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Sustainable Build

The Perfect Block Foundation

An ICCF block system made of recycled EPS foam proves easy to work with and less than the cost of a conventional concrete pour

As explained in the first post about the Hudson Valley River build GBA is following, minimizing carbon emissions is a primary objective. Therefore, limiting the amount of concrete used is key. For this reason, the BPC Green BuildersTrillium Architects team spec’d an insulating composite concrete form (ICCF) foundation, specifically The Perfect Block from Eco Building Systems.

Installing ICCF blocks
This project used roughly 1200 blocks and 130 corner pieces for a 5000-sq.-ft. foundation. The product comes in different shapes that include the standard block, corner pieces, and U-shaped blocks used to create other building features.

Project Manager Ben Bogie found The Perfect Block through Steve Baczek, who is a fan of the product. Manufactured in Arizona (and soon Virginia), it is made with ground recycled EPS foam that is mixed with binding agents and cement; the resulting block is roughly 87% insulation.

The difference between ICFs and ICCFs is that the latter is integral to the foundation system (vs. a way to contain concrete), meaning it forms part of the structure. Also, whereas ICFs are concrete cores sandwiched between two pieces of rigid foam, The Perfect Block ICCF is more like what Ben describes as “honeycomb cells.” In the case of this project, the foundation is a grid of 6-in. by 6-in. columns 12 in. on center, and 6-in. by 6-in. beams 12 in. on center—together, the vertical and horizontal structure create a latticework of support, or a screen grid. It provides continuous insulation and has an R-value of 28. Ben says the cost comes in just below that of a conventional concrete foundation wall. For this project, there was an increase because of current shipping costs; the material alone was $29K.

Cutting foam block with sawzall
The blocks cut easily with a handsaw or cordless Sawzall.

Installation is straightforward. The 4-ft.-wide by 10-in.-deep by 12-in.-tall blocks come palletized, are lightweight (about 40 lb. each), and are easily hand-lifted; they can be cut with a cordless Sawzall (or even a handsaw) and stacked directly on top of one another and secured with a foam adhesive—no running bond necessary.

Here, the bulk of the foundation is 6-ft. tall—that’s six blocks high. The crew installed #5 rebar on 24-in. centers (the rebar falls on the center of every other core) up to the height of the first three blocks (3 ft.). Then they tied in another piece with a 12-in. lap and stacked the final three blocks. Staggering the rebar in lifts meant they weren’t reaching up over 6-ft.-tall rebar to stack the blocks.

Getting the first course level and plumb is critical. The focus on consecutive courses is on being plumb; shims are used as the blocks get stacked to keep them on course. They are glued together with a continuous bead of adhesive expanding foam running the entire length of the wall on both sides and at the joints. The three-member crew stacked the entire foundation in two weeks. In addition to the speed at which it goes in, Ben notes another benefit: Due to the product’s coating, debris from cutting doesn’t  blow around the job site, which happens with standard EPS forms.

Stacking ICCF blocks
The first three courses are stacked onto 3-ft. rebar; concrete will fill the cores to lock wall, footing, and rebar together.

The one pitfall, according to Ben, is an engineer’s comfort level working with the product. In this case, the engineer’s plans called for #4 rebar 12 in. on center both vertically and horizontally. Instead the team went with #5 on 24-in. centers, which cut the schedule nearly in half. The engineer also spec’d a 1/2 in. of cement board on the exterior of the blocks because the ICCF manufacturer doesn’t have any test results to show the product’s performance in this environment. (Notably, they have a 23-year track record with no failures). The design-build team pushed back, feeling the precaution was unnecessary. Instead, they opted to use Rockwool Comfortboard on the exterior because they are confident it has enough compressive strength to distribute the soil-pressure load across the foundation wall.

Asked what he thinks about the system, Ben responds, “It earns its name, in my experience. We are looking at integrating it as a standard foundation for our future projects.”


Kiley Jacques is senior editor at Green Building Advisor. Illustration by Patrick Welsh. Photos by Brian McAward.


  1. user-723121 | | #1

    I have to wonder if this system is suitable for all soil types. In the Red River Valley of the north, 8" poured concrete walls are the norm with steel reinforcement. Water tables are high there seasonally and sumps run every couple of minutes in the spring and after heavy rains. Drain tile on both sides of the exterior footings is used. The RRV soils move a lot when frozen so the walls have to be able to withstand this.

    I like the system described here and the lower carbon footprint. Strength of this type foundation wall in demanding soils should be considered.

    1. jackofalltrades777 | | #3

      Most engineers will call for an 8" thick monolithic concrete pour wall for an ICF basement. Sometimes you MIGHT get away with a 6" thick wall but 90% of the time it's 8". So a honeycomb pour wall basement system would be a no-go in most areas. At least that is my take on it.

      I am not a fan of honeycomb walls for above grade applications, let alone below grade.

  2. boxfactory | | #2

    Would anyone have any experience with weather or not the cement that coats the bits of EPS, provides real world resistance to insects and rodents?


  3. steven765 | | #4

    I think the 1/2 cement board from the rim down to a few inches below grade is a good idea to protect from damage and give you a surface to screw/nail up stone veneer siding. Also just to protect the foam from weed trimmers, mowers and such over time.

  4. shumek | | #5

    There is a lot of experience in the use of this type of blocks in some parts of Europe, with Simprolit.

  5. Goodmanheat | | #6

    Honeycomb walls are fine below grade and above grade. This block is insect resistant. It does need to be water proofed because it absorbs water just like normal cocrete.

  6. ethan_TFGStudio | | #7

    This used to be called Rastra Block. I've lived in a Rastra block slab on grade home and can say it was quite comfortable.

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