CONCRETE SLAB FOUNDATION
According to a report written by the Survey of Construction, 54% of new homes built have a slab foundation. Slab foundations are perhaps the simplest form of foundation you can have for your home. There is something reassuring about knowing that your house is standing on a large solid piece of reinforced concrete. On top of that, the relative simplicity of the design means that it is quick to pour and therefore one of the cheapest construction styles available.
A concrete slab foundation, therefore, has a number of key advantages over more complex foundation types such as pier and beam foundation or crawl space foundation. However, simplicity doesn’t mean that concrete slab foundations are better across the board. There are situations where a concrete slab foundation may be better in the short term, but limiting in the long term.
This guide will cover all aspects of a concrete slab foundation, from definition to cost, to the strengths and weaknesses, so you can make the call on whether it’s the right foundation for you and your home.
Concrete slab foundations are not complex. Put simply, they involve pouring a large amount of concrete into a designated space, then allowing it to dry.
However, it is slightly more advanced than that. The concrete being poured is usually about 4 to 6 inches thick in the center, tapering slightly towards the edge where it is slightly thicker.
In addition, sand is usually placed under the concrete before it is poured. This allows for water to drain, thus preventing future problems caused by hydrostatic pressure.
In some cases, you can install a concrete slab foundation yourself, although you will need a good level of experience – if it sets incorrectly, it is extremely difficult to remove, and you can’t build on a house with an improper foundation. Installing a concrete slab foundation is a relatively simple task for a team of contractors. If you outsource one part of your home construction, this would be it.
For a full breakdown of costs of different types of foundations, see our guide on Average Cost of Home Foundation, which will discuss in more detail all of the specific elements, from installation to repair.
For a concrete slab foundation, you will pay around $5 per square foot for installation. This includes the cost of the materials and the labor to install it. For an average-sized home, therefore, you will likely pay somewhere between $4,600 and $20,000 to install a concrete slab foundation. More often than not, costs are at the lower end of this scale. As a rule of them, you should expect to pay around $10,000.
PROS OF CONCRETE SLAB FOUNDATION
There is a reason why more than 50% of new homes are built with concrete slab foundations – contractors and architects use them as the default option.
Although there are some scenarios in which a concrete slab is not the best option, they have several major advantages over other types of foundation.
The most obvious advantage of a concrete slab foundation is that of cost. Because of their straightforward design, they require very little customization and therefore the costs are much lower than other forms of foundation. They also have very few additional pieces, such as a pier and beam, so the cost of materials is also lower.
Whereas you will pay between $10,000 and $20,000 for a crawl space foundation, and around $10,000 for a pier and beam, the costs for concrete slab are typically much lower.
Again, because of the simplicity of a concrete slab foundation, they can be installed in very little time. The actual pouring of the slab takes less than a day.
There is prep work to do in advance of pouring, although, assuming that the weather is cooperative, the entire process should take less than four days. This helps to keep the cost of the labor down, further reducing the overall price.
Unlike a crawl space or a pier and beam foundation, a concrete slab foundation creates a tight fit with the ground, preventing any space underneath.
This means that there is no capacity for moisture to get underneath your home (at least, if the slab is correctly installed and doesn’t crack) so mold cannot develop. It also prevents space for pests to nest.
In addition, since there is no airspace underneath your home, your utility bills can be reduced. With a crawl space, you will effectively have to pay to heat the air under your home. This means that, if you live in an area with a cold climate, you can end up spending a great deal of additional money on utilities if you do not choose a concrete slab foundation.
Although a concrete slab foundation doesn’t sound like the most glamorous or stylish option, there is actually a great number of ways that you can customize a concrete slab foundation.
The most common of these are stained and scored concrete. This allows you to put your own twist on your foundation.
CONS OF CONCRETE SLAB FOUNDATION
Although the pros are fairly substantial, there are certain limitations to a concrete slab foundation.
One of the major considerations is that concrete slab foundations work extremely well when everything is functioning perfectly, they can be extremely difficult to work with when there is a problem.
This is particularly true in three main ways:
LACK OF SPACE
The lack of space underneath a concrete slab means that there is nowhere in the foundation to place utilities such as piping, ductwork, or the electrical panel or wiring.
In a crawl space foundation, all of this is easily accessible in the space under the home. With a concrete slab foundation, it needs to be installed in the walls of the house, making it less accessible for repairs. In new homes, this is less problematic, although, as your home ages and repairs become ever more in need of repair, this can become an inconvenience.
The one thing that can be installed into the concrete slab of the foundation is the plumbing for the house. While this does keep it out of the way, it causes serious problems if it needs repair. To access the pipes, you will need to jackhammer the slab in order to get to the pipes. Compare this with the ease of access of a crawl space.
Furthermore, because the pipes are encased in concrete, it can be difficult to notice that you have a leak; in most cases, the only sign of a leak is that your water bill is higher than usual.
Concrete slab foundations are optimally designed to deal with force from above. They are extremely strong when it comes to load bearing. However, they are extremely susceptible to foundation cracks if they face lateral force. In earthquake zones, therefore, a concrete slab can be a dangerous option.
Concrete slabs can also crack when faced with fluctuations in temperature (particularly freezing) and moisture levels. This makes them surprisingly vulnerable to environmental conditions.
If you live in an area of freezing winters, or on a flood plain, then it is likely that a concrete slab foundation is not the best option for you.
WHEN A CONCRETE SLAB FOUNDATION IS THE BEST
Concrete slabs are the best options in very many cases. The most obvious cases are the following:
Where the ground is flat
If the ground is flat, then pouring the concrete is easy. If there is a slight slope on the surface, then you can re-grade the land slightly. However, for steep slopes, a concrete slab will not be the best option and you’ll need to look to pier and beam foundations.
Where you're on a budget
If you want a reliable foundation without breaking the bank, you can’t really go wrong with a concrete slab. It’ll stand the test of time without requiring too much upkeep. Concrete slabs are significantly cheaper than other forms of foundation.
In temperate climates
In climates with moderate winters (i.e. where it doesn’t regularly go below freezing) a concrete slab will help save your utility bills. In the mild summers, you won’t need the ventilation from a crawl space, so creating a tight seal with the ground to prevent moisture has less of an effect on your heating bill.
Ultimately there is a reason why a majority of new builds use a concrete slab foundation.
The ease of installation keeps costs down and avoids complexity in the construction process.
In niche circumstances – such as building a home on uneven ground, in a flood plain, or an earthquake zone – a concrete slab may not be the best choice.
However, in the vast majority of homes across the United States, a concrete slab foundation is a solid, robust choice.
A foundation does its job well when you don’t have to think about it. A concrete slab foundation is the epitome of this concept.
If it does fail, it can be tricky to work with; however, a concrete slab foundation will give you years and years of solid performance, where your foundation isn’t something you worry about.