Ponding

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Ponding is the (typically) unwanted pooling of water, typically on a flat roof or roadway. Ponding water accelerates the deterioration of many materials, including seam adhesives in single-ply roof systems, steel equipment supports, and particularly roofing asphalt. On low-slope asphalt roofs, ponding water allows the oil solvent components of the asphalt to leach out and evaporate, leaving the roof membrane brittle and susceptible to cracking and leaking in the ponding location. [1] The time taken for water to saturate a zone, usually from rainfall, causing a pond to form, is referred to as the "ponding time" or "time of ponding". [2] [3] [4]

Contents

Cause

Most flat roof systems (properly called "low-slope roof systems") are designed with a slight pitch to shed water off the sides, usually into gutters, scuppers, internal drains, or a combination of these. [5] When a scupper or drain is clogged or fails for other reasons, storm water tends to pool around that low area. Over time, with each passing storm, the weight of the storm water will deflect the structural system beyond the structure's bending point, thus allowing a bigger puddle to form. As a bigger puddle forms more weight is applied to the structural system causing more bending, allowing an even bigger puddle, then more weight, until the structure fails. [6]

Construction codes

In the construction industry, the National Roofing Contractors Association (NRCA) defines roof ponding as "water that remains on a roof surface longer than 48 hours after the termination of the most recent rain event". [7] [8]

According to the 2009 International Building Code Chapter 15 "Roof Assemblies and Roof Top Structures" & Chapter 16 "Structural Design";

When scuppers are used for secondary (emergency overflow) roof drainage, the quantity, size, location and inlet elevation of the scuppers shall be sized to prevent the depth of ponding water from exceeding that for which the roof was designed ... Ponding instability. For roofs with a slope less than 1/4 inch per foot [1.19 degrees (0.0208 rad)], the design calculations shall include verification of adequate stiffness to preclude progressive deflection in accordance with Section 8.4 of ASCE 7. [9]

Ponding on land

When water is diverted into a lower area that has no outlet or is not suitable for drainage, water will begin to pool, and over time the weight of the water will create a deeper pool, allowing more water to sit, eventually creating a permanent water feature. Some municipalities recognize this as an issue on private land, such as the City of Indianapolis. [10]

Other municipalities see this as a great concern, such as the Kapiti Coast District, New Zealand where, "groundwater ponding is a chronic problem, that results in damp housing and waterlogged sections. The damage that it causes is less apparent than the damaging events associated with floods, but the duration of groundwater ponding, which can last for several months, makes it a serious issue for those affected". [11]

Ponding that forms on paved surfaces, like streets or parking lots that are not properly pitched, will cause issues such as deep puddles and crocodile cracking.

See also

Related Research Articles

<span class="mw-page-title-main">Roof</span> Top covering of a building

A roof is the top covering of a building, including all materials and constructions necessary to support it on the walls of the building or on uprights, providing protection against rain, snow, sunlight, extremes of temperature, and wind. A roof is part of the building envelope.

<span class="mw-page-title-main">Stormwater</span> Water that originates during precipitation events and snow/ice melt

Stormwater, also spelled storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil (infiltrate) and become groundwater, be stored on depressed land surface in ponds and puddles, evaporate back into the atmosphere, or contribute to surface runoff. Most runoff is conveyed directly as surface water to nearby streams, rivers or other large water bodies without treatment.

<span class="mw-page-title-main">Storm drain</span> Infrastructure for draining excess rain and ground water from impervious surfaces

A storm drain, storm sewer, surface water drain/sewer, or stormwater drain is infrastructure designed to drain excess rain and ground water from impervious surfaces such as paved streets, car parks, parking lots, footpaths, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems.

