Crawl Space to Basement Conversion: Footings vs. Caisson Foundations
Expanding your home by converting a crawl space into a full basement can dramatically increase your living space. However, your home’s foundation type, whether footings or caissons, plays a significant impact on the approach to design, excavation, and construction.
In this post, we explore the key differences between traditional footing foundations and caissons (or pier) foundations. Understanding these differences can help you plan your crawl space to basement conversion project effectively.
With a footing foundation, typically 8-12 inches of space are lost, forming a slight “ledge” around the interior perimeter.
Digging out a Crawl Space on Footings
What are footings?
In homes built on footings, the foundation walls are poured on top of horizontal concrete footings that range from 16 to 24 inches in width. These footings bear directly on stable soil, spreading the weight of the house evenly to prevent settling. These footings run continuously along the perimeter of the house and beneath any load-bearing walls, providing consistent support across the home.
This design requires a careful approach when converting your crawl space to a basement to avoid compromising the existing foundation’s integrity.
Excavation to Convert a Crawl Space to a Basement
When converting crawl spaces with footing foundations, excavation must be done in phases to minimize structural risk and prevent undermining the foundation. During this process, a few square feet are dug at a time, while temporary shoring is installed to support the floor system.
Then, once the soil is removed, an interior wall of around 8 to 10 inches thick is poured along the inside of the existing footings. This slightly reduces the amount of usable space you’ll end up with in your basement, creating a “ledge” around the interior basement perimeter.
For really tight spaces, full underpinning can be used to lose less space (only around 3 to 4 inches). This is a more labor-intensive process and can be done in the cases where maximizing basement space is your top priority.
Learn more about the rest of the crawl space to basement conversion process.
Design Flexibility
With footings,
- There are more structural constraints. Footings rely on the surrounding soil for support, which means careful attention must be given to avoid undermining the foundation during excavation. This can result in less flexibility for digging deeper or creating taller ceilings, as well as challenges in altering the layout due to the need to preserve the integrity of the existing foundation.
- You will have slight space loss. Typically 8-12 inches are lost around the perimeter of your new basement because the walls must be poured along the inside of the existing footings. This creates a slight ledge around the interior.
Excavating below a Broomfield, CO home on caissons to convert the crawl space into a basement
Digging out a Crawl Space on Caissons
What are caissons?
Caissons are concrete piers used to support homes that are built on soils that are weak, expansive, or unable to bear the load of the house. These piers go deep beneath the unstable soils and transfer the load of the home directly to the underlying bedrock. In a caisson construction, the walls “float” between these piers and do not bear directly on the soil, resulting in better stability and reduced risk of settling or shifting.
This foundation type is especially used on homes built on expansive soils. Expansive soils are certain soil types that expand or swell when in contact with water, and shrink when dry. If in contact with a traditional footing foundation, these expansive soils would continuously shrink and swell, causing the foundation itself to shift and crack. So, caissons are commonly used in these expansive soil areas here along the Front Range where other foundation types aren’t compatible.
Excavating Below a Home on Caissons
When excavating below your home to convert your crawl space to a basement, working with caissons is often easier and more efficient than working around a traditional footing foundation. Because the foundation is supported by caissons down to the bedrock and not directly on the soil, the entire crawl space can be dug out all at one time, rather than in small, strategic sections.
Because the new walls can be poured directly under the existing, you lose significantly less space (only around 2-3 inches) than you would with a traditional footing foundation. Rebar is drilled into the original foundation and into each side of the caisson during this process. Also, because we’re working with expansive soils in these cases, we isolate the walls from the surrounding soil to keep them safe from heaving. We are careful in waterproofing measures as well, including exterior dimple mats and interior footing drains to minimize moisture intrusion as much as possible.
Learn more about the rest of the crawl space to basement conversion process.
Design Flexibility
With caissons,
- More “open-concept” or versatile basement designs are possible. The lack of continuous footings allows for more of an “open concept” design. This gives you more freedom in how your interior walls and basement space are configured.
- You’re able to maximize ceiling height. With caissons, you can dig down further without having to worry about structure as much as with typical footings. This type of foundation is great for custom basement designs like golf simulators.
- There is minimal impact on existing structure. Since caissons transfer the load of the home directly to the bedrock, the surrounding soil can be excavated more freely without compromising the home’s stability. This allows for better design flexibility, including deeper basement levels, higher ceilings, and fewer restrictions on layout.
Convert Your Crawl Space to a Basement with PR Builders
Looking below your home for a place to gain some valuable square footage? See what’s possible with a crawl space to basement conversion. Our conservative approach to design begins with a soil test, foundation assessment, and a thorough understanding of your property.
PR Builders provides remodeling services, basement finishing services, and crawl space to basement conversions in Denver, Wheat Ridge, Centennial, and the surrounding areas in Northern Colorado.
