The Minnesota State Building Code requires footings to be a minimum of 42” deep in the southern part of the state, and a minimum of 60” deep in the northern part of the state. The diagram below shows the dividing line.
How deep do footings need to be?
Footing depth - varies based on frost line and soil strength (some footings can be shallow, while other must be deep) Concrete Calculator - Figure out how much concrete you'll need for your footings.
How deep do decks need to be in Minnesota?
Decks constructed near wetlands will have an increased potential for frost heave. The Minnesota State Building Code requires footings to be a minimum of 42” deep in the southern part of the state, and a minimum of 60” deep in the northern part of the state. The diagram below shows the dividing line.
What is the minimum size of footings for a retaining wall?
Minimum footing size of 20 inches by 8 inches shall be placed on soil with a bearing capacity of 2,000 psf. Minimum concrete compressive strength of footing shall be 3,000 psi. Provide propped cantilever wall: top of footing shall be 16 inches below the bottom of the concrete floor slab minimum.
Do footings need to be above or below the frost line?
Your footings need to be below your frost line to ensure that the frost cannot penetrate and wreak havoc on your deck! Remember to check with your local building services department to find the frost line requirements in your region, or use the average frost line in your state listed above.
How deep is the frost line in Minnesota?
Here are the 10 states with the deepest frost lines: Alaska - 100 inches. Minnesota - 80 inches.
How deep and wide do footings need to be?
The minimum depth of footings below the surface of undisturbed soil, compacted fill material or controlled low strength material (CLSM) shall be 12 inches (305 mm). Where applicable, the requirements of CBC Section 1809.5 shall also be satisfied. The minimum width of footings shall be 12 inches (305 mm).
What is the standard footing depth?
Depth of Footings Footings should extend to a minimum depth of 12 inches below previously undisturbed soil. Footings also must extend at least 12 inches below the frost line (the depth to which the ground freezes in winter) or must be frost-protected.
How deep should post footers be?
By code, the bottom of a footing must be at least 12 inches deep and below the local frostline—whichever is deeper—and bear on stable, undisturbed soil that is free of organic matter. And the code requires a minimum compressive strength of 2,500 psi for the concrete.
Do you put gravel under footings?
You do need gravel under a concrete slab, footing, or patio. Gravel provides a solid foundation for your concrete as it can be compacted. It also improves drainage, preventing water from pooling beneath the concrete.
Do concrete footings need rebar?
Do You Need Rebar in Concrete Footings? Including rebar in a concrete footing means that you can reduce the risk of the concrete being pushed and pulled apart – cracking – from ground force pressures. Knowing this, it is generally a good idea to use rebar in footings for any structure.
What is difference between foundation and footing?
Foundation is a structure which transfers the loads from the superstructure to the ground, while footing is the foundation which is in contact with the earth. A foundation can be shallow and deep, while a footing is a type of a shallow foundation. so, all footings are foundations but all foundations cannot be footings.
What size footings do I need?
You can look up the recommended footing size, based on the size and type of house and the bearing capacity of the soil. As you can see, heavy houses on weak soil need footings 2 feet wide or more. But the lightest buildings on the strongest soil require footings as narrow as 7 or 8 inches.
What is the depth of concrete footings?
A concrete footing should be 100mm deep by 300mm wide if the footing is for a free standing wall. The footing should be increased to 150mm deep and 450mm wide if the wall being built is a retaining wall. For larger retaining walls an engineer may need to be approached for advice.
How long should concrete footing cure before putting weight on it?
Allow the concrete to cure for one day before constructing your deck or placing heavy weight on the footing (if standard concrete mix was used, wait about 3 days to begin construction).
Why do footers have to be below Frostline?
If footings are not placed below the frost line, they can heave in the winter when the ground freezes.
How do you determine frost line depth?
Testing the exact depth relies on instruments known as frost tubes that consist of a small hollow tube that is inserted into a drilled hole in the frozen ground. Testers put a bag of water with measurement indicators into the tube and determine the depth based on the line at which the water freezes.
How do you determine your footing size?
How to Calculate Footing SizeDetermine the width and length of the cement slab in inches.Divide the width by 12 to convert it to feet. ... Divide the length by 12 to convert it to feet. ... Determine the depth or thickness that is required for the footing in inches. ... Multiply the width by the length and then by the depth.
How do I know what size footing I need?
To determine the size of the footing, a simple formula is used: Structural Load (lbs) / Soil Capacity (psf) = Footing Surface Area Required (sq. ft.)
How deep should footings be for a 6 foot wall?
All footings should be a minimum of 150mm (6") in depth, with the bottom 350 - 400mm (14-16") below ground level on most soils. For clay soil however, thicker and deeper footings should be used.
What is the minimum depth of foundation?
