To waterproof a crawl space, you need to stop water from entering the area under your home. Start by fixing downspouts, soil slopes, and other sources of outside water. If water still comes in, an interior drainage system and sump pump can help remove it. After dealing with liquid water, add a vapor barrier to the dirt floor. If the crawl space still has high humidity, mold, or damp air, encapsulation and a dehumidifier may also be needed.
Each crawl space has different needs. The right steps depend on where the water comes from and how much moisture is present.
Why Crawl Spaces Need Waterproofing
Water reaches a crawl space in three main ways. Surface water runs from the yard, roof, and driveway into vents, cracks, and the access door. Groundwater can rise through the dirt floor after heavy rain. Plumbing leaks and air conditioner drain lines can also leave water under the house.
North Georgia clay makes these problems worse because it drains slowly and can hold water against the foundation for weeks. Waterproofing helps deal with these water sources before other work begins.
Common Signs of Crawl Space Moisture Problems
Not sure whether you have a water problem or a humidity problem? Read our guide to crawl space moisture problems, causes, and fixes.
Standing water, mud, and water marks on the support piers are signs that you may need waterproofing. Condensation and a musty smell, even when the floor is dry, may point to a humidity problem.
Crawl Space Waterproofing, Step by Step
Here are the main steps to follow.
Step 1: Stop Water Outside the Foundation
A lot of crawl space water starts near the roof or yard. Check these areas before spending money on work inside the crawl space.
Downspouts. Extend each downspout at least 4 feet from the wall. If water pours out beside the house, it can collect near the foundation during a storm.
Grading. The soil should slope away from the house. Aim for a drop of 6 inches over the first 10 feet where the site allows it. Soil, mulch, and flower beds piled against the wall can cause water to flow toward the house.
Vents and access door. Water can enter through vents that sit at or below ground level. Vent wells or changes to the ground level may help. Seal gaps around the access door.
Window wells and driveways. If a driveway or concrete path slopes toward the house, water may collect near the foundation. The slope may need to be corrected or a drain added.
Some crawl spaces become much drier after these outside problems are fixed.
Step 2: Install an Interior Drainage System
If water still enters after the outside problems are fixed, groundwater may be coming through the floor or the bottom of the wall.
An interior crawl space drainage system collects this water before it spreads across the floor. A pipe with small holes sits in a gravel trench along the inside of the foundation wall. The pipe carries water to a sump basin.
A crawl space French drain outside the foundation can collect water from the other side. Interior systems are often used in existing homes because they may avoid digging up driveways and landscaping.
Step 3: Install a Sump Pump
The drainage system needs a way to move the collected water out of the crawl space. A sump basin sits at a low point and collects the water. A sump pump then sends it outside, ideally at least 10 feet from the foundation and toward a suitable downhill area.
A battery backup can help keep the pump working during a power outage. Heavy storms can bring water into a crawl space and cause power cuts at the same time.
The pump must be the right size for the amount of water entering the space. A pump that is too small may run too often and wear out sooner.
Check the sump pump every spring. Lift the float to see if the pump starts. Make sure the discharge line is clear and has no damage.
Step 4: Add a Vapor Barrier
Once liquid water is under control, the dirt floor can still release water vapor into the air. A vapor barrier covers the ground and helps reduce this moisture.
For basic protection, a 10 mil barrier can be overlapped by 12 inches, with the seams taped. It should also extend about 6 inches up the wall and be secured in place. The right setup depends on the crawl space and local code requirements.
For material choices, barrier thickness, and installation details, read our crawl space encapsulation guide.
Step 5: Consider Encapsulation if Needed
Waterproofing helps keep liquid water out. It does not always control humidity in the air.
If the crawl space has heating or cooling ducts, humidity stays above 65 percent in summer, or mold is growing on the wood, encapsulation may be the next step. Crawl space encapsulation usually includes a strong barrier sealed across the floor and walls, sealed vents, wall insulation, and a dehumidifier when needed.
Encapsulation should come after the drainage system is working. It should not be used as a replacement for fixing water that collects under the house.
To decide whether your crawl space needs it, read our guide on whether crawl space encapsulation is necessary.
Crawl Space Waterproofing and Moisture Control: Why You Need Both
Waterproofing and moisture control deal with two different problems.
Waterproofing stops liquid water from entering or collecting under the house. It may include fixing soil slopes, moving water away from the foundation, installing drainage, and adding a sump pump.
Moisture control deals with damp air and water vapor. A vapor barrier helps stop moisture from rising from the dirt floor. Sealing the crawl space and using a dehumidifier can help when humidity remains high.
