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Check your basement for Water Stains, Cracks and Bad Odors

Basement Basics

The foundation supports the structure above it and resists the pressure of the soil around it. Fixing any foundation problems is essential to preserve the durability and structure of your home. Without a sound foundation, problems are inevitable. If problems with the foundation exist, they will often affect other parts of the building. Also, problems that you discover in the basement should be remedied before any renovation work is done.

Full height basements are common in areas where the foundation of a home needs to be placed below the frost level. Unfortunately, basements are susceptible to water infiltration. common problem indicators are cracks in slabs, walls and footings, and basement moisture.

The Main Causes of Cracks and Leakage

  • Inadequate Grading around the house
  • Defective or missing gutters and downspouts
  • Improperly Designed Window Wells
  • Ineffective Drain Tile and Sum Pit
  • Improper Drainage with Under slab Ducts
  • Structural Cracks
  • Water Infiltration

Prior to the construction of your home, a big hole was dug in your yard. Next, the footing and walls of your home were constructed. Loose dirt was then poured to fill the footing, and the floor was then laid between the walls. A drainpipe was installed next. Finally, loose soil was filled over the pipe and around the exterior of the foundation walls. In short, your house is set in a bowl of hard earth, surrounded by highly absorbent loose soil and relying on a small pipe for proper drainage.

Eventually, the drainpipe can clog up and runoff water begin to force its way into your basement through the cracks and crevices of your basement walls and floor. Or worse, if the drainpipe was improperly installed, it may be too slow to drain to a storm sewer, or to an open area down and away from your home, especially if no sump pump has been installed to correct this problem.

A leaky basement can be a difficult dilemma because there are so many possible causes. Fixing a leaking basement ranges from the easy and inexpensive to the complicated and expensive. Unless you are highly experienced in dealing with the problems of a leaky basement, it is wise to consult a professional to find a cause of the leak and a solution for the problem. Trying to pinpoint the cause and a subsequent solution can involve a lengthy trial and error process that can result in additional damage occurring while you try to find a solution for the problem, so act immediately.

The best way to approach any building problem is to first do the things that are easy and low cost. Then proceed in a logical order doing the next least costly technique with the most positive likely result. With moisture problems, the best approach is to remove or control the source of the moisture, not to try to stop it at the last line of defense.

Fixing the Problem

First, the simplest and least costly techniques are to remove excessive internal moisture sources in the basement (humidifiers, cooking) and ventilate other sources (clothes dryer, bathroom). Second, if condensation in the summer is the problem, do not ventilate the basement directly with warm, humid air. Ventilation through an air conditioning system or with a desiccant-type heat exchanger is recommended.

Dehumidification can be used as a means of reducing the symptoms of humidity and odor in a basement, but it is not a permanent or complete solution.. In fact, if a dehumidifier is used in a basement with moisture problems, it may cause greater damage. By drying out the basement air, moisture is drawn into the basement more rapidly causing problems with the concrete and further damage to interior finishes.

It is appealing to solve a basement moisture problem with a membrane or coating on the inside. It is less expensive than a drainage system and seems to work for a time in some cases. The water is still there, however, and eventually these systems deteriorate or simply move the water to another pathway into the basement.

The recommended approach, after removing interior moisture sources, is to evaluate the gutters, downspouts, and surface grading around the house. These should be corrected first and may solve the problem. Then, if a moisture problem persists, proceed with an interior or exterior drainage system.

Step-by-Step Process

  1. Control interior moisture sources.
  2. If summertime, don’t ventilate with outside air.
  3. Correct grading, gutter and downspout system.
  4. Provide an interior or exterior drainage system.
  5. If the basement is to be finished, place a vapor retarder over the walls and floor before finishing.


  • A dehumidifier can help reduce the symptoms of humidity and odor, but does not solve the problem. A membrane or coating on the interior without providing drainage generally will not solve the problem in the long term.
  • Walls must be dry before insulating. Slabs must be warm and dry before carpeting.

Solutions Explained

Install Proper Gutters and Downspouts, and Correct Grading

A great number of basement water problems can be solved by handling rainwater and surface drainage properly, using gutters and downspouts with extenders or splash blocks to carry the water away from the foundation. Sloping the grade away from the house, which may require hauling fill to the site, is very important. This should be done before any below-grade drainage system is installed, since the above-grade corrections may solve the problem. Even if a drainage system is required, removing water at the source is necessary.

Exterior Drainage System

Installing an exterior drainage system is the most costly, but also the most effective water control approach. This requires digging up the area around the foundation and rebuilding it similar to a new house installation. It also requires digging up shrubs and other obstacles around the house. Usually, waterproofing and insulation are installed at the same time, in addition to making any repairs to the structure. Traditional exterior drainage systems use free-draining sand in the back-fill. Drain tile can be placed beside or on top of the footing. Level drainpipe installations are satisfactory. A minimum of 12 inches of coarse aggregate should be placed around the drain tile.

