Mature adult test question 1: Do you have life insurance?
Mature adult test question 2: Do you floss regularly?
Mature adult test question 3: Do you know what kind of foundation your home is built on?
Whether you consider yourself to be a full-on mature adult or not, wondering what kind of foundation your home is built on is really up there in the “things I never thought I would wonder about” category. But here we are . . . wondering about foundation types . . . nice!
In the United States, there are 3 very common types of home foundations. In Texas, there are 2 common foundation types with subtypes that we can tell you about.
If you’re wondering, “Who’s we?” Good question. We are Anchor Foundation Repair. We know a thing or two about home foundations because we have been fixing them for a good 35 years or so here in the Bryan, College Station, and Central Texas area.
This article will fill you in on the 3 common types of foundations in the US and give more details about the 2 common ones found in our state. Bet ya can’t wait to get started, but before we do, here’s the 3 common home foundation types:
- Slab-on-Grade Foundations
- Crawl Space Foundations
- Basement Foundations
All foundations have a few basic purposes for you. The first is to support the structure of your home. Foundations provide a way to keep groundwater away from you and the rest of your stuff. They also serve as a vapor barrier to both the water and soil under your home. These are all good things that keep your home solid, stable, and dry.
Ok, now we can get moving with some great “foundational knowledge” on the topic of common home foundation types.
1. Slab-on-Grade Foundations
Slab foundations are made with concrete and are poured onto the ground (aka grade). There are two different slab-on-grade foundation types: conventional and post-tension. We will go over what each of these foundation subtypes looks like, how they are made, and what they are good for.
Conventional Slab-on-Grade Foundations
Conventional slab foundations are the most prevalent of all home foundation types in Texas today. Slab foundations have been around and widely used since the 1950s. So if your home was built in the last 60 years or so, it’s probably a conventional slab-on-grade foundation.
Regular slab foundations can be most easily identified by the flat solid concrete piece that your home rests upon. You will see concrete near the ground on the outside perimeter of your home, you will feel concrete under the floors of your home. If you saw your home being constructed, you will see it as the footprint of your home on the ground shaped in concrete.
This type of foundation is made by pouring concrete all at one time directly onto prepared ground. The slabs are about 4 to 6” thick. A perimeter and grid of trenches are dug (looks a bit like an irregular waffle) to make the foundation. The concrete is reinforced with steel rebar throughout.
The edges aka “beams” of the foundation are thicker (from 24 to 30” or more). The beams go deeper into the ground around the perimeter of the home, while interior support beams tend to be less deep than the perimeter beams.
Building codes have changed over the years and older homes might have less thickness to all the support beams, making them more susceptible to movement. This is why the code has changed in later years.
Conventional slab-on-grade foundations are very popular in warmer climates like we have here in Texas. They are not used in colder climates where the ground freezes regularly and for long periods like in the northern United States. Generally speaking, they are easier and cheaper to install and are preferred by home builders because of this.
Post-Tension Slab Foundations
In the 1980s a newer slab style was developed called a post-tension slab foundation. This foundation type looks about the same on the outside as a conventional slab foundation for the most part. You would be able to see concrete around the outside edges of the home near the ground and feel/see concrete in the middle of the home.
The one way this type of foundation might look different is that you will see regularly spaced holes or pockmarks in the concrete sides (aka beams) around the edge of your home as shown in the picture.
The holes are there because of the way the slab is constructed with cables running in a grid throughout the concrete slab. The cables serve as the concrete’s reinforcement instead of using steel rebar like in the conventional slab. The cables come out the sides where the holes are located and then are trimmed once the concrete has cured.
A perimeter and grid of trenches are dug (still looks like a waffle, but the grid might be more regularly spaced) to make the post-tension foundation. A woven grid of cables is laid on top of and pulled through the concrete form boards. The cables are pulled tight into tension as the concrete is drying.
The engineering idea behind this technique is to make a slab that is more flexible to better handle expansive soils since the reinforcement cable is more flexible than steel rebar.
When this idea first started being used, many installers were not properly tensioning the cable which resulted in considerable movement and foundation failure rates. However, the method has come back into favor with an improved understanding of proper installation.
Post-tension slabs are a newer technique also for warmer climates. They are cheaper to construct due to the cost of the cable being lower than the steel rebar used in the conventional slab-on-grade method.
Homebuilders tend to like this cheaper cost, but there is some thought that this slab type is still not as durable as the conventional method. It’s too soon to tell because the method is just beginning to be used again in its improved form. We will know better in 20 to 30 years if the concept is living up to its potential.
Repairing Slab-on-Grade Foundations
There are two main methods for repairing slab-on-grade foundations. Both methods involve adding a system of vertical supports underneath the home. These supports go farther down into the ground to reach more stable soil conditions.
Most often, the vertical supports are installed underneath the perimeter of the home. But depending on where and how much foundation settlement has occurred, supports can be installed under the interior areas of the home as well.
One method or repair uses bell-bottom piers for this added support. The other method is called the pressed pile system. Each repair method has pros and cons, as well as different construction and installation techniques. We explain in detail the differences between the bell-bottom pier vs. pressed piles in another article if you’re interested.
