Foundation Design Considerations

The first thing you need to pay attention to is the bearing capacity of the soil underneath the home. This directly impacts your design specifics and more about the structure you’re designing and attempting to build.

However, some people may not understand a lot about construction or what this means. Here’s how to pay attention to the soil bearing capacity. 

• Shear Failure

The concept of “shear failure” is integral to the soil’s bearing capacity. That’s because the bearing capacity defines the maximum average contact pressure between the soil and the foundation that’s unlikely to result in shear failure.

When the foundation causes too much shearing stress in the soil, it compromises the strength of the soil and its ability to support a structure. If you don’t pay attention to the shearing stress you’re causing, you risk running into shear failure.

The best way to avoid shear failure is to pay attention to the soil bearing capacity of the particular soil you’re dealing with. That way, you’ll expand the structure’s stability and lifespan. 

• Soil Classes

An important part of soil bearing capacity has to do with the soil class underneath a home. That’s because different soil classes will have different amounts of load-bearing pressure. It’s important that you take that into account when you’re choosing how to design a structure.

What soils do you need to be more careful with, and which ones can hold more weight? The International Building Code provides a list of soil bearing strengths you can rely on for general ideas regarding load-bearing pressure. 

• Using a Penetrometer

If you’re looking for an easy way to determine the soil bearing capacity of a certain area more accurately, you may want to consider a penetrometer. This is a hand-held tool, making it convenient to use anywhere, and it helps you measure the pressure the soil can resist.

It’s important to remember that a penetrometer can generally give you an idea of the soil-bearing capacity. However, it’s not necessarily as accurate as a more professional but less portable tool. It’s not 100% foolproof.

You can learn a lot by consulting with a geotechnical engineer regarding this information. If you’re planning to build an entire home, you might just want to talk to a geotechnical engineer to get a better idea of what’s going on in the soil near the area you’re planning to build.

The next thing to take into account is the type of foundation you’re working with. The design considerations of a shallow foundation will be much different than the considerations in a deeper foundation.

Which one are you working with? What do you need to pay attention to? Here’s everything you need to know. 

• Shallow Foundation

A shallow foundation is a type of foundation that transfers the structural load to the earth that’s very close to the surface. There are many types of shallow foundations: you may find concrete footings, spread footing and mat-slab foundations regarded as shallow foundations.

Shallow footing design can be a completely acceptable decision for home foundation design. However, design consideration of a shallow foundation needs to take into account the fact that the home will be more prone to settling if not crafted properly.

With a shallow foundation, it’s even more important that you maintain your weight load to the proper amount. Otherwise, you’re certainly going to end up with a home that eventually sinks and settles into the ground. 

• Deep Foundation

As opposed to a shallow foundation, a deep foundation transfers the structural load to earth that’s much further into the surface. Typically, this is done to help avoid the design considerations of a shallow foundation that would allow for less weight.

A deep foundation often uses a pier foundation, such as push piers or helical piers. The piers push far underneath the structure and are installed directly into the load-bearing rock far underneath the home. That maintains the structure more fully.

Deep foundations can certainly hold much more weight than shallow foundations. However, they may not be necessary for all homes, especially if the home is relatively light and on a type of soil that can hold a substantial amount of pressure.

• Can You Change a Foundation Type?

What if you run into problems with your shallow foundation and want to change it into a deep foundation? Is it possible for you to cut off issues you’re having with shallow footing design by simply changing the home into a deep foundation?

Although it’s not always simple, it is possible. A JES expert can install a pier system underneath the foundation to essentially “convert” it from a shallow foundation into a deep foundation.

This process can be incredibly effective if you’re dealing with a home that’s trying to bear too much weight. Especially if you notice the home is starting to sink near the end of the building process, you will want to talk to a JES expert to see whether you can use a pier system to push the home back up.

The home’s weight is itself an important thing to take into consideration. There are many things that can contribute to a home’s weight, and it’s important to take all of those into account when you’re the one building the initial structure.

How does building weight impact the way you deal with foundation design considerations? Think of these important things. 

• Beautiful Design, Heavy Structure

One of the things many people don’t realize is that the building materials you choose have significantly different amounts of weight. In many situations, the more “beautiful” design materials like stone and marble will add a substantial amount of weight.

It’s important that you balance the “beauty” of the design with the fact that the home must be able to sustain those design choices. When you’re crafting a design, after all, that design will typically stay with the home for a long time.

If you really want to stick with some of these heavy and beautiful materials, consider going with a deep foundation right off the bat. That way, you don’t have to handle the design considerations of a shallow foundation. You can go into it with a deep foundation.

• Consider Real and Theoretical Weight

You don’t just want to think about the amount of weight you think will happen in the home on average. You also want to prepare for typically excessive amounts of weight. Sure, maybe the soil under the home can technically handle the weight of the home you’re building on top of it, but what about a family and all their belongings?

It’s never a good idea to max out the weight you’re putting on the foundation. The load-bearing weight chart in the International Building Code isn’t a recommendation for the amount of weight to add; it’s an upper limit you should keep in mind.

Always aim to keep your weight far below the high end of this framework. If you find that the weight is starting to climb to the higher end of the spectrum, consider talking to an expert to find ways to lower it.

• Think About Current and Future Projects

You know what you’re installing right now. It’s easy for you to consider the weight in the home as it stands. However, do you know what you or the homeowner will want to do with the home’s structure in the future?

If you’re leaving certain things unfinished or less finished than other areas of the house, it’s possible that the homeowner may want to add onto it. How will that future project affect the factors that need to be considered regarding foundation design?

Remember, you want to build a home that will last. These key design considerations should be top of mind when building the foundation and ensuring its longevity in the future.

Weather is a hugely important thing to keep in mind. In fact, while it’s rarely included among foundation design considerations, it’s one of the most crucial factors to consider because it can have a significant impact.

What are the most important types of weather to think about when you’re trying to understand home foundation design? Always note these weather conditions. 

• Rain and Drought

Soil expands when introduced to rain and shrinks when it dries. That’s natural, and it’s something you’re not going to be able to avoid altogether. What you can do, however, is prepare for it.

You need to consider whether, for example, the soil a home sits on is especially expansive soil, meaning it expands more than other soils when introduced to rain. If it is, you’ll need to introduce additional security measures to avoid home settling when it dries out.

Home settling will happen to pretty much every home to some extent, but it’s your job to make sure it doesn’t happen too much. That’s why you need to think about it.

• Potential for Flooding

This is both a natural and an infrastructure question. It’s up to you to make sure you build a structure with a sufficient drainage system, but you also need to take into account the area’s natural tendency to flood and the existing infrastructure in the area.

When an area floods, you’ll end up with substantially more hydrostatic pressure built up around the home’s crawl space or basement, and potentially even around important parts of the home’s main structure.

Take into account past flooding incidents and experts’ suggestions regarding future flooding incidents. Additionally, always make sure you incorporate the most up-to-date foundation design considerations regarding drainage systems. 

• Water Table

The water table is an important part of understanding how you’re going to best craft a drainage system that works for the home you’re designing. That’s because the water table, which represents the area where groundwater will naturally saturate an area, can change throughout the seasons.

For example, if you’re going to build a home on soil, you need to make sure it’s above the water table at all times. Otherwise, if the water table rises during the winter, you may find that the home ends up being flooded or nearly flooded.

This is something you need to take care of when you’re first surveying the site. If you don’t do your due diligence in surveying the site, you may end up with serious drainage problems that’ll happen for the rest of the time the home exists.