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Slab foundations are solid concrete flat surfaces—sometimes called slab-on-grade—4 to 6 inches in thickness anchored by footings set to a depth below the frost line. Crawl space foundations are elevated foundations that stand 18 inches to 4 feet above the ground. Slab and crawl space foundations appear in areas where basement foundations aren’t possible. Both foundation types have their advantages, and you can learn the pros and cons of slab and crawl space foundations with our comparison guide.
On This Page:
- What Is a Slab Foundation?
- What Is a Crawl Space Foundation?
- Environmental Impact
- Resale Value
- Is a Slab Foundation or Crawl Space Foundation Better For Your House?
- Slab Foundation and Crawl Space Foundation Considerations
- Sloped Lots
- Energy Efficiency
- Earthquake Resilience
- Repair Costs
- Water Damage in Crawl Space Cost
- Slab Foundation and Crawl Space Foundation vs. Other Options
What Is a Slab Foundation?
A slab foundation is a concrete foundation with a depth of 4 to 6 inches and has footings that extend below the frost line. Slab-on-grade foundations have a vapor barrier, and concrete gets poured over tied rebar or mesh with a base layer of sand or rock for proper drainage. The house sits atop the concrete foundation.
There are four types of slab foundations:
- On-grade slab (monolithic): A monolithic slab foundation has basic footings, a wire mesh for reinforcement, and a layer of sand or rock for drainage. The slab and footings get poured together at the same time. On-grade slab foundations work best in warm-weather areas that don’t experience freezing weather.
- Floating slabs: Floating slabs have detached footings that don’t anchor into the ground. They do have rebar or wire mesh for reinforcement. Homes don’t use floating slabs, but they work just fine for sheds.
- Conventional foundations (T-shaped): Conventional foundations have heavy-duty reinforcements and footings that go below the frost line. Conventional foundations extend past a home’s perimeter and get used in environments that experience frost. These foundations have stem walls that extend above the footings with a layer of concrete block between them.
- Raised slab foundations: A raised slab foundation is a hybrid of a slab and crawl space foundation with a perimeter wall and footings. The raised space gets filled with soil or rock for drainage and topped off with a layer of concrete.
What Is a Crawl Space Foundation?
A crawl space foundation is also known as an elevated foundation because a crawl space can be 16 inches to 4 feet off the ground. Crawl space foundations need professional grading, while the gutter system and landscaping must direct water away from the foundation because standing water can create mold and rot issues. Crawl space foundations also need a vapor barrier for proper ventilation.
Crawl space foundations come in two main types: a pier and beam foundation and a raised foundation. However, raised foundations include stem and cripple walls.
Types of Crawl Space Foundations
- Pier and beam: A pier and beam foundation uses slabs of concrete and wooden beams to support a home. A pier and beam foundation typically sits about 24 inches off the ground. Concrete beams with rebar are driven into the ground until they reach bedrock. Most homes built before the 1960s primarily used pier and beam foundations though newer homes have a slab foundation or a basement foundation.
- Stem wall: A stem wall foundation has concrete walls that transfer the home’s load to the footings.
- Cripple wall: A cripple wall is a raised foundation made with wooden stud walls between 14 inches to 4 feet in height and relies on compaction for support.
Slab foundations and crawl space foundations have two distinct looks, which can affect access to the house. A slab foundation allows entry to the home from ground level, while a crawl space foundation usually has steps or a ramp to the door. A slab foundation is a flat concrete surface, while a crawl space foundation can have wood beams or concrete walls.
|Slab Foundation||Crawl Space Foundation|
|Exposed flat concrete||Hidden concrete and wood|
|Basic, bland look||Can be open|
|Clean lines||Can have doors|
A slab foundation can cost less than a crawl space foundation because it requires less material. Slab foundations can take less time to build than crawl space foundations but typically need to get installed in one day. Crawl space foundations can cost more because they need additional items to protect the area against moisture issues.
A concrete slab costs between $3,600 and $7,200 for a 30-by-30-foot, 6-inch deep slab, including materials and labor. How do you choose a concrete contractor? You can start with a local concrete contractor or a house foundation contractor near you.
Crawl Space Foundation
A crawl space foundation costs $8,000 to $21,000 for materials and installation. Before installation, it’s important to factor in crawl space encapsulation costs, which sit between $1,500 and $15,000, with an average cost of $5,500. High-end insulation, like spray foam, can increase costs to upwards of $25,000.
Foundations require maintenance from time to time, but a slab foundation typically doesn’t require as much maintenance as a crawl space foundation. Foundations need regular inspection to detect any cracks or potential trouble spots. Any foundation issues need addressing quickly because of the damage a foundation in disrepair can cause to a home.
