How Deep Should a Foundation Be For a House?

All you need to know about the required depth of a house foundation to build correctly

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 If you are planning to build your own house, you need to follow the construction codes precisely if you want the building to be legally approved by the authorities. And sooner or later, you will face a common question that comes during concrete foundation construction: how deep should a foundation be for a house?

Since not all of us are professional builders here, we find it useful to tell you more about this subject. From this article, you will learn more about the minimum depth of foundation building regulations, as well as how deep your house’s foundation should be depending on the foundation type. Also, we will explain why following these regulations is mandatory, and how you can tell that your foundation is not in a good condition right now.

 Concrete Footing Depth Requirements

Figuring out your home’s concrete foundation depth is a mandatory step on the way to your new home. Home foundations need to be at the required depths to support the structure above them. But many people find it difficult to figure out how to calculate the foundation depth correctly. So here are a few hints for you.

house foundation depth requirements
The importance of foundation depth. itishouse.com

First of all, you need to know that house foundations have different depths. The depth of a house foundation will vary depending on certain factors, for example, the number of floors or the material used for the foundation. However, there are some common types of foundation and their recommended depths:

  • The basement foundation should be at least 8 feet deep
  • The crawlspace foundation should be at least 18 inches deep
  • The concrete slab foundation should be at least 18 inches deep
  • The depth of a wood foundation should be at least 1 foot
How Deep Should a Foundation Be For a House?
By vista.com

Another factor that influences the foundation depth is the number of floors in the house. Here are the corresponding foundation depth requirements for the houses with the different number of floors:

  • 1 floor: At least 3.5 feet below ground level
  • 2 floors: At least 4 feet below ground level
  • 3 floors: At least 5 feet below ground level
  • 4 floors: At least 6 feet below ground level
  • 5 floors: At least 7 feet below ground level
Three-storey cottage
By vista.com

Finally, there is one more nuance that may affect the depth of your home foundation that people often tend to forget about. See, the type of foundation used in your house can differ depending on the location of the property. For example, 96% of homes in the West South Central region in the United States used concrete slab foundations in 2015. On the other hand, the East North Central and Middle Atlantic regions had full or partial basements for their foundations because of the colder climates.

Of course, these are just some general numbers. This is why below you can find a piece of more detailed information on how deep foundations need to be depending on the foundation type.

Basement Foundation

How Deep Should a Foundation Be For a House?
By vista.com

Using this type of foundation is quite popular because it gives people some extra space that can be used either as a living area or as storage quarters. So if you are planning to build a basement foundation, note that according to construction codes, a full basement foundation needs to be at least 8 feet deep. 

At this depth, it will be able to provide an underground living area that matches the surface area for the rooms found at ground level. Moreover, when you are planning to build a basement foundation, you need to note that footings have to be at least 1 foot below the frost line and at the same depth for previously undisturbed soil!

Crawlspace Foundation

How Deep Should a Foundation Be For a House?
By itishouse.com

For those of you who don’t know what a crawlspace is, it’s a space under the first floor of a house with a height that is not high enough for an average person to stand. Crawlspace foundation depths should follow regulated codes, such as Figure R403.1 (3) of the International Code Council (ICC). This code states that the depth of this type of foundation should not be less than 18 inches.

This comprehensive code compiles all building, plumbing, mechanical, fuel gas and electrical requirements for non-commercial one- and two-family dwellings in one convenient code. The regulations cover dwellings and townhouses up to three stories. 

codes.iccsafe.org

How Deep Your Concrete Slab Foundation

To be able to define how deep your concrete slab foundation should be, first of all, you need to know that this foundation type commonly comes in three variations:

  • T-shaped foundations that are used for supporting the home
  • Slab-on-grade foundations (often used for the kinds of ground that don't freeze)
  • Frost-protected foundations (only good for heated structures)
How Deep Should a Foundation Be For a House?
By vista.com

Concrete slabs should be not less than 18 inches below ground. Also, the thickness of each slab should be no less than 9 inches and the width should be at least 24 inches. Also, if the house is above the clay, the footing width should increase to at least 30 inches.

Wood Foundation

Treated wood is often used by builders as a stable foundation material for different homes. At this point, we must remind you that not every type of wood can work as a foundation material for a house! But some types of wood, such as Cyprus, can effectively support heavy structures!

As for the depth of a wood foundation, it should not be less than 1 foot in-depth and should be below undisturbed ground. Also, some wooden foundations need steel supports. This is needed to increase the stability and security of homes, especially when placed in relatively low-quality soil.