Free-draining Membrane or Board

It can be expensive to haul pea rock or sand to a site for back-filling purposes. Instead, a drainage mat can be placed against the foundation wall and then back-filled with any soil on site. The drainage must have a free-flowing path to the perforated drainpipe below.

Draining to a Sump

All exterior drainage systems must drain to a sump that can be pumped out. The sump must have an airtight, childproof cover

Interior Drainage Channel above the Concrete Slab

In most cases when water is entering the basement, an interior drainage system is installed. The simplest and least costly approach is a drainage channel adhered at the base of the wall and the floor slab. Water is collected and drained into a sump using another channel placed on top of the slab, then through a trap to the sump basin. The sump should have an airtight, childproof cover. This system is best suited to a concrete wall with cracks. It does not solve the problem in masonry walls because water remains in the block cores at floor level and the water level is only lowered to the top of the slab. With this approach, the water is not completely removed from the space. The result is that humidity, mold, and mildew can still be a problem. This system cannot drain groundwater from under the floor slab.

Interior Drainage Channel within the Slab Edge

Another technique is to place a drainage channel at the base of the wall on top of the footing. This requires removing and then replacing the concrete along the slab edge. The drainage channel is connected to a drainpipe leading to the sump. The sump should have an airtight, childproof cover. This approach is effective for concrete masonry walls with water problems because it drains the block cores completely. Holes must be drilled at the base of every block core to permit drainage. This may require removing more than the minimum amount of concrete to fit the drill in. These systems have different shapes and prices depending on the product installed. Because moisture is allowed to penetrate the block cores, it is essential to cap the tops and place an air-vapor barrier on the wall.

Interior Drainage System Beneath the Slab

The most effective of the interior drainage systems is a perforated drain pipe installed inside the perimeter of the footing. This requires removing and replacing concrete at the slab edge. By placing the drainpipe beneath the slab, it drains the area to a lower level. Similar to an exterior system, the drainage pipe connects to a sump. The sump should have an airtight, childproof cover. A critical component of this approach is the dimpled plastic sheeting placed at the base of the wall and beneath the slab edge. Dimpled sheeting is similar to a small egg crate and permits free drainage down the wall and across into the drainpipe. It is less expensive than many specialized drainage channel systems. In low permeability soils, this system cannot accept rising groundwater unless there is an aggregate layer under the slab.

Finishing a Basement with Moisture Problems

Using the interior drainage system, a polyethylene vapor retarder is placed over the foundation wall before installing finishes. No interior vapor retarder should be placed over batt insulation when finishing walls if there is already a vapor retarder on the foundation walls. There should be an interior air barrier (such as the wall finish material) sealed at the top and bottom plates and at all penetrations. Rigid insulation is placed on the floor and then covered with a decay-resistant plywood sub floor.

Complete Interior Drainage System with a Finished Interior
For basements with severe problems, it is possible to use the interior drainage system and extend the dimpled plastic sheeting over the entire wall. The sheeting serves as a vapor retarder and forms a drainage layer connected to the drain pipe below. This is particularly effective if the wall is to be finished. A second interior vapor retarder should be avoided, however, if batt insulation is used. There should be an interior air barrier (such as the wall finish material) sealed at the top and bottom plates and at all penetrations.
The dimpled plastic sheeting can also be placed over the floor and covered with rigid insulation and a tongue and groove plywood sub floor. This forms a vapor retarder and drainage layer on the floor.

Problems with Finishing

If a basement has moisture entering through walls or floor, covering it with any kind of wall finishing material or carpet is likely to make it worse unless the water is dealt with first. Wet carpet and moisture under wall coverings are excellent places for mold and mildew growth that can lead to health problems. Generally, when the relative humidity (RH) is above 60 to 70 percent, problems occur with mold and mildew growth.

Mechanical Ventilation

Mechanical ventilation pipes connected to a suction fan can be fabricated to the dimpled sheeting. This draws moist air from beneath the sheeting and dries out the floor. It also assists in controlling radon and other soil gases.

Hiring A Professional

While a homeowner can attempt to repair unchanging cracks, professional help is essential for:

  • Assessing and correcting changing cracks
  • Solving leakage problems so that they will not recur
  • Lowering floors and underpinning or reinforcing foundations
  • Adjusting structural elements
  • Assessing loads and structural capacity
  • Correcting ad freezing and frost heaving problems
  • Correcting major pest infestations (which can cause structural damage)

The cost of fixing foundation problems depends on the condition of the existing foundation, access to problem areas, amount of work required (especially below-grade), and the time involved.

This paper is intended for informational purposes only. Nothing contained herein constitutes legal, financial or other professional advice. Transmission of these materials is not intended to create, and receipt does not constitute, any relationship of any kind between the provider and the recipient. Some of these points may not apply in your area. Different term and conditions may vary from state to state and province to province. All articles, text and photographic material presented here is for the use and pleasure of the recipient only. Download PDF

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