Concrete is strong but not as much as its reinforced counterpart. The best way to reinforce your concrete foundation is to add rebar. It will increase the overall tensile strength of your footing and allow it to support a heavier structure.
Before you pour your foundation, you will question yourself: “How much rebar do I need?” This post will explain how to calculate your rebar needs step by step.
3 Steps to Calculate Rebar Needed for Concrete Footing
You have to take the following steps to determine how much rebar you should buy for your foundation:
1. Calculate Linear Footage of Your Concrete Foundation
Let’s say your foundation is 100 feet long and 60 feet wide. The first thing you have to do is calculate the linear footage of your footing. Note that a linear foot is a one-dimensional measurement. It’s not the same as a square foot. So you have to add all sides of your footing instead of multiplying the length by width.
So, here is the formula: 60+60+100+100 = 320 linear feet. Now, let’s calculate how much rebar you need for this length.
2. Calculate the Rebar Needed for Your Foundation
Footings may have varying thicknesses depending on the soil type. They should be at least 12 inches wide if you build a house on clay, sand, sedimentary rock, or other soil with a load-bearing value between 1,500-4,000 pounds per square foot.
Typically, footing rebar requirements include one rebar for every 8 inches of footing width. Let’s say your footings are 16 inches thick. Given that, you need two rods through the width of your footings.
So you have to multiply 320 (the linear footage of your foundation) by 2 (number of rebar sticks required across the width of your footings). You will get 640 feet of rebar.
Typical rebar length includes 20, 30, 40, and 60 feet rods, and you can buy rebar of the desired length online. Let’s calculate how many rods you need based on typically available rebar lengths:
- Twenty feet – 32 rods.
- Thirty feet – 21.3 rods.
- Forty feet – 16 rods.
- Sixty feet – 10.6 rods.
3. Calculate How Much Rebar in Foundation Wall You Need
Building codes require placing rebar within every 4 feet of the foundation wall. The foundation walls stand on the footings and create space for the basement. Consequently, the total length of foundation walls will equal the combined length of footings. In our example, it’s 320 feet. So you have to divide 320 by 4, which equals 80. It is the number of slots for reinforcement across your foundation.
If your footings are 16 inches thick, multiply 16 by 80. You will get 1,280 inches or 106.6 feet of rebar. In total, your foundation will require 746.6 feet of rebar.
What Will Happen If You Add Too Much Rebar?
You may falsely believe that too many rods will make the building stronger. But it actually will make it more susceptible to failure. Too much reinforcement prevents concrete from distributing evenly, resulting in concrete-free voids inside the foundation. On top of that, steel rods change their volume with temperature fluctuations, and too many of them will create excessive compression force in the concrete. Eventually, the foundation will crack.
What Will Happen If You Get Too Little Reinforcement?
If the concrete doesn’t get enough reinforcement, it will crack even faster under tension loads. Pure concrete has a tensile strength of 300-700 psi, while reinforced concrete demonstrates 3,000-6,000 psi. An international building code for rebar in concrete specifies that concrete strength in foundation walls must be at least 3,000 psi.
So not enough rods mean your building won’t carry the designated loads. Your foundation and retaining walls will crack soon, leading to an urgent revamp.
Final Thoughts
Calculating rebar for your concrete foundation is easy if you know the parameters to consider. Keep in mind the total linear footage and thickness of your footings and foundation walls. In our example, a 100×60 foundation with 16-inch-thick footings requires 746.6 feet of rebar.
Article Submitted By Community Writer