So now you know how deep a home foundation should be and what it depends on. And since you are now aware of the depth range for the foundations of a different type, it will be easier for you to figure out how deep the foundation of your house should be.

Why Depth Of Foundation Matters

Some of you might be wondering why the depth of concrete foundations and other foundation types matters so much. Well, there are a few factors that make foundation depth really important:

  • A house with an improper foundation depth is more prone to damage
  • An improper foundation depth can lead to cracks in the walls
  • Improper foundation depth may lead to fractures

And this is not a complete list of problems you may face as a homeowner if the foundation of your house is not deep enough. read on to learn what else it can lead to.

How to Tell That Residential Foundation Is Bad

The foundation is literally the base of your home. This is why it must be durable and strong, as well as deep enough. If a house foundation is in a bad condition, it may lead to serious damage to the whole structure. Below you can find some of the signs that might confirm if your home is sitting on a problematic foundation:

Fractures

If you notice any foundation cracks, wall crevices, or floor fissures, those can be signs of a bad foundation. Of course, it is reasonably normal for homes to develop some cracks over time, but large gaps mean trouble! For example, the following must be taken care of immediately:

  • Gaps starting at ¼ inches
  • Fissures within the 0.20- to 0.59-inch length

Also, take it into account that, if you see horizontal cracks, they may indicate problems with excessive water pressure affecting your foundation. But you should be afraid of vertical crevices more because they mean that the perimeter is under significant pressure!

Descent

Homes on top of bad foundations or foundations with improper depth might sink or have settlement problems. For example, you may notice that your home has become lopsided or the angle of this unevenness increased gradually.

Should this problem occur, it often means that there are gaps in the foundation settlement. Moreover, these openings are generally vertical, causing houses to become unlevel. 

The nasty thing about this problem is that it’s quite hard to notice when it starts! So be attentive and if you see small ½-inch dips in a particular area of the house, don’t leave them unchecked and unfixed! Otherwise, the problem can worsen, causing the home to dip to 2 to 4 inches!

Door Malfunctions

This is another problem that homeowners face when they have a house with an improper footing depth. If you have a door that sticks or doesn’t open or close properly, it may be a sign that the particular doorway is misaligned. But if several doors around the house have these issues, it can mean that you have serious problems with the foundation!

With this information in mind, it will be easier for you to notice even the smallest flaws in your house’s functioning. Like that, you will be able to prevent the progressing problem when it has just begun to develop. 

So, you are now fully informed about all the information regarding house foundation depth. We told you how deep it should be and explained why different foundation types have distinct depths. In addition, now you have a list of the required foundation depth rates. 

Moreover, we shared some helpful facts with you that will allow you to keep an eye on your home foundation and notice even the smallest flaw the second it appears. With that, you will manage to fix it or maybe even prevent the problem, not letting it progress.

Facts

Here are some records for the deepest foundations in the world:

  1. The Burj Khalifa: The Burj Khalifa in Dubai, the world's tallest building as of my knowledge cut-off has a foundation that descends an astonishing 164 feet into the ground. This massive depth is necessary to support the skyscraper's height of over 2,716 feet.
  2. The Petronas Towers: The foundations for the Petronas Towers in Kuala Lumpur, Malaysia, which were the tallest buildings in the world from 1998 to 2004, go down 394 feet. They are supported by 104 concrete piles, each measuring about 5 feet in diameter.
  3. Shanghai Tower: The Shanghai Tower in China has a foundation that extends approximately 282 feet deep. The building itself soars to a height of 2,073 feet, making it the second tallest in the world as of my knowledge cut-off.
  4. Average Residential Home: In contrast, an average residential home in the United States usually has a foundation depth between 18 inches to 10 feet depending on the location and local building regulations. In areas with a deep frost line, the foundation might be even deeper to prevent frost heave.
  5. Unusual Foundations: Some houses, especially those in flood-prone or unstable soil areas, are built on pile foundations, where long, sturdy poles are driven deep into the ground to support the structure above. In these cases, the depth can be significantly more than the standard - reaching up to 20 to 60 feet deep or even more, depending on the site conditions.
  6. Foundation for The Statue of Liberty: A fascinating example of a deep foundation for a non-building structure is the Statue of Liberty. The iconic statue sits on a concrete and granite foundation that goes about 65 feet deep!

