Basement waterproofing can be broken down into two categories. The first is surface water that enters a basement or below grade structure from the foundation walls including basement windows, foundation cracks, pipe penetration leaks, sill or box beam and wall seepage. The second is groundwater that enters a basement through the floor slab or appears in an area known as the cove joint, which is where the floor and walls meet and is commonly referred to as hydrostatic pressure.
Identify Water Problem
Most property owners are faced with the task of trying to decide which or both of these problems exist and choosing between waterproofing contractors who sometimes differ on opinions. Homeowners faced with a basement water issue are also faced with the challenge of educating themselves on the techniques used to remedy the problem. Most unsuspecting homeowners are lured into the belief that applying waterproof paints or compounds to the interior foundation walls will end their water problems. However, eventually these coatings deteriorate overtime or simply won’t handle the pressure of water exerted from the wall.
Basement waterproofing or basement dewatering should start on the home’s exterior, with the most logical principle that water should never accumulate around a foundation. With this simple rule in mind, property owners should take note of the following ideal conditions. Landscape garden beds and landscape areas should pitch water at least 15 feet away from the foundation. Soil should not be added to within two inches of the sill plate or top of the foundation. When downhill slopes permit water to flow towards a foundation a subsurface drainage system, a drywell or re-grading should be considered. Gutter downspouts should be extended or sloped 15 feet away from the foundation and window wells that accumulate water should be corrected. Foundation cracks and leaks should be repaired.
With these basic guidelines in place there is the issue of subsurface water. Ground or trapped water can fluctuate seasonally in response to the amount of rainfall. This causes a hydrostatic pressure of water that pushes through basement slabs in many homes. The most common solution for hydrostatic pressure is a drainage system or a French drain. A foundation drainage system has four main components: the drainage pipe, gravel or drainage stone, the concrete that covers the gravel and the discharge system that consists of a sump basin and sump pump. All of these elements must be installed for the system to function properly.
Basement waterproofing systems are an important aspect of a home especially if it is prone to the effects of seepage. A properly installed and maintained basement drainage system will remove water before it has a chance to rise above the level of the basement floor. Water is then diverted to a sump well recessed in the floor where a pump discharges it to a safe location. Basement waterproofing systems are usually installed along the interior portion of the buildings foundation. Most systems are retrofitted into homes when exterior drainage systems are not present or have failed.
Over the past few years many builders and developers have installed interior systems during construction to minimize liability and meet local building codes. There are two popular methods of installation in today’s market. The first is on top of the footing, also known as the shallow depth method, in which a rectangular shaped channel is installed 2-4 inches under the basement floor along the foundation perimeter. The channel collects the water that runs down the wall into a gap where the floor and wall meet and then channels it into a collection basin equipped with a sump pump. In most cases this method can relieve hydrostatic pressure. The more popular method is a deep channel drainage system, typically installed along the perimeter of the foundations, footing or the lowest point on the foundation wall under the basement slab. This procedure generally requires the removal of approximately 12-18 inches of concrete slab where the floor and wall meet and excavation of subsoil at the side of the footing. A drain tile in the form of a perforated pipe or channel, combined with washed gravel, is laid parallel to the footing with a slight pitch to a collection tank where a sump pump is located to discharge water.
With either method of installation, a battery back-up pump should be installed to prevent failure during power outages. The sump pump basin should have a cover that is airtight. All discharge pipe penetrations should be sealed to prevent moisture from escaping the pump basin. When foundation moisture problems are present, accountable waterproofing contractors will choose to install a form of vapor barrier, secured to the foundation walls, that allows seepage into the system without allowing soil vapors, radon gases, hydrocarbon gases or ground moisture to escape into home. In all cases the floor is then re-cemented, sealing the open trench.