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Sheathing Celotex Homasote & Other
SHEATHING, FOIL FACED - VENTS
SIDING TYPES, INSTALLATION, DEFECTS
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STUCCO WAll FAILURES DUE TO WEATHER
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STUCCO OVER FOAM INSULATION
STUCCO PAINT FAILURES
SURFACE GRADING, SITE DRAINAGE
Thermal Expansion Cracking of Brick
TREES & SHRUBS, TRIM OFF BUILDING
TRIM, EXTERIOR CHOICES, INSTALLATION
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WATER BARRIERS, EXTERIOR BUILDING
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WINDOWS & DOORS
Site grading & related methods for roof runoff & water control: this article describes how to use surface grading around buildings to control surface runoff or roof drainage. We explain how to install and use a French Drain or drywall to dispose of roof runoff on flat building sites. This article series discusses how to choose, install, diagnose & maintain roof gutters & downspouts, & roof drainage systems to prevent building leaks and water entry.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Methods for Disposing of Roof Runoff: Surface Grading, Swales, French Drains, Drywells, Seepage Pits, & Storm Drain Connections
Our page top sketch showing proper surface contouring or grading and slope around a building is provided courtesy of Carson Dunlop Associates. Also see DOWNSPOUT / LEADER DEFECTS and see GUTTERS & DOWNSPOUTS for other sources of wet basements or crawl spaces caused by problems with the roof drainage system.
Our photo at left shows a client pointing out a common source of wet basements or crawl spaces: the downspout spills roof drainage right by the building foundation.
More details conspire to invite water inside at this point including in-slope grade (soil slopes towards the building), and a basement walkout entry whose sidewalls form an "insider corner" to help trap surface runoff and groundwater against the structure.
Notice also that low deck with very limited access below. Often a deck is built before final site grading is complete, resulting in in-slope grade below the deck too, trapping roof spillage, gutter overflows, and surface runoff against the building foundation wall.
Directing surface runoff away from buildings is second only to proper handling of roof drainage in keeping out foundation leaks and stopping wet basements. It is important to get water away from the foundation as quickly as possible. Finish grade should slope away from the building for at least 10 to 15 feet, and should not contain low spots that will make water ponds.
Our photo (left) illustrates poor site-drainage design. Runoff from a hillside (left) accumulates in a low area close to this home. Proper construction of a swale at the hill bottom might correct the trouble, or deeper, more extensive drainage may be necessary. While the home was new it was not flooding but we expect that eventually the water, soil and silt accumulation at this home will lead to serious basement water entry problems.
Quoting from Carson Dunlop Associates' Home Reference Book:
Definition of a Swale: a swale is a gentle "ditch" that conducts water away from a building. Instead of the near-vertical sides of a drainage ditch, however, the sides of a swale slope gently and can be covered with grass or sometimes other plantings. To function properly, the bottom of the swale is not level, but instead it too slopes to a destination from which water can be discharged at a safe distance away from the building.
At some problem sites a swale may drain to one or more CATCH BASINS that in turn drain or are pumped to a storm drain or other final destination.
Foundation ditches: Do not do what we have found at some flooding basements: an in-slope grade problem that was trapping surface and roof runoff against the house was "fixed" by digging a ditch right against the foundation wall in an attempt to carry water away. The ditch digger simply had built a water trap to guarantee that water would be sent against the foundation wall.
If your building site is flat, or worse, at the bottom of a hill, it can be difficult to keep surface runoff away from the building and also tough to dispose of roof runoff or drainage since simply using gravity to send water away from the building won't work. In these conditions typical solutions to disposing of roof runoff include:
Using a French Drain to Dispose of Roof Runoff
How do we get rid of roof runoff if the site is flat and there is no available municipal storm drain system into which we can send water by gravity or by pumping stations?
Definition of catch basin: A catch basin, unlike drywell, is a water-tight container designed to receive water from roof or surface drainage. The catch basin may itself empty into a storm drain, a downhill surface area, or it may be incorporate a sump pump to move water to an uphill disposal site or storm drain. The details of catch basins used to collect roof drainage or surface runoff are shown below.
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