# How to install a flash (for a vent pipe ) properly



## OldNBroken (Jun 11, 2008)

Can't give much information without knowing what type of roof and flashing you have.


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## Michael Thomas (Jan 27, 2008)

Gnfanatic said:


> Hey guys. This week I am going to be cutting a 4.5 inch hole in my roof and install a concentric vent for the boiler. I bought the 3-4 inch boot flash (metal) for the roof. Here is the question. I know the TOP of the flash goes UNDER the *roof shingles*. But what about the sides of the flash??? I was told it lays on *top of the tiles* but then wont water go right under it and cause a leak??


Is this a shingle roof, or a tile roof?


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## Gnfanatic (Oct 28, 2009)

sorry about that guys, I bought this.......

http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053



and 2 layers of shingles on the roof.


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## tinner666 (Mar 14, 2005)

1/2 over the shingles, 1/2 under like this larger one. http://www.albertsroofing.com/Power Vent Installation.htm

Take that one back to HD and get a black ABS boot. When the rubber top breaks in 4-5 years, the ABS one is much easier to fix. Just cut the flange off and slide the new top over the broken one. 
When the top goes south on that aluminum one, water will pour in.


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## tinner666 (Mar 14, 2005)

Oh. what are you going to do with the caulk? Take it back too.


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## Slyfox (Jun 13, 2008)

The bottom of the flashing should be over the shingles.
(should cover self sealer/nail line of shingles)
The sides will be partially covered, at least 2/3'rds.
The top will be completely covered.

You do not need to place the flashing under both layers of shingles,
just under the top layer.

When/if you run a bead of your black jack roof cement only do it on the top and sides, not the across the bottom.
Your roof cement should not be exposed either, run the bead on top of the flashing and under the shingles.


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## Gnfanatic (Oct 28, 2009)

Thanks Sly, I appreciate the help. It going to be tricky getting the sides over it without damaging anything . First I need to take 12 inchs of snow off the roof! such fun!


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## Gnfanatic (Oct 28, 2009)

Guys,I returned the metal one and got the ABS piece. I was planning to do it today but time was running out and will do it tomorrow morning. I have a question for you guys. I was planning to use a 4 1/2 inch hole saw to drill the hole in the roof but I cannot make is straight becasue the drill bit is not long enough. Should I get a longer drill bit for a guide OR is there a diff way to do this??? 


thanks!!


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## tinner666 (Mar 14, 2005)

Depending on the pipe size, and the roof slope (ie-3" pipe, 4/12 slope might be 4" x 5-1/2" hole), a hole saw seldom does it completely. We use 'Tiger-saws'/ sawzalls. A keyhole saw will also work. 
After using the holesaw, remove any shingles necesary before using a keyole saw.. It will dull in a hurry cutting shingles or felt!


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## jimpick (Dec 30, 2010)

I don't believe you have been given good advice.

First off I would go with the aluminum flashing. The plastic flashing has a tendancy to buckle up on the bottom side in time do to the heat of the roof. This can lead to insects or bats getting into your attic. The second is you shovel your roof off, I have replaced many plastic flashing's that have cracked in the cold because they were hit by a shovel. Out of the about 800 roofs I have worked on almost all of the flashing repairs I have done have been because of the plastic boot rubber prematurely failing. If you go with a metal flashing go with aluminum as the galvanized rust and will leave streaks on your roof, the aluminum will not.

The next problem is with the statement of not putting roof cement under your flashing. According to the Ceertainteeds Master Shingle Applicators Manual this statement is incorrect. The reason that cement is put under the flashing is because of wind driven rain or snow. I have seen where wind driven rain had destroyed 4 room of drywall after hurricane Katrina. In addition this cement is part of the specification set for by ARMA (American Roofing Manufacturing Association).

The best way to install this flashing is as follows.

1. Remove the shingles above and beside the vent hole.
2 Place the flashing on your pipe and mark were the rubber stops. Then pull it up and off the pipe.
3. Take some clear caulk and run a ring around the pipe were you made the mark for the rubber.
4. Place cement on the bottom side of the flashing staying back .75-1 inch from the edge and slide it back down the pipe. This should seal the rubber gasket to the pipe and the roof deck. then nail the flashing to the roof deck.
5. Now cut the shingles to the flashing but keep a gap of about 3/8-1/2 inch from where the flashing rises off the deck. By keeping a gap here on the sides and top the water will flow faster off the flashing. If water sets here it can cause the shingle to deteriorate faster, or wick under the shingles. 
6. Once the shingle is cut to size put cement on the bottom of the shingle where it makes contact with the flashing and nail it down. This cement will also keep water from wicking under the shingle. In addition it will help keep the shingle from blowing off in high wind.

