Many delightful older homes have a serious flaw: namely, a damp basement. These humidity problems can be mild (musty smells and a clammy feeling) to severe (flowing water or frequent puddles). So how can these flaws be remedied?
Solutions can be divided into two general categories. This article will address exterior solutions, while a future article will address interior solutions.
How does water enter a basement?
In most climates, the soil outside a basement foundation is always damp. Moreover, most basement walls—including poured concrete walls, concrete block walls, stone walls, and brick walls—allow moisture to enter your basement. The moisture can enter as a liquid (through small cracks in the wall) or as a vapor (because concrete and masonry walls are vapor-permeable). When soil is saturated with water, the hydrostatic pressure of the water on the outside of your wall increases. (Hydrostatic pressure is the pressure exerted by a fluid due to gravity. Hydrostatic pressure increases in proportion to the depth of the fluid, measured from the fluid’s surface, because of the weight of the fluid exerting downward force from above.) When this hydrostatic pressure is particularly high, as it might be when the soil is saturated due to a heavy rainstorm or rapid snow melt, water can trickle or squirt into your basement through cracks in the wall, or appear on the basement floor as a puddle.
Some sites have an additional problem: the presence of a subsurface spring that flows continuously or seasonally. Such springs rise from below, and they can show up in a basement as a small trickle or a major flow.
Code requirements for new homes
New homes with basement foundations are required by most building codes to have a footing drain system as well as dampproofing compound on the exterior side…