As per Cl. 7.2, IS:1904, All foundations shall extend to a depth of at least 50 cm below the natural ground level.
How Wide an Isolated Footing Needs to be
An isolated footing is rectangular or square in nature. It usually supports a single structural column. In some cases it can support more than one column however this arrangement is not as common.
How Applied Load Effects how Wide an Isolated Footing Needs to be
We can now explore how the applied load effects the width of an isolated footing. Lets say that we wish to double our original load (increase from 1,500kN to 3,000kN), this means that the footing area will also need to double.
Final Thoughts
This article has been a very high level look at the sizing of footings. For a more thorough example including a step-by-step process on how to actually calculate the depth and width of an isolated footing, take a look at THIS article.
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Quentin Suckling is a full time practicing Structural Engineer based in Melbourne Australia. He has been practicing in the local market at tier 1 engineering consulting firms over the last 16 years. View more posts
How deep should a seismic slab be?
In Seismic Design Categories D 0, D 1 and D 2, interior footings supporting bearing or bracing walls and cast monolithically with a slab on grade shall extend to a depth of not less than 12 inches (305 mm) below the top of the slab.
What is the minimum compressive strength of concrete?
Concrete shall have a minimum specified compressive strength of f ' c , as shown in Table R402.2. Concrete subject to moderate or severe weathering as indicated in Table R301.2 (1) shall be air entrained as specified in Table R402.2. The maximum weight of fly ash, other pozzolans, silica fume, slag or blended cements that is included in concrete mixtures for garage floor slabs and for exterior porches, carport slabs and steps that will be exposed to deicing chemicals shall not exceed the percentages of the total weight of cementitious materials specified in Section 4.2.3 of ACI 318. Materials used to produce concrete and testing thereof shall comply with the applicable standards listed in Chapter 3 of ACI 318 or ACI 332.
How many inches of fill is required for a concrete stem wall?
Concrete stem walls that are not monolithic with slabs-on-ground or are not otherwise laterally supported by slabs-on-ground and retain 48 inches (1219 mm) or less of unbalanced fill, measured from the top of the wall, shall be constructed in accordance with Section R404.1.2.
What is the code for precast concrete?
Precast concrete foundations shall be designed in accordance with Section R404.5 and shall be installed in accordance with the provisions of this code and the manufacturer's installation instructions.
How high above the ground should a foundation be?
On graded sites, the top of any exterior foundation shall extend above the elevation of the street gutter at point of discharge or the inlet of an approved drainage device a minimum of 12 inches (305 mm) plus 2 percent. Alternate elevations are permitted subject to the approval of the building official, provided it can be demonstrated that required drainage to the point of discharge and away from the structure is provided at all locations on the site.
What type of steel is used for knee wall?
Fasteners used below grade to attach plywood to the exterior side of exterior basement or crawlspace wall studs, or fasteners used in knee wall construction, shall be of Type 304 or 316 stainless steel.
How far from the bottom of a foundation should a 4 bar be?
4 bar within 12 inches (305 mm) of the top of the wall and one No. 4 bar located 3 inches (76 mm) to 4 inches (102 mm) from the bottom of the footing.
What happens when you bury a footing in the ground?
Once your footings are buried below the frost line the ground will act as a barrier to insulate the soil below the footing from freezing in the winter.
Do you have to dig a foundation deeper than a flat surface?
If you are building into the side of a steep hill or beside a retaining wall you will have to maintain the minimum distance to grade not only vertically but also laterally. In order to achieve a suitable lateral barrier you may need to dig your foundation much deeper than on a flat surface.
How wide should a house footing be?
As you can see, heavy houses on weak soil need footings 2 feet wide or more. But the lightest buildings on the strongest soil require footings as narrow as 7 or 8 inches.
How does soil bearing capacity relate to the size of footings?
So, how does soil bearing capacity relate to the size of footings? The footing transmits the load into the soil. The lower the bearing capacity of the soil, the wider the footing needs to be. If the soil is very strong, the footing isn't even strictly necessary just the soil under the wall would be enough to hold the building up.
How much does a 12 inch footing weigh?
A 12-inch footing is 1 square foot of area per lineal foot, so the code is saying that the portion of a two-story wood house that bears on the outside walls weighs about 2,500 pounds maybe a little conservative, but reasonable.
Do masons need footings?
Regardless of bearing requirements, masons and poured-wall contractors want footings for their block or their forms to sit on. But the lesson to take is that when soils are very strong, (4,000-psf capacity or better), the footings may not be strictly necessary from the standpoint of bearing.
Do you have to do engineering on a house?
In practice, you don't have to do this engineering on most houses. The amount you'd differ from a standard code-compliant footing isn't worth worrying about. Unless you have retaining walls or some other special situation, an engineers fee probably isn't justified.
Why should water pipes be set below a frost line?
