Grading that can collect and hold water near and next to a foundation wall can cause basement flooding. Flooding into a finished basement area can lead to mold growth within 48 hours. Long term water leakage can cause wood rot to wall framing members and can damage the foundation. Stored items can become damaged after a flood into a basement.
I find grading problems on almost every home that I inspect. Most flooding will occur in the spring when the ground begins to thaw and spring rain arrives. The grade is just like a roof on a house. A grade that pitches towards a home can direct water to the home. This can be critical during the winter when the ground is frozen and snow covered. A heavy rain can quickly cause flooding next to a foundation wall and then leak into the basement. Heavy rain can occur any time during the year.
Question the owner about any past flooding into the home. Check your disclosure statement if you have a disclosure law in your state. Flooding of a basement can be one of the worst surprises a new home owner encounters. I have seen a home that was flooding on the day of the home inspection and the owner said they never had water during the 10 years that they lived there. This is possible. Every 6-8-10 years can be very wet. I saw the 10th wettest year in my area. Any possible evidence of past flooding is important to determine before you buy the home so that you can make an informed decision on purchase or negotiation with the seller.
Ideas to reduce basement water leakage:
Pitch all grades away from a home. The ground adjacent to the foundation should be sloped away from a building at a slope not less that 1 inch per 1 foot of grade for a distance of not less than 8 feet. Note: If the house has a hill side directed to the house even this above recommendation could be defeated. In some cases a grade and below grade drain needs to be installed to direct water away from the ground adjacent to a foundation. An engineer sometimes needs to design such a drain. I have seen a case where a curtain drain was needed and the cost was almost $20,000.
Drain water from gutters into dry wells placed at least 20 feet from a building. Again, this relates to soil conditions, general pitch of the surrounding grade, house elevation as the house sits near coastal flood plain areas or wet land areas. High water tables can be located 3-4 inches below a basement slab year round in some homes. Many people drain their sump pumps into town or city sewers which is illegal in most areas.
Keep grass clippings away from the perimeter of the home. Grass clippings can raise the grade around a house over time and create low moat areas in the perimeter gardens that can hold water. In most cases the water will travel down into the earth and then find small cracks and openings in the foundation and end up in the basement.
To sum it up: A basement is a hole in the ground. Do not make it easy for water to fill the hole.
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