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 House
Moisture 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 Issue
To 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.
Four systems transmit moisture from the exterior of the structure to the inside of the basement:
- The flow of liquid water.
- The suction that is caused by capillary action.
- Diffusion of vapor.
- The movement of air.
Poor construction with cracked, sinking foundations is also blamed for difficulties. Houses and basements may be physically solid in many circumstances, but they are often not equipped to manage water drainage. It is typical to fail to slope the ground surface away from the foundation or to lack a sufficient gutter and downspout system. Subsurface drainage systems that are either missing or inoperable are also rather common. These issues may be addressed and rectified if a systematic method is utilized. 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.
Symptoms
- 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 Rain
A 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 Moisture
People 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 Air
Basement 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 Suction
Moisture 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 Floor
Warm 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 Walls
The 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 Grading
Problem: 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 Downspouts
Problem: 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 Wells
Problem: 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 Ineffective
Problem: 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 Ducts
Problem: 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 Cracks
Problem: 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 Overview
The 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 Solution
Dehumidification 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 Solution
Remaining 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 Strategy
Assess 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.
Notes
- 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.
Approach 1: Build Adequate Gutters and Downspouts, As Well as Suitable Grading
Many basement water issues may be avoided by correctly managing rainfall and surface drainage by installing gutters and downspouts with extenders or splash blocks to direct water away from the foundation. It is critical to slope the gradient away from home, which may need bringing fill to the site. Before installing any below-grade drainage system, this should be done since above-grade modifications may address the issue. Even if a drainage system is needed, draining water as much as possible at the source is essential.
Approach 2: Outside Drainage System
Putting an outside drainage system on an existing structure is the most expensive and effective water management method. This entails excavating the area surrounding the foundation and reconstructing it like a new home installation. Digging up plants and other barriers surrounding the home is also required. Waterproofing and insulation are often completed concurrently, along with any structural repairs. Backfill for classic outside drainage systems is free-draining sand. Drain tile may be installed next to or on top of the footing. The installation of level drain pipes is good. Around the drain tile, a minimum of 12 inches of coarse aggregate should be used. Transporting pea rock or sand to a location for backfilling might be costly. Instead, a drainage mat may be laid against the foundation wall and then backfilled with whatever soil is available. The drainage must flow freely to the perforated drain pipe below.
Approach 3: Above the Concrete Slab, There Is an Inner Drainage Canal
When water enters the basement, an internal drainage system is usually constructed. A drainage canal attached at the base of the wall and the floor slab is the simplest and least expensive solution. Water is collected and drained into a sump basin through another channel installed on top of the slab, then via a trap. The sump should be airtight and childproof. This method is best suited to a cracked concrete wall. It does not address the issue with masonry walls since the water stays in the block cores at floor level, and the water level is only decreased to the top of the slab. The water is not evacuated from the area using this method. Consequently, humidity, mold, and mildew may still be an issue. This technology is unable to drain groundwater from under the floor slab.
Approach 4: Inside the Slab Edge, an Inner Drainage Channel
Another method is to install a drainage channel on top of the footing at the base of the wall. This necessitates the removal and replacement of the concrete around the slab border. The drainage channel is linked to a pipe that leads to the sump. The sump should be airtight and childproof. Since it thoroughly drains the block cores, this method is useful for concrete masonry walls with water issues. To allow for drainage, holes must be bored at the base of each block core. This may need removing more concrete than the minimum quantity specified to fit the drill. Depending on the product fitted, these systems come in various forms and pricing. Since moisture is permitted to permeate the block cores, it is critical to cover the tops and coat the inside basement walls with a vapor-retarder coating.
Approach 5: Underneath the Slab Internal Drainage System
A perforated drain pipe put within the perimeter of the footing is the most efficient internal drainage system. This necessitates the removal and replacement of concrete at the slab border. The drain pipe is placed under the slab to drain the area to a lower level. The drainage pipe, like an outside system, links to a sump. The sump should be airtight and childproof. The dimpled plastic sheeting put at the base of the wall and under the slab edge is a significant component of this strategy. Dimpled sheeting looks like a little egg crate and allows for unimpeded draining of the wall into the drain pipe. It costs less than many specialist drainage channel solutions. This method cannot handle increasing groundwater in poor permeability soils unless an aggregate layer is underneath the slab. This solution should be supplemented with an active soil gas management system that links to the sump and perimeter drain pipe.
Conclusion
The moisture in a basement is complex and can be caused by a variety of factors. The solutions discussed here may help to reduce the amount of groundwater collected around the foundation wall and floor slab. Still, it’s essential to understand all contributing factors to identify the root cause effectively. A comprehensive assessment helps ensure the best remedy for your particular situation. Bedrock Restoration can provide a detailed inspection of your basement and make the necessary repairs to ensure it is dry and safe for you and your family. Contact us today to get started!