Some homes need both. If you have standing water, deal with that first. Once the water problem is fixed, check whether the crawl space still has damp air, condensation, or mold.
Vapor Barrier vs. Waterproofing: What Is the Difference?
A vapor barrier and a waterproofing system do different jobs.
A vapor barrier covers the dirt floor to reduce water vapor entering the crawl space. It can help keep the space drier, but it does not remove standing water or stop a major leak.
Waterproofing deals with liquid water. Depending on the problem, it may involve outside repairs, drainage pipes, and a sump pump.
If water collects under your home, do not rely on a vapor barrier alone. Fix the source of the water first, then add a barrier to help control moisture.
Basement vs Crawl Space Waterproofing: What’s the Difference?
Basements and crawl spaces can both have water problems, but the work needed may be different.
A basement is usually a larger space with full-height walls. Water can enter through wall cracks, floor joints, or the basement floor. Repairs may include crack sealing, interior drainage, a sump pump, or outside waterproofing.
A crawl space is a low area under the house. It often has a dirt floor, support piers, pipes, and air ducts. Waterproofing may involve fixing the yard slope, adding drainage under the house, installing a sump pump, and covering the ground with a vapor barrier.
Both basement and crawl space waterproofing aim to keep water away from the home and help prevent damage. The right method depends on where the water enters and how it moves around the foundation.
For more information about water problems in basements, visit our basement waterproofing services page.
What to Check Before Waterproofing Starts
Two things need attention before drainage work begins.
Structural damage. Water that stays under a house for a long time can damage the wood supports. A contractor should check the floor joists, girders, and sill plates for rot. Damaged wood may need to be replaced before a barrier covers the area. See our crawl space repair services to learn more about structural repairs.
Mold. If mold is growing on the wood, it may need to be treated before the space is sealed. Covering the area without dealing with the mold and its moisture source will not solve the problem. Our crawl space repair guide covers common moisture, mold, and structural problems.
Get a Waterproofing Plan for Your Crawl Space
Tri-State Waterproofing has worked on crawl spaces across North Georgia, Tennessee, and the Carolinas for over 20 years.
An inspection can help find where the water comes from, check for damage to the wood supports, and explain which repairs are needed first. Some homes may only need downspout extensions and a vapor barrier. Others may need a drainage system and sump pump.
Call 770-637-4026 or request a free crawl space inspection.
Crawl Space Waterproofing FAQs
What Is the Difference Between Crawl Space Waterproofing and Encapsulation?
Waterproofing helps keep liquid water out by fixing drainage problems and moving water away from the foundation. Encapsulation seals the crawl space with a barrier to help control water vapor and humidity. Waterproofing should come first when standing water is present.
Can I Waterproof a Crawl Space Myself?
You may be able to extend downspouts, fix small grading problems, and install a basic vapor barrier yourself. Interior drainage and sump pump installation can involve digging, electrical work, and water discharge lines. A professional can check what your crawl space needs and whether a permit is required.
How Much Does Crawl Space Waterproofing Cost?
Small outside fixes may cost a few hundred dollars. An interior drainage system with a sump pump may cost $1,500 to $6,000, depending on the length of the system and access to the crawl space. A vapor barrier adds to the cost. Full encapsulation is usually priced separately.
Does a Crawl Space Need a Sump Pump?
Not every crawl space needs a sump pump. If water does not collect under the house and there is no groundwater seepage, you may not need one. If water keeps coming in after heavy rain, a drainage system and sump pump may be needed.
Will Waterproofing Fix a Musty Smell?
It can help if the smell comes from standing water. If the floor is dry but the air is damp, or mold is growing on the wood, you may need more moisture control. This may include a vapor barrier, sealing the crawl space, or using a dehumidifier.
How Do I Control Moisture in a Crawl Space?
First, fix any leaks and stop water from collecting under the house. Make sure downspouts carry water away from the foundation and check that the soil slopes away from the house. If groundwater still enters, you may need drainage and a sump pump. A vapor barrier can help reduce moisture from the dirt floor. If the air stays damp, sealing the crawl space and using a dehumidifier may help.
Do I Need a Dehumidifier After Waterproofing a Crawl Space?
Not always. If waterproofing fixes the water problem and the crawl space stays dry, you may not need a dehumidifier. If humidity remains high, condensation appears on pipes, or mold keeps growing, a dehumidifier may help. Check the humidity after the water problem has been fixed before deciding.
What’s the Difference Between Basement and Crawl Space Waterproofing?
Basement waterproofing deals with water entering a larger space with full-height walls and a floor. Crawl space waterproofing deals with water under a house, often around a dirt floor, support piers, and low walls. Both may need drainage, but the method depends on the space and the source of the water.