<span class="mw-page-title-main">Permeable paving</span> Roads built with water-pervious materials

Permeable paving surfaces are made of either a porous material that enables stormwater to flow through it or nonporous blocks spaced so that water can flow between the gaps. Permeable paving can also include a variety of surfacing techniques for roads, parking lots, and pedestrian walkways. Permeable pavement surfaces may be composed of; pervious concrete, porous asphalt, paving stones, or interlocking pavers. Unlike traditional impervious paving materials such as concrete and asphalt, permeable paving systems allow stormwater to percolate and infiltrate through the pavement and into the aggregate layers and/or soil below. In addition to reducing surface runoff, permeable paving systems can trap suspended solids, thereby filtering pollutants from stormwater.

A blue roof is a roof of a building that is designed explicitly to provide initial temporary water storage and then gradual release of stored water, typically rainfall. Blue roofs are constructed on flat or low sloped roofs in urban communities where flooding is a risk due to a lack of permeable surfaces for water to infiltrate, or seep back into the ground.

<span class="mw-page-title-main">Flat roof</span> Type of roof

A flat roof is a roof which is almost level in contrast to the many types of sloped roofs. The slope of a roof is properly known as its pitch and flat roofs have up to approximately 10°. Flat roofs are an ancient form mostly used in arid climates and allow the roof space to be used as a living space or a living roof. Flat roofs, or "low-slope" roofs, are also commonly found on commercial buildings throughout the world. The National Roofing Contractors Association defines a low-slope roof as having a slope of 3 in 12 (1:4) or less.

<span class="mw-page-title-main">Waterproofing</span> Process of making an object or structure waterproof or water-resistant

Waterproofing is the process of making an object or structure waterproof or water-resistant so that it remains relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environments or underwater to specified depths.

<span class="mw-page-title-main">Retention basin</span> Artificial pond for stormwater runoff

A retention basin, sometimes called a wet pond,wet detention basin, or stormwater management pond (SWMP), is an artificial pond with vegetation around the perimeter and a permanent pool of water in its design. It is used to manage stormwater runoff, for protection against flooding, for erosion control, and to serve as an artificial wetland and improve the water quality in adjacent bodies of water.

The United States Environmental Protection Agency (EPA) Storm Water Management Model (SWMM) is a dynamic rainfall–runoff–subsurface runoff simulation model used for single-event to long-term (continuous) simulation of the surface/subsurface hydrology quantity and quality from primarily urban/suburban areas. It can simulate the Rainfall- runoff, runoff, evaporation, infiltration and groundwater connection for roots, streets, grassed areas, rain gardens and ditches and pipes, for example. The hydrology component of SWMM operates on a collection of subcatchment areas divided into impervious and pervious areas with and without depression storage to predict runoff and pollutant loads from precipitation, evaporation and infiltration losses from each of the subcatchment. Besides, low impact development (LID) and best management practice areas on the subcatchment can be modeled to reduce the impervious and pervious runoff. The routing or hydraulics section of SWMM transports this water and possible associated water quality constituents through a system of closed pipes, open channels, storage/treatment devices, ponds, storages, pumps, orifices, weirs, outlets, outfalls and other regulators.

<span class="mw-page-title-main">Rain garden</span>

Rain gardens, also called bioretention facilities, are one of a variety of practices designed to increase rain runoff reabsorption by the soil. They can also be used to treat polluted stormwater runoff. Rain gardens are designed landscape sites that reduce the flow rate, total quantity, and pollutant load of runoff from impervious urban areas like roofs, driveways, walkways, parking lots, and compacted lawn areas. Rain gardens rely on plants and natural or engineered soil medium to retain stormwater and increase the lag time of infiltration, while remediating and filtering pollutants carried by urban runoff. Rain gardens provide a method to reuse and optimize any rain that falls, reducing or avoiding the need for additional irrigation. A benefit of planting rain gardens is the consequential decrease in ambient air and water temperature, a mitigation that is especially effective in urban areas containing an abundance of impervious surfaces that absorb heat in a phenomenon known as the heat-island effect.

Domestic roof construction

Domestic roof construction is the framing and roof covering which is found on most detached houses in cold and temperate climates. Such roofs are built with mostly timber, take a number of different shapes, and are covered with a variety of materials.

