Do you have a wet crawl space? Many houses have this problem. Crawl space foundations have always been popular with builders and developers, because they’re easier and less expensive to construct than basement foundations. But these shallow foundations often develop major problems that are caused by excess moisture. If water is leaking into the crawl space through wall or floor areas, it creates ideal conditions for mold and wood rot. Mold creates foul smells that can leak into your living space, while also producing airborne spores that are hazardous to breathe. Left untreated, mold can develop into wood rot that damages critical structural members.

What’s involved in crawl space waterproofing?

Crawl space moisture problems can be solved using proven waterproofing methods. But it’s important to have this work done by a contractor who specializes in crawl space repairs. Crawl space waterproofing can be performed on its own, or it can be part of the crawl space encapsulation process. Either way, the waterproofing materials and techniques are the same. 


The first step in any crawl space waterproofing project is to identify where and how water is coming into the crawl space. A crawl space repair contractor will be able to determine these details during a free crawl space inspection. The most common waterproofing strategy involves several key elements. In most cases, the contractor will install an interior French drain system around the inside of the crawl space foundation. This drainage system captures water that leaks into the crawl space and conveys it to a sump pit, where a crawl space sump pump is installed. The sump pump comes on automatically when water in the sump pit reaches a predetermined level, discharging the water to the exterior.


Depending on the condition of crawl space foundation walls and how much water is leaking into the crawl space, it may be necessary to cover the walls with a heavy-duty plastic membrane. This moisture barrier will capture wall leakage and direct it into the drainage system, preventing water from collecting on the crawl space floor.


Controlling moisture with a crawl space dehumidifier

If your crawl space has had moisture problems for an extended period of time, or if mold is found during a crawl space inspection, your contractor may recommend installing a crawl space dehumidifier. This heavy-duty appliance will dry out the moisture that has collected in wood framing (joists, subflooring, posts) and other porous materials, stopping further rot and mold growth. This type of dehumidifier is equipped with a humidistat that enables you to set a target level of dryness in the crawl space air. Once this level is reached, the unit turns off automatically. Connecting the dehumidifier to the drainage system eliminates the need to empty the appliance. 

The cost of crawl space waterproofing

The free crawl space waterproofing estimate you get from a crawl space specialist will include an itemized breakdown of all the repairs and improvements that need to be done. Crawl space waterproofing costs depend largely on the linear feet of drain lines that need to be installed, plus the cost of installing a sump pit and sump pump. The installation of waterproof wall covering and a dehumidifier will obviously increase your waterproofing cost, but these additional items may be necessary when more severe moisture problems are encountered.