Posted on November 04, 2014
Insulating Concrete Formwork (ICF) systems have been around for the past 30 years.
Formwork is a temporary structure that is set up to contain concrete during pouring and hardening. The formwork, which is usually constructed of wood or steel, is removed after the concrete has hardened. Unlike conventional formwork, insulating concrete formwork becomes a permanent part of the structure. ICF consists of twin-wall expanded polystyrene (EPS) or extruded polystyrene (XPS) panels or blocks that are shape-molded to create a formwork for the walls of a building. Polystyrene ties, or webs, are molded into the panels. The ties, which are recessed slightly to prevent thermal bridging, perform the following three important functions:
This formwork is then filled with concrete to create a robust structure. The insulatingconcrete forms are thermally efficient, providing both complete thermal insulation anda uniform surface ready for the direct application of most finishes and proprietarycladding systems. ICFs have a variety of green properties, which are summarized in the following table.
|Elimination of wood waste||Avoids use of wooden formwork, at least half of which is discarded and land filled after a few uses|
|Avoidance of toxic chemicals||Avoids use of toxic substances as form releasers|
|Energy efficiency||ICFs reduce conduction losses through walls and reduce air leakage|
|Fire resistance||Composites are extremely fire-resistant, due to concrete’s innate fire resistance|
|Acoustical properties||Reduce sound by as much as 87.5% compared with wooden walls.|
Elimination of Wood Waste
Within each category of ICFs, individual brands vary in their cavity design. “Flat wall” systems yield a continuous thickness of concrete, like a conventional poured wall. “Waffle grid wall” systems have a waffle pattern in which the concrete is thicker at some points than others. “Screen grid” systems have equally spaced horizontal and vertical columns of concrete completely encapsulated in foam.
By avoiding the use of wooden formwork, ICF eliminates an important source of wood waste in construction projects. Wooden formwork is often thrown away after a single use, although it also is generally possible to disassemble the formwork and re-use it several times before it must be discarded. Although discarded formwork can be recycled, the widespread use of form releasers such as diesel fuel, motor oil, and home heating oil limits the practical potential for reuse. (Soy and other biologically based form releasers, which are safer, are also available.) An estimated 50% or more of all formwork is discarded.
Buildings constructed with ICF exterior walls require an estimated 44% less energy to heat and 32% less energy to cool than comparable frame houses.
ICF walls using polystyrene foam are R-17 to R-26, compared to wood frame’s R-9 to R-15. As a result, ICF walls should cut conduction losses through foundation and above grade walls by about half. Additionally, ICF walls are tighter. In tests, ICF houses averaged about half as much infiltration (air leakage) as frame.
The evidence suggests that ICF walls may be safer than wood walls in a fire. Concrete is one of the most fire-resistant building materials. The EPS foams in ICFs are manufactured with flame-retardant additives. These prevent the foams from burning by themselves. If a fire occurs, the EPS will only burn while a flame is applied directly to the foam. The smoke from burning EPS is reportedly no more toxic than wood smoke.
According to the ICFA, only about one-quarter to one-eighth as much sound penetrates through an ICF wall as through a wall made of wood. ICF walls’ sound insulating properties account for their growing use in multi-unit residential construction. However, other sources note that ICF’s sound insulating effectiveness is highly dependent on design factors.
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