A slab foundation doesn’t need much maintenance. However, it’s important to check for moisture with the foundation, make sure gutters drain away from the foundation, and keep an eye on tree roots because they can damage a slab foundation. A root barrier can help prevent tree roots from reaching your home. You can also maintain a consistent indoor temperature because the temperature in your home can cause the concrete to expand and contract if it experiences wild temperature swings.
Crawl Space Foundation
Crawl space foundations need regular inspection and upkeep. Crawl spaces need proper encapsulation to prevent any moisture issues. Crawl spaces also need monitoring to prevent pest problems, like bugs and rodents, both of which can damage wood. It’s best to clean them routinely to avoid issues.
Both slab and crawl space foundations have excellent durability. A slab foundation can have a longer lifespan than a crawl space foundation because it doesn’t require as much upkeep. A crawl space can have less durability because they have more potential for problems.
Concrete has tremendous durability and can easily last 80 to 100 years when used in a slab foundation. Slab foundations can crack, however, if soil shifts or the area experiences an earthquake. Slab foundations can also suffer damage if tree roots start growing under the foundation because they can cause cracks. Any kind of foundation crack can cause concern for the house’s integrity.
Crawl Space Foundation
A crawl space foundation has less durability than a slab foundation but it works well in earthquake-prone areas and areas with shifting soil because it can handle the movement better than a solid concrete slab. If properly maintained, a crawl space can have good durability but moisture and pests must get monitored closely.
Foundation installation costs range between $4,000 and $15,000, with an average cost of $9,000. A crawl space foundation typically costs more than a slab foundation because it requires more work and additional materials. It’s important to know the cost of concrete per square foot before hiring a concrete contractor so you can find the best deal. It’s possible to install a concrete slab on your own, but one for a home is best left to professionals because it requires several people.
Slab foundations cost $12,000. A monolithic slab foundation can cost between $7,000 to $20,000 or $5 to $16 per square foot, on average. The slab’s thickness and the job size will impact the total cost.
Crawl Space Foundation
A pier and beam crawl space foundation costs between $9,000 and $17,500 or $7 to $14 per square foot, on average. Crawl space foundations have additional costs for insulation, vapor barriers, dehumidifiers, and sump pumps, if necessary.
- Insulation costs $1–$5 per square foot
- Vapor barriers cost $0.50–$0.70 per square foot
- Dehumidifiers cost $1,300–$2,800
- Sump pump installation costs $650–$2,050
Concrete can last for many decades as long as you prevent moisture issues and tree root problems. Slab foundations are known for their long lifespans. Crawl space foundations can have long lifespans, too, but they require more maintenance to reach them. In some areas, a slab foundation doesn’t work well because it doesn’t provide a basement.
A slab foundation can last the house’s lifespan if properly maintained. Proper maintenance includes water abatement and management by directing water away from the foundation. Moisture can damage concrete, and shifting soil can also lead to cracks in the concrete.
Crawl Space Foundation
A crawl space foundation can have a life span between 15 and 50 years, depending on the maintenance. Crawl space foundations are more susceptible to repairs and maintenance because they need moisture mitigation. Crawl spaces also tend to attract pests and animals, so it’s best to do prevention work to dissuade them from entering the space.
The use of concrete for a foundation has an environmental impact. A study showed deeper foundations have more of an impact than shallow foundations because they use more materials. A 2019 article in The Guardian deemed concrete the most destructive material on Earth partly because the industry emits 2.8 billion tons of carbon dioxide.
Concrete tends to stay intact for up to 100 years or more, which means it can remain around even after a house has been razed. Concrete can absorb heat, which can impact items on it and nearby. Slab foundations can flood more easily than crawl space foundations because the water has nowhere to go.
Crawl Space Foundation
Crawl space foundations can use less concrete but remain susceptible to mold and mildew growth because of moisture issues. Mold can create poor air quality and a host of respiratory issues. Proper encapsulation can help prevent mold and moisture issues.
Both foundation styles can help with your resale value, but a few variables come into play. It’s best to have a foundation that coordinates with those in your community. High-quality building materials can help boost the resale value, and the energy efficiency of your foundation can help with your return on investment. A slab foundation can have better energy efficiency than a crawl space foundation because it can block air underneath the subfloor from entering the home.
A slab foundation blocks air infiltration from below and can improve energy efficiency. You can also insulate the exterior of a slab to potentially cut energy costs 10% to 20%. The resale value of a slab foundation will vary based on its age and the region. A slab foundation home isn’t ideal in the midwest or rocky areas.
