Editor's note: This story is adapted from the U.S. Department of Housing and Urban Development's Residential Rehabilitation Inspection Guide, 2000. Click here for other stories in this series.
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Buildings with pitched roofs can have a variety of drainage systems. With a sufficient overhang, water can drain directly to the ground without being intercepted at the roof edge. Usually, pitched roofs end in gutters that are drained by downspouts.
Low-slope roof drainage is accomplished in one of three ways:
- without gutters or downspouts,
- with gutters and downspouts,
- or by downspouts that go down through a building's interior.
Drainage without gutters and downspouts can damage the exterior wall with overflow. If the roof has no gutters and downspouts or interior downspouts, carefully examine the exterior walls for signs of water damage. Gutter and downspout materials are usually galvanized steel, aluminum, copper, or plastic.
Gutters
- Gutters should have a minimum ratio of gutter depth to width of 3 to 4
- The front edge should be one-half inch (13 mm) lower than the back edge
- Four inches is considered the minimum width except on the roofs of canopies and small porches.
Make certain all gutters are clean and slope uniformly, without low areas, to downspouts. If there is a screen or similar device to prevent anything but water from flowing into the gutter, check its condition, fit, and position, to be sure water really can enter the gutter. Check gutters without screens or similar devices to be sure that basket strainers are installed at each downspout.
Check the physical and functional condition of all gutters. Joints should be soldered or sealed with mastic. Also examine the placement of gutters: the steeper the roof pitch, the lower the gutter placement.
On roofs with lower slopes make sure gutters are placed close to the roof's surface. Hangers should be placed no more than three feet apart. Where ice and snow are long lasting, hangers should be placed no more than 18 inches (460 mm) apart. Wherever a gutter is exposed, check the strength of its fastening to the roof fascia or building exterior. Rusted fasteners and missing hangers should be replaced.
Ice dams
Ice dams can form on pitched roof overhangs in cold climates subject to prolonged periods of freezing weather, especially those climates with a daily average January temperature of 30 F (-1 C) or less. Heat loss through the roof and heat from the sun (even in freezing temperatures) can cause snow on a roof to melt. As water runs down the roof onto the overhang, it freezes and forms an ice dam just above the gutter. The ice dam traps water from melting snow and forces it back under the shingles and into the building's interior.
Check the edge of the roof overhang for evidence of ice dams and observe the eaves and soffit for evidence of deterioration and water damage. Check gutters and the immediately adjacent roofing for the presence of electrical de-icing cables, which may be evidence of an ice dam problem.
When the interior inspection is made, check the inside of exterior walls and adjacent ceilings for signs of water damage. If the house has an attic, check the underside of the roof deck at exterior walls for signs of water damage.
Downspouts
Downspouts should be checked for size. Seven square inches is generally the minimum except for small roofs or canopies. Check downspout attachments; there should be attachments or straps at the top, at the bottom, and at each intermediate joint. Check straps for rust, deformation, and failed or loose fasteners.
Check the capacity of the drainage system. At least one downspout is usually needed for each 40 feet (12 m) of gutter. For roofs with gutters, make sure that downspouts are clear and that they discharge so water will drain away from the foundation.
For low-slope roofs without gutters, interior downspouts cannot be examined from the roof, but check that basket strainers are in place. During the interior inspection, examine areas through which interior downspouts pass for signs of water damage. On buildings with multiple roofs, one roof sometimes drains to another roof. Where that happens, water should not be discharged directly onto roofing material.
Check to be sure that water is always directed to a gutter and that higher gutters discharge to lower gutters through downspouts. Occasionally, wooden gutters and downspouts are used, usually in older or historic residences. They may be built into roof eaves and concealed by roof fascias. Wooden gutters are especially susceptible to rot and deterioration and should be carefully checked.
Pitched roofs in older buildings may end at a parapet wall with a built-in gutter integrated with the roof flashing. Here, drainage is accomplished by a scupper (a metal-lined opening through the parapet wall that discharges into a leader head box that in turn discharges to a downspout). Check the leader head box to be sure it has a strainer. Check the scupper for deterioration and open seams and check all metal roof flashings, scuppers, leader head boxes, and downspouts to make certain they are made of similar metals.
