The image demonstrates roof drainage discharging into the planter next to the residence which is a common problem observed at hillside properties. Roof gutter downspouts must never be allowed to discharge next to the foundation system. Note the stucco damage to the side of the residence due to excess water within the planter.
Another example of improper surface drainage control - the roof gutter downspout discharges over the rear yard slope, causing a moderate amount of erosion to occur.
Roof gutter downspouts must be connected to solid subsurface drain pipe which conducts drainage to the street or approved location.
Yard drains are important to eliminate areas of surface ponding. Yard drains, sometimes referred to as area drains, must be placed in proper locations. A drainage contractor is better suited to identify areas where surface drains are needed, especially within planters located next to the residence or in low spots on the site. Area drains must be connected by solid subsurface drain pipe which conducts drainage to the street.
Area drains are also provided in concrete decking to collect surface runoff.
Channel Drain in Decking A common surface drainage control devices utilized to collect larger areas of surface drainage then normally collected by smaller area drains.
Sump Pump Pit Sump pumps are often necessary when the surface of the property descends below street grade. Collected site drainage must be discharged to the street, thus requiring a sump pump system. The system typically includes a large catch basin (seen in the picture) and one or more sump pumps within the catch basin.
Side Yard Drainage Swale Open concrete drain located along the edge of the driveway. Open drains are easier to maintain and clean than subsurface drain pipe. Cracks in the drain must be sealed to prevent excessive infiltration of drainage into the subsurface.
Retaining Wall Subdrain and Waterproofing Picture shows the proper installation of a 4-inch diameter perforated subdrain pipe behind the newly constructed retaining wall. Waterproofing has been applied to the back site of the wall. Following installation of the drain pipe, the excavation will be backfilled with 3/4 inch gravel and a cap of 24 inches of compacted fill. A concrete drainage swale will then be constructed behind the wall to collect surface drainage.
Faulty Exterior Grade The exterior grade in this picture is about the same elevation as the interior grade. Loose stone pavers with grass joints allow surface ponding to occur, promoting interior moisture penetration and possible flooding during heavy rains. Faulty Grade 2 In this image, decking was installed without lowering the soil level first. As a result, the decking is blocking underfloor air vents. In addition, surface drainage now flows under residence.
Construction in Drainage Course This image shows a swimming pool which has been constructed in axis of a natural drainage course. To protect the pool from damage caused by concentrated drainage, mud and debris, a concrete drainage swale has been constructed around the pool location. the open concrete drain conducts drainage to the street. The drain has also been provided with about 18 inches of freeboard to help channel mud, drainage and debris within the concrete swale.
Storm Drains The most effective way to handle concentrated drainage within the street is by a storm drain system. Not all hillside areas are serviced by storm drains. Where storm drains are not present, street curbing is essential to prevent flooding on the site or erosion caused by uncontrolled discharge to street drainage onto your property.
This picture shows a typical concrete drainage swale, also known as a "V" drain or "V" ditch. The purpose of the drain is to intercept surface runoff on the slope to reduce the amount of infiltration into the slope. Slope drains are very effective in improving overall slope stability. Slope drains can vary in width from one foot to over 10 feet, depending upon the application and size of the slope. For construction of compacted fill slopes, grading codes establish guidelines for the width and placement of slope drains.
Deflection walls are utilized on ascending slopes above residential developments to help divert upslope drainage and debris to an appropriate location. In this image, the deflection wall is poorly maintained. Three feet of loose debris has accumulated behind the wall, burying the underlying drainage swale. As with all drainage control devices, periodic cleaning and maintenance are required.
Chain link debris fences are employed on slopes where rocks and soil are washed downslope. The debris fence is much stronger than an normal chain link fence and is typically anchored back into the slope with tieback wires. Debris fences require periodic debris removal to function properly.
SUBSURFACE MOISTURE ISSUES
Retaining walls which have not been provided with proper waterproofing applications can experience periodic moisture penetration. White, chalky efflorescence is a clue of moisture penetration. Basement retaining walls commonly experience moisture penetration. Occasionally, spalling and crumbing (image 1) (image 2) of the exposed retaining wall face occurs which subjected to chronic moisture penetration. The susceptibility to concrete degradation is also a function of the chemical characteristics of the concrete mixture.
UNDERFLOOR DRAINAGE ISSUES
Vent and Access Protection
Exterior drainage can enter into the residence subfloor through ventilation openings and access opengings. One method of reducing the moisture under the residence is to provide a hood over the access opening. Care must be taken to ensure that air flow is not overly restricted by the hood.