latter case, the form factor of the concrete grout was a grid-shaped pattern.  The downside of this pattern was having areas between the post and beams in which  there was no structured material at all (only EPS foam) and thus became subject to  potential penetration. Also, due to the square grid structure, there was limited inherent in-plane shear resistance (see illustration at left in Figure 1).

In  an  effort  to  incorporate  enhanced  shear  values  and  provide  a  solid  concrete  envelope, the next evolution resulted in grid shapes with in ll in between the webs.  Called a “waffle grid” system (see illustration at right in Figure 1), it proposed to  resolve some of the issues of the post and beam structure. However, in practice, there  were  difficulties  in  assuring  proper  placement  of  the  concrete  without  significant  voids.  And  the  slender  cavities,  even  when  properly  filled,  provided  limited  shear  resistance. In active seismic zones or potential high wind zones, there were concerns  about durability. As  enhancements  in  the  chemistry  and  manufacture  of  plastics  occurred  that  facilitated  improvements  in  durability  and  utility  of  plastic  connectors  (typically polystyrene), the response to these issues was to design ICF forms that provided for  a uniform  at concrete wall sandwiched between two panels of EPS that were held  together by polystyrene connectors, typically called “webs” (see Figure 2). These   at-wall  systems  began  to  emerge  in  the  1970s  and  are  the  predominant  systems  today. Characteristically, they have a uniform concrete section of 4–12 in. or more  of steel-reinforced concrete, sandwiched between two layers of EPS foam averaging  about  5  in.  in  total  thickness.  The  thermal  resistance  (R-value)  of  the  assembly  is chiefly derived from the EPS foam.

Today’s typical ICF building system is an intelligent building product that combines an array of functions into a relatively simple and easy-to-use module. These  forms are characterized by the following:


•  They provide the form to contain concrete during placement.
•  The form stays in place afterward and reduces form waste to the 1%–4% range.
•  They employ a module size (typically 48 in. long × 16 or 24 in. tall) that is readily managed manually without requiring lifting equipment.
•  Connectors or webs are molded in place in manufacturing and are typically  modern durable polystyrene plastics that are UV resistant.
•  These connectors are spaced 6–8 in. apart in the horizontal plane and  have additional function in providing clips or  fingers that secure the rein- forcing steel.
•  Additionally, virtually all  at-wall ICFs have embedded furring strips into  which  fasteners  (typically  screws)  are  inserted  for  attaching  interior  and  exterior claddings.
•  Because the EPS insulation is continuous throughout the wall (except at  window  and  door  openings),  the  thermal  resistance  of  the  wall  assembly  (commonly R-24+) is uniform.
•  The wall system provides both an air barrier and a vapor barrier as inherent elements of its design (a weather-resistant external barrier may still be  required).
•  An average ICF wall provides acoustic separation across its boundary that is significant and always sensible to the occupants.
•  The foam is removed in channels to provide chases to install electric or  plumbing utilities, eliminating, at least in residential applications, the need  to use conduit.

There are numerous benefits that accrue within the domain of construction with  ICF systems:

•  Durability. ICF is, at its core, standard Portland cement-based, steel-rein- forced  concrete.  The  temporal  and  structural  durability  of  cast-in-place  concrete  is  well  known  and  understood.  When  encapsulated  between  the  concrete and a cladding and protected from UV and physical damage, the  EPS foam has a durability projected to be similar to that of concrete. An  ICF structure arguably is a 200- to 500-year durable building without a requirement for structural modi cation.

•  Practicality. ICF construction can readily be introduced to and undertaken  by  any  number  of  the  building  trades.  It  requires  less  specialized  train- ing and accumulated skill than most other forms of construction that can  be  used  for  building  efficient  envelopes.  James  Dillingham,  P.E.,  D&Z  Engineering, Shingle Springs, California, says,

I know of no other construction methodology for external envelopes that can  be done with the same assurance of success on the first project as is the case  with ICF. I am very comfortable with recommending it to first-time contractors  or  reasonably  prudent  owner–builders.  I  would  not  endorse  any  other  building system in this way.

•  In its design, ICF accommodates readily the subsequent trades that  finish out the structure (electricians, plumbers, sheet rockers, plasterers, finish  carpenters, etc.) with minimal change in their installation practices in frame  construction. Specialty tools and equipment are not required. Importantly,  it is an advanced building system that is fundamentally practical to deploy  broadly across the entire spectrum of construction in North America.

•  Scalability. Conveniently, ICF modules are manually manageable without  the requirement for mechanical devices for placement. As such, ICF works  effectively  across  projects  of  virtually  any  scale,  from  100-ft2  kiosks  to  23-story high rises and everything in between.

•  Risk management. The construction world is one in which risk management  is  a  significant  element  of  the  practice.  ICF  walls,  with  concrete  as  their  core, are by nature a reduced-risk material with which to work. Assuming  proper concrete mix design and proper placement, the long term behavior  of  an  ICF  wall  can  be  well  evaluated.  Mold  and  mildew,  biodegradation,  and other processes that affect frame walls constructed with organic mate- rials have essentially no effect on ICF.

•  Geographic  and  climate  zone  applicability.  ICF  construction  works  famously across virtually all climatic environs. From Fairbanks, Alaska, to  Miami, Florida, and from San Diego, California, to Portland, Maine, in all cases ICF contributes significantly to the effectiveness of the structures. In  some areas the primary bene t is reduced energy requirements; in others it  is enhanced safety, and in others its temporal durability is a key factor. ICF  can be used anywhere and, although variable, it returns value that exceeds  that of conventional frame structures.

•  Hazard protection. Across North America, there are multiple natural hazards for which historic construction practices have provided, at best, limited  protection. These include tropical storms, hurricanes, tornadoes, wild re,  and  earthquake.  Construction  with  ICF  can  substantially  mitigate,  or,  in  some cases, largely eliminate occupant risk from these hazards. (For example, by the inclusion of a concrete roof system [ICF or otherwise], a residence can be built to withstand the wind forces of a Fujita 5 tornado.)

•  Realized energy savings. While dependent upon climate zone, specific  design,  and  the  operating  behavior  of  occupants,  in  broad  strokes  ICF  homes realize a 30%–50% reduction in the consumption of fuels to provide  climate control within the structure. When combined with additional build- ing practices and systems, the reduction can be 60%–80% less than that of  a comparable frame structure.

•  Cost of construction. ICF approaches the cost of conventional frame construction. The major factors of cost between ICF and frame construction are  experience of the installation crew and the sensitivity of the design relative  to the construction methodology. Design–build firms that are experienced  in ICF construction as of 2010 are bidding residential projects at the same  price  for  ICF  as  for  well-insulated  2  ×  6  in.  frame  construction.  As  ICF  becomes  more  widespread,  it  is  anticipated  that  broad  parity  with  frame  construction will occur. Over the next decade, building codes will be continuing the shift toward requiring greater energy efficiency. In that enhanced  environment, it is a near certainty that ICF construction will become one of  the more cost-effective means of achieving these future standards.