14 Questions to Ask a Commercial Concrete Contractor Before Hiring
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The foundation is the first element of your structure to be constructed, supporting all other components.
As expected, a well-constructed foundation is critical to the lifespan of your structure. However, the type of concrete foundation is also of importance.
Slab foundations are one of the most common types used. This article will provide a full breakdown of everything to know about slab foundations, including:
Table of Contents
1. What Are Slab Foundations?
2. Benefits of Slab Foundations
3. Drawbacks of Slab Foundations
4. Types of Slab Foundations
This type of foundation is made of one flat concrete slab, usually poured directly on the ground over a layer of sand. Often, this slab doubles as the floor of the structure. The concrete pour for the slab is about 4-6 inches thick with rebar or wire mesh for reinforcement.
With foundations as simple as a slab, it can mistakenly be considered inferior. However, slab foundations benefit many projects, and here’s why…
Slab foundations have lower construction costs and are typically more affordable to install than others, like crawl spaces or full basement foundations.
They also require fewer materials, less excavation, and less labor, further lowering the bottom line.
Slab foundations are relatively low maintenance, as no concerns about moisture in crawl spaces or basement leaks exist.
If you want faster construction, slab foundations are the way to go. They can be poured in a day or two and require less time to cure than more complex systems, speeding up the overall construction process.
Since the foundation is poured directly on the ground, there is no crawl space for pests like termites or rodents to inhabit, reducing the chance of infestation.
Without a crawl space or basement, there are fewer concerns about mold and mildew accumulating in the structure from damp conditions.
Concrete has excellent thermal mass properties, which can help with energy efficiency by stabilizing indoor temperatures and reducing heating and cooling costs. The absence of a crawl space means fewer air leaks and better insulation, which contributes to even lower energy bills.
Learn more: Maximizing Energy Efficiency with Insulated Concrete Forms: A Comprehensive Guide
Concrete slab foundations are incredibly long-lasting, highly durable, and resistant to fire, rot, and insect damage, making them ideal for high-risk areas.
When properly installed, slab foundations settle less over time than pier or beam foundations, reducing the possibility of necessary foundation repairs in the future.
A slab foundation works well where the ground doesn’t freeze, as there’s no need to worry about frost heave or deep concrete footings.
Unfortunately, slab foundations have some downsides. These limitations and disadvantages make slab foundations inadequate for some projects.
Since plumbing and electrical wiring are often embedded in the slab, accessing them for repairs can be challenging and costly. Any issues that arise may require cutting into the slab, which is disruptive and expensive.
In buildings with a crawl space foundation, there is room to crawl under the structure and make repairs. Not so with a slab foundation.
Slab foundations don’t provide below-ground storage or additional living space like basements. This limits storage options, which can be a drawback in structures requiring extra space.
Also, if you plan to add rooms or modify the building in the future, the slab can limit your flexibility, especially when expanding plumbing or electrical systems.
Since slab foundations are poured directly onto the ground, foundation problems can arise from cracks due to soil movement, tree roots, or settling.
These cracks can weaken structural integrity or even allow moisture to seep through. While minor cracks can often be repaired, larger structural cracks may require more extensive fixes.
In colder climates, slab foundations can make floors feel cold, as there is no buffer from the ground. Insulating the slab or installing radiant floor heating can mitigate this. However, it will increase the project’s cost.
In areas with freezing temperatures, slab foundations must be carefully designed (such as with frost-protected shallow foundations) to avoid frost heave, which can cause significant damage.
In some climates, especially in humid areas, moisture can condense on the slab’s surface, making it feel damp. Vapor barriers can mitigate this, but again, at an added cost.
Also, since slab foundations are closer to the ground, they are more vulnerable to flooding in low-lying areas or regions with heavy rainfall.
Related: Why Are Vapor Barriers So Important in Concrete Construction?
Slab foundations make for unforgiving floors. Concrete is a hard surface, and when used as the base of the floor, it can be uncomfortable to stand or walk on for long periods. It can also be tough on dropped items, increasing the chance of breaking things.
