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Flashing or sealing around vent stacks

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Robert Massmann
10/23/2007
I have a new house with a snap seam steel roof. I think the vent stack seals were installed incorrectly. Installation progression was (1) tar paper, (2) vent boot assembly (3) metal roofing, and last seal with silicone caulk. Shouldn't the steel roof have gone down before the vent boot and the boot flange would have been sealed with silicone and secured to the roof.
Guest User
10/23/2007
Robert, I don't want to get into details about roofing styles---what one roofer does compared to another roofer (that's about the flashings), but I will tell you, the silicone will not last as long as your roof. It is not a good sealant, it dries out and becomes hard in just a very few years and some brands don't last a year. [email protected]
Todd Miller
Isaiah Industries, Inc.
10/24/2007
Wade is correct. A butyl sealant would be better and, of course, Robert, you and I have since you posted been emailing about this as well.
Brian Selig
Architectural Building Components Metal Roof and Wall Panels
10/25/2007
The water will never end up on the standing seam panel if the boot is below the panel. Sealants are not miracles in a tube. Even Butyl does not like UV exposure. On metal roofs, vent pipes can be addressed with an EPDM boot (http://www.itwbuildex.com/dektite.htm) over the metal roof panel.
Guest User
10/26/2007
I had a thought about handling the vent flashing like the roofer did. My idea was to use a standard lead boot under the metal and have it come thru a tight fitting hole (cut with a holesaw). But my concern was with finding a sealant thet could hold up. The EPDM boots are not very attractive on a residential roof.
Guest User
10/26/2007
Greg, You've got it right. On thru the panel fastened metal, we cut a hole and install a dektite on top of the panel. Butyl tape or a sealant like NP-1 is used between the dektite and the metal panel. On standing seams we run what we call a slipsheet. We run a panel past the vent 6 inches or so. We then put our flashing on, usually lead even though it is dissimilar metal. We then run a sheet from the bottom of the flashing to the ridge, this sheet being cut out (actually a big slot) for the penetration. The ends of this sheet and the sides next to the pipe are nicely folded back and under giving a nice finished appearance with no cut edges. Everything is hemmed. You just have a slot as wide as the penetration that the flashing shows thru. This kind of detail is only done on higher end metal panels. It is time consuming an labor intensive to do it on agricultural panels. [email protected]
Guest User
10/27/2007
Wade, That is a great idea and sounds like it would work very well. Budget only allows for the AG panel that I am going to install over an existing roof with horizaontal and vertical battens. My plan is to put the lead boot thru the bottom of the panel and form it to the profile of the metal and then glue it in place with some type of urethane. And then a bead around the outside area as well. I found a product that looks like it will hold up (GEOCEL 2300 tripolymer sealant). My other thought is that since it is going over an existing roof in good condition, even if a small leak started the original roof would prevent it from doing any damage to the house. Let me know what you think.
Guest User
3/8/2010
Did you ever try DAP Sidewinder? I used it on a Steel Roof around Roof Stacks that had been leaking for years. The building is a church in Carson City, NV. The heat in the summer and the chill in the winter are both extreme and the wind is extreme also. I removed all of the old caulking - which was crystallized (The building was then about twenty-five years old)- in 2002 or in 2003 and applied the "Sidewinder". In the seven or eight years since application the caulking has remained pliable - AND there are no leaks.
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