| Building Science Servicesby Rodney Harkness |
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SURFACE WATER CONTROL ("drainage") is the single most important and most often neglected protective feature of dwelling lots and buildings. Drainage refers primarily to surface water control or storm water control. Well designed, constructed and maintained drainage features and systems will promote the comfort, usefulness and durability of any building. Anything less than this will promote unhealthy conditions, curtailed usefulness, greatly increased repairs and the degeneration of every and any aspect of the building, its premises and contents. Uncontrolled water, in its various forms, is the everyday worst enemy of land architecture and property.
Most habitable areas have need for good surface water control. The North Central portion of the US has a relatively wet climate with an average annual rainfall of 36 inches, including snowfall of 45 inches, and is often damp and moist. This is a lot of water, and it has to drain (or run off) to somewhere. In the process of getting into a stream, creek, river and eventually the ocean, it follows the downward contours of the land. Water will of course enter loose, porous or rocky soil, or follow underground channels, but this accounts for only a small portion of the overall dynamic. (For more information on subsurface water, see "Soil: The Nature of Drainage" and "Water Tables" Other areas of the country or world may have less actual rainfall, but must design for snow melt or occasional wet weather and storms.
Land surface contours are always modified by any construction process.
Most non-level lots have some degree of surface contouring developed by nature. Land surface contours are always modified by any construction process. Intelligent respect for natural surface runoff during site improvement can include permanent protection from threatening accumulation on the site. Carelessness either in initial site water control planning or in later maintenance will always lead to damaging water flow or moisture build-up.
Some degree of clay content is a component of soil in most areas of the country --and the world in general. Cities and built areas are commonly situated in regions with a high content of clay in the soil. Clay has the ability to stop the flow of water, absorb it, and hold it for extended periods of time --sometimes months. When soil with even a modest percentage of clay becomes wet, it becomes pliable and soft. Fill soil containing clay which lies next to next to buildings may take on surface water and become water laden, and stay that way for years below the surface, with only minimal new inputs of water. It is common for the ground immediately next to a building to appear dry, while below the surface enough water has accumulated to make the subsurface back-fill soil wet. With continuous inputs of new water, enough to offset evaporation, capillary action and osmosis, clay soil can stay wet and soft for decades. When this wetting extends to the footer under a wall, the supporting soil may shift allowing the footer to move, usually downward. This is the most common explanation of the typical step cracks found in many foundations and the brick/stone/masonry walls they support. If the wetting is sudden and severe, shear cracks (vertical cracks travelling upward through several masonry units) commonly appear. This water resistance and absorption is also the soil characteristic that make high clay soil useful to redirect and favorable control surface water.
All waterproofing systems of buildings must be complimented by good general surface drainage to preserve property and life. Drainage systems are provided to intercept and direct the flow of water to prevent damage to an area or structure from run off or seepage. Each of these two (waterproofing and surface drainage) require its own method of control and design to ensure a level of protection equivalent to the potential hazard. Surface drainage systems are designed to collect and dispose of rainfall runoff. The two basic types are the ditch, or open system, and the pipe to catch basin or storm sewer. Combinations of the two are common. "French drains" are a hybrid of the open ditch and storm sewer, but French Drains are better for handling long term slow moving water rather than surface or storm run-off.
Subsurface drainage systems, which include French Drains, are designed to intercept and dispose of natural ground water, underground flow, or seepage downward from surface sources. These systems are used around foundations, under floors and under playing courts, ball fields, around swimming pools, and adjacent to roads. Each system must be provided with a discharge either by a gravity drain or a sump pump.
n a typical building site, drainage begins with the roof and terminates at the boundary line.
On a typical building site, drainage begins with the roof and terminates at the boundary line of the property. The drainage system includes gutters, downspouts, drainpipes and rain water director pipes; gravel piled against foundation and appendant piping; ground slopes, soil curbs, ditches and subsurface area drains.
The building owner need not understand the intricacies of the drainage system, but should follow a few simple procedures on a regular (yearly) basis: inspect the gutters, during a moderately heavy rainfall, for leaks; check downspouts for cracked seams or disconnected fittings or extremely sharp bends or turns where leaks can occur; observe that water travels freely down drainpipes and that drainpipes are not blocked or clogged; clean gutters at least one a year; where there is no drain pipe at the termination of a downspout, add a drain board or section of pipe that will get the water at least 48" (four feet) away from the structure; where drainpipes exit to daylight (usually on a hill) keep them free and clean to drain unobstructed.
A few rules to keep in mind: when replacing downspouts, place seams out for ease of inspection (you probably won't hear this anywhere else); make sure all sections of roof, however small, have a gutter and downspout; keep all ground immediately next to the building or foundation sloping away from the building; seal all cracks or separations in concrete or other pavement, especially when adjacent to building; provide some form of surface water relief on the high side of any building where damp conditions exist; fill holes or depressions in ground adjacent to building with soil; provide a soil curb against the foundation. [NOTE: The "seams out"/"seams in" argument on downspouts is mostly about aesthetics, seams out may be a little unsightly close up, but a few feet away, the appearance of the seam disappears. The benefit usually out weighs the aesthetic.]
If all conditions herein described are met and a problem continues, read ourinformation sheets on "Basement Dampness" and "Foundations". It is wise to hire a qualified home inspector to occasionally inspect the property and buildings for proper drainage as often problems occur gradually over an extended period of time and are not noticed by the owner.
The dynamics of water are powerful and continually active. When water freezes, it expands, heaving bursting, cracking and crushing. |When water evaporates it expands developing tremendous pressures. When it melts it travels along the voids the ice has created traveling far, wide and deep. Water flows along the path of least resistance to the lowest available level carrying with it anything that floats, flows or dissolves. In time, water can abrade even the toughest of materials. In its various forms, water penetrates nearly everything and anything both from the surface downward as liquid, and in the form of vapor, from the lowest area to the highest and farthest away, including the roof.
It is not possible to properly maintain a building and neglect the drainage. Drainage is the first and the last item attended to in the construction of a building and it must never stop working. Unfortunately too few building owners have learned this, as deficient drainage is at the top of the list of issues causing building problems. Good drainage is an absolute must.
When you need to be sure, call us. We do consulting-at-a-distance, and can solve many problems over the phone. Locality is not a barrier to at-a-distance consulting that can be done for virtually any place in the USA, and often other areas as well.
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