When assessing any moisture difficulties, it is best to tackle the easy and low cost problems first. Addressing obvious drainage issues such as downspouts, negative grade should be attempted before undertaking any major basement waterproofing solutions. When dealing with moisture issues specifically, it is advisable to remove or control the source of the moisture, and not simply to try and stop it at the last line of defense.
More often than not the simplest and least costly projects are removal of extra internal moisture sources in the basement area, such as Humidifiers and any sort of cooking, and to ventilate other sources, such as the clothes dryer or bathroom. Also important to note, if condensation in the summer is the problem, do not try and ventilate the basement with the warm, humid air from outside. Instead, try using an air conditioner system and/or a desiccant - type heat exchanger.
While a dehumidifier will temporarily alleviate the symptoms of a humid and odorous basement, it is not a permanent solution, and if used for too long, can actually be responsible for even more extensive damage. If a dehumidifier is used to dry out the basement air, it will draw moisture into the basement more rapidly than before, resulting in efflorescence and spauling of concrete and additional damage to the finishes.
A simple, appealing solution to the basement moisture problem is to coat the area on the inside or employ the use of a membrane. These solutions are not as costly as a drainage system, and will work for a time in some cases. Unfortunately, the water is still there, and in most cases the seal will eventually break, or the water will simply be rerouted into the basement via another pathway.
After dealing with the sources of interior moisture, it is recommended that the gutters, downspouts, and surface grading around the house be evaluated. Fixing these issues may solve the problem outright. If the problem continues despite this, then proceeding with an interior or exterior drainage system is advisable. The rest of this publication is dedicated to describing these techniques. If your basement has water problems, it is recommended that you deal with the water problems before completing the basement.
It is recommended that an active sub-slab depressurization system including a wash-rock layer below the slab be included. This technique may reduce the amount of moisture vapor entering the home, as it pulls moist air from beneath the slab. As an added bonus, it will also help monitor the levels of other soil gases such as radon. Also, blocking and sealing all open connections to the soil outside the foundation, but below the slab, is highly advisable.
If more information on soil gas management is required, there is an electronic (PDF) booklet available from the Environment Protection Agency entitled;" Building Radon Out"
The Process in Steps
- Control interior moisture sources.
- Do not ventilate with outside air in the summer.
- Repair and maintain the gutter, downspout system, and grading.
- Set up an exterior or interior drainage system.
Helpful Tips to Remember:
- While a dehumidifier can reduce the symptoms of humidity and odor, it is not a long term solution and should not be used as one.
- Without proper drainage, internal coating and/or membranes will not be a long term solution.
- Before carpeting or insulating, make sure that the walls and slabs are warm and dry.
APPROACH 1:
Install Proper Gutters and Downspouts and Correct Grading
|
|
Many basement water problems can be solved simply by installing proper rainwater and surface drainage options such as gutters and downspouts that carry water away from the foundation. It may require hauling fill to the site, but it is very important to slope the grade away from the house. This should be completed before attempting any below-grade drainage systems, since the above grade solution may solve the problem. Regardless of whether or not a drainage system is required, removing water at the source as much as possible is mandatory. |
APPROACH 2:
Exterior Drainage System
|
|
One of the more expensive solutions, but also the most effective way to deal with water control is to install an exterior drainage system at the existing building. However, this approach requires digging up the area around the foundation and rebuilding in a way that is reminiscent of new house installation. It should be noted that this will require the removal of shrubs and other obstacles located around the edge of the house. Traditionally, free-draining gravel is used in the backfill of external drainage systems. Drain tile can be placed beside the footing. Free-draining Membrane or Board
|
APPROACH 3:
Interior Drainage Channel above the Concrete Slab
|
|
When water is entering the basement where the floor and the wall meet, it is necessary to place a drain tile at the cove on the interior. The cheapest and simplest strategy is a drainage channel attached to the base of the wall and the floor slab. Water is collected and then run through a channel located on top of the slab, where it drains into the sump. The water then runs through a trap and into the sump basin, which should have a childproof cover and be airtight. It should be noted that his system is best suited to concrete walls with a plethora of cracks, since masonry walls retain water in the block cores at the 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, resulting in humidity, mold, and mildew, and should not be expected to drain groundwater from under the floor slab. |
APPROACH 4:
Interior Drainage Channel within the Slab Edge
|
|
Placing a drainage channel at the base of the wall and on top of the footing is also another common technique, though it does require removing and then replacing the concrete along the slab edge. The drainage channel is connected to a drain pipe leading to the sump, which should have an airtight, childproof cover, and holes must be drilled at the base of every block core to permit drainage. This approach drains the block cores completely, and as a result is effective when applied to concrete masonry walls. Depending on the product that was installed, the systems will have different shapes and prices. Since moisture is allowed into the block cores, it is essential to cap the tops and to place a vapor-retardant on the interior basement walls, and should not be expected to drain groundwater from under the floor slab. |
APPROACH 5:
Interior Drainage System beneath the Slab
|
|
The most effective interior drainage system is the perforated drain pipe installed inside the perimeter of the footing, though this requires the removal and replacement of the concrete at the slab edge. Placing the drain pipe beneath the slab allows drainage into a lower level, and similar to an exterior system, the drainage pipe connects to a sump, which should have an airtight, childproof cover. A crucial part of this technique is the dimpled plastic sheeting or gravel base that is 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 of the wall into the drain pipe. It is less expensive than many other similar, specialized drainage channel systems, and it should be noted that in low permeability soils, this system cannot handle rising groundwater, unless there is an aggregate layer under the slab. 1” river rock gravel is best for this application. |
