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Pros and Cons of Crawlspace Foundations

Published October 29, 2020

What You Should Know about Crawl Spaces

 

Open floor plans, huge kitchens, floor-to-ceiling windows, spa-like bathrooms, main floor laundry rooms and outdoor living spaces are all top of mind when designers and potential homeowners speak of building – or buying – a dream home. A conversation that’s mostly in the background revolves around the home’s foundation – definitely not as exciting as the features that make a home attractive and appealing.

However, choosing the kind of foundation on which to build a house is one of the most important decisions in home construction. So it’s crucial for homeowners to understand the current structural foundation systems.  

Basically, a home's foundation is the load-bearing portion of the structure, typically built below ground. House design, geographical location and climate, soil and moisture conditions, and budget dictate the kind of foundation selected for any given home. The three types of    foundations commonly used in modern residential construction are:

Open floor plans, huge kitchens, floor-to-ceiling windows, spa-like bathrooms, main floor laundry rooms and outdoor living spaces are all top of mind when designers and potential homeowners speak of building – or buying – a dream home. A conversation that’s mostly in the background revolves around the home’s foundation – definitely not as exciting as the features that make a home attractive and appealing.

However, choosing the kind of foundation on which to build a house is one of the most important decisions in home construction. So it’s crucial for homeowners to understand the current structural foundation systems.  

Basically, a home's foundation is the load-bearing portion of the structure, typically built below ground. House design, geographical location and climate, soil and moisture conditions, and budget dictate the kind of foundation selected for any given home. The three types of    foundations commonly used in modern residential construction are:

  • Slab
  • Basement
  • Crawl space

Whether you choose a basement, slab, or crawlspace foundation, it must perform these three things very well:  

  • Support the structure above
  • Keep out groundwater
  • Act as a barrier to water and soil vapor

In this article, we’re going to focus on the crawlspace – its advantages and disadvantages – and how it may make sense for some potential homeowners.

Crawlspace foundation with floor joists installed

This crawlspace foundation comprises a perimeter concrete footing and vertical 2-by framing forming the crawlspace walls. Floor joists have been installed at the top of the crawlspace, ready for the rest of the house to be built (photo credit:  Cstiteler © Dreamstime).

 

What is a Crawlspace Foundation?

Basically a shallow basement, a crawlspace foundation is an elevated structure – roughly 1.5 to 3 feet high – and as the name suggests, with just enough room for someone to crawl through rather than stand in it. The crawl space is the area between the ground and the home’s main level. While a basement can be used as a living space, a crawl space usually provides only enough room for access to mechanicals and limited light storage.

In addition to elevating the home off the ground – unlike the slab foundation – a crawlspace can “store” and allow easy access to utility areas such as air conditioning, heater, ductwork, insulation, plumbing, and electrical wiring. Crawlspaces can be especially convenient in areas with high moisture where excessive water can build up. The off-the-ground support keeps it away from moisture that can cause damage.

French style home with 1 story and three bedrooms designed for a crawlspace or slab foundation

This stunning 2,854-square-foot French style home with 1 story and three bedrooms is designed for a crawlspace or slab foundation but can also be constructed with a basement foundation (Plan #142-1209).

 

Advantages

·      Considerable savings compared with a basement. According to realtor.com, a crawlspace for an average-sized home can cost as little as $8,000 to $25,000 compared with a range of $75,000 to $150,000 for a basement.

·      A quick and more comfortable way of gaining access to the home’s wiring, piping, and ductwork facilitates easy repairs and future upgrades compared with a slab. Because of this accessibility, plumbing can be reconfigured within the crawl space should homeowners want to change the location of the kitchen and bathroom.  

·      Floors tend to be warmer – unlike with a slab foundation – because the crawlspace is insulated and vented

·      Better for dense, poor-draining soils like red clay

·      Easier insect inspections

·      May provide storage

 

Disadvantages

  • It takes longer to build compared with a slab foundation
  • Stairs are required to enter the home
  • Moisture that can be a breeding ground for mold and fungi is a potential problem and health issue – even with the installation of state-of-the-art vapor barriers. So it’s very important to have the crawl space checked out periodically for moisture issues.
  • Similar to slab foundations, crawlspaces provide the home little-to-no protection from storms and inclement weather.
  • Need to insulate the exterior walls to make heating and cooling more efficient. An open crawl space without controlled airflow costs more money and makes heating and cooling more difficult
  • Difficulty in reselling the home – especially if most of the homes in the neighborhood have full basements

A great advantage crawlspace foundations have over slabs is access to mechanicals and utilities like plumbing, ductwork, electrical wiring, and more. This crawlspace has a support wall running down the center and easy access underneath the house (photo credit: Jason Finn © Dreamstime).

