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nowwhatnapster 07-24-2012 02:18 PM

Leaky vent stack, need advice on materials and install

If you can't guess by the photos, it leaks. This will be my first time replacin...... installing a flange.

Can someone link me to the best type of flange/flashing for this application? The pipe is cast iron and the outside diameter is 4 1/2". The surface is not terribly pitted. The top edge sits 8" from the roof and the bottom edge is 10", hopefully that is up to code height wise. Not like we get that much snow in Connecticut (2010/11 winter being the exception)

I am assuming I need to pipe some roofing cement on the bottom side of the flange and under the shingles I'll be lifting up. I'll wait for a nice hot day and cross my fingers the shingles don't crack on me, because there is no way I'll match that roof color. Its got another 5 to 10 years on it.

Do I bother nailing the flange at all? The closest we got to a hurricane was Irene. If I do nail the bottom edge should I just put some tar over the nail heads to seal them?

tinner666 07-24-2012 04:33 PM

Here's a link to a power vent install. It's the same as yours, only LOTS bigger. No need for cement anywhere. I just toe-nail the sides down so the shingles cover the nails.. One nail in each upper corner.

Buy 2 of the ABS 3 in 1 collars, Tear for the 3" pipe, (it looks like ?). I cut the entire flange off the second one and just slide it down the pipe to cover the rubber boot on the first one. Should last 15-20 years that way.

Windows on Wash 07-25-2012 07:47 AM

Interesting vent flashing approach. :eek:

tinner666 07-25-2012 02:54 PM

2 Attachment(s)

Originally Posted by Windows on Wash (Post 973802)
Interesting vent flashing approach. :eek:

You think? It's a simple fix when the call comes in and that's what went south in the 8th year. Doing it on install makes it last longer.
Here's one I did when the owner didn't want copper or lead.
By comparison, here's a no-caulk collar still going strong on a 1951 house. I took the pic in Dec.

tinner666 07-25-2012 02:57 PM

I need to take pix of the stack of aluminum ones in the shop that have the ruber ring. When they go south in the 8th. year, the water pours into the house. The rubber is at roof level, not on top of the dome.

nowwhatnapster 07-26-2012 10:42 PM

I picked up flashing similar to the photo below from HD yesterday. This is actually a photo of the other vent pipe on my house. Looks to be in ok shape except those nails at the bottom of the flashing bother me. They shouldn't be there/should be covered in cement?

Hopefully I'll get to install this weekend.

Windows on Wash 07-27-2012 07:51 AM

You can purchase replacement boots at HD or Lowes.

That boot looks okay and appears to be installed pretty well. Might be a good time to swap them both out and yes, a dab of sealant on the exposed nails is a good idea.

mae-ling 07-27-2012 10:00 AM

Seal with roofing cement/tar between back of shingles and top of flashing where it goes under the shingles or over the shingles.
Assuming thisa is not a not tar type flashing

tinner666 07-27-2012 10:01 AM

Yours looks OK so far, but the corners should never have been nailed. When I used to use those, I'd flex the flange so corners ctayed tight and the toenail the flange so the nails were under the shingles.

That's the type I quit using. When that rubber fails, it fails right in that crease and water will pour into the house. The ABS ones will split too, but won't leak as bad. Doubling extends their life. Or just wait 10 years, buy a new one, cut the flange off and slide it over the existing to reseal it.

vandel777 07-27-2012 03:28 PM

i would suggest going with a hard plastic pipe flange, here is link that shows you the process of the in-stallion ( it didnt quite mention where which course of shingle is the right one to go under the flange before nailing it to the roof deck. the way i judge mine is when i get up to the pipe i will want the top of the shingle to be atleast 1/4 to half way up pipe (note: not every pipe flange you go to shingle will have the exact placement, therefore shingling up to them leaves you with a different distance from the top of your shingle to the pipe, it could be little bit below the pipe or above so if your below the pipe chances are you should throw another course of shingles on before you nail the pipe flange to the roof deck.
along most of these style pipe flanges will a risen piece of plastic for the water to follow down, so when your going to nail your flange make sure you keep your nails on the outside of this water guider.

let me know if my info helped any :D

nowwhatnapster 08-03-2012 11:33 PM

Thanks for the info about the full plastic flanges. I went with the cheap aluminum/rubber flange by oatey. The roof only has about 5 to 10 years on it, so I will replace these with something better when the time comes.
Starting to get into the finer details of this task and I have a few more questions.

I picked up some Karnak #19 Flashing Roof Cement. I am not entirely sure if this is the right product for the job. Can anyone confirm?

I was trying to find hot-dipped galvanized roofing nails at my local HD but wasn't having any luck. All I could find was electroplated. Am I looking for the wrong kind of nail? Is there a better kind of nail I should be looking for?

Also, what length of nail should I be looking for? I know its supposed to penetrate 3/4" into the deck, but I'm not sure how to measure so I get the right length. I beleive there is only 1 layer of shingle, felt, and clapboard decking.

joecaption 08-03-2012 11:40 PM

SIlicone or that caulking will work, just needs a small dab.
1-1/4 nails, if there installed under the shingles elecro plated will work.

nowwhatnapster 08-04-2012 12:17 AM

Would aluminum nails be superior to the galvanized variety for this application?

My googling confirms your recommendation of 1-1/4" for a single layer of shingle. Thanks.

Michael Thomas 08-04-2012 08:29 PM

Even year I inspect dozens of rubber-gasket type vent stack flashings which have failed.

IMO, the "old school" solution of a lead flashing bent inwards over the top of the stack is FAR superior.

I have seen literally thousands of these - without finding one which has failed except as a result of mechanical damage.

nowwhatnapster 08-05-2012 12:30 AM

Well the job is done. I did not execute as well as I could have. I think I made some mistakes, but I don't think it will leak unless we have a major storm that blows rain up and under the exposed flashing.

Here are some pictures. I'll let you draw your own conclusions:
#1 - Removing the shingles & makeshift flashing

#2 Same as #1 just further along.

#3 Cut a replacement shingle because the old one was hacked to fit and in two pieces. Also note the first nail I drove on the far right of that shingle I put in the strip by accident. I covered it with roofing cement.

#4 Flashing in place with roofing cement applied to top. I did not apply any cement on the underside, I was thinking this was a mistake, but at the time I was unsure and decided omitting it would not be a huge error. Feel free to correct me here. Also note that I only nailed the top 2 corners of the flashing. In hindsight I should have put 1 nail in the middle of the top edge and probably 2 midway down the flashing on the edge. Again, I was unsure and felt omitting would not be a huge error.

#5 another shot of the 2 nails at the top. Again I feel I should have put 1 in the middle. I used hot galvanized nails 1-1/2". Tad longer than needed, but they were readily available.

#6 Final product. I re-used some of the shingles that I felt were in good condition so my repair would not stand out so much. Perhaps I can spray paint the black shingles so they blend better. The black splotch on the red shingle is from the old "flashing" it peeled off easily and was not terribly tacky nor missing particulates so I decided to reuse it.

I will definitely do a better job next time around. A little more research and time to execute would have made today's job better I feel. The only major thing I am concerned is that I did not nail the flashing farther down. The more I think of it the more I feel a gust of wind might lift it out of position. Thoughts?

@Michael Thomas, the lead flashing that goes all the way up and into the pipe does seem the superior method of flashing. I saw a copper variation of this online which I would prefer over the lead which would eventually leach into the run off.

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