How to Waterproof a Crawlspace?

Written By Adam Paul - Waterproofing Expert

Crawlspace waterproofing is the process of preventing water, moisture, and humidity from entering the underfloor area located between the soil and the ground floor of a building. You should always use quality products and expert methods for the crawlspace waterproofing. Aqviz experts have prepared the following step-by-step guide by considering 15 years of crawlspace waterproofing experience. We highly recommend that you follow these steps for a long-lasting and healthy crawlspace.

9 Steps for crawlspace waterproofing

Inspect the crawlspace
Clear and clean the crawlspace
Improve the crawlspace drainage system
Seal crawlspace vents and openings
Apply crawlspace wall waterproofing
Install crawlspace vapor barrier
Add insulation and thermal protection (optional)
Install a dehumidifier in the crawlspace
Final inspection and maintenance of the crawlspace

1. Inspect the Crawlspace

Before starting crawlspace waterproofing, we highly recommend that you inspect it properly. Crawlspace inspection should be done to identify the water damage, identify the water sources, and identify the condition of the crawlspace.

At first, you should inspect the entire crawlspace for water damages signs such as mold and mildew growth, musty odor, wood rotting, wood warping, dampness on the walls and floor, paint peeling, water stains on walls, metal corrosions, efflorescence on the crawlspace walls, higher humidity, insect infestations, and standing water.

Then check foundation walls for cracks, examine plumbing lines for leaks, and ensure vents are not contributing to excess humidity in the crawlspace to determine the source of the water.

Next, check the floor of the crawlspace to determine the proper grading interior and exterior of the crawlspace to identify the ground condition of the crawlspace.

To inspect the crawlspace properly, Aqviz experts recommend that you download this crawlspace inspection guide.

add inspection list here.

2. Clear and Clean the Crawlspace

Before installing any waterproofing system, the crawlspace must be cleaned thoroughly. You should remove all loose debris, deteriorated insulation, and organic material from the crawlspace floor.

If there is standing water in the crawlspace, use a shop vac or portable sump pump to remove it completely. Then allow the crawlspace area to dry using high-powered fans or air movers for 24 to 48 hours.

Crawlspace cleaning process helps to adhere sealants and vapor barriers and prevents mold from being trapped beneath the waterproofing layers over time.

3. Improve Crawlspace Drainage System

After the crawlspace cleaning process, you should install an interior French drain system around the perimeter to collect and redirect water away from the foundation.

Then place a sump pump in the crawlspace at the lowest point to automatically evacuate collected water during storms or flooding.

Exterior crawlspace drainage system should be improved by ensuring that gutters are unclogged and downspouts discharge water at least 6 feet (1.8 meters) away from the structure to prevent soil saturation near the walls.

4. Seal Crawlspace Vents and Openings

Next you should seal crawlspace vents and openings in the crawlspace because uncontrolled airflow and moisture vapor enter the crawlspace through vents, pipe penetrations, and rim joists. Therefore, you should seal all the vents, openings in the crawlspace using foam boards and vent covers.

You can use spray foam or rigid insulation to fill gaps around pipes, electrical wiring, and HVAC ducts in the crawlspace. You can use an expanding foam to seal rim joists and structural framing to block humid air from circulating inside the crawlspace.

You should seal the crawlspace to prevent condensation and maintain a dry environment.

Step 5: Apply Crawlspace Wall Waterproofing

Then you should apply a cementitious waterproofing membrane or liquid-applied membrane using a trowel or roller to seal small cracks, pores, and mortar joints in the concrete or masonry walls.

If there are deep cracks and damage, you can use a crack injection method to seal them completely. After applying the waterproofing method, it should be allowed to cure fully within 24 hours.

Crawlspace wall waterproofing is essential to stop lateral water intrusion and prepare the surface for vapor barrier installation.

Step 6: Install Crawlspace Vapor Barrier

After sealing the cracks and damages, you can install a vapor barrier in the crawlspace. You should lay a reinforced polyethylene sheet, 6 to 20 mil thick, across the entire crawlspace floor area. Overlap each seam by at least 12 inches (30 cm) and seal with waterproof tape or butyl adhesive to create a continuous barrier on the crawlspace ground.

Extend the vapor barrier up the foundation walls at least 6 inches (15 cm) and secure it with mechanical fasteners and caulk. This sealed system prevents ground moisture from entering the crawlspace and keeps the area dry year-round.

Step 7: Add Insulation and Thermal Protection (optional)

Install rigid foam insulation boards in the crawlspace along the foundation walls to help stabilize temperature and reduce energy loss in seasonal temperature swings.

We highly recommend you avoid using fiberglass batt insulation in the crawlspace ceiling, as it absorbs moisture and supports mold growth over time.

Proper crawlspace insulation works better with vapor barriers to improve comfort and energy efficiency in the living spaces above.

Step 8: Install a Dehumidifier in the Crawlspace

After the insulation process, you can install a dehumidifier in the crawlspace. A dehumidifier is installed in the crwalspace if it has continuous moisture production.

After placing the dehumidifier in the crawlspace, connect the drainage hose to the sump basin or an exterior outlet to remove accumulated water safely away from the crawlspace.

