Masonry Magazine July 2011 Page. 22
MOISTURE MANAGEMENT
# Sump Basket
Sump Banket 30
#8
Oversized drain field surrounding the sump basket allows water that is held in the reservoir prior to the sump pump being activated by the float, to be readily available for the sump pump ensuring a productive pump cycle. A larger volume productive pump cycle reduces stress on the pump created by too frequent, low volume on and off cycles. The larger, deeper sump basket with the oversized drain field also creates a reservoir that can accommodate water surges. (See Image #8.)
Employ a gas-tight sump basket lid with designated outlet hole gaskets and brackets that facilitates proper installation of moisture and gas venting stacks. This sump basket configuration can be mechanically vented with an inline fan system. The mechanically fastened sump basket lid is a safety device and code in most states. The venting of soil gases from the sump basket and the connecting drain tile/drain field details has a number of positive aspects. One of the most beneficial aspects is that the venting of these gases creates a slight negative pressure in these details that discourages soil gases from entering the living space of the building envelope.
Building professionals have been engaged in a long, ongoing struggle over two concepts: drainage vs. waterproofing and venting vs. sealing. Is it better to seal water out with waterproofing or drain it away? Should contaminated air be vented out or sealed out? It is only by combing waterproofing with drainage and venting with sealing that we truly have an acceptable solution to each question.
For many years manufacturers of waterproofing and sealant materials have controlled the market. They had the marketing dollars to influence the consumer, so they have held sway. There have been few manufacturers with either the money or a reason to dispute the efforts of the waterproofing and sealant manufacturers to push product.
As a result of this imbalance of forces, waterproofing and sealant companies have won the day and instilled a sense of security with many building professionals. In many cases this sense of security is well-founded as many sealants and waterproofing products of today are nothing short of fantastic.
However, there is a caveat: While these materials have improved, the labor force that installs them has not. If we can accept, for the purpose of this discussion, that the labor force has declined, we must find a way to counteract it. That counteracting force is the inclusion of sound, proven drainage and venting practices.
Another negative force that must be addressed is construction design detail conflicts. Sometimes, drainage and venting are in direct design conflicts with waterproofing and sealing. Construction details that have high quality drainage, waterproofing, venting and sealing components perform better and last longer than details that don't have all four.
So how does this pertain to below-grade construction? One primary example is a construction detail where the basement floor comes in contact with the exterior perimeter wall and the footing that supports it. (See Image #7.)
There are a number of moisture management concerns that need to be addressed at the intersection of the basement wall, structural footing and basement floor.
Temperature transfer
Condensation
Water Infiltration
Soil gas/contaminated air infiltration.
The temperature transfer concerns start with a large mass of concrete like the structural footing. This cold sink excesses because the footing is located at the lower point of the basement construction and is in constant contact with the surrounding fill temperatures that hover around 540F. Another factor that affects the temperature of this detail is the fact that is away from any heat source and because the basement wall rests on the footing and is exposed to fill temperature around 54°F. The bottom of the basement wall and the footing transmit the 54°F temperature to the edge of the concrete floor. This results in the inside corner where the basement floor meets the basement wall being constantly cooled to 54°F. This cooled surface temperature may represent a dew point temperature and the diminished airflow in the inside corner is a recipe for condensation. (See Image #2.)
The voids that remain between the surfaces of these three construction details also represent entrance paths for both air and water. What seems like the obvious remedy (caulk and seal these voids off) may not be the best long-