Cutting a Hole in Your Roof Installing a Vent Pipe DIY Old House Crazy

Cutting a Hole in Your Roof Installing a Vent Pipe DIY Old House Crazy

Cutting a Hole in Your Roof Installing a Vent Pipe DIY

Holy Toledo! This is a scary job for a DIYer. Think about it. Youre cutting a hole in the only thing that is protecting your home from an endless stream of the most devastating force nature has to throw at your most important, and expensive, investment: water. But worry not. Like most home repairs, this really isnt all that complicated or difficult. However, if you do it poorly, it could cost you thousands in water damage.

Can you find the other code violation? It's blue and doesn't have a cover.

A friend asked me to help him eliminate a sewer odor that had been coming and going since he lived in his house. You might have just thrown up a little in your mouths, I know. It was one of those things where, just when it got bad enough to hire someone to fix it, it would go away for months at a time. Then, I started this blog, and hes all like maybe that guy knows how to fix it.

After rooting around in the crawl space and attic, we discovered the culprit. Some A-hole plumber (yes, many professionals are A-holes that dont do the job professionally) installed a sewer vent that vented directly into the attic. In their defense, they did install a vent filter to pass code. Poorly. Heres the deal: whenever you run a drain to the sewer, youre required to run a sewer vent up and out. In well planned new construction or renovation, you can link these vents together to minimize the number of pipes coming out of the roof. In crazy old houses, which we love, there are often many generations of pipes coming out of the roof. The really old ones are cast iron. The newer vent pipes are PVC. We needed to finish the job of this old plumber.

New vent pipe extension

The first thing we needed to do was remove the old PVC coupling so that we could add a new one. The only way to separate PVC that has been bonded is to cut it. That PVC glue youve seen isnt actually glue. It is a solvent that dissolves the PVC a little and chemically welds the two pieces together. They cannot be separated after this has occurred. We used a small hand saw to remove the old coupling, then slid a new pipe extension over the older pipe. As you can see in the photo, we angled it up using two 45 degree elbows so that our roof hole would be a little higher up the slope of the roof.

Once we had the pipe extension connected, we figured out where the new vent pipe would need to pass through the roof using a piece of scrap wood held flush with the pipe. Where the scrap wood hit the understructure of the roof, we drilled a hole straight through to the outside. Standard practice is to drive a nail through, but my friend was heart set on using a drill.

Down the attic ladder we went, climbing up the roof ladder to find our drill bit like little kids hunting for Easter eggs. Hooray! After we located the bit, we began separating the asphalt shingles and cutting out a space for the flange to go.

The flange needs to fit snuggly around the vent pipe and should go under as many layers of shingles as possible. Furthermore, the flange should only be exposed on the bottom half (the upper half should be covered by shingles). Asphalt shingles are brittle when new, so we were extra careful not to damage any shingles that we didnt need to. These were not new, so this took some care.

Once the shingles were prepared and some nails were removed (lift up the shingles and pull out any nails that are blocking your flange from sliding up), we used a drill to make a pilot hole, and then a jigsaw to cut out a circle roughly the size of our pipe. The hole needs to be taller than your pipe diameter, as the pipe isnt passing through the roof at a perpendicular angle.

Now that the hole was cut, my friend ran back down the ladder and up into the attic so that we could connect the vent pipe through the roof. This can be a little tricky and required some readjustments and recuts of shingles to make it all work. Dont sweat it. That is normal. After the pipe was through the flange and the flange was under the shingles, we used roofing nails to secure the flange to the roof.

Use roofing nails to secure the flange to the roof

But wait! We just spent all this time being careful not to damage any shingles and then we stupidly drove nails through them. Isnt that more holes in the roof. Yes. It is. But thats why they make roofing tar, quite possibly the nastiest stuff on earth. Wear old clothes because once this stuff touches your clothes, its over. Theyre ruined. We bought a tube of tar (you need a caulk gun) and used it to reglue the upper shingles down, cover the nail heads, seal all of the edges, and patch a few other vents on the roof that had started to crack. This stuff is also great for sealing leaking gutters or any other places where water leaks.


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