What Depth Do Footings Have To Be?
The first thing that needs to be understood is the difference between footings and foundations. A foundation is used when building a house or other structure such as a garage, shed etc. The purpose of the foundation is to support the weight of the structure while it’s being built. For example if you’re building a house, your goal would be to build up all of those walls so they form a solid wall with no gaps in them.
Then once the house is finished, you’d pour down concrete around the outside of the house. Once that was done, you’d use your new home as a foundation for another structure like a garage or even a swimming pool.
So how does one go about building up walls without using foundations? Well there are two ways: either you could dig out piles of dirt and then fill in any holes or you could lay bricks over top of the dirt and then pour concrete on top of that. Both methods will work but the method that works best is going to depend upon several factors such as where you want to place the foundation and how much space you need.
Footings are the foundation itself. They’re usually made from crushed rock (sometimes called gravel) which is placed into a hole in the ground and filled with soil. When you put down concrete, it goes around these footings. Both methods will work but one method is much faster than the other.
Footings are used when digging out soil or filling in holes. They’re typically made from crushed rock, sand and gravel mixed together to make a firm footing. Soil is usually dug out by hand and then filled in with concrete or brick (or sometimes both). The depth that these footings need to go will vary depending upon the type of soil you’re working with and sometimes the nature of your project.
If you’re just building a small deck, then you may need to dig out the soil a few feet in every direction but if you’re building something bigger like a house or other structure, then you’ll not only need more space to build but also more support. If you’re building a two-story house and you want to build a deck on the back, then chances are you’ll need footings that are at least 8 inches thick and reach at least 6-8 feet down. This is overkill but it’s better to be safe than sorry because if the footings aren’t thick enough or strong enough then they can cause a lot of problems later on down the road.
For the most part, each footing is going to need to be 2 cubic feet in size. Each cubic foot can range in size from a little bigger than a grapefruit to a little smaller than a basketball. It just depends on the type of soil that you’re working with and how deep you need to go. Concrete footings are measured by how many of these cubic feet can fit into a 10 foot by 10 foot area.
A 10 by 10 area can hold 100 cubic feet of concrete (which equals 1200 cubic inches). Concrete is heavy so if you need footings that are 12 inches thick, you’re going to need at least a 6 by 6 area (36 cubic feet or 1824 cubic inches).
If you don’t need your footings to be quite that strong, then you can cut back on the size somewhat but the thicker the footing, the more stable your structure is going to be. Keep in mind that if you’re building over soft or weak soil then your concrete is going to need to be stronger. The good thing about using footings is that they can be easily replaced if your house starts to sink.
How do you build sturdy footings and what tools do you need?
Step 1: Mark Out Your Area Show All Items
Measure out the area that you’re going to be digging in. The edges should be straight lines and it doesn’t hurt if they’re at 90 degree angles to each other. If you’re working with a sloping backyard, then you may find that the distance from the highest part of the ground to the lowest part is more than 12 inches. You’ll want to make each line at least 12 inches high so that when you fill in the area in between with soil, it’s still going to be above the 12 inch minimum.
The corners of your excavation area should also be marked out with string or a rope. You don’t need to measure the exact distance from each corner unless you plan on digging down exactly 4 feet in every direction. (If you’re digging a hole for a “residential” purpose then a depth of 4 feet is recommended because it’s deep enough to qualify as being buried according to most state laws) You can use the lines that you’ve already drawn and the strings to measure out the edges of your square or rectangle.
Step 2: Remove the Soil Show All Items
Using a shovel, dig down into the ground until you hit solid rock. It’s always recommended that you use a type of digging device but sometimes you just have to do things the old fashioned way.
Once you’ve hit rock, use the pick side of your shovel to loosen up the edges and then pry them out. Repeat this process until you’ve gotten all of the desired rock out of the way. You don’t need to dig down any farther than 6-8 feet unless you’re trying to get water out of a well or something similar.
Sources & references used in this article:
- Two-and three-dimensional bearing capacity of footings in sand (AV Lyamin, R Salgado, SW Sloan, M Prezzi – Géotechnique, 2007 – icevirtuallibrary.com)
- The effect of embedment depth on the undrained response of skirted foundations to combined loading (F BRANSBY, M RANDOLPH – Soils and Foundations, 1999 – jstage.jst.go.jp)
- Bearing capacity of footings over two-layer foundation soils (RL Michalowski, L Shi – Journal of Geotechnical Engineering, 1995 – ascelibrary.org)
- Experimental investigation of impulse characteristics of transmission line tower footings (N Harid, H Griffiths, N Ullah, M Ahmeda… – Journal of Lightning …, 2012 – orca.cf.ac.uk)
- Strain influence diagrams for settlement estimation of both isolated and multiple footings in sand (J Lee, J Eun, M Prezzi, R Salgado – Journal of geotechnical and …, 2008 – ascelibrary.org)
- Settlement performance of pad footings on soft clay supported by stone columns: a numerical study (MM Killeen, BA McCabe – Soils and Foundations, 2014 – Elsevier)
- Behavior of embedded footings supported on geogrid cell reinforced foundation beds (TG Sitharam, S Sireesh – Geotechnical testing journal, 2005 – astm.org)