How to Build an ICF Home

How to build an ICF home

Learn about the different components of an ICF house.

What are ICFs?

Insulating Concrete Forms are also known as “ICFs” and often referred to as “Insulated Concrete Forms.” ICFs are created by integrating a high-density plastic structural web embedded in two outer layers of Expanded Polystyrene ,”EPS”, or Extruded Polystyrene, “XPS” foam. This web provides a support structure for each side of the form and for reinforcing materials. The wall is created by sandwiching concrete between each of these layers. Designed to provide stronger, more comfortable, quiet and highly energy-efficient structures; they are easy to construct and their lifespan is hundreds of years longer compared to regular construction methods.

How are ICF Buildings Constructed?

Buildings are constructed using a running bond interlocking manner with the most common size of 4 foot long and 16 inch high blocks. Height and length may vary in some instances depending on the manufacturer. A cavity is created evenly spaced webs that give the block its strength. Thickness, or the width, of the cavity can vary from 4 to 12 inches or more. The most common wall sizes are 6 and 8 inches.  Most manufacturers offer corner blocks, 45 degree blocks, brick ledge forms and taper top blocks along with various accessories and fittings. Some blocks are fully-reversible, adding to the ease of construction. ICFs allow for unlimited design flexibility. Radius walls, multiple elevations, and other architectural features are easily constructed using ICFs.

Horizontal reinforcing (Rebar) is installed as the forms are being placed. Bracing or alignment systems made specifically for ICFs are installed when wall become too high to reach from the ground. These bracing systems have foot plank brackets for the placement of the planking to complete the stacking of forms. Concrete is poured, generally one level at a time.

The vertical steel is placed before each pour. If the structure above is a continuation of ICFs, a cold joint dowel would be placed to tie the next pour to the first. Most bracing systems have adjusting turnbuckles which allow the walls to be perfectly straightened as the pour is finished. Most companies offer training and technical support in addition to providing installer manuals, pre-engineered tables, CAD details, and engineering models.

Click here for a visual walk through of ICF construction.

BuildBlock Interior Wall Model

What are the Parts of an ICF?

Molded plastic webs are an integral part of the form technology. They are also the nailer or strapping, for interior and exterior finish attachments. Spacing for the vertical nailers can range from 6”, 8” or 12” depending on the manufacturer. The thickness of the EPS or XPS will vary between 1 ½”, 2”, 2 ½” etc. with the industry standard being 2 ½ inches. Testing shows that beyond 5” of foam (2 ½” on each side) the added insulation does little to justify the added cost due to the concrete mass’ ability to slow thermal bridging. Thermal bridging is the process of heat transfer through the path of least thermal resistance (R-Value).

Multiple floors are easy to install using special embedments made specifically for ICF construction. This keeps the floor system inside the envelope eliminating cold and hot spots. Temperatures are more even throughout the structure with very little difference between floor and ceiling. Window and door bucks are made of lumber, composite wood, vinyl or steel and can be premade and placed as the walls are erected.

How Strong are ICFs?

ICFs meet or exceed standards set by building codes. Because the EPS foam panels remain in place after the pour the building season can be extended in colder climates because the concrete is protected. The reinforced concrete inside the ICF forms provide a moist cure which creates much stronger concrete than conventionally poured walls that have forms stripped usually within a day of pouring.

Quiet & Disaster Resilient

ICF walls can withstand hurricanes and tornado force winds while keeping noise at a minimum. ICF walls have a Sound Transmission Class (STC) of 50 or higher, so noise stays outside or stays inside. ICF walls offer roughly a 70% noise reduction compared to an average home.

The majority of all ICFs are made using EPS as opposed to XPS material. There are two primary reasons for this: XPS has a lower permeability rating of water in the ground and EPS is inert, with no CFCs, HCFCs, Formaldehyde or any volatile organic compounds. XPS cells contain insulating gases in addition to air that eventually diffuse out of the cells, thus lowering the insulating value. The Long Term Thermal Resistance (LTTR) of XPS is therefore less than its “initial” R-factor.

The R-value of EPS remains constant over the life of the product because the manufacturing process uses normal air, rather than a special gas, to expand the beads in the product. Non-toxic, ICF do not emit VOCs nor do they off gas other chemicals like many engineered wood products.

Are ICFs Safe in a Fire?

ICF walls can attain up to a 4 hour fire rating using a flat wall system. The reinforced concrete can withstand very high temperatures and stay intact. Waffle grid or Screen Grid and Post and Beam are other form of ICF but are not as prevalent as the solid flat wall systems. They do create an affordable alternative in some cases.

Do ICFs Really Cost More?

The cost of ICFs is surprisingly affordable compared to traditional construction and can often be accomplished with little or no increase in cost. The national average of approximately three percent over the cost of wood varies by region, but the 40 to 70 percent savings on energy costs quickly offset the upfront difference and continues saving for the life of the structure. When you realize the lifespan for an ICF structure reaches into hundreds of years as opposed to an average of 80 years for a wood structure; the savings really add up.

When you stack and pour ICF walls they are almost immediately ready for interior and exterior finishes. Wood construction requires 2×4 or 2×6 studs, a bottom plate, two top plates, headers, jack studs, cripples, corner bucks, exterior sheathing, and house wrap. Additional caulking and sealing to close up voids after all that cutting, then fiberglass insulation and an interior vapor film if required. With ICFs you stack and pour and you’re ready, that fast.