When it comes to draining water from around and under basements there is a single preferred method and a whole host of less desirable methods. This preferred method is named many things but has a few basic elements that engineers and professional waterproofing contractors prefer.
1. Sealed System
2. Pitched Drain Piping
4. Below Slab Drainage
First of all, any plumbing system must be sealed from the living area to prevent increasing humidity levels which can lead to mold growth, higher radon levels and bacteria growth. This can be seen in many older homes which have a damp and musty cellar smell due to poor drainage and open cavities in floors and walls.
Secondly, any plumbing system must be based on the simple principal that water, among other things, flows downhill. Without positive slope, pitch, water will sit in place opposed to flowing downhill to a collection point where it can be directed away from the foundation.
Next, water enters a basement from a path of least resistance. Often times this path is the cold joint between the footing and wall. Water can migrate through this joint due to pressure caused by the downward force that saturated soils place on the footing.
Lastly, interior drainage systems must remove water from beneath the basement floor. As many homeowners know, basement floors become cracked due to water that is trapped below the concrete floor. This trapped water is constantly looking for a path of escape and can crack a concrete floor very easily.
So with this information in hand it becomes very simple to determine the best interior basement drainage system. The system must be closed, or sealed from the living space. This will include a sealed sump pit and sealed piping system that is laid around the perimeter of the basement walls. Many systems have open backs designed to capture water that is running down the walls. These open back systems will capture wall water but remember if things can get in they can also get out. These open backed systems allow water vapor and radon an easy path to your living space. Closed or sealed systems prevent this phenomenon from happening by their very nature of being sealed from living spaces.
Open backed systems have another primary fault and that is the fact that they are laid on top of the footing. Concrete footings are poured flat so that the basement walls can be poured or laid upon a flat surface. Any drainage system that is laid on top of the footing cannot be pitched to drain the water that they collect. The water sits in these systems promoting mold and bacteria growth which can cause clogging and health concerns. Also, if you place drainage pipe, along with a bed of clean gravel, next to the footing you will gather the water before it comes in contact with the basement floor. By doing this you can prevent floor heaving and cracking. Open backed systems that sit on top of footings must have the water rise above the bottom of the concrete floor before they can accept any water. Closed systems allow water to enter much earlier and since they are next to the footing they can be pitched toward a sump pit for collection and discharge.
Before you contract any waterproofing company to solve your basement moisture problem keep the above items in mind and demand that the proper techniques are used. Now that you know what must be included with your new basement drainage system, ask questions and do not be fooled by their slick answers.