If you are damaging the seal down strip or not using new shingle make sure you seal the shingle where this strip is missing or damaged.

Sorry this is long, hope it helps.


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## Slyfox (Jun 13, 2008)

jimpick said:


> I don't believe you have been given good advice.
> 
> First off I would go with the aluminum flashing. The plastic flashing has a tendancy to buckle up on the bottom side in time do to the heat of the roof. This can lead to insects or bats getting into your attic. The second is you shovel your roof off, I have replaced many plastic flashing's that have cracked in the cold because they were hit by a shovel. Out of the about 800 roofs I have worked on almost all of the flashing repairs I have done have been because of the plastic boot rubber prematurely failing. If you go with a metal flashing go with aluminum as the galvanized rust and will leave streaks on your roof, the aluminum will not.
> 
> ...


Were not teaching a newbie roofer how to properly install a pipe flashing in a State with hurricane codes, were giving advice to a home owner on how to properly install it himself 'DIY" in a manner in which it will not leak.

No, you don't/shouldn't use a shovel to remove snow from your roof.


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## jimpick (Dec 30, 2010)

Sorry if I ruffled your feathers. It needs to be installed correctly whether it is done by a DIYer or a new roofer. The above directions are correct nation wide and will insure that the roof will not leak. Vent stacks are notorious for leaking because of incorrect installation.

It has been my experience that people like to know why something is done the way it is explained. The hurricane Katrina remark was just a example, a example that applies where ever high winds can happen.


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## Slyfox (Jun 13, 2008)

jimpick said:


> Sorry if I ruffled your feathers. It needs to be installed correctly whether it is done by a DIYer or a new roofer. The above directions are correct nation wide and will insure that the roof will not leak. Vent stacks are notorious for leaking because of incorrect installation.
> 
> It has been my experience that people like to know why something is done the way it is explained. The hurricane Katrina remark was just a example, a example that applies where ever high winds can happen.


No need to be sorry, I was not offended by anything you said.

You did show me how I made mistake tho, this is the World Wide Web and
I should have asked the OP where he was located before I responded because roof installations spec's are different from one area to another.

I know exactly where you coming from because I have installed roofs in several southern states where the type of procedure you refer to is the way the flashing's are installed.

My comment about teaching a newbie roofer was incomplete.
I meant we weren't teaching a newbie roofer in an area like yours in which the procedure you explained is needed/required.
A newbie roofer in my area would be taught the way Tinner and I explained.
Also in my area, like Tinners, we do not use any caulking or roof cement when installing our flashing's, which is why Tinner made mention of taking the black jack back to the store.
I suggest the OP use it even tho I wouldn't because he doesn't have over 30 years experience like Tinner and I do so the roof cement will be an extra precaution.


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## Gnfanatic (Oct 28, 2009)

Alright guys. I did the job this morning. The shingles were not very forgiving at all. they cracked easily and I had to be extremely cautious. I did it the way you guys told me to do it. I got a tad sloppy with the black jack just to me make me feel more comfy about the install. I am hoping this wont leak and planning to tear off all the shingles and re-roof in a year.\


thanks again and Happy New Year


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## Slyfox (Jun 13, 2008)

Hope it holds up for you.
Happy New Yeas to you also.


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## DIY Granny (Mar 20, 2011)

Good morning Gentlemen, I have a leak around a vent pipe on my new asphalt shingle roof. Is this something I can fix myself or should I contact a roofer? The roof is about a year old and out of guarantee. I live in Central Texas and we are in the midst of a drought right now, but when the rains come they are torrential. We get strong winds from both north and south, but this stack happens to be on the north side, not that it makes a difference. I've read Jimpick's instructions and think I may be able to follow them; I still have extra shingles in the event I tear up the existing ones. Thanks in advance.


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## kwikfishron (Mar 11, 2010)

Welcome to the forum. 

Warranty or not if it’s only a year old I’d call your roofer back first.
If he cares anything about customer satisfaction he’ll take care of it.


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## springtxroofing (Mar 21, 2011)

tinner666 said:


> Oh. what are you going to do with the caulk? Take it back too.


Why did you buy caulk? You should be using a silicone based product. Unlilke caulk, silicones properties allow it to expand and contract with temperature changes preventing leaks. Look for a product called NP1.

Avalanche Roofing & Restoration
www.springtxroofingcontractors.com


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## DIY Granny (Mar 20, 2011)

kwikfishron said:


> Welcome to the forum.
> 
> Warranty or not if it’s only a year old I’d call your roofer back first.
> If he cares anything about customer satisfaction he’ll take care of it.


