Description: Flashing a change in roof slope usually involves copper sheets 8 or 10 feet in length. They lap over the lower roof and are lapped by the upper roof. A cant of some kind is used to raise the roofing material and keep it from direct contact with the copper surface, to minimize line corrosion.
There are many combinations of roofing materials and corresponding numbers of appropriate details for each condition. The details shown are valid for shingle, tile, and slate roofing. The conditions are representative of typical installations.
The recommended minimum thickness of copper is 16 oz. unless slate or tile roofing is used in which case 20 oz. copper is used.
9.6A. Change of Roof Slope - Wood Cant
This detail shows a shallower pitched roof joining a steeper pitched roof below. The copper flashing extends under the upper roofing at least 6". It laps the lower roofing a minimum of 4". The ends of each sheet should lap over the preceding one at least 4". The lower edge of the flashing is hemmed for stiffness.
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The cant strip shown is wood fastened by copper straps, spaced 2'-0" apart, soldered to the copper flashing. A copper cant can be used instead, as shown in Detail 9.6B.
9.6B. Change of Roof Slope - Copper Cant
In this detail the steeper pitched roof is above the one of lower pitch. The flashing method is similar to the one shown in Detail 9.6A.
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9.6C. Flat to Sloped Roof with Gravel Stop
This detail shows a flat built-up roof joining a lower pitched roof. Here the flashing extends a maximum 4" under the built-up roofing. It also has a built-in, formed gravel stop.
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The lower edge of the flashing is hemmed and cleated to the sheathing at 12" O.C. As an alternate, a lock clip can be used as shown in Detail 9.6D.
9.6D. Change of Roof Slope - Alternate Wood Cant
This detail shows an alternate cant. The wood cant is nailed to the sheathing. It is then covered by the copper flashing. The lower edge of the flashing is hemmed and held by a lock clip. Alternately, cleats at 12" O.C. can be used as shown in Detail 9.6C.
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For Additional Information:
- Flashings and Copings - Fascias and Gravel Stops, for additional information on gravel stops.
- Flashings and Copings - Ridges and Hips, for related conditions.
- Flashings and Copings - Valleys, for additional information on valley conditions.