This article briefly explains moisture sources, moisture movement methods, and common basement moisture concerns. Finally, a step-by-step procedure is described for each issue and numerous specific alternatives to fixing the problem.
An Issue That May Harm Your Health and Your HouseMoisture issues in existing basements are fairly prevalent but often misunderstood and undertreated. This may not be a big issue in a seldom utilized basement and isolated from the living quarters above. Most basements, however, are linked to the rest of the home by ducting or other openings. Moreover, basements are increasingly being converted into completed living and sleeping areas. Moisture problems are not only bothersome and uncomfortable in these circumstances but may also lead to health issues. Mold and mildew may develop in moist carpets and behind wall coverings. Basement water issues are treatable, but they come at a cost.
Understanding the IssueTo resolve basement moisture issues, it is vital to first determine where the water is coming from and what processes allow it to enter the basement. There are just three moisture sources:
- Rainwater or groundwater liquid.
- Humidifiers, unvented clothes dryers, restrooms, and stoves, as well as moisture in concrete after construction, are examples of interior moisture sources.
- Humid air from the outside enters the basement and condenses on cold surfaces.
- The flow of liquid water.
- The suction that is caused by capillary action.
- Diffusion of vapor.
- The movement of air.
- Water seeped through the walls.
- There is standing water on the floor.
- A damp ring surrounds the saturated foundation of concrete block walls.
- The air is damp and humid.
- Summer condensation on cool walls and floors.
- Mold, mildew, and odor.
- Carpet or wood deterioration.
- Rot and deterioration of wood headers, joists, sill plates, and columns.
- Wall covering staining and blistering.
- Spalling of concrete or masonry due to efflorescence.
Sources of Basement Moisture
Groundwater and RainA 1-inch rain drops 1,250 gallons of water on a 2,000-square-foot house’s roof. Some water enters the basement due to improper grading, gutters, and downspouts. Flooding or seasonal site conditions may also cause the below-grade water table to increase. This is why drain tile systems are advised around basement walls, even on sandy or gravel soils.
Sources of Interior MoisturePeople and their actions cause moisture within basements. Humidifiers, unvented clothes dryers, bathing, and cooking are all common causes. These operations expand once basements are completed. Another internal source is the moisture contained in fresh concrete after construction. This may equate to 0.2 gallons per square foot of the wall and 0.1 gallons per square foot of floor in a normal home. A new property may take months or even years to settle into its surroundings.
Ventilation with Humid Outdoor AirBasement windows can be opened for fresh air in the summer. If the air outside is warm and humid, it will condense on the chilly basement walls and floors. Many people detect this dampness and feel they have a basement wall leak when, in reality, the moisture comes from condensation.
Moisture Movement Mechanisms
Capillary SuctionMoisture is moved through porous materials via capillary suction. Water may be carried upward and laterally via microscopic pores in the concrete footing and slab. This action causes a damp ring at the foot of many basement walls. This is quite prevalent in cold joints. Water may rise substantially due to capillary pull, as seen below: The kind of soil and the degree of capillary rise:
- Gravel – A few inches or less.
- Sand – 1 to 8 feet.
- Silt – 12 to 16 feet.
- Clay – 12 to 20 feet.
Air Leaks Through the Walls and the FloorWarm air rises and causes a stack effect in most homes. This creates a negative pressure in the basement and pulls wet air in via foundation cracks or holes, including open sump pits. As a result, sumps should have an airtight lid. Moist air is pulled through the block cores of a concrete block foundation, particularly if they are left exposed at the top course.
Diffusion of Vapor Through Foundation WallsThe transport of moisture in the vapor state through a substance is called vapor diffusion. It is determined by the material’s permeability and the driving power of the vapor pressure difference. Vapor may flow from wetter ground to drier basement interior via concrete walls and flooring in a basement. This process is slowed by vapor retarders such as foundation waterproofing and polyethylene.
The Most Common Causes of Basement Moisture Issues
Insufficient GradingProblem: Water is channeled into the basement if the land surrounding a foundation is flat or slopes toward the house. The soil next to the home is often backfilled without sufficient compaction and eventually sinks. This is particularly true under stoops, where water may gather against the basement wall. Solution: Put soil around the house on a slope of at least 1 inch per foot away from the foundation wall for at least 6 feet.
