Our DIY Addition: How to Construct a Fox Blocks Foundation

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The foundation of a DIY addition is probably one of the most important elements you’ll build. It will support the rooms on top of it and transfers the load of each room onto the ground below. When deciding what type of foundation you will build, there are many factors to consider, including the weight of the building on top of it, the bearing capacity of the soil below it, and the ease of installation. After mulling over each of these factors at the beginning of the construction process, we opted to go with a Fox Blocks foundation for our DIY addition.

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Traditional foundations are typically constructed by building a makeshift forms that hold the concrete as it dries. Those temporary forms are then removed after the concrete cures. A Fox Blocks foundation is similar in concept, but also very different. Fox Blocks, or Insulated Concrete Forms (ICFs), serve as a form for the foundation’s concrete, but remain in place. These forms act as support for the concrete as it dries and provide insulation surrounding the concrete throughout the life of the home.

Like a traditional foundation, a Fox Blocks foundation must be built on footings. To create our footings, we built temporary frames made out of scrap lumber inside an excavated trench which was dug deeper than our desired crawlspace depth. Rebar was placed inside the footings and set into the ground below to anchor the footings to the ground.

The area where we built our foundation was prone to water retention, so we added a drainage system around the perimeter of the DIY addition, with pipe going through the footing area to ensure that no water would get inside the crawl space after construction was finished.

In addition to rebar anchored into the ground, we also used metal reinforcements inside the concrete to strengthen the footings even further. This metal piping was placed around the perimeter of the addition and in four other concrete footings placed in the center of the addition area to support the new build in the middle.

 

The purpose of these footings is to support the foundation and prevent settling as the addition ages. The dimensions of footings needed in a new construction depend on the size of the structure that will sit upon them, the type of soil surrounding them, and the soil bearing capacity. 

After the temporary forms were constructed, the concrete was poured directly into the trench. We used a concrete truck to pour the concrete into the area, then we spread it throughout the trench to fill the entire space. A two-by-four was used to smooth out the concrete after it was poured to be sure that it was level all the way across.

As the concrete was setting, we added taller rebar into the wet cement, which will connect the footings to the Fox Blocks foundation that will sit on top. Each piece of rebar was spaced according to the Fox Blocks specifications so they would fit correctly into the space.

After the concrete had time to completely cure, we removed the temporary forms we constructed and filled in the remaining space in the trench with gravel. After that, it was time to construct the Fox Blocks foundation. These foam pieces fit together so easily! It’s like building with life-size Legos. Each piece interlocks with the other and can easily be cut to size using a hand saw.

We built some framing around the Fox Blocks to for some extra support while we poured the concrete. The supports were made from scrap lumber and were removed after the concrete had been poured.

When the Fox Blocks go together, they leave seams where the pieces meet and at the spots where you’ve made a cut. To seal these seams in and keep the wet concrete from leaking out, we filled those seams with expandable foam. The foam went all around the bottom where the Fox Blocks meet the concrete footings and any larger cracks we noticed.

The opening at the top of the Fox Blocks is pretty small, so we used a concrete hopper to funnel the concrete into the slots. A vibrating tool was also needed to make sure the concrete spread evenly throughout the Fox Blocks and that it reached all the way to the bottom.

The concrete hopper hooks right on to the concrete truck’s chute and works as a funnel to guide the concrete into the slots at the top of the Fox Blocks. It makes pouring the concrete into the forms a little simpler and a lot less messy.

After the concrete was poured, we leveled it off using a two-by-four the same way we did with the footings. and allowed the concrete to cure for a few days. After that, we removed the support posts and added treated wood along the top so the walls would have something to set on top of. 

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