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Installing Shingles

After installing drip edge and underlayment along the eaves and rakes, apply one course of starter strips. You can buy precut starter strips or make them by ripping shingles in half lengthwise. Starter strips should overhang the eaves drip edge by about 1/2 inch. Follow manufacturer instructions to determine shingle offset to avoid alignment of joints (see shingle offiset illustrations). Avoid pieces narrower than 6 inches at rakes, and don't drive nails closer than 3 inches to the roof edge. For added wind protection at rakes and around penetrations, bed shingle "tabs" in a quarter-size dot of roof cement applied at regular intervals about 1 inch in from the edges (to avoid squeeze-out).

Credit: Tim Healey

Credit: Tim Healey

 

Valley Flashing

Open valleys (see illustration) feature a prominent strip of metal flashing (typically copper or aluminum), which easily sheds water and snow and provides protection from wind-driven rain when properly fabricated and installed. For long valleys, overlap flashing at least 12 inches (lower piece under upper) and avoid seams near eaves where snow, ice, and debris can accumulate. In high-wind areas, caulk flat seams or hem and interlock seams—especially on shallow-pitched roofs. To allow for expansion and contraction, fasten copper using copper tabs clipped to hemmed edges.

Credit: Tim Healey

Where steep roofs of unequal pitch meet, use a W-shaped valley flashing; the raised ridge running down the center slows the flow of water and reduces the chance of leaks from overwash.

Closed-cut valleys (see illustration) install faster because they require cuts on just one side. Where roof planes are of unequal size or pitch, locate the cut edge on the larger, steeper roof plane where possible to avoid driving water between shingle layers. Seal layers along the cut edge with roof cement for added protection.

Credit: Tim Healey

Launch Slideshow

"Tamko Valley"

"Tamko Valley"

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    In the "Tamko" valley, one slope (the shallower, if applicable) is completed first, with its courses running through the valley by at least 12 inches.

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    Next, full shingles are nailed end-to-end along a chalk line; a bead of roofing mastic adds insurance against uplift.

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    The opposite slope is completed with square-cut corners toeing the valley line.

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    Jim Bennette

    A dab of mastic glues the sawtooth tips to the valley starter.

In the "Tamko" closed-cut variant (see "Tamko" valley photos), shingles from one side of the roof are laid through the valley. Then full shingles are laid end to end along a line offset 1 inch from the center of the valley. The remaining roof plane is shingled, with square-cut shingles forming a sawtooth pattern at the valley.

Woven valleys (not shown) are sometimes used with tabbed shingles and require the most installation time. They are not recommended with heavier laminated shingles, although they are sometimes appropriate for short, shallow valleys at crickets and small dormers.

Existing Flashing

Best practice is to replace existing metal flashing with new material rather than rely on someone else's workmanship. The exception is copper through-wall counterflashing at masonry—provided it is properly installed, shows no signs of corrosion, is compatible with new step flashing metal, and is of a heavy enough gauge that it can withstand temporarily being bent upward while other flashing work is completed under it. Otherwise, install new counterflashing (see "Chimney Flashing Details").

Chimney & Dormer Flashing

Joints where a dormer or masonry chimney penetrates the roof deck will leak if not properly flashed (see "Dormer Flashing Details" and "Chimney Flashing Details" illustrations).

If there is no cricket behind a chimney, build one that matches the roof pitch. Make sure that cricket valleys are properly flashed (see Valley Flashing illustrations) and that they channel water away from the masonry corners.

Take care to ensure that new and existing flashing is compatible to avoid corrosion from galvanic reaction (see "Galvanic Series" table).

Use a self-adhering membrane as a first layer (some manufacturers may require a primer to improve adhesion to masonry). When retrofitting masonry step flashing and counterflashing, follow the details shown to ensure secure fastening and proper drainage.

Credit: Tim Healey

  • Credit: courtesy F.J. Moore Manufacturing

Galvanic Series

When different metals come in contact, the more "active" metal will corrode. The farther apart metals are in the galvanic series, the greater the potential corrosion.

When different metals come in contact, the more active metal will corrode. The farther apart metals are in the galvanic series, the greater the potential corrosion.

When different metals come in contact, the more “active” metal will corrode. The farther apart metals are in the galvanic series, the greater the potential corrosion.

Flashing Vent Pipes

Every roof has at least one vent stack (usually PVC or ABS) poking through it. The inexpensive boots commonly used to flash these penetrations rarely last as long as the roofing does. A better solution is to wrap the pipe with a compatible peel-and-stick flashing, then cover it with metal that both integrates into the roofing to promote drainage, and also hides the pipe. One of the best premade solutions we've seen is a metal "plumbing vent flange" from F.J. Moore Manufacturing (800.658.2331).

Available in copper or in galvanized or painted steel for a variety of pipe diameters, it can be used for new work or mounted over an existing rubber boot. The base can be adjusted on site to match the roof pitch. The company also makes a "special pitch" model for new work, which consists of a sleeve and base plate of galvanized steel or copper custom-soldered to match a specified pitch.

  • Credit: Jim Bennette

  • Credit: Jim Bennette

Ridge Vents

Contrary to conclusions drawn during the 1990s, recent research suggests that venting has less effect on asphalt roofs than do shingle color and site orientation of the roof. There are, however, many good reasons to vent a roof (see "Roof Ventilation Update," Oct/07), but one of the most compelling is to meet the manufacturer's warranty requirements. Check the shingle wrapper: If venting is required for the roofing you are using and the roof you are considering is unvented, raise the issue with the homeowner before you start the roof work.

Where ridge venting is used, extend and cap the vent material across the entire length of the ridge (see photo) to avoid a pinched look at rakes or gable ends (see photo).

Credit: Tim Healey

Kick-Out Flashing

Kick-out flashing diverts water away from siding and trim where roof eaves intersect with exterior walls. While it is possible to site-bend metal into a workable kick-out flashing—especially when also flashing with self-adhering membranes or tape—prefabricated plastic or metal kick-out flashing is inexpensive, looks good, and is easy to install.

Michael Chotiner is a contributing editor to JLC.