Expert Advice

  1. Consider Soil Type: Your foundation should reach a depth where the soil is stable. The type of soil on your site will greatly influence the depth of your foundation. For instance, clay soils expand and contract significantly with moisture changes, requiring a deeper foundation than sandy soils.
  2. Local Building Codes: Check your local building codes. They often specify a minimum depth for foundations, typically around 3 feet or below the frost line, whichever is deeper.
  3. Keep the Frost Line in Mind: If you're building in an area that experiences ground freezing and thawing, consider the frost line - the maximum depth where the ground will freeze. Your foundation should extend below this line to avoid frost heaving, which can damage the foundation and the structure it supports.
  4. Groundwater Level: Groundwater can also influence the depth of your foundation. A high water table may require a shallower foundation coupled with additional waterproofing measures.
  5. Load-Bearing Capacity: The depth of the foundation is also influenced by the load-bearing capacity of the soil, which reflects how much weight the soil can safely support. The more weight your house exerts, the deeper your foundation may need to be.
  6. Structural Requirements: Larger, multi-story buildings require deeper foundations than smaller, single-story buildings. Consult a structural engineer to determine what's appropriate for your project.
  7. Slope of Land: For sloping lands, stepped foundation can be a good option. The depth of the foundation will be varying in this case, deeper at the high-end and shallower at the low-end.

Safety

  1. Professional Supervision: Always make sure that the digging of the foundation is supervised by a qualified professional engineer or architect. Foundation work is not a DIY project and it requires detailed knowledge of structural engineering and building codes.
  2. Soil Testing: Before digging the foundation, perform thorough soil testing to determine its type and bearing capacity. This will help in determining the proper depth and type of the foundation.
  3. Safety Gear: All workers should wear the appropriate safety gear when working on the foundation. This includes hard hats, safety goggles, gloves, and steel-toed boots.
  4. Trench Safety: Excavations for foundations can be dangerous. Ensure that trench supports or shoring is in place to prevent the walls of the trench from collapsing.
  5. Weather Conditions: Be cautious of weather conditions that can make foundation work more dangerous. Rain can make the soil unstable, while extreme cold can make the ground hard and difficult to work with.
  6. Follow Building Codes: Ensure all work complies with local building codes and regulations. These codes are there to ensure safety and quality, and failure to comply can result in severe penalties.
  7. Underground Utilities: Before digging, check for the location of underground utilities such as water and gas lines or electrical cables. Hitting one of these during digging can have serious consequences.
  8. Emergency Plans: Have emergency plans in place. Workers should be trained on what to do in case of an accident or injury.

 

These guidelines should help ensure a safer work environment when digging the foundation for a house. However, it's always recommended to work with experienced professionals who are aware of all the necessary safety precautions. Safety should always be the number one priority on any construction site.

Frequently Asked Questions

How Long Do House Foundations Last?

House foundations last differently depending on the materials used. For instance, poured concrete slabs should last 80 to 100 years.

What Is The Strongest Foundation For A House?

Rock is regarded as the strongest foundation to build a home because certain types of rock like bedrock, limestone, and hard chalk have high-bearing capacities.

How Much Does It Cost To Put A New Foundation?

A new foundation under a standard $1,200-square foot home has an average cost range of $4,500 to $40,000.
How Does Soil Type Affect Foundation Depth?

Expansive, compressible, or unstable soils may require a deeper foundation to ensure stability and prevent settlement.

Foundation Requirements For 2 Story House
  1. The foundation of a 2-story house must be designed to support the weight of two floors, the roof, and any additional loads. This often requires a more substantial foundation compared to a single-story home.
  2. The type of soil on the property plays a significant role in the foundation requirements. For example, expansive clay soils may require a deep, reinforced concrete slab or pier and beam foundation, while sandy soils may be suited to shallower, spread footing foundations.
  3. The building codes in your area will dictate specific requirements for foundation design, including depth, width, and the type and amount of reinforcement needed. These codes are typically based on local soil conditions and climate factors.
  4. The foundation must be constructed to resist lateral forces such as wind and earthquakes. In areas prone to seismic activity, this may require the incorporation of specialized seismic design elements.
  5. A professional engineer should be involved in designing the foundation for a 2-story house. They will consider factors such as soil type, load-bearing capacity, and local building codes to ensure the foundation is safe and durable.
  6. Foundations for 2-story houses often require more extensive excavation and preparation than those for single-story houses. This can increase the cost and construction time, so it's important to plan accordingly.
  7. Proper waterproofing and drainage are also crucial for the foundation of a 2-story house. This helps to prevent water damage and maintain the integrity of the foundation over time.
     
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Comments

Nikita Sawayn:
Hi! Could you please tell exactly what a foundation depth be for a 2-storey building should be? Thank you very much!
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