Concrete block foundations are stronger and less expensive than poured concrete foundations, and they are easier to construct than other foundation types. However, flaws in construction can lead to issues down the line, so we recommend hiring a professional to install a block foundation. In this guide, we’ll break down block foundations, how they’re constructed, their pros and cons, and what to keep in mind if you’re considering one for your project.

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What Is a Block Foundation?

A block foundation uses stacked concrete masonry units, or CMUs, to create a solid base for a building. These hollow blocks are mortared together, often reinforced with steel rebar, and filled with grout for added strength. The entire structure rests on a poured concrete footing, which spreads the building’s weight evenly across the ground.

Check out the video below for a quick visual of footings and how they are constructed. General contractor Tom Silva watches a crew in Charleston prepare for and pour the footing for a home addition.

Block foundations have been around since the early 1900s. Around 1900, Harmon S. Palmer invented the first hollow concrete blocks, changing the game for builders and architects. Since then, they’ve become a popular choice for homes and structures because of their reliability and affordability. Concrete blocks are also easier to transport and work with than poured concrete.

CMU block foundations are surprisingly strong despite their modular design. The compressive strength of individual blocks means they can hold a significant amount of weight without cracking or buckling. Reinforcing the blocks with rebar and grout makes them even stronger.

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How Are Concrete Blocks Used?

Builders use these versatile blocks for a variety of structures, including the following:

Concrete block foundations can be used for almost any structure—as long as the builders establish the proper footing and abide by all building codes. They’re often used for basements and crawlspaces, too, but may require extra waterproofing compared to a poured foundation.

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Concrete Blocks vs. Poured Foundation

Both poured concrete and block foundations are durable and capable of supporting heavy structures. See how these two models compare based on cost, installation, strength, and more below:

*Cost data in this article sourced from Angi.

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Pros and Cons of Block Foundations

Block foundations are strong and easy to transport. However, they’re also more prone to leaking because of their structure. Here are the key pros and cons:

Pros:

• Strong compressive strength, especially with reinforcement
• Easier to transport and handle during construction
• Doesn’t require as much heavy machinery for installation

Cons:

• Less natural insulation, possibly leading to higher energy costs
• More sensitive to leaks because of multiple joints
• Requires more waterproofing and water mitigation than poured foundation

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How To Prevent Leaks and Cracks in Your Foundation

Water can be a foundation’s worst enemy. If you live in an area with heavy rain or snowfall, take the following steps to prevent your foundation from leaking and cracking:

• Check for proper grading: Make sure the ground slopes away from your house so water doesn’t pool near the foundation.
• Use a waterproof sealant: Apply a waterproof sealant designed for masonry or concrete blocks.
• Consider a waterproofing membrane: Products like PolyWall add an extra layer of moisture protection.
• Drill weep holes: If you notice persistent dampness, drilling small holes at the base of the wall using a 3/8 bit can help drain trapped water before caulking and sealing.
• Add drainage systems: For below-grade foundations, install exterior and possibly interior crawl space drainage to help manage water flow.
• Maintain gutters: Keep gutters clean and make sure your downspouts direct water away from the foundation.
• Manage your trees: Roots can interfere with foundations, so be cautious about planting trees too close.
• Install a sump pump: In areas with high water tables, a sump pump can keep your crawl space dry.
• Have regular inspections: Check for cracks or signs of wear and repair any cracks quickly.
• Get expert advice: For serious issues, consult a structural engineer or professional contractor.

For more basement waterproofing tips, check out the video below from This Old House:

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DIY vs. Professional Block Foundation Installation

While you can learn how to build a concrete block foundation yourself, we recommend hiring a professional. Your home’s foundation is a critical structural element, so mistakes can be costly. Construction errors can lead to instability, water damage, and expensive repairs down the road. 

Masons have the tools and expertise to get the job done right. They can assess the soil, calculate proper loads, and ensure adherence to local building codes. Professional masons hold licenses that demonstrate their qualifications and carry insurance to protect you in case of unforeseen issues. They may offer free foundation inspections, too.

Taking preventative measures to avoid water damage is crucial when installing a block foundation. Professionals should construct drainage channels around the structure’s perimeter before the project gets underway.

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Our Conclusion

A concrete block foundation is ideal for many structures because of its strength and durability. It can hold a massive amount of weight, and if it’s built and maintained properly, it can last a lifetime.

It’s best to work with a qualified professional. Contact a reputable contractor for an assessment and quote.

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FAQ About Block Foundations

Are block foundations good or bad?

When constructed correctly, block foundations are strong and durable. However, they do have some downsides. Proper construction, extra waterproofing, and good drainage are important for preventing water intrusion and cracking.

How long do block foundations last?

With proper installation and quality materials, concrete block foundations can last for 100 years or longer. Regular inspections and prompt repairs help extend their lifespan.

What is a block foundation made of?

A block foundation is made of concrete blocks joined with mortar. For added strength and stability, the blocks’ hollow cores may be reinforced with steel rods and poured concrete. 

Is a block foundation cheaper than poured?

Block foundations are typically cheaper than poured concrete foundations. A block foundation costs between $10 and $20 per square foot, while poured concrete costs $4–$25 per square foot for a slab or $10–$60 for walls. Your final cost will depend on the size and complexity of your project, as well as local labor and material prices.

Are cinder blocks the same as concrete blocks?

Modern concrete blocks are concrete masonry units (CMUs)—not cinder blocks. Cinder blocks were an older type made with coal cinders, which aren’t commonly used today. While people sometimes use the terms interchangeably, CMUs are the standard now.

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