Reinforcement of walls, footings, and floors

Reinforcement adds tensile strength to concrete. Concrete excels in compressive strength, but is weak in tensile; yet much of the anticipated loads on concrete walls, footings, and slabs are tensile! For this reason reinforcing steel is added. The combination of concrete and steel produces a product stronger than either one of them is alone.

Walls experience tensile loads from the backfill pressing on the sides. Without reinforcing steel installed, this will eventually cause the concrete to crack. The cracks will continue to grow larger as long as the load remains in place, eventually resulting in a failure of the waterproofing, misalignment from one side of the crack to the other, height differences in the wall, and even complete failure of the wall. The installation of re-steel in appropriate amounts reduces the amount of cracking, and stops the cracks from growing larger.

Footings experience tensile loads from uneven distribution of weight and uneven compaction/settling of soil. This causes the footing to want to "stretch" along it's length. Without re-steel, this load will result in a crack in the footing which will result in a crack in the wall. Eventually this crack can become quite large, resulting in height differences in the wall. The installation of appropriate amounts of re-steel reduces the amount of cracking, and stops the cracks from growing larger.

Slabs experience tensile loads from uneven distribution of weight, shrinkage/expansion, frost heaves, and uneven compaction/settling of the soil. This causes the floor to want to stretch, just like footings; resulting in cracking and large, misaligned gaps. The proper installation of appropriate reinforcement will minimize cracking and misalignment.

Commercial

At R-Value Concrete Structures, LLC we have been involved in commercial poured walls since we began. In fact, my first 10 years of concrete experience were strictly in commercial applications. Much of that experience was as a foreman. Perhaps then you can imagine my surprise when we began to pour residential structures and I learned what the industry standards were for reinforcement in walls, footings, and floors. In commercial construction it was normal to reinforce an 8" wall with #4 bar at 12" on center. A 16" footing would have 2-#5 bar continously. Slabs always had either wire mesh, fibermesh, or steel fibers. Nothing was ever poured without some sort of reinforcement! Commercial work is designed to last a long time with minimal cracking and no failures. Most of it is designed by a structural engineer.

Residential

In contrast to commercial, residential seemed ridiculously under-reinforced. It is quite normal to have zero reinforcement in footings and floors, and walls have minimal. The Michigan Residential Building code is confusing on this point. Table R404.1.1(1) allows a standard 8" poured wall to use no reinforcement if it is in sand; while Table R404.1.1(2) requires a #5 at 48" on center vertically. From what I have seen, it seems more contractors take the approach of the first table, just leaving a few short rod protruding from the footing, but not running the full height of the wall.

The first table; R404.1.1(1) specifies the required thickness of an unreinforced wall, based on it's height, backfill height, and soil classification. Table R404.1.1(2) specifies the reinforcement for a given thickness of wall based on it's height, backfill height, and soil classification. Yet the first table calls for no rod in an 8"x8' wall with 7' of backfill in sand; while the second table requires a #5 bar at 48" on center for a wall with the same specifications!? In an effort to understand why these two table read so differently I called an inspector and asked why. He was unable to explain it to me, except to say that they use table 2 for masonry walls. But the table heading clearly reads that each table applies to both poured concrete and masonry walls, even having different columns and specifications for each! So this explanation didn't sufficiently answer my question either. The inspector did say that he liked to see a vertical rod every 4' or so, but the size was undefined as well as the horizontal reinforcement.

Suffice to say that the code is rather unclear on wall reinforcement, and that the vast majority of contractors install an insufficient amount. There certainly are reputable contractors properly installing reinforcement, but one needs to search them out and ask how much rod will be installed on their project. Properly installed rod on a clay site can run an additional $4.00/lineal foot for an 8' wall; not to mention the $0.75/lineal foot for the footing rod. On a standard 32'x40' house, this adds up to nearly $700! This is one reason an ICF quote from R-Value is difficult to compare to a poured wall quote. We install a proper amount of reinforcement in both footings and walls by consulting engineering tables provided by the ICF manufacturers which meet (exceed) Michgan code requirements as well as my own commercial-bred expectations for what should be installed.

For our flatwork we highly recommend reinforcement, and use it whenever possible. I can only think of a few times in the last 4 years that we have poured a slab, approach, or sidewalk without some sort of reinforcement. This too makes our estimates higher than the competition. Wire mesh adds $0.25/sq.ft. to slabs, fibermesh adds $0.10/sq.ft. On the previously mentioned 32'x40' home, this would add $320 or $128 respectively. Of course these numbers are higher for most of the homes we build, since many are quite a bit larger.

Conclusion

R-Value is in this industry for the long haul. And this means that our buildings are too. We seek to provide the absolute highest in quality, understanding that it means taking a bit more time and effort, and spending some more on reinforcement. We aren't interested in building our walls, footings, and flatwork the way much of our competition does, even though it means our estimates will be $1,000 higher than someone using little to no reinforcement. The foundation of your home is it's most important part, yet it is the most difficult to upgrade later. A wise man will spend the money up front on wider footings and reinforcement to achieve enduring quality and ensure that his investment will last.

"The members of R-Value Concrete Structures have exceeded my expectations" --Adam Bearup, Hybrid Homes; an R-Value Customer