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Pipe Sub-Flashing For Metal Roofs Pipe Sub-Flashing For Metal Roofs
Pipe Sub-Flashing For Metal Roofs Pipe Sub-Flashing For Metal Roofs
The sub-flashing or "Drip-Pan" is used as a third line of defense against water infiltration around roof protrusions such as plumbing vents, electrical masts and various round-shaped chimneys.  It can be made out of any like-metal (it should be made out of the same metal as the roof covering i.e. do not install an aluminum drip pan beneath a copper or steel roof due to the potential for galvanic corrosion).

1.  Cut a 12" X 12" or larger piece of flat stock.

2.  Fold 1" along the sides inward approximately 170 degrees (you don't want to flatten the fold-over as this would allow water to seep out the sides).
3.  Fold 1" along the top inward approximately 170 degrees.
4.  Fold 1" along the bottom up to 90 degrees.
5.  As shown in the photos, cut a 4 - 6 tab in the bottom and fold it back down so that it will lie flat on the roof deck.
6.  Finish folding the bottom sections that are standing at 90 degrees inward to approximately 170 degrees.
7.  Draw out the pipe hole that you will cut into the center of the drip-pan.
8.  Important:  Cut the hole 1" SMALLER.
9.  Using your tin snips, cut 1" long tabs spaced at approximately 1" that you will fold up along the wall of the pipe.
10.  Before installing the drip-pan, caulk around the base of the pipe where it meets the roof deck using urethane sealant.  You want to use enough sealant that when the drip-pan is installed, caulk squishes out between the tabs.
11.  Install the drip-pan.  Caulk should squish out from between the tabs.
12.  Fasten the drip-pan to the roof deck using a roofing nail in each corner (make sure the nails on the lower corners are higher up so that they do not sit in water).  Apply a dab of sealant over the head of each nail
13.  Using a hammer, gently flatten the tabs against the pipe.
14.  Apply urethane sealant around the base of the pipe and the drip-pan.
15.  If installing a metal pipe sleeve, make certain that the tabs are INSIDE the sleeve.

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