In the U.S., roughly 15% to 20% of new homes are built on crawl spaces. That’s on top of about 27 million existing homes built on crawl spaces. This space beneath your home can be the foundation for its success or the groundwork for its problems — here’s what you need to know.

What is a crawl space?

A crawl space is a type of foundation that features short walls no taller than 4 feet. The resulting space between the home’s first floor and the ground allows people to crawl underneath the house — hence, the name — to access the plumbing, HVAC, electrical, insulation, and even floorboards for maintenance.

A crawl space is less expensive than a basement because it requires less excavation and material for the foundation walls. Usually unheated, a crawl space may be ventilated to permit airflow through the crawlspace. Unfortunately, these vents can let moisture in, causing many of the crawl space issues we’ll touch on below.

Potential problems in the crawl space

If your house smells musty, you might have mold in your crawl space. As much as half of the air on the first floor of your home comes from the crawl space. Air enters through ducts that allow air from the crawl space to mix with air in the house or by the stack effect, which pulls air from the crawl space to the upper floors. If mold is present in the crawl space, the air filtering upward will smell musty.

Causes of mold in the crawl space include:

•  A possible sewage backup due to a clog in the sewer line
• Decaying organic matter such as manure, leaves, or dead animals
• Groundwater leakage
• Plumbing leaks

Here are some solutions to the above problems:

• If you have a sewage leak, contact a disaster restoration company to fix and clean it up. The average price homeowners pay for sewer line repair is $2,556. You can expect to spend between $1,073 and $4,054, depending on the severity of the damage.
• Cover crawl space walls and floors with a vapor barrier to prevent water and moisture from seeping through foundation walls. Vapor barriers can cost $0.25 to $1.50 per square foot, for an average installed cost of $1,200 to $4,000.
• Seal crawl space vents to prevent outside air from entering. High humidity levels make pipes and ductwork “sweat” with condensation. “When the air conditioner is on, ductwork in the crawl space drips like rain,” says Brenda Kusturin, customer service representative for Crawl Space Experts.
• Install a dehumidifier to keep humidity levels in check. For a crawl space, it can run $1,500 to $2,000.
• Install a perimeter drainage channel. The national average cost to install French drains is $4,500 but can run as high as $10,000.
• Add a sump pump in the crawl space to eliminate pooling water. The average cost of a sump pump is about $250. Professional installation can add $100 to $200.
• Adjust the grading around your house to enable water to flow away from it. The national average cost to regrade your yard is $1,300.
• Hire a plumber to fix leaky pipes. Plumbers typically charge between $45 and $90 per hour.
• Keep gutters and downspouts clear.

Problem #2: Moisture damage

The American Society of Home Inspectors reports that more than 60% of the homes in the U.S. have had water or moisture in their basement or crawl space. Moisture can damage a home’s foundation, warp hardwood floors, rot support beams, invite pests, cause mold, and even raise energy bills.

Damp crawl spaces also attract wood-destroying fungi, species of fungus that digests moist wood, resulting in wood rot.

Causes of water in the crawl space include:

• Ground that slopes toward the house
• Gutter and downspout issues
• Over-saturated ground soil due to heavy rain
• Storm sewer backups
• Flooding

Encapsulation

Because a water or moisture problem in your crawl space often results from a combination of issues, a package deal may be the answer: encapsulation.

Encapsulation includes vapor and thermal barriers, insulation, a drainage system, and a dehumidifier. During the encapsulation process, professionals seal the vents, replace damp and damaged insulation, and lay a thick vapor barrier on top of the ground.

Encapsulating the crawl space can resolve moisture issues and prevent mold. Other benefits include eliminating insect infestation, protecting your home’s structural stability, and improving your home’s energy efficiency.

On average, encapsulation costs between $5,500 to $7,500.

Add a dehumidifier

You can solve minor moisture issues with a dehumidifier, costing $1,860 to $2,510 on average. You should hire a professional for this task to ensure you’re placing the dehumidifier in the best spot.

