Insulating Concrete Forms (ICF’s) are a relatively new method of construction. ICF’s provide many features which are advantageous to the owner. ICF is gaining acceptance and use as a method of construction both nationally –here in the US- and internationally.
ICF’s are typically like large hollow rectangular blocks made of Styrofoam type material. These blocks are stacked and the hollow core is then filled with ready mix concrete (delivered in a concrete truck). Steel rebar is typically placed in the wall cavity for tensile strength.
The resulting structures are very strong, well insulated, relatively inexpensive and easy to assemble.
Here are some of the benefits of ICF construction, as described by the ICF Builders Network:
High performance R-values
No air infiltration
Permanent performance no downgrading over time
Shifts thermal loading from peak periods
Lower cost to heat and cool
No air infiltration means no dust or allergens
No cavity walls for mold, mildew, bugs or rodents
No off-gassing of materials
High wind resistant
Fire rated assembly
Strength is permanent
Will not rot or decay
Resistant to termites (the concrete)
No maintenance requirements
High sound attenuating
Enhances steady temperatures
Peace of mind during inclement weather events
Low maintenance structure
May attribute to lower insurance costs
Quick (depending on installer)
Conducive to Exterior Insulation Finish Systems (EIFS)
Fully code accepted cast-in-place concrete walls
Time tested and proven
ICF construction is indeed advantageous for all those reasons listed above. However this type of construction can be made even better and this is what I’ll be talking about today.
Problems with ICF
First, thermal mass benefits associated with ICF construction are not truly maximized. This is because heat is stored in the concrete, where it is subsequently released to the interior space of the building. In order for this thermal mass effect to be efficient, the heat should be readily transferrable between the concrete of the wall and the interior of the building. ICF construction insulates between the interior space and the concrete wall. That is, there is foam insulation on the inside wall; this insulation prevents heat from travelling between the interior space to the concrete wall, and also prevents heat from being released from the wall to the interior space.
As I discussed earlier on this blog, thermal mass benefits are maximized if the exterior surface of a concrete or masonry wall is insulated. When the inside surface of a wall is insulated, the thermal mass benefits are reduced. Insulate the outside for maximum efficiency: insulating the inner surface of a wall reduces thermal mass benefits. ICF methods insulate the inner surface of the wall.
Another shortcoming of ICF technology is its inability to provide an effective roofing system. Currently ICF technology is only used to make vertical walls. It is generally not used for roofing. If ICF technology could be used for roofing systems, the benefits of this technology would, quite simply, extend to the roof.
Currently, a close cousin to ICF’s can be used for roofing. This technology is known as Structural Insulated Panels, or SIP’s. One of the disadvantages of SIP’s is that they are not poured in place, like ICF’s, but are pre-cast, and must be placed with a crane. A truly integrated system which would bring the ICF approach to roofing would provide a simplified construction, using the same technique for the entire building envelope, including the roof. With such an approach, all of the benefits associated with ICF construction –as listed toward the beginning of this post- would extend to the entire building structure, including the roof. SIP's commonly do not incorporate concrete, and are not as strong as the rest of an ICF building: this is a weak link.
A Whole New Approach
What is described below is frankly a much better approach to ICF construction than is currently practiced by industry today. This method greatly increases thermal efficiency and maximizes thermal mass benefits of a concrete wall by not insulating the interior of the concrete wall. It also extends the ICF construction method to the roof, and brings all the benefits of ICF construction to the roof.
First, an inflatable bladder is set up and inflated. This bladder provides the formwork, scaffolding and support for the ICF triangular blocks. This bladder is essentially the size and shape of the interior space of the finished building. The concrete is poured from the top, and allowed to flow directly against the inflated bladder, which creates the interior surface of the form. This means that no insulation is wasted to insulate the inner surface of the building. It also greatly reduces the amount of foam insulation required for ICF construction, increasing thermal mass benefits and efficiency.
Second, ICF forms are assembled around the inflated bladder. These triangular forms utilize the interlocking design, and are further strengthened and reinforced by the tensile elements (e.g.: steel cable, rebar, etc.) which are woven into the walls and roof as they are assembled. This approach allows for extensive design flexibility, and can include vertical walls, square corners, cylinders, arches, domes and any combination of these elements. These shapes will be hollow, and made from foam. They assemble around the inflated bladder.
The ICF forms shown in this schematic patent illustration are able to be made on a simple two-piece mold without any undercut. This greatly simplifies their manufacture, and makes them inexpensive to produce, as described in one of my stupid poems.
To make a roof, the bladder is inflated, the blocks are assembled, and concrete is then poured from the top and allowed to flow down to form a consolidated, massive wall. There are holes in the sides of the triangular foam blocks which allow the concrete to flow between blocks; from the top of the pour to the bottom of the foundation.
If the building’s height is too great to withstand the weight of wet concrete, and a blow-out would result, then the building is simply assembled and poured in smaller vertical sections, so that the head pressure of wet concrete is reduced, preventing a blowout. Once a section is poured and cured, then additional foam block are added for the next section to be poured.
Once the building has been poured and the concrete has been allowed to properly cure, the bladder is simply deflated and removed, and is ready for another job. The interior wall of the structure is now exposed concrete, providing increased thermal mass benefits and efficiency.
These bladders are commercially available, and create a very effective scaffolding and formwork: as I described earlier on this blog, here and here.
By using this construction method, what is created is much stronger, faster to assemble, less expensive and able to withstand hurricanes, tornadoes, earthquakes and other severe structural loading events.
Currently my company is seeking a partner to bring this technology to market. Too many ICF manufacturers seem “in love” with their own technology, and are unwilling to see beyond current practice in industry. This is a huge opportunity for the right organization. We may just “bootstrap” this technology and launch it ourselves. It is an exciting time!
I covered a lot with all this. Questions? Comments? Drop me a line.