News & Insights

The Pros and Cons of ICF Foundations

Carl Christianson

One question with ICF foundation houses is the flexibility of making changes during the project: How easy is it to change things once the ICF’s have been set? Answer: Very difficult and time-consuming. Below will help to explain some of the problems with changes while under construction.

Recently we have run into a few snags on a project where the plans have not been quite as clear as we needed. Wall elevations and exact window sizing are required at the forefront of construction on ICF homes. When ICF walls go up, there is little room for changes after the fact. Careful consideration goes into laying out walls, windows, and doors before any block is laid due to the significant amount of time it takes to change after the ICF system has been assembled. Think of these blocks as large Legos; Adding a window or door in a wall or moving one is not as simple as in-filling the old one and cutting a new one.

ICF blocks are fabricated to have internal webbing between the foam forms. The foam offers amazing insulation values, while the webbing offers rigidity to the forms and serves to support re-bar within the foam. The webbing also provides an attachment point for interior finishes such as Sheetrock and exterior finishes such as siding.

The internal re-bar becomes part of the ICF structure and is laid with every course of the ICF walls. Once laid it is wired in place to the webbing to help stabilize the walls and prevent shifting of the block, as well as add structural strength to the concrete that will be poured within the open cells. When changes are made to this system you may have to remove each layer of ICF block to get to the area where the change occurs. Each layer has re-bar that must be snipped, pulled, then replaced, and webbing lines must remain centered over one another to stay on layout. Since re-bar is overlapped  by 2′ on each end and is often placed in in 16′ pieces, you can imagine how one small change can mean a large amount of forms being pulled and work to be done. Once the change area is reached, the shifting will most likely require the cut portions to be discarded to retain a factory end. ICF ends are also keyed into one another and a cut piece must be discarded unless it can be re cut to a smaller length and re-used. At $20 each this change can quickly get expensive, just in material. While the blocks can be reused if pulled apart carefully there is also the risk of damaging them while doing so and if the blocks do not reconnect with the same precision, it often requires the last course to be altered to avoid elevation changes in the wall.

Another consideration affecting window and door placement is how tight ICF blocks need to be fitted to the window and door block outs called “bucks”. These block outs must be within 1/4″ of the cut foam and then foam filled to the wood support before pouring the walls. Reinforcement and stiff backs must be added in these locations as often the web of the ICF blocks has been weakened due to cutting the block down in these areas. Where internal webbing has been cut due to the window or door laying out in the middle instead of the end of a block careful attention must be made to prevent blow outs of the weakened block units. When altering ICF or making cuts in the ICF systems due to non-conforming layouts with the ICF options, the effort and time required can triple.

However, there are significant benefits to ICF foundations. When all information is available early, ICF is the fastest way to build foundations and walls. One 2400 square foot house recently took only 14 days from footing to completion and day 18 saw the trusses being set and dry in starting. This project also had all electrical in the walls at the time of the ICF block setting and a total of 22 windows and three exterior doors.  Note that the design of this house also utilized jogs and offsets that allowed the use of standard ICF blocks without customizing.

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