Insulated Concrete Forms

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Insulated Concrete Forms Part II – Doing the Project

by Kim Kinrade

One of the most fun builds I've ever made is with Insulated Concrete Forms, the stay-in-place interlocking foam blocks that are filled with concrete to provide structure for a home. Most of the product is made from expanded polystyrene (EPS) which is pumped into precision molds. As I wrote in my previous article on ICF, “Why Wood?” the combination of cement, steel reinforcing encapsulated by two-inches of EPS gives an airtight, warm and sound-proof home impervious to most of the deteriorating forces – water, insects and weathering – that plague wooden structures.

As I mentioned before there are many different types of ICF block and you can find out information on all of them by visiting the Insulated Concrete Form Association. If you are serious about using this technology order their book. Insulating Concrete Forms for Residential Design and Construction, available from ICFA, includes an in-depth discussion of design principles, details, types of ICFs, field assembly, and performance and cost data.
You then choose the type you want by price, style, design benefits and/or availability. The majority of ICF manufacturers have some sort of Lego™ type interlock I chose Nudura because of availability in my area and ease of use. The web centers that hold the block together and hold the reinforcing rods in place are already installed on the block and do not have to be separately inserted except on the specialty pieces like corners and “T's.” The webs are hinged so when the block is pulled apart they extend as wide as the webs allow: 6”, 8” etc. (As well, the cleats are large and they lock better than other brands. They don't break off as easily either.) The shrink-wrapped bundles contain four (4) 6-foot sections encased in shrink-wrap which makes them easy to load and store. Some manufacturers, such as Intregra-Spec, package their wall units and webs separately which also makes for good portability. Other products include: Arxx, LOGIX, Polysteel, Fold-Form, ECO-Block, Premier, BuildBlock.
The most important consideration for using ICF is the budget which should not be decided only by the price of the block. Other ICF building costs include steel reinforcing, bracing, cement and pouring surfaces and accurate estimations from the sub-trades. A lot of time and money can be squandered by bringing in subs that are not used to working with ICF. (Large mistakes can mean drilling large holes for plumbing and conduit, or even taking out a cement-filled wall.) So make sure you have trades who can do the job right and on price.
According to the ICF Builders Network's website here are the best specs for ICF: The block should be readily available locally and have good distributor support for both supply and technical advice. Delivery should be included in the deal. Even though the product is light, it is very bulky in large quantities. The block design should be able to support the architectural ideals of the customer. This is, if they want decks, for instance, there should be an available support system to accommodate the decks. The block should be manufactured to strict tolerances so that every piece is identical. The block should be strong enough and have enough webbing support so that there are no weak spots that require excess strapping for vertical support. The block should be designed go together in minimum time with minimum alterations. Slump concrete placed with boom pump should support 4’ lifts of 6” at 1 cu yd / minute. The slump is used to determine the consistency of concrete. A high slump value is indicative of a more fluid concrete. The wastage of the block should be minimal; 2-3 blocks a project. The block is durable enough to withstand voids, blowouts, and moderate handling force. It is a standard block, one that does not cause extra labor and modifications because of an unusual design. (Unless you are experimenting, but few homebuilders are in the category) The block can take the pressures of directed concrete flow and fill the walls without deflections or bulges. The blocks are easily cut without special power tools. (One problem we had with the fixed, hinged webs was that, to get a single wall portion we had to cut the plastic web) The block has highly visible markings for affixing drywall and siding and for cutting.

The following pictures show a few scenes from my first build. It is a do-it-yourself project with help from a qualified installer.

In this first photo you can see the large, interlocking cleats and how the product is shrink-wrapped for easy portability. The material is a high-density polystyrene form (EPS) and each form is 12 sq.ft of wall area. Typically the wall provides an insulation value of R22 and 3 hour fire rating resistance. There are also specialized 90 and 45 degree pieces for the corners. The standard form units have external dimensions of 96" in length and 18" in height with an

overall wall thickness of (11 1/2") which in turn encloses a (6 1/4") thick concrete wall. The EPS sides of the unit are (2 5/8") in thickness. The black pieces are the webs which are molded in the walls of the block and provide anchoring for siding and drywall screws.		As with any building project good footings are needed to support the structure. With ICF building, vertical reinforcing is needed to hold the walls onto the foundation. This is a heavier gauge steel than the horizontal rebar and will be wire-tied to ones extruding from the foundation.

The first row of block is put down and held into position by 2 X 4 inch strapping on each side. This is easily nailed into the green cement. Care must be taken to make sure the first row is level. A laser transit works well for this job. As with any project, if the first row is out of level the mistake gets bigger as the wall goes higher.

Each new layer of block is staggered over the one before (just like Lego™!) and reinforcing rod is then snapped into the tailor-made hooks in the web. The steel rods are overlapped by two-feet on the ends for continuity of strength. The manufacturers supply tables for the gauge of steel for reinforcing and the amount of it that will go into the walls. These tables have wall widths, designated headers above the windows and doors, and threshold tolerances.		Once the walls are up four feet it is usually ready for the first pour although seasoned installers can go up to as much as 14 feet and higher. It is essential that the walls are braced using the specifications laid out by the manufacturer. “Blow-outs” are bulges that occur when the pressure builds up in an area that is not braced. I used wood bracing and strapping – and it worked well – however with bigger projects you should look into renting bracing and staging that is usually available from your ICF supplier.


The cement is dispersed by a pumper truck and the crews use either mechanical vibration or manual stimulation to make sure the cement gets into every place. Vibrators ensure an even spread of the cement into all the crevices and are helpful in preventing “blow-outs.”		Before the pour window boxes are crafted and specially-bent reinforcing is used in the headers over the windows and doors to make sure these skinny areas can take the stress from the roof trusses. In this photo the radiant heat piping has been installed on the slab before the final cement pour.
The 2 x 4's are embedded into the cement floor to provide anchoring for the walls. The 3-story condominium complex in the background is constructed with ICF.


The trusses are anchored onto the tops of the eight-foot walls. Drywall is screwed into plastic plates which can be located by columns of patterns on the ICF. On the outside walls, siding is screwed on following the same patterns. (The pink insulation in the foreground is for a small, heated storage shed out in the back.)		This 1600 square-foot home is heated through 4-zones of in-floor tubing. The system is put together on an OSB board in the plumbing shop, in a controlled environment, and brought to the site where it is bolted onto the wall. This is very cost effective as it takes little time to hook up the labeled floor zones, hot water needs and electricity.
Notice the small electric tankless system that supplies the total heating and hot water requirements for the home.