|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
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
15. If installing a metal pipe sleeve, make certain that the tabs
are INSIDE the sleeve.