Is That a LEGO House?
Updated: Dec 7, 2020
Skip to the end for time-lapse videos of the entire assembly!
We’ve tossed around the acronym ICF a lot, but we haven’t really gotten into exactly what that means yet. Simple version: ICF stands for Insulated Concrete Forms. These are small modular blocks consisting of two panels of Styrofoam linked by a (generally) plastic bar that are stacked like LEGOS in the shape of your house. In stacking them, a void is left in the center of the wall that is filled with concrete once the walls are assembled and the rebar is placed. The voids are most commonly 6” in average homes or 8” for larger structures, with 3” of Styrofoam on either side of the concrete which stays in place after to form insulation for the home. As you can imagine, this makes for not only an incredibly thermally efficient home, but also a super strong one. According to ICFMag.com, “compared to standard wood 2×6 construction, the six-inch core is in excess of nine times stronger and the eight-inch core is significantly stronger still.”
Living in what’s known as Tornado Alley made that strength a huge selling point for us. It was also one of the reasons we chose to use ICF forms for our roof as well as the walls, something which is less common due to the more cost prohibitive nature of the roofing panels.
Up to the point of taking delivery of the ICF forms, we’ve done all of the work ourselves from road building to excavation and to constructing the footers. The ICF wall and roof construction, however, we decided was better left to the licensed and bonded professionals. Our simple rectangle shape and small square footage simplify the task, but the complexity of the roof and extensive (and expensive!) bracing required really place this task beyond the weekend DIYer. Besides the scope and inherent dangers involved, it would take us many months to complete the task in equivalent person hours. And finally, most ICF suppliers require you to be trained/licensed to install their products before they’ll even sell the product to you.
Even though we already got all of the ICFs to the jobsite, the contractor still needed to bring in his tools and bracing equipment. Normally, this is brought in on a large utility trailer and unloaded at the jobsite.
But not ours. That would just have made things easy.
The long, narrow, and winding dirt road to our build site prevented easy access and unloading. The best our contractor could do was park ¼ mile away and forklift each item one at a time down to the jobsite. On other trips, additional items were brought in on a smaller trailer.
Building the first courses of wall happened fairly quickly since everything is at ground level. In no time at all we had the perimeter of our house defined. Over the next few days, the walls got higher and higher giving us our first glimpse of the shape of our house. There was no time to rest though; we had to plan out and install all of the conduit penetrations for our exterior lights, electrical outlets, air conditioning, exhaust vents, and fresh air vents while they built around us. It wasn’t difficult to install, just difficult to account for and exactly locate every single input and output. Once poured, there is no changing them. Sure, you can drill through 6” of solid high-strength concrete... but we’d rather not.
As the walls approached the top, the bracing was installed. It provides a catwalk for the workers up high but most importantly keeps the walls in place until the concrete sets. The foam itself is just as brittle as that common in product packaging. Without bracing, concrete would burst out of the walls like a broken dam. Though, there is still always a risk that the wet concrete will find another weak point in the foam joints... (Hmmm, does this sound like foreshadowing to anyone?)
Once the walls were complete, it was time for the roof panels. These bulky panels were awkward to maneuver on the ground, I can’t imagine how difficult it was to place 12’ up in the air. Yet our contractor team still completed the roof in 2 or 3 days. For us, it felt like magic to see the progress each time we stopped to check. Most of the projects we’d been working on up until this point had been large scale, or of a type where a day’s worth of work may not be readily seen, so it was incredibly satisfying seeing actual progress happening before our eyes.
Last but not least, the roof bracing was installed inside the house. Most ICF contractors have their own wall bracing but hardly any have ICF roof bracing since, as we mentioned earlier, ICF roofs are less common than walls. This heavy-duty bracing had to be rented by the contractor from a large city over an hour away. Picking those up, unloading, and setting up took several days. With that complete and lots of fine tuning including the rebar installation, the house was ready to pour!
Tune in next time for the lessons we learned about pouring an entire house’s worth of concrete!