Water Managed Foundation System
Most basement water leakage is due to either bulk moisture leaks or capillary action with no water managed foundation system. Bulk moisture is the flow of water through holes, cracks, and other discontinuities into the home’s basement walls. Capillary action occurs when water wicks into the cracks and pores of porous building materials, such as masonry block, concrete, or wood. These tiny cracks and pores can absorb water in any direction–even upward.
The best approaches for preventing these problems will depend on the local climate and style of construction and adding a water managed foundation system, but the following general rules apply to most basement designs.
1. Keep all untreated wood materials away from earth contact.
2. Provide drainage, such as gutters, to conduct rainwater away from the house.
3. Slope the earth away from all sides of the house for at least 5 feet at a minimum 5% grade (3 inches in 5 feet). Establish drainage swales to direct rainwater around the house.
4. Add a sill gasket to provide air sealing.
5. Install a protective membrane, such as caulked metal flashing or EPDM-type membrane, to serve as a capillary break that reduces wicking of water up from the masonry foundation wall. This membrane can also serve as a termite shield on top of the insulation board.
6. Damp proof all below-grade portions of the foundation wall and footing to prevent the wall from absorbing ground moisture by capillary action.
7. Place a continuous drainage plane over the dampproofing or exterior insulation to channel water to the foundation drain and relieve hydrostatic pressure. Drainage plane materials include special drainage mats, high-density fiberglass insulation products, and washed gravel. All drainage planes should be protected with a filter fabric to prevent dirt from clogging the intentional gaps in the drainage material.
8. Install a foundation drain directly below the drainage plane and beside the footing, not on top of the footing. This prevents water from flowing against the seam between the footing and the foundation wall. Surround a perforated 4-inch plastic drain pipe with gravel and wrap both with filter fabric.
9. Underneath the basement’s slab floor, install a capillary break and vapor retarder, consisting of a layer of 6- to 10-mil polyethylene over at least 4 inches of gravel.
BASEMENT WATER MANAGED FOUNDATION INSULATION PLACEMENT
In most cases, a basement should be considered a conditioned space with insulation installed in the exterior basement walls.
Even in a house with an unconditioned basement, the basement is more connected to the other living spaces of the home than to the outside. This makes basement wall insulation preferable to insulating the basement ceiling.
Advantages of basement wall insulation include:
• Basement spaces, whether conditioned or not, are warmer and more comfortable.
• Compared to insulating the basement ceiling, insulating basement walls:
— requires less insulation (1,350 square feet of wall insulation for a 36- by 48-foot basement with 8-foot walls, compared with 1,725 square feet of basement ceiling insulation),
— more easily achieves continuous thermal and air leakage boundaries because basement ceilings are typically penetrated with electrical wiring, plumbing, and ductwork,
— requires little, if any increase in the size of heating and cooling equipment–the heat loss and air leakage through the basement ceiling is similar to that through the exterior walls of the basement.
• Piping and ductwork are located within the conditioned volume of the house so they do not require insulation for energy efficiency or protection against freezing.