As well as you should also place a digital hygrometer in the crawlspace to monitor humidity levels regularly and adjust settings as needed.

Crawlspace dehumidifier helps to maintain the humidity between 40%-50% RH, which prevents moisture damage in the crawlspace.

Step 9: Final Inspection and Maintenance of the Crawlspace

Once crawlspace waterproofing is complete, conduct a final inspection to confirm that all seams, edges, and barrier overlaps are sealed correctly.

Check for gaps or exposed areas that could compromise the moisture barrier. Schedule crawlspace maintenance checks every 6 to 12 months to evaluate the performance of the sump pump, drainage lines, and dehumidifier.

What Tools and Materials Are Needed for Crawlspace Waterproofing?

Crawlspace waterproofing requires specific tools and materials to inspect, seal, drain, insulate, and protect the underfloor space from water and moisture intrusion.

Here is a complete list of tools and materials used for crawlspace waterproofing

Materials for crawlspace waterproofing

Vapor barrier sheeting (12-20 mil reinforced polyethylene)
Waterproof tapes (seam tape or butyl adhesive)
Polyurethane caulk or construction adhesive
Waterproofing membranes (cementitious/PU waterproofing)
Rigid foam insulation boards (XPS or polyiso)
Sump pump system
Perforated drain pipe (for French drain system)
Gravel or drainage stone (¾ inch washed)
Drainage matting or dimple board
Crawlspace-rated dehumidifier
Vent covers or foam vent plugs
Mechanical fasteners (plastic pins or masonry anchors)
Moisture-resistant vapor barrier tape
Spray foam insulation
Hygrometer (humidity monitor)

Tools for crawlspace waterproofing:

Utility knife (for cutting vapor barrier and insulation)
Safety equipments
Measuring tape
Caulking gun
Cordless drill/driver
Hammer
Staple gun
Work gloves
Protective mask or respirator
Headlamp or work light
Plastic sheeting or tarp (for work surface)
Shop vac or wet/dry vacuum
Portable fan or air mover
Bucket and sponge (for cleaning surfaces)
Level and straight edge (for drainage slope checks)

What can Cause Damage to Crawlspace Waterproofing?

Crawlspace waterproofing damages occur when moisture management systems fail or materials degrade over time.

Here are the main 8 Causes of Crawlspace Waterproofing Damages.

Tears and punctures on crawlspace vapor barrier due to heavy foot traffic, sharp debris, or improper installations allow ground moisture to seep through.
Gaps at seams and unsealed wall edges on crawlspace vapor barrier due to improper sealing break the vapor seal and reduce its moisture-blocking effectiveness.
Sump pump failure in crawlspace due to electrical issues, clogged pumps, or float switch malfunctions prevents active water removal and leads to water buildup.
Clogged or crushed drainage pipe in crawlspace systems due to sediment buildup, root intrusion, or pipe collapse blocks proper water flow and causes drainage failure.
Dehumidifier malfunction or neglect in crawlspace due to undersized units, mechanical failure, or lack of maintenance leads to poor humidity control, condensation, and mold growth.
Foundation wall cracks or shifting in crawlspace due to structural movement or untreated settling create new moisture pathways through walls and footings, leading to water intrusion.
Poor maintenance or skipped inspections in crawlspace allow minor issues like loose seams, sump pump failure, or drainage obstructions to escalate into major waterproofing failures.

Can Crawlspace Waterproofing Be Done in Any Season?

Yes, crawlspace waterproofing can be done in any season, but dry conditions during spring or fall offer the best working environment. You should avoid waterproofing during heavy rain or frozen ground, as wet or frozen surfaces affect material adhesion and drainage work.

How Long Does Crawlspace Waterproofing Take?

Crawlspace waterproofing for a 1,000 sq.ft area typically takes 2 to 4 days, depending on the severity of moisture, the number of repairs, and the system complexity.

What Thickness Vapor Barrier Should Be Used in Crawlspace Waterproofing?

For effective crawlspace waterproofing, use a 12 to 20 mil reinforced vapor barrier. Thicker barriers offer better puncture resistance, long-term durability, and improved moisture blocking, especially in high-traffic or uneven soil areas.

Do I Need a Sump Pump in Every Crawlspace Waterproofing System?

No, a sump pump is required only if the crawlspace has active water seepage, a high water table, or poor soil drainage. Crawlspace waterproofing with only vapor barriers may be sufficient in dry climates or elevated foundations.

Can I Skip Wall Sealing if I Use a Vapor Barrier on the Floor?

No, crawlspace waterproofing is incomplete without wall sealing. Moisture often enters through porous foundation walls. Applying a liquid membrane or waterproof coating is essential to block lateral seepage and protect framing structures.

Is Crawlspace Waterproofing a Permanent Solution?

Crawlspace waterproofing provides long-term protection, but it requires periodic inspection and maintenance. Sump pumps, dehumidifiers, and drainage lines should be tested and cleaned regularly to keep the system functional.

Does Crawlspace Waterproofing Add Value to the Home?

Yes, crawlspace waterproofing improves structural health, energy efficiency, and indoor air quality, which adds long-term property value and reduces repair costs. A properly waterproofed crawlspace is a strong selling point in real estate markets.