Crawl Space Foundation
A crawl space foundation gives you easier access to things like your plumbing, electrical, and heating and cooling vents, which can appeal to a homebuyer who enjoys DIY work. A crawl space can also turn away a homebuyer who isn’t interested in the upkeep of a crawl space. But if the area dictates that it’s beneficial to have a crawl space, it could help sell the home.
Slab Foundation and Crawl Space Foundation Considerations
Choosing a slab foundation or a crawl space foundation can come down to which one fits best in your region, given ground considerations and climate situations. Other factors include:
- Sloped lots
- Energy efficiency
- Earthquake resistance
- Repair costs
- Water damage
Each type of foundation can have advantages over the other.
Slab foundations typically do not get installed on sloped lots because of excavation and shallow footings needed. Sloped lots can suffer from shifting soil, compromising a slab foundation. A crawl space foundation can work better on sloped lots because footings can be used to level the home’s flooring.
A slab foundation won’t encounter pests as much as a crawl space foundation, but they can still burrow under the foundation. Crawl space foundations can suffer from pests like termites and rodents that like to chew on wires and wood. It’s best to prevent any kind of entry into the crawl space and keep the space clean. Exterminators can treat the area before the crawl space gets installed.
Slab foundations have moisture resistance, and a waterproof barrier can prevent water from entering the home. Slab foundations, however, aren’t great in flood areas because they sit at ground level. Crawl space foundations need encapsulation to prevent moisture issues, but they work well in flood- or hurricane-prone areas because they sit above the ground. If water gets trapped in a crawl space, it can lead to mold and wood rot.
A slab foundation is more energy efficient than a crawl space foundation because there isn’t any space for cold air or hot air to pass under the floors. A crawl space needs insulation to improve energy efficiency. Otherwise, cold air can penetrate the floors. Hot air can also rise through the floors in warmer months and keep an AC unit running longer to cool a home.
A slab foundation does not provide much resilience against an earthquake and will crack in a large earthquake. A crawl space foundation is less likely to crack because it has piers that attach to footers, while the wood beams can absorb some shock waves. Crawl space foundations have more flexibility than slab foundations.
A full foundation replacement costs $25,000 to $115,000. If you see signs of damage or settling, such as cracks, it is important to repair them right away. Foundation repairs cost an average of $4,800, but a local foundation repair company can provide accurate costs for your specific project.
Slab foundation repair costs can range from $500 to over $6,000. They can be costly because it’s difficult to access pipes under the slab and could need multiple fixes like underpinning and mud jacking, which can cost more than $8,000.
Crawl space repairs cost $150 to $3,000 for flood damage, mold and mildew growth, or pest infestation, while encapsulation damage can cost up to $15,000.
Foundation repairs cost $2,000 to $7,000 or more. You might need to replace or shore up supports, fix cracks, and relevel the house. A pro typically secures it with piers, piles, or mudjacking.
You’ll also want to ask your pro about any related soil issues that might cause the foundation to settle further or cause other problems.
Water Damage in Crawl Space Cost
Water damage restoration costs around $1,200 to $5,400, with extreme flooding costing up to $10,000 to fix. You can prevent water damage through encapsulation and waterproofing, but that adds up to another $15,000.
With flood damage, you’ll want to hire a local water restoration company. You might also have to restore or replace walls or individual wooden beams, which can range up to $2,000. Mold removal and fixing insulation damage will increase the cost.
A crawl space can provide a storage place in a dry climate that doesn’t experience flooding, which could help you choose it over a slab foundation. Items stored in a crawl space need proper sealing and should prevent anything from getting into it. A slab foundation does not provide any additional storage.
Is Slab Foundation or Crawl Space Foundation Better for Your Home?
Use this table to help determine whether a crawl space or slab foundation is right for you.
|Factor||Slab Foundation||Crawl Space Foundation|
|Appearance||Dull||Has design possibilities|
|Cost||$7,000 – $20,000||$9,000 – $17,500|
|Lifespan||50 years or more||15 to 50 years|
|Resale Value||Yes, when installed in proper region||Yes, when installed in proper region|
Slab Foundations and Crawl Space Foundations vs. Other Options
Slab foundations and crawl space foundations aren’t the only types of foundations. Where installation works best, basement foundations offer an excellent choice because they can provide living space and storage. Basement foundations cost between $24,000 and $44,500. Cinder block foundations are another option. Cinder block foundations cost between $11,500 and $19,000.Start Your Foundation Project Today