Friday, October 11, 2013

Plumbing Vents 101

UPDATED on Saturday morning to add more photos...

I literally had to pour a glass of red wine and get some dark chocolate to have the stamina for this post.  I know, cry me a river, right?  

And really, now that the plumbing roof vents are in, I feel sort of stupid about how simple they are and how complicated I made them.  Daniel tells me that my whole house will be that way; that no one part is that difficult, and when I'm done I'll say, "Oh, well, it wasn't as difficult as I expected."  For my sake, I hope he's right.  My learning curve has been a slow easy arc on many topics, and a vertical jump on others.  At the moment, I am daunted by reservoir tanks.  Back a few weeks when I was preparing for my roof installation, plumbing roof vents were terribly daunting.  WELL.  Allow me to simplify for you and spare you my agony.

Here's my other most comprehensive post on this topic (I think all of my other posts related to plumbing vents were just whining...)

Okay.  So, the plumbing vent is a 2 inch diameter of PVC pipe.  Except that I learned that the size of PVC pipe is measured on the inside of the pipe - so really you want 1.5" PVC if you bought a 2" drill bit.  (That's the first time I'm saving you time on this project.)

Next, decide where you want your vent to be located.  Ideally you don't want it to have to make any 90 degree turns - so, for example, decide where your kitchen sink will be and install the plumbing vent between the nearest two wall studs.  Same for your bath - figure out where your shower head and sink will be - you can connect those two lines together and just have one vent.  And place that vent between the nearest two studs.  Be sure you look for obstacles - window framing, joist hangers, skylight, etc.  You need a straight shot up to through the roof - and the skylight has a minimum flashing requirement, so be sure and consider that.  I didn't have a ton of choices for placement, but fortunately my limited choices were very acceptable with my floor plan.

So you've decided where they go.  Now you have to drill the hole.  In the Gifford model, I had (from the bottom up) the top plate of the wall, the 4x6 cedar (purlin), the Shafer Shelf (makes the top plate a double top plate) and then part of a 2x4" that is standing on it's narrow edge that the rafters attach to.  (In this photo you cannot see the 2x4" on it's edge.)  We centered it front to back on the top plate, but then adjust it back towards the exterior wall just a touch.

A hole saw won't work for this job - it doesn't go deep enough.  One method is the drill bit that I wrote about in the post (linked) above.  It came with this weird screw in the center.  All that screw seemed to do was jam us up so we took it out and put a drill bit in its place.  It worked like a champ.

That set up (along with a makeshift extension for the very last part of the drilling) got us through to the 2x4" that is standing on it's narrow edge.  Then the drill bit shown above didn't work because there wasn't anything to anchor the center drill bit into.  A note here: you want to be sure that you are not taking away more than half of that 2x4 on it's edge, because you'll lose structural integrity.)

It took a while to drill through all those layers - we took turns.

For the 2x4 we (okay John) took a hole saw and approached from the top down - inside the house - below the rafters and above the top plate.  It was tricky because of the angle - the rafters and roof sheathing prevented a totally vertical approach - but we could nibble away at it.  We initially planned to use a chisel, but the hole saw did actually work.

When you get a reasonable start on it, test the opening with your PVC pipe.  Our hole was just a shade small/jagged and the pipe wouldn't pass through.  John cleaned it up with a sander:

Eventually you'll have a hole all the way through:

Then you have to drill a hole through the roof plywood sheathing.  We (oh all right JOHN) used a hole saw from outside on a ladder, drilling down into the roof sheathing.  The angle is tricky - hard to get the hole saw started because half of it catches before the other half - but eventually it works.   We sawed off a piece of PVC pipe at an angle and held it against the underside of the roof plywood and traced it with a Sharpie to determine the necessary opening.  It must be oval, not round because of the roof pitch.

On the second one we used a jigsaw and cut a rectangle.  No reason not to - it's faster, and in the end it doesn't show anyway.

Cutting the vent hole with the jigsaw

I don't know how John even GOT this photo - was he up on the ladder with me?? LOL
For the outside up on the roof portion, you need a rubber "boot" that fits over the pipe and is sealed (screwed and caulked) onto the roof.  See my previous post about boots - but here's one of the small brown ones I ordered online:

(You cut the appropriate ring to accept the size pipe you bought.)

Spray paint the ends of the PVC to match your roof (get the first few inches inside, too).

And then when it's dry, insert it into the hole you drilled, and use metal strapping to hold it in place.
(This is temporary strapping for me, so the attachment is sloppy.  Just ignore that...)  So here is the inside view of it all in place:

At this point, the bottom end of the pipe is just dangling in the air, not connected to anything.  But when I do the rest of my plumbing I can just use a coupling and connect it to the next piece of pipe.

The pipe comes out the roof.  The pipe boot goes over it.  Caulk around the pipe inside the boot.  You caulk and then screw the boot onto the roof, and then caulk on top of it again, and spray paint the whole kaboodle (shielding the roof with a piece of cardboard - thank you Jason!)   Here is the view from outside - hardly noticeable.

And now?

Plumbing vents?  CHECK.


  1. You're observant Craig! YES and it's spectacular. I'll write about it today...

  2. Overhead piping can be spooky! Good call


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