Several different types of foundations fall under the “slab foundation” category. All use concrete slabs as the base, but each has distinct features, benefits, and disadvantages.
The best choice for your project would depend on the specifications of the site it will be built upon and the structure it needs to support.
In a monolithic (or continuous pour) slab foundation, the concrete is poured all at once, with the thickened areas under load-bearing walls and the outer edges of the slab acting as footings. This single layer of concrete forms a solid slab.
This slab foundation is best for a home’s foundation, especially in warm climates where the ground rarely freezes.
It also works well for single-story buildings or lightweight structures on flat, well-drained sites, such as:
A monolithic slab foundation can also benefit areas with a high water table that makes digging difficult.
These foundations are also speedy and cost-effective to install. This is because there is no need for deep footings.
However, they are less effective in regions with expansive soils or frost heave.
This type of stem wall foundation includes a footing poured below the frost line and a slab poured on top of the footing. The “T” shape provides extra support for the foundation in colder climates.
A T-shaped slab foundation is best for homes or buildings in regions with freezing temperatures, where frost heave could be an issue.
It would also benefit projects that require added stability — such as multi-story homes and heavier structures — as it offers more robust support.
These foundations are great for areas prone to frost heave and provide more robust support during wintertime.
The downside is that it is more expensive and time-consuming to build than monolithic slabs.
Designed to protect against frost, this slab incorporates insulation around the perimeter of the foundation to reduce the risk of freezing and allow the foundation to be placed closer to the surface.
FPSF foundations are most beneficial for:
Some of the advantages offered by these foundations include reducing excavation costs, allowing construction in colder regions, and protecting against frost.
The only downside is that it requires precise insulation installation, which is another cost incurred.
Related: Learn more about Construction Footings
When the entire foundation slab acts as a raft (spreading the load over a large area), this is known as a raft slab foundation. This method is used in areas with weaker soil, as the raft distributes the load evenly.
Because they come with a reduced settlement risk, these foundations are best for construction on weak or expansive soils (like clay), where the load must be distributed over a larger area.
Raft slab foundations have higher material and labor costs, making them unsuitable for smaller, lightweight buildings.
After the concrete has been poured and cured, post-tensioned slabs are reinforced with tensioned steel cables. The tension in the wires helps counteract the tensile forces that the slab may experience. These foundations are another option for areas with expansive or shifting soils like clay.
They can also be used for expansive residential homes, as well as commercial buildings with variable soil conditions and structures needing extra reinforcement due to load requirements.
Post-tension slabs are highly resistant to cracking caused by soil movement, so they are suitable in areas where other slabs might fail. However, they are more expensive and complex to install.
Related: Post-tension Foundations
A suspended slab foundation is an elevated slab above the ground, usually supported by piers, beams, or columns. The void beneath helps prevent direct contact with the ground.
These foundations are often used for sloped or uneven sites where a traditional slab would be impractical. They are also popular in areas prone to flooding, as the elevation helps keep the structure above water.
Multi-story buildings requiring a robust foundation with air circulation also use suspended slab foundations.
They are suitable for areas with poor drainage and allow flexibility on complex sites.
However, they are more expensive and labor-intensive to construct, requiring precise engineering.
Waffle slab foundations feature a grid of beams (ribs) in both directions underneath the slab, creating a “waffle” pattern that strengthens the foundation without significantly increasing its thickness.
They are best for large residential and commercial buildings in areas with expansive soils, and locations prone to seismic activity, as they provide excellent load distribution.
Projects requiring a lightweight yet strong foundation would benefit from waffle slab foundations.
Waffle slabs have an excellent strength-to-weight ratio and are ideal for expansive or shifting soils. Their disadvantages are that they require careful engineering and design, and cost more than standard slabs.
Related: An Overview of Slab Construction
Slab foundations are primarily straightforward, durable, and economical options for both residential and commercial construction. But they are just one option for a concrete foundation.
Contact FMP Construction today to discuss all your foundation options.
