Common Foundation Types and Why Should You Care

Deniz Kahramaner

Sep 29, 2022

Prelude

Deniz Kahramaner is the Founder & CEO of the data-driven Real Estate Brokerage Atlasa. His mission is to help home buyers understand the tradeoffs of different home options using big data and analytics. Feel free to reach out to Deniz if you need help with the home buying or selling process at deniz@atlasa.com.

Introduction

When looking to buy a home, the first thing you look at might be the bathroom, the bedrooms, the closet space, the size of the kitchen, and so on and so forth. More often than not, the thing that gets overlooked in real estate in favor of a quick buck is the most important: the foundation of the home. There are a few different types of foundations that a home may have, and not all of them are safe with consideration of the earthquake frequency in California. Here are the types of home foundations that you might see while looking for homes in the Bay Area or California in general.

There are two layers to the question of foundation: its form and its components. The form can be considered the “style” of foundation, which would include Perimeter foundation (crawlspace), Slab-on-grade, mat foundation or Basement. When it comes to the question of “components” of a foundation, that addresses the materials with which the foundation is made. These components can include things such as concrete, brick, or wood.

Foundation Types

There are three to four main forms of foundation that a home’s foundation may take. These forms include Perimeter, Slab-on-Grade, Mat Foundation, and Basement. Each of these types of foundations has its advantages and disadvantages and often is chosen based on environmental factors. Here are the different foundations and their details:

Perimeter Foundation

Perimeter foundations are often referred to as “Post and Pier” or “Pier and Beam.”
This type of foundation establishes a crawl space underneath the home through which one may access piping, electrical, and plumbing parts of the structure that would be difficult to access otherwise.
Perimeter is one of the older types of foundation and a method that was typically utilized prior to the 1960s.

Slab-on-Grade

This type of foundation has no crawl space and is, almost always, concrete.
Slab-on-grade is pretty much exactly what it sounds like. It is a flat concrete slab that functions as both the base of the home and the bottom floor.
Slab-on-grade (and concrete of foundations) was developed during the 1940s in response to the influx of returning WWII veterans in need of housing.

Mat Foundation

A mat foundation (sometimes called a raft) is a large circular or rectangular slab that holds the entire load of the building.
It is most commonly used for large high-rise buildings that are placed over poor-quality soil.
The slab includes reinforcements of steel rebar (as pictured above) placed before the concrete is poured over. This is used to reinforce the concrete and disperse the load of the building.

Basement Foundation

Basements, as one might have seen in a 90s horror film or two, are typically one or more floors of a building that are at least partially below ground level.
Basements are popularly created using concrete but have been made using other materials such as brick. This can be especially seen in Victorian or Edwardian homes in the San Francisco Bay Area.
Basements were commonly seen in newer homes in the 1950s.

Foundation Materials

Foundations can be made of multiple different materials, including brick, concrete, and wood.

Brick foundations are usually seen in Edwardian or Victorian homes, as it was regularly used prior to the mid-20th century. Atlasa has an entire article that talks about brick foundations and the dangers that come with them, which you can read on Medium here.

Wood is a common material used in the construction of a house and on occasions it could be used in full for the foundation. An all-wood foundation is considered to be cheaper, faster, and simpler to construct than concrete or masonry (brick) foundations and is rare to see. The downside to wood foundations is that it is much less durable, constantly need dry soil to be maintained around the base, and will not last as long as concrete or masonry.

Concrete foundations are typically seen in new constructions and homes that were built after the 1940s. These foundations are preferable due to the extensive earthquake-prone nature of the State of California. The struggle with certain types of concrete foundations is that over time as settling happens, the foundation can acquire cracks ranging from hairline cracks to major cracks that would need to be looked at by a licensed structural engineer.

Marina Concrete is another type of concrete used in foundations; however, it is rarely identified by inspectors since it has few properties that differentiate it from other concrete foundations. Marina concrete is different due to its sedimentary properties and is commonly found in older houses that have little to no steel reinforcement. The “Marina” name differentiates this concrete due to the usage of beach sand and can result in some surface deterioration over time.

Concrete Masonry Units or CMUs as commonly referred to by inspectors are the economical solutions for some structural elements. Some builders use the CMUs (also known as cinder blocks) as a foundation material but they can be used to build commercial walls and elevator shafts. If the CMU cells are not grouted, it could result in bulging in the middle due to the lateral load.

These materials are the main materials that one will find in the construction of foundations (at least in California) and, for numerous reasons, each has its advantages and disadvantages. Generally, the decision on what type of foundation should be used is not done arbitrarily and depends on a number of different factors. These factors, in a short list, include:

Climate
Lot Grade
Soil Type
Home Style/Design
Cost and Pricing
Utilities and Accessibility

How do I know if my foundation is good or bad?

In California particularly, a good foundation can never be over-emphasized, as the high frequency of earthquakes, shaking, aftershocks, and settlement can significantly damage a home’s foundation. That damage, which usually shows up in cracks, can be increased if a foundation sustained significant damage on top of the already existing cracks due to settlement. It can be incredibly expensive to replace a foundation. Thus, when buying a home, it is undeniably important that a potential buyer has a good idea of what the status of the foundation is. Similarly, as a homeowner, one should have good knowledge of the state of their home’s foundation, as its quality can negatively affect potential sale value in the instance any damage is not fixed.

During a home inspection, the inspector will typically observe the foundation whether by crawling into the subarea or in the garage, and will determine the type of foundation, as well as the condition. A good foundation typically will be noted to be in “serviceable condition” and may have some hairline cracks noted due to settlement. Each property is different, and while the wording can be broad, it is important to look at the accompanying photos. As you can see from the images below, this is one of those examples.

This property has some minor cracking due to settlement and efflorescence stains indicating that there was water present. The water had dried and evaporated into the concrete which left this mineral deposit.

Below you will find an example of a foundation that has experienced more significant settlement with worsening and bigger cracks.

There are many cases in which a foundation can be found to be lacking whether it be due to moisture issues, dry rot on the posts, or settlement cracks but in our experience, the most interesting solution was when a home was found utilizing a car jack as part of its foundation in place of a wooden post.

So what now?

Obviously, one can never truly know what is under their home until they take the time to look. Atlasa makes sure to look into all the pieces of a home — especially the foundation. The form of a foundation and the material that the foundation is built with is a significant matter. It is a factor in the home buying process that should not be understated or overlooked. The struggle with identifying foundations and their potential risks is an underreported challenge that we at Atlasa work day and night to conquer.

If you are entering into the buying or selling process, know that Atlasa has the real estate industry expertise and the transparent work ethic to find the right seller or buyer for you. We pay attention to details and we don’t overlook the things that matter. To get in contact with an Atlasa realtor about your current or future home, contact us now at [deniz@atlasa.com](mailto: deniz@atlasa.com).

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Deniz Kahramaner is the Founder & CEO of the data-driven Real Estate Brokerage Atlasa. His mission is to help home buyers understand the tradeoffs of different home options using big data and analytics. Feel free to contact Deniz if you need help with the home buying or selling process at deniz@atlasa.com.