Good drainage in and around buildings is vitally important to their stability and longevity. Around the Inland Northwest, Criterium-Pfaff Engineers have personally observed hundreds of homes and buildings whose foundations have settled, cracked, leaned, and rotted as a result of poor drainage. From our experience it is the single most common cause of damage to buildings and the most common cause of structural consultation requests.
7 Signs of Poor Drainage
Here’s how to identify possible drainage issues around the home or building:
- Puddles against the foundation after a rain or thaw
- Ground that slopes toward the building with signs of erosion around the building
- Stained and flaking foundation walls
- Stains around foundation wall cracks
- Horizontal cracks in the foundation
- Leaning or bulging foundation walls
- Unusual settlement
Symptoms of high groundwater levels include water on the floor of the basement or crawl space. Stains on the floor, lower walls, and columns are possible evidence of past high groundwater.
When it comes to homes and buildings, unwanted water runoff is a major issue. This includes runoff which normally comes from rain and snowmelt, as well as groundwater.
Runoff comes from:
- Driveways and patios sloping toward the building
- Neighboring properties, streets, or hillsides that are higher than the building
- Over-irrigated yards and plants near the building
The danger occurs when water accumulates near a building (or a retaining wall) for an excessive period of time. The weight of the accumulated runoff against a wall causes hydrostatic pressure against the wall. Additionally, in the winter, the water against the foundation wall can freeze near ground level which cause enormous frost pressure against the wall. These pressures can be enough to crack and deform a foundation wall by pushing it inward-especially on older buildings. Besides pressure, the water can find its way inside through cracks, form tie holes, and even through the concrete itself causing flaking of the interior concrete, stains, mold, etc.
Groundwater is the result of water that has infiltrated into the ground. When the groundwater level (water table) rises, it can enter basements and crawl spaces. Groundwater can result in rot of structural members in contact with moisture over an extended period of time, interior damage, mold, and staining. Moisture also attracts wood destroying organisms such as termites and carpenter ants.
Both runoff accumulation near the foundation and high groundwater levels can also reduce the weight bearing capacity of the soil supporting the foundation by fluidizing it (think mud) and result in settlement resulting in sloping floors, walls, and roofs along with cracking, sticking doors and worse.
4 Solutions for Poor Drainage
If a drainage problem is observed, here are some potential solutions:
- Install gutter/downspout systems with the downspouts directed downslope away from the building. Clean them in the spring and autumn to remove debris.
- Re-grade the soil to direct runoff away from the home (most codes require a minimum of ½ inch of downward slope across the first 10 feet from the home)
- In extreme cases, may require excavating and installing a French drain system around the problem area at the base of the foundation to carry water to an open drain or drywell away from the home.
- One or more sump pumps to collect ground water and pump it to a point well away from the home.
In all cases, this excessive water should not be directed to a neighboring property. Most municipalities have regulations to restrict runoff from one property to adjacent properties.
Our engineers at Criterium-Pfaff Engineers have years of experience in both identifying poor drainage and its results. We are available to consult with you to identify drainage problems, recommend solutions, and to investigate and recommend repairs to damaged areas as a result of poor drainage.