Water pipes should always be set below a frost line to prevent them from freezing in the winter. It’s also important that the footings for a building or a deck well below the frost line so the posts don’t shift as the ground freezes and thaws.
What is the best way to dig a hole?
An auger is the fastest way to dig holes and can save you a lot of time and money even with the cost of renting.
How deep is the frost line?
The maximum frost line depth is 100-inches as seen near the tip of Minnesota, North Dakota, and Alaska, all the way to zero inches in Florida, southern Arizona, and southern California.
Do sprinklers have to be buried in the ground when digging?
Anytime you are digging, it’s best to know the frost line as you will know how deep the water pipes are so you can avoid them. Here in Los Angeles where the ground doesn’t freeze, the irrigation and sprinkler pipes are not buried very deep, so you need to be extra careful when digging around them.
Who is Timothy Dahl?
Timothy Dahl. Timothy is the founder and editor of Charles & Hudson and former editor at Popular Mechanics, This Old House, and Lifehacker. His work has been published on Wired, Bob Vila, DIY Network, and The Family Handyman.
What happens when you break a footing in half?
When expansive soils grab on to the walls of a footing and pull it up, the bell at the bottom will hold the footing in place until the pressure exerted by the frost exceeds the tensile strength of the concrete. Once that happens, the footing will simply break in half.
How do deck footings heave?
How Deck Footings Heave. When a deck is attached to a building, the part of the deck that gets supported by the earth needs to have proper frost footings. The most common deck footing is basically a big chunk of concrete poured in to a hole in the earth. The goal is to have this chunk of concrete go deep enough in to the ground ...
What is the most common problem with decks in Minnesota?
One of the most common problems with decks in Minnesota is frost heave. Today I’ll explain how this works, why it matters, and what steps can be taken to help prevent damage from frost heave when building a deck. How Frost Heave Works. When expansive soils freeze and expand, the earth rises.
How deep should a footing be in Minnesota?
The Minnesota State Building Code requires footings to be a minimum of 42” deep in the southern part of the state, and a minimum of 60” deep in the northern part of the state. The diagram below shows the dividing line. While footings need to be deep enough in the soil to prevent frost heave, the depth of the footing is only one part of the equation.
How to stop soil from pulling up on concrete?
One step that can be taken to help prevent soils from grabbing on to the footing is to use waxed cardboard tubes for the footings, often referred to as sonotubes.
How to keep soil from grabbing on footing?
One step that can be taken to help prevent soils from grabbing on to the footing is to use waxed cardboard tubes for the footings, often referred to as sonotubes . The Family Handyman web site has a great cutaway photo of a footing with one of these tubes, used with permission below.
What is structure tech?
Structure Tech specializes in the moisture testing of buildings for the purpose of determining if there is moisture located behind the exterior wall cladding. A moisture inspection of your property has been requested.
How deep do footings need to be to prevent frost heave?
How deep do footings need to be to prevent frost heave? There’s no magic number. When there is a lot of snow on the ground, the snow acts like a layer of insulation and reduces the frost depth. When it’s a winter with very little snow, like the type Minnesota experienced in 2011-2012, the frost depth will be much deeper than usual. Outdoor temperatures obviously make a difference, and so does proximity to water. Decks constructed near wetlands will have an increased potential for frost heave.
What happens when you break a footing in half?
When expansive soils grab on to the walls of a footing and pull it up, the bell at the bottom will hold the footing in place until the pressure exerted by the frost exceeds the tensile strength of the concrete. Once that happens, the footing will simply break in half.
How do deck footings heave?
How Deck Footings Heave. When a deck is attached to a building, the part of the deck that gets supported by the earth needs to have proper frost footings. The most common deck footing is basically a big chunk of concrete poured in to a hole in the earth. The goal is to have this chunk of concrete go deep enough in to the ground ...
How to prevent heaved footings?
Another step to prevent heaved footings is to ‘bell’ out the bottom of the footing, as shown in the photo above. The ‘bell’ shape at the bottom prevents soils from pushing the footing up and out, but it can also lead to a fractured footing.
How deep should a footing be in Minnesota?
The Minnesota State Building Code requires footings to be a minimum of 42” deep in the southern part of the state, and a minimum of 60” deep in the northern part of the state. The diagram below shows the dividing line. While footings need to be deep enough in the soil to prevent frost heave, the depth of the footing is only one part of the equation.
What are the problems with decks in Minnesota?
One of the most common problems with decks in Minnesota is frost heave. Today I’ll explain how this works, why it matters, and what steps can be taken to help prevent frost hea ve when building a deck.
How to stop soil from pulling up on concrete?
One step that can be taken to help prevent soils from grabbing on to the footing is to use waxed cardboard tubes for the footings, often referred to as sonotubes.