Install a sump pump

If there’s standing water in your crawl space, you’ll need to install a sump pump to move moisture out of the area. Submersible sump pumps sit in a pit in the deepest part of the space, while pedestal sump pumps sit outside of the water. Both automatically activate when water is detected and pump the water outside through a discharge pipe.

The average cost to install a sump pump is $1,100, a reasonable investment to protect your home from costly water damage. Plus, a sump pump may add value and marketability to your home when it’s time to sell.

Repair systems contributing to water in the crawl space

If your gutters and downspouts are damaged or clogged, they’re not properly directing water away from your home, which can lead to moisture in the crawl space. Replacing gutters and downspouts ranges from $580 to $1,516. However, yours may just need a good cleaning. Professional gutter cleaning costs between $149 and $219 for a single-story house, or $237 to $297 for a two-story home.

Digging and replacing sewer lines to prevent future storm sewer backups can cost between $50 and $200 per foot. The average total is $2,250 to $5,750.

Replace waterlogged wood

To eliminate moisture and related issues, you should also replace any rotted support beams. Unfortunately, this is not a cheap repair: it can cost anywhere between $1,500 and $5,000, depending on the material.

Hire a pro for a multifaceted solution

Keep in mind that the water damage in your crawl space may be limited to one specific area, reducing the cost to fix its cause. You may save money and aggravation if you first hire a home inspector or basement waterproofing company to assess the situation and help you make a plan.

Kusturin shares that her company, like many others, offers free inspections. They start with a visual examination. If the inspector sees any sign of damage, he will then tap on or probe the wood in search of structural damage. An inspector may also use a moisture meter.

Problem #3: Rotten smell

Culprits behind the foul smells emanating from your crawl space may include:

• Trash left behind from contractors
• Dead animals or animal droppings
• Moldy soil
• Sewage backup

Crawl down to remove the source of the odor

To eliminate odors, you or a professional must enter the crawl space to remove debris, animal carcasses, and other rotting items.

You can hire a company to perform a simple crawl space cleaning for $500 to $4,000, depending on size, accessibility, and condition. If soil is the source of the smell, a professional may install a vapor barrier for around $1,200 to $4,000.

Problem #4: Pest infestation

Pests cause structural, insulation, and wiring damage in your home. Even worse, they can trigger allergies and other health issues for your household members. For example, cockroaches can spread six types of parasitic worms, seven kinds of human pathogens, and 33 types of bacteria, including E. coli and salmonella.

Prevent pests from entering the crawl space

Prevention is always best. Keep the critters out of your crawl space with these solutions:

• Seal the vents and holes
• Remove shrubbery from around the foundation
• Install a vapor barrier
• Control the moisture level
• Consider encapsulation
• Investigate pest control options 

An exterminator can cost anywhere from $200 to $4,000. Kusturin points out that a pest control company can treat the area, but only a licensed contractor can repair the damage.

But before you call a pest control company, you may want to give it a try on your own. Here are some tips to keep unwanted visitors out of your crawl space:

• Cover the tunnels outside your house
• Cut off their food supply
• Remove dead rodents
• Install lights to scare them away
• Remove breeding nests
• Remove their trail
• Fill burrows
• Repair the damage
• Replace insulation that pests have inhabited

Some sources suggest placing ammonia-soaked rags or mothballs in the crawl space to encourage larger pests to move along. 

Problem #5: High energy bills

A vented crawl space allows air to draft into your home, leading to increased energy bills as you attempt to regulate indoor temperature. If your crawl space walls aren’t insulated, your home is even less energy efficient.

Here’s how you can improve your crawl space’s insulation to reduce energy bills:

• Add R-19 insulation or higher in the crawl space. The higher the R number, the better the insulation is at slowing down heat transfer. Insulation cost ranges from $398 to $893.
• Install a vapor barrier at least 6 millimeters thick on the ground to prevent moisture seepage and radon gas.
• Install vent covers to keep air out. The price depends on the size of your vents but can be as little as $26.99. 
• Caulk and seal cracks and joints.

Care for your crawl space