 

Before You Decide

  • Carefully review the benefits and disadvantages of a crawlspace foundation
  • Check if your property lot is suited for a crawlspace – remember that sloped lots and places with warm and dry climates work best for crawlspaces. 
  • And as shown in a 2018 analysis of foundation preferences by the NAHB, there are considerable differences in various regions of the country.
  • Finally, it’s always a good move to discuss plans with your realtor, contractor, and designer regarding the most suitable choices for you – given the area, climate and landscape. Local engineers can also give you useful information and advice about the foundation that works best for your property.

 

Where are Crawlspaces Popular?

Geography plays a major role in foundation type choices. In colder regions across the country – New England, the Midwest, Mid-Atlantic (Delaware, Maryland, New Jersey, New York, Pennsylvania, Virginia, Washington, DC and West Virginia), homes are constructed with full or partial basements. In regions with warmer climates, slab and crawlspace foundations are more typical.  

An analysis by NAHB (National Association of Home Builders) of the 2018 Census Bureau’s Survey of Construction – on the most commonly used foundation by U.S. Regions – showed that nearly 47 percent (46.9%) of new single-family homes started in the East South Central region has a crawlspace. The region includes Alabama, Kentucky, Mississippi, and Tennessee – states that have warm weather. For more than a decade now, the share of new homes built with crawlspaces has been on the rise. From a low of 17.6 percent in 2004 to the highest level of 47 percent in 2017.   

Map of the United States showing popularity of foundation types in various regions

This map shows the regions of the U.S. where basements, slab, and crawlspace foundations are most predominant (source: NAHB).

 

Unlike slab foundations that are limited to flat or nearly flat properties because of their shallow footings, crawlspace foundations work well on sloped lots because less excavation is necessary. On the low side of the lot, “a two-foot deep trench might be needed, while on the high side, a four-or-five-foot trench might be necessary, but the trench need only be two feet wide.”

And because crawlspace foundations are prone to dampness, they are best suited for homes in warm and dry climates.

Contemporary Farmhouse with 12-ft.-tall ceilings, 3 bedrooms, 2 full bathrooms, and a half bath

A crawlspace foundation is a good choice for this attractive one-story Contemporary Farmhouse. The home has 12-foot-tall ceilings with 3 bedrooms, 2 full bathrooms, and a half bath (Plan #198-1008).

 

How Do You Build One?

When contractors build a crawlspace, they dig a deep trench (extending below the frost line) sized to match the perimeter of the house and pour a concrete footing. They then lay short concrete block walls, build short wood frame walls, or pour concrete walls on top of the footing to support the house. The walls that extend from the footing close the space off except at entrance and ventilation areas. When the home is built, it will then space off except at entrance and ventilation areas. When the home is built, it will then be elevated off the ground.

Concrete form for footing of a crawlspace foundation

The first step in building a crawl space is to excavate a trench below the frost line around the perimeter of the house’s footprint. Next, install a form and pour concrete to form the footing for the foundation (photo credit: annazdasiuk © 123RF.com).

 

With modern technology, engineers have developed ways to keep crawl spaces dry – and water out – by using perforated pipes and gravel in the floor of the crawl space and the trench around it. A well-built crawl space should be insulated and sealed with vapor barriers, and all exposed masonry should be covered on the inside to prevent condensation.

Crawlspace foundation under construction

This crawl space illustrates the parts you might find in a such a foundation: perimeter concrete footing and a wall extension of concrete block or, in this case, wood stud framing. The walls will be enclosed  and vents installed later. A floor comprising a vapor barrier, gravel, and concrete will also be laid later. Sometimes the crawlspace floor is left as dirt and/or gravel and covered by a vapor barrier (photo credit:  Cstiteler © Dreamstime).

 

In addition to vapor barriers, here are other ways to prevent or minimize moisture issues:

  • Proper grading around the home, which directs moisture away from the structure
  • Installing, maintaining roof gutters and downspouts
  • Adding downspout extensions and exit lines that move water farther from the home
  • Waterproofing inside and outside the crawlspace
  • Including crawlspace ventilation
  • In some cases installing a dehumidifier

Crawlspace foundation with vapor barrier on the floor to reduce moisture intrusion

One way to solve moisture-related issues is to install a vapor barrier – shown here inside a crawlspace over a dirt floor – to keep moisture out of the space (photo credit: Crawlspace under House by TradeCrawlspaces under license CC BY-SA 4.0).

 

With a lot of thought, research and understanding, you may start looking at crawlspaces in a new light. Ultimately, the choice for your home depends on personal preference and a price that makes sense.

 

Additional Source:

Basement Guides

 

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