I took your advice and contacted my contractor who got the roofer on the job first thing this morning. It's a good thing I did because the problem was not the flashing, but that the workers forgot to tilt the new stack (at least that was the explanation). I would not have caught that and wasted a lot of time and energy. 
Ya'll be careful on those houses!


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## federer (Aug 20, 2010)

finally found this thread on how to flash! thanks for all the advice and tips. Granny-what do you mean by tilting the new stack?


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## federer (Aug 20, 2010)

tinner666 said:


> Depending on the pipe size, and the roof slope (ie-3" pipe, 4/12 slope might be 4" x 5-1/2" hole), a hole saw seldom does it completely. We use 'Tiger-saws'/ sawzalls. A keyhole saw will also work.
> After using the holesaw, remove any shingles necesary before using a keyole saw.. It will dull in a hurry cutting shingles or felt!


thanks for the advice. i bought a hole saw but that may not be enough as i realize now. how can you cut precisely with a sawzall though? i have a reciprocating saw but i am not sure I can make a perfect circle with it. should i use a hole saw first to make an outline?


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## federer (Aug 20, 2010)

jimpick said:


> I don't believe you have been given good advice.
> 
> First off I would go with the aluminum flashing. The plastic flashing has a tendancy to buckle up on the bottom side in time do to the heat of the roof. This can lead to insects or bats getting into your attic. The second is you shovel your roof off, I have replaced many plastic flashing's that have cracked in the cold because they were hit by a shovel. Out of the about 800 roofs I have worked on almost all of the flashing repairs I have done have been because of the plastic boot rubber prematurely failing. If you go with a metal flashing go with aluminum as the galvanized rust and will leave streaks on your roof, the aluminum will not.
> 
> ...


thanks for the detailed post. i am using new shingles that I am going to cut. i just want to be clear-you want to cut the shingles so that they overlap the flashing but leave about 1in. space between the 2 materials? Also, can you please indicate what kind of nails should I use to nail down the new shingles?

this is where i will be installing the vent-about a few feet from the existing one in the pic


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## federer (Aug 20, 2010)

Gnfanatic said:


> Alright guys. I did the job this morning. The shingles were not very forgiving at all. they cracked easily and I had to be extremely cautious. I did it the way you guys told me to do it. I got a tad sloppy with the black jack just to me make me feel more comfy about the install. I am hoping this wont leak and planning to tear off all the shingles and re-roof in a year.\
> 
> 
> thanks again and Happy New Year


can you post some pics?


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## Gnfanatic (Oct 28, 2009)

Well, its been a few months and several thunder storms. I have no leaks. thanks for the help guys!


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## federer (Aug 20, 2010)

dining sets said:


> creative post.


whose post?


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## federer (Aug 20, 2010)

Gnfanatic said:


> Well, its been a few months and several thunder storms. I have no leaks. thanks for the help guys!


thanks for the pic! were you able to cut the hole with a hole saw?


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## Gnfanatic (Oct 28, 2009)

not for the roof. The bit wasnt long enough and I was worried the hole was not going to be straight. I used a sawsall


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## federer (Aug 20, 2010)

Gnfanatic said:


> not for the roof. The bit wasnt long enough and I was worried the hole was not going to be straight. I used a sawsall


how did you make a perfect circle with a sawzall?


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## kwikfishron (Mar 11, 2010)

federer said:


> how did you make a perfect circle with a sawzall?


Who says the hole needs to be a circle or perfect.:whistling2:


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## Gnfanatic (Oct 28, 2009)

was not perfect, I used a coffee can and lined it out with a marker. It is a circle, looks like a circle but not perfect  . As long as it was not hacked and doesnt leak


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## federer (Aug 20, 2010)

oh ok. in my mind i was thinking it needs to be good enough so it doesnt leak. but that's what the flashing is for...duh haha. 

but anyways i think i am going to hire a roofer to come out since i am using spray foam and I don't want to risk anything leaking down the road to ruin anything....what's a rough estimate to install a exhaust fan and cap it? $300?


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## handy man88 (Jan 23, 2007)

Gnfanatic said:


> Well, its been a few months and several thunder storms. I have no leaks. thanks for the help guys!


I'm not a plumber and don't know the code, but is it kosher to have 90 degree bends on vent pipes or should they be more steeply angled?


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## Gnfanatic (Oct 28, 2009)

The boiler allows 90 degree bends for venting and intake. I read the manual thoroughly. you deduct so many feet allowed per a bend ( I think 10) plus the town inspector saw everything and gave me a co


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## federer (Aug 20, 2010)

from what i read it's best not to do 90degrees but it can be done


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