<span class="mw-page-title-main">Asphalt shingle</span> Type of shingle

An asphalt shingle is a type of wall or roof shingle that uses asphalt for waterproofing. It is one of the most widely used roofing covers in North America because it has a relatively inexpensive up-front cost and is fairly simple to install.

<span class="mw-page-title-main">Sustainable drainage system</span>

Sustainable drainage systems are a collection of water management practices that aim to align modern drainage systems with natural water processes and are part of a larger green infrastructure strategy. SuDS efforts make urban drainage systems more compatible with components of the natural water cycle such as storm surge overflows, soil percolation, and bio-filtration. These efforts hope to mitigate the effect human development has had or may have on the natural water cycle, particularly surface runoff and water pollution trends.

A roof coating is a monolithic, fully adhered, fluid applied roofing membrane. Many roof coatings are elastomeric, that is, they have elastic properties that allow them to stretch and return to their original shape without damage.

Membrane roofing is a type of roofing system for buildings, RV's, Ponds and in some cases tanks. It is used to create a watertight covering to protect the interior of a building. Membrane roofs are most commonly made from synthetic rubber, thermoplastic, or modified bitumen. Membrane roofs are most commonly used in commercial application, though they are becoming increasingly common in residential application.

<span class="mw-page-title-main">Bituminous waterproofing</span> Roll roofing and waterproofing material

Bituminous waterproofing systems are designed to protect residential and commercial buildings. Bitumen is a mixed substance made up of organic liquids that are highly sticky, viscous, and waterproof. These systems are sometimes used to construct roofs, in the form of roofing felt or roll roofing products.

Asphalt roll roofing

Asphalt roll roofing or membrane is a roofing material commonly used for buildings that feature a low sloped roof pitch in North America. The material is based on the same materials used in asphalt shingles; an organic felt or fiberglass mat, saturated with asphalt, and faced with granular stone aggregate. The installation process, known as Torch On Roofing, is often used on commercial properties in North America.

<span class="mw-page-title-main">Crocodile cracking</span> Distress in asphalt pavement

For concrete cracking see Crazing

<span class="mw-page-title-main">Ice dam (roof)</span>

An ice dam is an ice build-up on the eaves of sloped roofs of heated buildings that results from melting snow under a snow pack reaching the eave and freezing there. Freezing at the eave impedes the drainage of meltwater, which adds to the ice dam and causes backup of the meltwater, which may cause water leakage into the roof and consequent damage to the building and its contents if the water leaks through the roof.

References

  1. "Building Envelope Design Guide - Roofing Systems | Whole Building Design Guide". www.wbdg.org. Retrieved 2016-08-11.
  2. Infiltration Theory for Hydrologic Applications. American Geophysical Union.
  3. Brutsaert, Wilfried (2005-08-11). Hydrology: An Introduction. Cambridge University Press. ISBN   978-0-521-82479-8.
  4. Delleur, Jacques W. (2010-12-12). The Handbook of Groundwater Engineering. CRC Press. ISBN   978-1-4200-4858-2.
  5. Griffin, C. W.; Fricklas, R. L. (1996). Manual of low-slope roof systems (3rd ed.). New York: McGraw-Hill. pp. Chapter 3: Draining the Roof. ISBN   9780070247840. OCLC   33244913.
  6. "Investigation, analysis and design of an experiment to test ponding loads on flexible roof systems" by Duncan Stark, published by Oregon State University, June 2008
  7. "The Evils of Ponding Water" October 31, 2009, by Paul Graham
  8. "Extensive Range of Single Ply Roofing and Waterproofing Systems". William Carey. Retrieved 2015-03-01.
  9. 2009 international building code, by International Code Council in Books
  10. indy.gov
  11. Urban planning - managing surface water and groundwater ponding" by Michelle Malcolm, Craig Martell, and Brydon Hughes, Sinclair Knight Merz Ltd. Kapiti Coast District Council 2008