Footing Drains Keep the Basement Dry from the Outside
ABOUT FOUNDATION DRAINAGE
Run it to daylight
Wet basements are common. Even some new-home owners complain of wet basements.
If the slope of the building site allows, perimeter drains should connect to solid pipe that runs to daylight. The solid pipe should be sloped at a minimum pitch of 1/4 inch per foot, although a steeper slope is better. If there is more than 200 linear feet of foundation, add a second outlet or increase the size of the outlet pipe from 4 inches to 6 inches.
When there isn’t enough pitch on the lot, the exterior drains should be connected to a sump pump in the basement via a 6-inch line that penetrates the footing near the sump location.
MORE ABOUT FOUNDATION DRAINAGE
Water that seeps through a basement foundation or is forced upward by hydrostatic pressure can be collected in an interior drain system and routed to a sump for removal. However, if you know that groundwater is likely to be so big a problem that you have to relieve hydrostatic pressure with a perimeter foundation drain system and sump pump, you should seriously consider something other than a full basement foundation.
INSTALLING AN EXTERIOR DRAIN
Dig a trench as deep as the bottom of the footings.
Lay filter fabric first. Unroll 6-foot-wide filter fabric along the trench, lapping the material up the sidewalls of the foundation. Spread the excess fabric away from the foundation.
Add crushed stone and pipe. Over the filter fabric, lay a 3-inch layer of crushed stone, and then install the 4-inch rigid PVC pipe all the way around the foundation. The perforated pipe can be installed level. Window wells should be tied to the drain with solid 4-inch PVC. Add crushed stone to a level about 8 inches above the top of the footing, and then pull the excess fabric over the top of the stone and lap it against the foundation wall.
Finish with coarse sand. A 6-inch layer of coarse sand spread on top of the fabric will prevent soil from washing into the fabric and clogging its pores.
INSTALLING AN INTERIOR DRAINAGE SYSTEM
Create a sub-slab drainage field.
Put down an 8- to 10-inch-deep layer of crushed stone before the basement floor is poured so that the entire area beneath the slab drains. Above the crushed stone, install a layer of extruded polystyrene insulation topped with a puncture-resistant vapor barrier, such as cross-laminated high-density polyethylene, which will prevent any below-grade moisture from rising into the basement.
Install an plastic interior perimeter drain.
In most cases, this consists of perforated 4-inch pipe. Proprietary drainpipe systems are also available, usually at a higher cost. All are designed to pick up water where the basement wall meets the the floor and drain it to a sump, from which it can be pumped out.
Put in a sump pump. Water that’s collected on the inside of the foundation is piped to a cavity, or sump, set below the level of the floor. Use a pump that’s automatically activated by rising water to move water outside and away from the house. If local codes allow, the sump can be connected to the sewer system. (A sump pump could be connected to exterior footing drains if they run to daylight away from the house.)
Battery-powered backup pump.
In areas where flooded basements are common, a battery backup system for the sump pump ensures that the system will work when the power goes out. A maintenance or inspection schedule for the sump pump should be included in the homeowner’s manual. Installing a sump-pump pit cover that achieves an airtight seal will improve the home's air tightness and reduce the risk of radonColorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles. entry.