What Is a Block Foundation? (2024 Guide)
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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 the pros and cons of block foundations, compare them to poured foundations, and show you how to keep your basement dry with effective water mitigation techniques.
What Is a Block Foundation?
A block foundation is constructed out of concrete masonry units, or CMUs. These hollow blocks are stacked on top of a poured concrete footing and mortared together to form the walls of your foundation. For added strength, contractors typically reinforce the hollow blocks with rebar—they insert vertical steel rods into the footing before it dries, thread them through the first few rows of blocks, and pour grout or another filler into the remaining empty space.
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.
Harmon S. Palmer designed the first hollow concrete blocks at the turn of the 20th century. Since then, American architects have frequently chosen concrete blocks for house foundations because of their compressive strength 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.
How Are Concrete Blocks Used?
Concrete blocks are used for a variety of structures because of their versatility. Common structures with concrete blocks include the following:
- Commercial buildings
- Concrete block walls
- Garages
- Landscaping retaining walls
- Mobile homes
- Residential homes
- Sheds
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 are often used for basements and crawlspaces but may require extra waterproofing measures compared to a poured foundation.
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:
| Factor | Concrete Block | Poured Foundation |
|---|---|---|
|
Cost |
$10–$20* per square foot, or $1–$2 per block |
$4–$25 per square square foot for slab; $10–$60 per square foot for walls |
|
Installation Time |
Longer; each brick needs to be individually installed |
Shorter; concrete is poured as one slab |
|
Leaks |
More susceptible to leaks because there are joints between blocks |
Less susceptible to leaks because it has no joints |
|
Strength |
Strong compressive strength, which means it can support heavier top weight |
Stronger laterally than horizontally, which means it can better withstand soil pressure |
|
Transport |
Easier to transport because concrete blocks are lighter than wet concrete |
More equipment is needed to transport, which can drive up the cost |
* Cost data in this article was sourced from Angi.
Pros and Cons of Block Foundations
Block foundations are strong and easy to transport. However, they are more prone to leaking due to their structure. Review the key pros and cons below.
How To Prevent Leaking and Cracking
For more basement waterproofing tips, check out the video below from This Old House.
DIY vs. Professional
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.
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 everything goes according to plan, it can last a lifetime.
To ensure proper sealing and drainage, homeowners should work with a qualified professional. Contact a reputable contractor for an assessment and quote.
FAQ About Block Foundations
Are block foundations good or bad?
Concrete block foundations can be a good choice due to their strength, durability, and ease of installation. However, they do have some downsides. Proper construction, extra waterproofing, and good drainage are crucial to prevent 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. Homeowners should inspect their block foundation annually for cracking or signs of water damage, reapply sealant periodically, maintain effective drainage around the foundation, and repair cracks promptly.
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?
Yes, 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?
Sort of. The concrete blocks used today are concrete masonry units (CMUs)—not cinder blocks. Cinder blocks were the original type of concrete block, and they did actually contain cinders. Modern concrete blocks do not use cinders, so the term “cinder block” is technically outdated but still used colloquially.
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