Masonry Magazine July 2011 Page. 20
MOISTURE MANAGEMENT
Image 6.
The basement needs to be waterproofed, drained, and backfilled ASAP!
Secondly, "Don't take shortcuts!" Do not skip any of the important construction procedures. The foundation of the entire project is literally being fabricated. If any part of it is either hurried or omitted, the entire project is at risk. Working cohesively as a team is crucial. There are usually several subcontractors involved including plumbers, electricians, waterproofers and excavators. The coordination necessary to keep these subcontractors on schedule is also crucial.
Additionally, there is a real danger at this time that one or more subcontractors will, because of gross negligence, ignorance or other reasons, undo important drainage or waterproofing details. Studies have shown that as much as 85 percent of all labor time conducted on or near waterproofing systems is conducted by labor that has no understanding of how these systems are supposed to function.
Decide What Works: Key Plan Elements
ESTABLISHING a moisture-management plan results in a positive outcome for a below-grade construction project. Following these critical steps (the plan) leads to an optimal end product and good site-preservation practices.
Select a sound building site with good soil and good drainage. Finding the right location is the first step in the process. A location that is too low and soil that doesn't drain invites moisture problems.
Be sure construction details are structurally sound. Details, details, details, the right details make or break any construction project. It is imperative that all design details work together. A poorly designed detail can invite moisture into the project.
The exterior surface of the basement walls and footing should be waterproofed. There are numerous high-quality waterproofing systems to choose from. Some of these systems consist of two parts. There are systems that feature a waterproofing material that faces the weather and is backed with a drainage material, and there are systems that are a sheet stock material with a pattern on the back that provides drainage. Both of these systems, when placed on the outside surface of the basement, provide waterproofing on the exterior surface and a predictable drainage plane behind it to move water from a high point to a low point.
Drainage systems should be located at the lowest elevation of the basement construction detail. This system usually incorporates drain tile and a sump basket system. Choose a high-quality rigid or flexible drain tile; the most common tile dimensions are four, six and eight inches. The drain tile should be installed along the interior and exterior sides of the exterior perimeter wall and footing with a connecting pipe of smaller dimension running through the footing at its base. (See Image #6.)
Note: A structural engineer should do the required engineering to facilitate this detail. Connecting the exterior drain tile to the interior drain tile serves two important purposes. First, it provides a drainage pathway for water in an exterior drain tile of a full in-ground basement to have access to the sump pump and sump basket located in the interior of the basement. This facilitates it being pumped out and away from the basement detail. Second, it provides immediate elimination of potential water pressure build up. Prevention of this phenomenon is a must in maintaining a below-grade moisture management system.
Connection of the vertical drainage planes on the exterior of the perimeter wall systems to the drain tile system is important. Any restriction of moisture flow at this point may cause water pressure build up. This transition from vertical to horizontal is accomplished in a number of ways. The two most common are:
Systems that actually have connecting components as part of the system (see Image #6)
Systems with a drain field consisting of stone. (See Image #6.)
Vertical wall drainage systems that are installed on the interior surface of exterior perimeter walls. The systems provide a passageway for moisture (in its liquid state) to drain from a high point of entry to a drain tile and drain field system at the lowest point of the construction detail. They maintain a separation (barrier) between concrete or CMU basement walls