Slab vs. Crawl Spaces: What is the Difference? | Building Contractors Association of Southwestern Idaho | Boise, Nampa, Caldwell, Idaho | Treasure Valley
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Slab vs. Crawl Spaces: What is the Difference?

A strong foundation is essential to the safety and longevity of any home. In most cases, the type of foundation contractors use will depend on the style of the home and the geographic location. Two of the most common types are slab foundations and crawl space foundations.

Slab Foundation vs. Crawl Space

With a slab foundation, the property is constructed on top of a thick, level concrete slab. For a crawl space, exterior concrete walls raise the foundation a minimum of 18 inches above ground level, which leaves access space for wires, plumbing and storage. When compared to full basement foundations, both slab and crawl spaces are less expensive. These types of foundations are also suitable for many parts of the country.

What is a Slab Foundation?

Concrete is poured four to eight inches deep on a level surface with thicker concrete around the perimeter. There is often a layer of sand or crushed gravel beneath the slab to help with drainage. Slab foundations are more popular in warm climates versus cold climates because they’re prone to cracking when exposed to sub-zero temperatures.

When done properly on well-graded land, slab foundations can last decades. In terms of longevity, it helps that slab foundations are resistant to mold, mildew and damage from pests.

Slab Foundation Pros

Quick to Construct

Slab foundations are monolithic, meaning the entire foundation is poured at once. Often the slowest part of the process is leveling out the grade. Everything moves along quickly once it’s time to pour the concrete. That is one reason why slab foundations are favored among high-volume builders.


Not only are slab foundations the least expensive to construct, but there also can be more long-term savings because of the low-maintenance needs and general durability.


Made of concrete and reinforced with bars, slab foundations are solid — which leads to a long lifespan. Slab foundations are also resistant to mold, mildew, pest damage and other hazards that can cause problems with other foundation types.

Slab Foundation Cons

Can’t Be Built on a Slope

The  ground must be completely level for slab foundations.  If you are constructing a home on a steep slope, that eliminates slab foundations from contention unless you are very creative with the design.

No Extra Space

Because slab foundations are built directly on the ground, there is no space underneath for wires, pipes or storage. Often, water and gas lines are embedded into the slab foundation.

What is a Crawl Space?

Homes with crawl space foundations are elevated above the grade. The two types of crawl space foundations are block-and-base foundations and pier-and-beam foundations.

Crawl space foundations are built between 18 inches and four feet above the ground with exterior support walls. Because the slope under a crawl space can vary, the ground does not have to be completely level. However, crawl spaces are more expensive than slab foundations and may require more maintenance to ensure the space is properly ventilated.

Crawl Space Pros

Suitable for Sloped Lots

Crawl spaces are commonly found on uneven or hillside house lots for good reason. Rather than flattening out the grade, the crawl space foundation can be elevated enough to remain level.

Easy Access to Plumbing or Wiring

With crawl space foundations, plumbing lines, gas pipes and electrical elements are often housed within the gap between the ground and floor of the home. Then, if maintenance is needed, everything is easier to access.

Crawl Space Cons

Requires Monitoring and Maintenance

A damp, dark, enclosed crawl space can make an inviting breeding ground for mold, mildew and pests. If left unchecked, this can create serious foundation problems. Crawl spaces are not well-suited to areas with high humidity or precipitation.

More Costly to Construct

Compared to monolithic slab foundations, crawl spaces are much more complicated to construct. On average, a crawl space costs more than two-and-a-half times the amount of a slab foundation.

Shorter Lifespan than Slab Foundations

Because of the materials used to construct crawl spaces and the greater potential for problems with mold, rot and pests, crawl spaces have shorter average lifespans than concrete slab foundations.

Sponsored by Mono Slab EZ Form.

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