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Buying a House with a Crawl Space: What to Look For

Tuesday, May 18th by Kristina McGovern


Moisture problems, water, and pests are common problems found in open crawl spaces. Use this guide to know what issues to look for when buying a home with a crawl space and your best options for repair and prevention.

Exterior view of an open crawl space foundation vent

Open foundation vents allow moist outside air into the crawl space, which leads to corrosion, mold, mildew, and wood rot. (Credit: Quality 1st Basement Systems)

Crawl spaces are popular in residential construction in many regions of the United States because they are cheaper than full basements but more functional than slab foundations. These spaces have a very low ceiling height (typically 1 foot to 3 feet high), providing access to plumbing, electrical wiring, and ductwork for heating and cooling systems. However, when built and maintained incorrectly, they also pose a hazard to the health, comfort, and safety of your home.

The crawl space is sometimes referred to as the "gut" of the home. Much like your body's gut, the condition of your crawl space affects the overall health of your home. This is why when buying and owning a property with a crawl space, it's important to inspect for crawl space damage, such as mold, wood rot, and termite infestations.

Whether you're considering buying a home with a crawl space or building one, this article will explain the major problems to be aware of in homes with crawl spaces AND discuss solutions for fixing these problems should you come across one (or all) of them.

  1. Crawl space vents
  2. Signs of a moisture problem
  3. Water
  4. Pests

First, let's discuss what a crawl space is and how it's different from other types of foundations.

In residential construction, there are three common foundation types: a basement, slab, and crawl space. The major characteristics of each type are explained below:

  • Basement foundations are constructed with concrete masonry units (CMUs) or poured concrete walls. A basement is generally at least six feet high with a footprint that matches all or most of the floor space of the level above. Basements can be either finished or unfinished and often serve as storage areas and house water heaters, furnaces, and other equipment.
  • Slab foundations (sometimes called slab-on-grade) are exactly what they sound like - a thick concrete slab on top of which the house is built. Slab foundations are an inexpensive option in climates where the ground doesn't freeze and thaw. A downside of slab foundations is access to water and drainage pipes can be a challenge since they are typically installed underneath concrete.
  • Crawl space foundations are built with poured concrete or concrete block walls that elevate the bottom of the house above grade (ground level), providing an accessible area to reach plumbing and wiring for maintenance. Crawl space foundations usually require additional support walls or columns beneath the interior of the house.

Now that you know the major differences between a basement, slab, and crawl space, you might be wondering why some homes have a crawl space instead of a basement or slab.

The two primary reasons homes are constructed with crawl spaces are cost and accessibility. The best type of foundation is based on many factors, including the house design, geographical location, climate, and soil and moisture conditions. If you're planning or in the process of new construction, your builder will choose the best foundation given these factors. However, if you're buying an existing home, you're typically stuck with what you get, with some exceptions.

Whether you're considering buying a house with a crawl space or in the process of building a new one, there are four major problems to watch out for. These issues and our recommended solutions are discussed below.

  1. Crawl space vents: open or closed?

    Exterior view of open crawl space vents

    Open crawl space vents let in damp air, cold air, and pests. (Credit: Quality 1st Basement Systems)

    When walking around the exterior of the house, take note of whether the foundation vents into the crawl space are open or closed. At one time, it was thought that crawl spaces should be ventilated with outside air to control moisture and dry out the crawl space. However, research has shown that letting in outside air adds more moisture in the crawl space and it can lead to condensation, mold growth, and wood rot.

    Solutions for Open Crawl Space Vents

    Crawl space encapsulation can significantly improve moisture control, offer energy savings, and provide a healthy space under the home. Covering the crawl space vents is an important step in the crawl space encapsulation process. Vent covers block the air movement that would otherwise occur through open vents. The crawl space vent covers installed by Basement Systems contractors are made of rugged PVC and are immune to moisture damage.

  2. Signs of a moisture problem

    In many locations, moist outside air coming through open crawl space vents condenses or collects on cool surfaces, such as water pipes and air ducts, causing corrosion, mold, mildew, and rot. While you may be more likely to notice the symptoms listed below if you're shopping for a home during the humid spring or summer months, they can occur any time of year.

    Fiberglass insulation on a crawl space floor

    Sagging or fallen crawl space insulation can be a sign of a moisture problem.

    Common problems with unsealed crawl spaces:

    • Mold or moisture damage in the crawl space
    • Musty odors in the living area
    • Condensation ( or "sweating") on air conditioning ductwork or equipment
    • Condensation on water pipes in the crawl space
    • Damp or sagging insulation
    • Buckled hardwood floors above the crawl space
    • High humidity in the living area
    • Insect infestations
    • Rotted wood framing or joists

    For more on crawl space moisture, check out Why Your Crawl Space is Damp, Smells Musty, and Has Mold.