2. Crawl Space Foundations
So far, we have talked about slab foundations that lay directly on the ground. Crawl space foundations do not lay on the ground but instead are elevated and have space between the ground and the bottom of your house.
An average crawl space clearance is 2 feet between the ground and your home and you can easily crawl underneath, hence the name “crawl space”. But there are definitely many homes built with both much shorter and taller clearance distances between the ground and the home.
Crawlspace-type foundations are typically found in older homes built before the 1950s. This was before the newer slab-on-grade technique became widely used.
There are two different types of crawl space foundations: block and base foundations and pier and beam foundations. We will go over what each of these foundation subtypes looks like, how they are made, and what they are good for.
Block and Base Foundations
The block and base foundation type looks like it’s “up on blocks”. You can see under the home all the way around and there are little stacks evenly spaced underneath the home elevating it. The stacks can be made of a variety of different materials like timber, stone, brick, concrete blocks, or poured concrete.
A simple skirting or latticework may surround the outside edges to make it look nicer. A good old farmhouse is likely to have a block and base foundation. This type of foundation is the oldest style currently seen in homes that are still in use. The home would be older, maybe built in the 1920s or earlier. But also new block and base homes can be found in more rural areas.
These foundations are made with a larger block buried in the ground and smaller concrete or stone blocks stacked on top of those and then probably some wood blocks or pieces on top of those to shim the house in place.
Since this is the oldest style of foundation, newer techniques have been developed that are an improvement. There is nothing wrong with this kind of foundation. They can be very long-lasting as evident in the houses that have been standing for a long time. This concept is still used today for mobile and modular homes but not usually in standard new home construction.
Pier and Beam Foundations
A pier and beam foundation is similar to the block and base in that it is elevated with stacked blocks or piers throughout the middle sections. But the outside perimeter of the house is supported with a “beam” or short wall of concrete blocks, bricks, or poured concrete on the outside that goes into the ground about 24” or less.
In other words, instead of skirting around the perimeter, it will be something more solid and every so often there will be ventilation holes along the foundation edges to let air circulate under the home.
This pier and beam method is a slight advancement over the block and base foundation and has more continuous support all around the edges of the home due to the perimeter “beam” made of more solid material.
Pier and beam foundations do allow space and air under the home, making it easier to access plumbing should there be a problem. This style of foundation has the potential to last a long time with periodic maintenance.
Repairing Crawl Space Foundations
Repairing crawl space foundations is different from repairing slab-on-grade foundation types. Since there is a crawl space underneath the house, repairs can easily be made by . . . wait for it . . . crawling underneath the home. This involves making adjustments to existing support blocks through shimming or adding new supports where ones have been damaged beyond repair.
Every 5 to 8 years this foundation type can be easily checked and adjusted to maintain proper elevation. That maintenance doesn’t always happen though and sometimes more involved repairs are needed.
Occasionally, drilled vertical supports are needed under the perimeter of a pier and beam home. The techniques used would be the same as for the slab-on-grade repairs with a choice of either bell-bottom piers or pressed piles. There are some pros and cons to those methods when using them on crawl space foundation homes.
3. Basement Foundations
What’s the best way to tell if you have a basement foundation? Don’t worry, this is an easy one. If you have a basement, then you have a basement foundation.
I guess there could be someone who has never seen a home with a basement. So just to explain, a basement is an underground level of your home that is below the main entrance at ground level.
You would go down a set of stairs to get to your basement. The basement is the same shape as what is above ground. Basements double the square footage of a one-story home due to this extra (hidden) level.
We don’t typically have basement foundations in residential Texas homes so we won’t talk about them too much. Basement foundations are better for colder climates where the ground regularly freezes and slab-on-grade foundations would not work well. That is why you don’t see them around here.
How do I know if there is something wrong with my foundation?
No matter what type of foundation you have, there are symptoms that you would see if the foundation were failing to perform. Here are a few of the kinds of things you might see around your home that indicate a foundation problem:
- Diagonal Cracks on Interior Walls
- Exterior Stair-Step Brick Cracks
- Doors Sticking or Not Latching
- Gapping or Separating Exterior Trim
- Movement of Interior Trim and Other Inside Fixtures
These true signs of foundation problems can show up in homes of all foundation types. One symptom that only shows up in crawl space foundation homes is loose and bouncy floors. Since the home does not rest on the ground, foundation shifting can result in floors that give and feel springy because there is nothing directly underneath them.
There are also some things that homeowners see around their homes that are false signs of a foundation problem.
What else do you want to know about home foundations?
There are so many ways to go from here. Do you want to know more detail about what exactly foundation repair means? Do you want to understand the causes of foundation problems? Do you want to hear about foundation inspections?
At Anchor Foundation Repair, we have been serving the Brazos Valley community for two generations and have repaired thousands of homes in the area. In addition to completing repairs for you when you need them, we have a mission to educate all homeowners about the world of foundation repair.
We do this so that you feel great about your choice of foundation repair contractors, even if it’s not us. For more solid information about foundation repair-related topics and services – all in easy-to-understand “non-industry” language – check out our full array of articles in the Learning Center.