Concrete Slab or Crawl Space: Which is a Better Option?

The most basic difference between concrete slab and crawl space foundations is the height of the house. But there are other differences too, such as the merits, demerits, and the cost, as given in this Buzzle article.
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Tip for choosing between concrete slab or crawl space
Did You Know?
Termites can build long tunnels in crawl spaces, sometimes as long as 4 feet long, in order to reach timber.
A house foundation, though not one of the most glamorous of parts, is still one of the most important. In fact, it may be THE most important part of your house. After the house is complete, you can repair the walls, paint, and roof with relative ease, but where the foundation is concerned, things are not so simple.

Apart from basement foundations, the other two types of foundations are concrete slabs and crawl spaces. The main difference between these being; while the former involves laying a flat slab under the house, in the latter, the house is raised higher on support beams, resulting in a space below the house that you can 'crawl' into. While concrete is generally used for slabs, for constructing crawl spaces, other materials like timber also have to be used. But when choosing a foundation, you have to go into certain details. Check out this crawl space vs. concrete slab comparison to get a better idea.

BASICS
Concrete Slab
  • A concrete slab is laid down by excavation of soil and pouring concrete in the mold formed. Concrete slabs are on average, 6 to 8 inches thick.
  • Concrete beams are present at the slab edges for support, reaching down to below the frost line for insulation.
  • Steel reinforcement is laid down before pouring the concrete.
  • A layer of gravel may separate the concrete from the soil.
  • Gradation of the land is required prior to slab laying, as massive earth-moving equipment may damage the slab if gradation is done later.
  • Concrete slabs are ideal for a clay type soil and a high water table region.
  • The plumbing, electrical conduit, and other connections are generally placed below the slab, or are enclosed in the concrete.
  • Utilities like HVAC are routed through the attic.
Crawl Space
  • A crawl space is like a smaller version of a basement, but in which an adult generally cannot stand up completely. The height varies from 16 inches to 4 feet.
  • It is built by excavating the ground, and then installing piers or pilings that raise the house several feet up.
  • Stem walls or reinforced concrete beams skirt the foundation perimeters, lifting the first floor up.
  • A vapor barrier can be placed below the crawl space to keep out moisture.
  • Utilities like plumbing, electrical conduit, and HVAC are installed in the crawl space. They may require insulation to prevent freezing during winters.
  • This type is ideal for a low water table region, where deep excavation is possible.
Concrete Slab

Crawl Space

ADVANTAGES
Concrete Slab
  • Less excavation required.
  • Less time requirement. Concrete slabs can be poured one day, and work on the walls can begin the next day itself.
  • Good for senior citizens or people with knee problems who can't climb stairs. Construction of a handicapped access is possible.
  • No chance of radon gas leakage.
  • The slab has a cooling effect during summers, as it absorbs excess heat from the environment and gives it to the surroundings.
  • Durable foundation that lasts for years.
Crawl Space
  • It provides a semi-access area, where shelves can be made for storage.
  • Raising the house gives a stately look, increasing market value.
  • Prevents water from entering the house during rains, storms, etc.
  • Easy access to plumbing, duct-work, and electrical systems, since they are placed in the crawl space.
  • Can be installed in sloping areas.
  • The airflow in the crawl space helps reduce temperature in summers.
DISADVANTAGES
Concrete Slab
  • Water may enter the house during stormy weather.
  • The floor laid right on the slab may have a hard, cold feel.
  • The slab releases heat to the surroundings, which may cause excessive cooling in winters.
  • Freezing temperatures may cause slab shifting, in extreme cases.
  • Plumbing is laid below the slab, making access and repair difficult.
  • Redesigning the structure may be difficult.
  • Invasive tree roots, weak soil structure, and tremors may cause cracking of the slab.
  • Raising damaged slab foundations using jacks is difficult.
Crawl Space
  • Molding of basement walls if moisture level increases.
  • Pests like rats and termites may invade the basement.
  • Chances of gas leakage.
  • Extra expenditure on insulation.
  • May lead to foundation problems if soil strength is weak.
  • Deeper excavation of soil is required for crawl space construction.
  • Homes may 'suck' air out from crawl spaces (called the stack effect), which may be dangerous if disease-causing spores are present in the crawl space.
COST
Concrete Slab
  • Construction of slabs is much cheaper due to low depth of excavation and less labor costs.
  • Since the utilities are placed below or embedded in the slab, it may be difficult to repair them. First, the floor tiles may have to be dug up, leading to high repair costs.
  • In case of a cracked slab, high repair costs may be incurred.
Cost: Depending on the area, $2.5 to $8/sq ft, plus additional costs for steel reinforcement and finishing.
Crawl Space
  • Higher cost incurred in crawl space construction, because of deeper excavation of soil required.
  • Since utilities are easily accessible in a crawl space, it is much cheaper to repair them.
  • Extra expenditure is incurred in placing an insulation layer below the crawl space.
Cost: $5 to $12/sq ft, plus additional costs for insulation, anti-termite treatment, etc.
Laying a slab foundation instead of a crawl space can save you $5,000 to $10,000 initially, but in the long run, a crawl space foundation may be more economical when compared to the astronomical costs involved in utility repair for slab foundations. It is important to call a third party inspector to analyze the soil conditions on-site, before settling on any particular choice.
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Published: August 13, 2014
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