Roof vent caps--seeking wisdom!


I am finishing our third floor and will be hiring someone to install the vent caps in the roof for a secondary plumbing stack and for two air vents (for a range vent fan and a bathroom vent fan). Our house is 130 years old and has seven steep gables. There is a trap door (sealed shut) two-thirds of the way to the top of a gable, which is elevated from the shingles and covered with some kind of a membrane, that I would like to have the vents go through, rather than cutting a hole through the shingled part. (The roof was replaced three years ago.)

Here’s the thing. I want to know what I’m talking about when I hire someone so they can’t take advantage of us. I’m not getting up on that roof to inspect their work, but my husband (who has no building experience) will be taking video and pictures with his drone.

What kind of vent caps should we buy? What material should the plumbing vent be? (Inside the house it will be 2" schedule 40 ABS, but I have read that ABS isn’t good for the exterior. We live in Iowa, so our temperature ranges from over 100 F in the summer to -20 F in the winter.) And what about flashing? (BTW, the trap door is at the same pitch as the gable, just elevated from it.)

Thank you in advance for any and all input!


Your plumber is responsible for what type of pipe is necessary and meets code and for the installation.

The roofer will just come in after the plumber has the pipes sticking through the roof and flash them. The plumbing vent most likely just gets a simple neoprene ring pipe collar/boot. Broan makes a very nice quality vent cap for bathroom and kitchen fans.

Normally on a sloped roof you would have the roofer pull a few shingles to install the flashing, and have no problems. If you have a membrane on the section you are installing them you will need to determine what it is and why it is there. You don’t simply stick vent flashing into a membrane.

You need to upload some puctures on here. If That section is the same pitch as a he rest of the roof, why was it not singled with the roof.

You might be able to just have the plumber stuck the pipes through then have a roofer shingle that to match the rest of the roof.


Keep your drone for playing with. Hire a professional roofer to install your pipe flashing and don’t worry. You can’t know what your talking about or doing by just simply getting the info here. I must ask…Have you and your husband been screwed by a contractor in the past?


Yes, repeatedly, which is why I have learned how to do everything myself–so I know it’s done right, even if I hire someone to do it. But our roof was an enormous project, done by a company that only does enormous projects and has a long waiting list. If I could get them, I wouldn’t worry, but here in small-town Iowa, there are lots of contractors who nod and smile and say they can do anything, and leave you with a mess. I don’t want my roof to be left with a mess.

When the roof was done, the trap door was still functional; that’s why it wasn’t shingled. But when we had spray-foam insulation done, we sealed it shut.


Thought maybe that was the case. As a roofing contractor in business for 27yrs I have to answer for the last idiot on a regular basis. I wasn’t being short or rude its just obvious to me when a customer has been burnt before. Try going to certainteed website and look at how they reccomend a pipe flange be installed at roof. Get a contract assuring that installation procedure will be followed. Ask contractor to take pics of each stage of install…that should be more than enough to ease your mind. Call a couple reputable general contractors and or your local building supply for a couple referrals. NOT LOWES OR HOME DEPOT…box store referrals are useless due to their constant employee turnover.