Defective or Missing Gutters and DownspoutsProblem: Defective or missing gutters and downspouts drive rainfall toward the foundation perimeter. A downspout that lacks an extension or splash block is worse than none. It collects massive rainfall from the roof and deposits it in a single concentrated spot near the basement. Solution: Install at least one downspout for every 50 linear feet of a roof eave. Water should be discharged at least 4 feet beyond the wall. Rain drainage is effectively directed by slanted concrete walkways surrounding basements.
Inadequately Built Window WellsProblem: Window wells function as a drain close to the basement wall. They are often designed incorrectly, directing any water toward the base rather than away from it. Solution: Window wells should be filled with 3/8- to 3/4-inch coarse aggregate from the footing to the window sill. A supplementary drain tile extension should be installed from the footing to the base of the window well.
The Drain Tile and Sump Pit Are IneffectiveProblem: Many current homes lack a subsurface drainage system. This dates back to when basements were not utilized as living spaces. In other circumstances, the systems fail for reasons like pipe collapse, silt and/or tree root clogs, or a damaged connection to the sump. A pump is frequently installed in the sump pit to move the water to the ground surface outside the foundation wall. This pump has the potential to fail. Solution: See the methods 2–5 that follow.
Inadequate Drainage With Under-Slab DuctsProblem: When heating ducts are put under a basement floor slab, the drainage system may be constructed at a height that is too high. In effect, the duct functions as a drainage system. Mold infection might have major health repercussions if standing water is inside the heating duct. Solution: Heating ducts installed under the basement floor must be insulated, waterproof, and sloped to drainage and cleaning stations. Under the ducting, a drain tile and coarse aggregate may be installed.
Structural CracksProblem: Cracks in concrete and concrete block foundations are common. These may be severe if the floor joists are not correctly linked to the foundation wall, allowing the wall to shift. Cracking is sometimes caused by soil settling. Cracks are common when walls meet solid constructions, such as a fireplace. Drainage usually eliminates water from fractures, although maintenance may be required. Solution: Appropriate footing design is necessary, as is a correct link between the foundation wall and the building above.
A Basement Moisture-Resolution Options OverviewThe easiest way to handle any construction challenge is to start with simple and low-cost solutions. Next, in a logical sequence, do the next least expensive procedure with the highest likelihood of success. When dealing with moisture issues, the best technique is nearly always to eliminate or regulate the source of the moisture rather than trying to stop it at the final line of defense. Initially, and least expensively, eliminate excessive internal moisture sources in the basement (humidifiers, cooking) and ventilate other sources (clothes dryer, bathroom). Second, if condensation is a problem in the summer, avoid immediately ventilating the basement with warm, humid air. Using an air conditioning system or a desiccant-type heat exchanger for ventilation is advisable.
Dehumidification Isn’t a Long-Term SolutionDehumidification may help reduce the symptoms of humidity and odor in a basement, but it is not a long-term or perfect solution. Using a dehumidifier in a basement with moisture issues may do more harm. Moisture is pulled into the basement more quickly when the air is dried out, producing efflorescence and spalling of concrete and severe damage to interior finishes.
Interior Membranes or Coatings Are a Short-Term SolutionRemaining a basement moisture issue with an internal membrane or coating is enticing. It is less costly than a drainage system and seems to function in certain circumstances. Nonetheless, the water remains, and these systems fail or redirect the water to another passage into the basement.
Recommended StrategyAssess gutters, downspouts, and surface grading: After eliminating indoor moisture sources, the suggested procedure is to check the gutters, downspouts, and surface grading surrounding the home. These should be addressed first since they may resolve the issue. Interior or exterior drainage system: If the moisture issue continues, an interior or external drainage system should be installed. All of these methods are detailed further below. If you want to complete a basement with water difficulties, you must first deal with the water problem. Sub-slab depressurization system: An active depressurization system with a washed-rock layer under the slab is advised. This pulls wet air from under the slab, which may assist in lessening the amount of moisture vapor entering the residence via slab holes. It also aids in the management of radon and other soil gasses. Sumps and other exposed soil connections outside the foundation and under the slab should be plugged and sealed.
A Step-by-Step Procedure
- Control the sources of indoor moisture.
- Avoid using outdoor air for ventilation during the summer.
- Proper grading, guttering, and downspouts.
- Install a drainage system, either inside or outside.
- A dehumidifier may help alleviate the symptoms of humidity and odor, but it will not address the issue.
- A membrane or coating on the inside that does not provide drainage will not fix the issue in the long run.
- Before insulating, the walls must be dry. Before carpeting, the slabs must be warm and dry.