    Solutions for Crawl Space Moisture Problems

    While installing a vapor barrier in the crawl space isn't a requirement in most states, research has shown that sealing off the crawl space from the ground and humid outside air can minimize moisture in the crawl space. Crawl space encapsulation refers to the process of sealing the crawl space to prevent humid outside air from getting in. Doing so can significantly reduce the risk of crawl space problems. Each state has an adopted version of the International Residential Code with specific requirements for unvented crawl spaces.

    Crawl space floor and walls covered with CleanSpace vapor barrier

    CleanSpace permanently separates the home from the ground to keep away mold and insects.

    To encapsulate the crawl space, the contractor will install a heavy-duty liner over the soil, foundation walls, and piers. They will seal all holes and gaps between the crawl space and the outside and between the crawl space and the interior of the home. This includes fixing or replacing the crawl space door to create a tight seal and covering crawl space vents. A dehumidifier should be installed to control the humidity level in the crawl space.

    Basement Systems offers advanced systems and accessories installed nationwide by local contractors to provide effective crawl space repair and to convert a nasty crawl space into a healthy one.

    Issues avoided with crawl space encapsulation include:

    • Mold/mildew
    • Wood rot and structural damage
    • Floor failure
    • Decreased insulation R-values
    • Increased heating and cooling bills
    • Odors
    • Insect infestations
    • Allergy aggravation
    • Poor indoor air quality

    Many times, homeowners will notice some of these issues, such as unusual odors or worsening allergy symptoms, but they don't attribute these symptoms to a problem in the crawl space.

    For more on crawl space smells, read our post What's That Smell? Identifying Crawl Space Problems with Your Nose.

  3. Water

    Puddle of water on a crawl space floor

    A puddle of water in the crawl space is a sign of a water problem that should be addressed.

    If there are puddles of water in the crawl space, this means that water got into the crawl space either from a plumbing leak or groundwater or that rainwater could be seeping in from outside. This also tells you that either there's no drainage system or the drainage system isn't working. Many homes have a "low point drain" that's either in the wrong spot or becomes clogged. Whatever the situation, standing water in the crawl space can cause wood rot and structural problems, attract unwanted pests, and can lead to mold growth and foster termites and carpenter ants that can damage your home.

    Here's more on water in the crawl space.

    Solutions for a Wet Crawl Space

    Water should be directed away from the exterior of the home and foundation with proper gutters, downspouts, sloped soil, and foundation drainage. A sump pump and perimeter drain should be installed in an encapsulated crawl space to prevent the crawl space from turning into a swimming pool if there's a plumbing leak or unexpected water event. The SmartSump from Basement Systems is the only sump pump specifically designed for crawl spaces, with an alarm that sounds in the event of a plumbing leak in the crawl space or pump failure.

  4. Pests

    Dead mouse on a crawl space floor

    Mice and other pests often make themselves at home in vented crawl spaces.

    Crawl spaces can become a home for pests if not properly maintained. Some of the most common crawl space invaders include rodents, such as mice and rats, and insects, such as termites, cockroaches, spiders, carpenter ants, and more. Occasionally, you may also find larger pests, like raccoons and possums. These pests can wreak havoc on your crawl space and the rest of your home. They can damage insulation, gnaw through wiring and air ducts, and damage your home's wooden framing and supports. Unfortunately, pests don't stop at your crawl space. They can follow air ducts, water pipes, and holes for electrical wiring into your home.

    Check out how to Solve the Mystery Lurking in Your Basement or Crawl Space, including crawl space pests.

    Solutions for Pests in the Crawl Space

    A home inspection should reveal a current or past pest infestation. Effective moisture control solutions can help prevent a future pest problem in the crawl space. This includes sealing all openings, using crawl space encapsulation with a high-density liner, and installing a dehumidifier to regulate the crawl space environment. It should be noted that some building codes require that a portion of the foundation wall below the wood floor framing remain visible to allow for termite inspections in a sealed crawl space.

Conclusion: Is a crawl space foundation good or bad?

Crawl spaces are only bad when they are built and maintained incorrectly. With proper installation and maintenance, sealed crawl spaces provide benefits that outweigh vented crawl spaces. If you buy a house with a crawl space, an experienced crawl space repair contractor can help you make improvements or convert it with crawl space encapsulation. The cost of a CleanSpace crawl space encapsulation system depends on a variety of factors, including the size and condition of your crawl space and the exact products installed. For a free crawl space repair estimate, contact us to schedule a no-obligation consultation with your local crawl space encapsulation contractor.

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