For the newer inspectors there may be some confusion on the need for exterior water management when reading posts in this section. First, for all practical purposes all concrete foundations will crack, but not all cracked foundations will leak. Explaining all the reasons why concrete foundations crack is reserved for another topic, I am limiting this post to exterior water management only. Something else to keep in mind as we discuss this topic is foundations have two basic functions:
- Transfer the house loads to the soil, typically through a footing.
- Retain exterior soil.
To simplify lets group concrete foundations (crawlspace & basements) into two groups; ones that leak and ones that do not. Let’s start with foundations that leak. In order for a foundation to leak we obviously need two things; an exterior source of water and an avenue for water to enter the basement or crawlspace. Water typically enters in one or more of the following ways:
- Over the top of the foundation wall.
- Through openings such as a foundation vents, windows and doors.
- Through wall cracks, utility holes, form-tie holes, construction joints, including the joint between the wall and the footing.
- Under the footing.
Exterior water sources can be grouped in four basic categories:
- Natural surface flow from rain water.
- Natural subsurface flow from ground water.
- Permanent or seasonally high water tables.
- Man induced water leaks from broken pipes, irrigation systems, leaking swimming pools, etc.
Methods used to stop a water leak will vary depending on how accurate you are at identifying the water source and the path the water enters the basement or crawlspace. From these two lists you can see there are a large number of combinations when you consider the possibility of multiple water sources and multiple ways water can enter a basement or crawlspace.
Keep in mind if you are successful at stopping water from entering the basement or crawlspace you may have only treated the symptom to a larger problem. Remember the two basic functions of a foundation have to be preserved in order for the foundation to work. Here are a few examples:
Example 1: Surface water enters a crawlspace through the foundation vents.
- Solution A: Intercept the water before it reaches the foundation with the use of a swale or berm and redirect around the foundation.
- Solution B: Raise the grade at the foundation and use a window well to protect the foundation vents, if necessary.
**Discussion: **In this example if your solution eliminated surface water from entering the crawlspace vents AND the two basic functions of the foundation were preserved, then you have solved the problem. In this case and all following examples other solutions are only limited by experience and creativity.
Example 2: Subsurface water enters through a crack in the basement wall, i.e. the surface grading and gutter management were good.
- Solution: Excavate and repair the crack, install external waterproofing and improve the perimeter drain tile system if necessary.
Discussion: In this example the solution eliminated subsurface water from entering the basement, however one or both of the two basic functions of the foundation maybe compromised. If subsurface water is reaching the exterior foundation wall the soil under the footing may become saturated. Saturated soil has less load carrying capacity, which can result in settlement problems. Second saturated soil next to the foundation wall is much heavier and increases the horizontal wall load, which can result in wall shoving. In this case the solution was incomplete. Intercepting the subsurface water flow may require the installation of a curtain drain or some other method of preventing subsurface water from reaching the foundation wall.
Example 3: Water enters under the footing into the basement, i.e. the surface grading and gutter management were good.
- Solution: The solution will require more information such as:
o Is the water leaking in around the entire perimeter of the basement?
o Does the ground surface appear saturated?
o What is the soil profile?
o Is this a recent event or an ongoing problem?
o Has the water usage increased, indicating a water line leak?
o The list goes on depending on visual clues and possibly test results such as soil borings.
Discussion: In this example the solution requires determining the exterior water source. In some cases like this the cost to determine the water source may be cost prohibitive or it may be as simple as the basement was built in a swampy area with poorly drained soils. You just can’t fix stupid sometimes.
In closing I want to mention the obvious, even if a basement doesn’t have a leak, exterior water management is still required to preserve the two basic functions of a foundation, unless you live in a desert.