Discover The Benefits of Insulated Concrete Forms (ICF) Foundations

by | Sep 14, 2023

A close-up photo of an insulated concrete form (ICF) block, which is a few inches thick foam sandwiching a thin plastic skeleton to hold the two sides of foam together. The concrete gets poured in between the foam over the plastic skeleton.

What are the benefits of using insulated concrete forms, otherwise known as ICFs and how does it relate to Net-Zero housing?

A Net-Zero house is insulated on all (6) sides, and Powerhouse designs with structural insulated panels (SIPs), so we have R-29 SIPs walls all around, R-49 SIPs roof above, and 4” R-20 foam under the slab-on-grade.

A diagram from a plan set depicting a cross-section of a footer detail. The text starting from the top and going clock-wise reads, "6.5" SIP panel, R29." "Housewrap." "Hardiplank." "metal flashing over ICF blocks." "concrete wall 6" above grade." The stem wall is shown as the portion starting where the concrete meets the wall plate to the top of the horizontal footer portion.  The horizontal footer portion is labeled as "spread footing." Under the spread footing is labeled "crushed rock." There is a circle within the spread footing on either side and is labeled "form-a-drain."  Above the spread footing is a label "Geotextile." Within the footing is a line that runs down the center and is labeled "rebar per engineering." On the outside of the footing is a label "ICF block 2-5/8" foam R23.6." Under the slab is the label "4" foam R20." The slab is labeled "4" concrete slab." Going up the wall are the labels, "1/2" PT ply plate." "2x fir." "12" J bolt spacing per engineering." "1/2" GWB."

Powerhouse Designs: Typical SIPs wall with ICF Foundation

The edge of the slab also needs insulation, otherwise there would be a weak spot and heat would leak out through the slab perimeter, into the stem-walls (which are exposed to the weather).

We solve this problem by pouring the stem-walls into R-24 insulated concrete forms (ICFs) which complete the insulted shell of this Net-Zero home.

A photo of 3 crew members placing insulated concrete form (ICF) blocks on a jobsite.

Concrete has been poured into foam wall-forms since the ‘80s. The hollow blocks go together like Legos with the required rebar clipped inside, and once full of concrete, the Styrofoam block remains in place performing the job of insulation, and containing concrete while wet. The process is fast and clean, and has lower labor costs compared to traditional concrete forming.

A photo of a crew member standing on top of braced ICF blocks holding a concrete hose and guiding the flowing concrete into the gap in between the foam.

We use NuDura R23.8 ICF blocks to form the stem walls, and retaining walls when we need them. The NuDura blocks are great since they concertina-down to transport. ICF blocks are available in many thicknesses with many variants for different construction requirements. We use 6” walls and usually only order inside-corners, outside-corners and 8’ straight blocks. The NuDura blocks have hard plastic structural strips that accept screws for siding and drywall.

A photo of the foundation form prior to insulated concrete forms. Shown is wood form lined with a material liner, two lines of rebar running the length inside and topped with hat-channels running perpendicular.

The blocks sit atop the hat-channel that spans the footing form. We use Form-a-Drain footing form when extra drainage is need and like the ICF’s does not need a form-board to be stripped-down after concrete is poured. The Form-a-Drain replaces 8” footer boards, is hollow, and drains water away from the foundation foot.

A close-up photo of the form-a-drain which is black pvc rectangular piping divided in the middle with 4 lanes of inch long slits running the length of the channel.

To protect the foundation, a metal cap/ cladding system is used that wraps the exterior ICF foam from the sill plate downwards below-grade with roofing metal, leaving no visually, or thermally exposed concrete.

A photo of the exterior a finished house looking at the corner. We can see that where the first floor ends and therefore the siding, starts brown metal ICF wrap.

ICF’s are great! They perform two functions: (1) insulation, and (2) concrete form, they are a smart solution for our thriving Net-Zero, and increasingly Net-Positive SIPs housing in Washington state!

A photo of a small foundation footprint, where the ICF blocks are all installed and braced, ready for the concrete pour.

If you have questions about ICFs or just want to get started designing your new home, contact us!

Edited by Nicole Miller