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Thread: Running Vents through finished walls

  1. #1
    DIY Junior Member jpb123's Avatar
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    Default Running Vents through finished walls

    Could someone explain to me how to line up holes in the floor plate and top plate of a finished wall (accessed from the basement and the attic) to run a 2" vent? I am leaning towards running a vent to an existing stack in my attic rather than installing an aav and thinking about how I am going to line up the holes so that a straight section of pipe can be pushed up through the holes is leaving me a little puzzled. How do you pros do it?

    Thanks.

  2. #2
    DIY Member Hotbacon's Avatar
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    laser or plumb bob?

    Edit - Sorry, just re-read your question and realize your issue now. Unfortunately, I have nothing to offer w/ that situation.
    Last edited by Hotbacon; 01-26-2012 at 12:09 PM.

  3. #3
    DIY Senior Member bluebinky's Avatar
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    You can try measuring from something that's known to be the same in both spaces -- like an outside wall. If you are careful, that can get you close enough. However, you also need to know where the studs are as well as any wiring, etc.

    Not a pro, but I always end up cutting a hole in the bottom of the wall if not more. Also, you may need mid-story support to meet code. I don't have the code book here, but I believe 2" abs requires support every 6 feet vertically, or something like that.

    I miss Texas, there the procedure is to stand in the attic and shoot straight down...

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    If I absolutely had to do what your asking....say for instance a guy wanted to pay me alot of money to do it that way and I had plenty of room to do the work in,this is how I would do it.

    I would start in the attic by drilling a hole through the top plates. If given the choice I would use a 3" hole saw. I then would take a high powered flashlight and look down the wall to make sure I had a clear path to the bottom plate. If I can see the bottom plate and nothings in the way I would use as many drill extension as it took to reach the bottom plate and I would drill a pilot hole. Once I had the pilot hole drilled I would go in the basement and drill up with the size bit needed for the diameter pipe I was using.
    To secure the vertical pipe you could pump foam insulation into the cavity.

  5. #5
    Test, Don't Guess! cacher_chick's Avatar
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    I start by drilling the hole down through the top plate to see down the stud bay and make sure there is nothing in the way.

    Once this is confirmed, measure to determine the distance to each wall stud. Now go down near the baseboard on the main floor and use a studfinder and the measurements to line up where the hole should be from stud to stud.

    Often you can look up at the subfloor from the basement and see where the nails are coming through from the wall's bottom plate. Drawing up a set of lines 3-1/2" apart in line with the nails will give a good idea where the plate is.

    I'm not afraid to cut out a 12" square of drywall if it's going to make the job a lot easier, but more often than not it is unnecessary.

    When the layout makes exact measurements a challenge, don't be afraid to cheat- I use a long 1/8" bit to drill through the baseboard at an angle that puts the bit through the bottom of the bottom plate as close to center as possible. (The hole in the baseboard is easily hidden with a dab of wood putty when the job is done.) By measuring and picking my angle carefully, the bit will be sticking out of the subfloor in the basement's overhead exactly where it needs to be drilled upward.

    To make sure everything lines up, drill straight up from the basement with a 1/4" bit first and have someone shine a flashlight up though the hole while you look down from the attic. It will be easy to see if you need to adjust 1/4-1/2" to one side or the other before you drill the full-sized hole up from the bottom. You can also drop a plumb bob down to see how things are lining up.

    If the basement has low ceilings it's easiest to drop a stick of PVC down from the roof. Use blocking between the basement ceiling/floor joints to keep the pipe from falling too far down when you feed it in. 1 stick will reach fine from basement to attic if your house has 8 foot ceilings.

    If you are only going to the attic to connect to another vent, you must push the pipe up from the basement. Most basements are not deep enough to stand up a stick of PVC unless the floor is open to provide more room. A stick of PVC will flex a bit, but 2" is pretty hard to do much with.

    If you can't get a full length piece started up, you will need to put a half stick up, glue on a coupler and then attach the second half. The downside to this is that a 2" coupler will require a 3" hole. This doesn't leave anything left of the bottom plate, so drive a few 3-1/2" long screws up from below to keep the bottom plate well secured on each side of the hole.

    Use a stack clamp in the attic to secure the pipe at the top. If the holes are lined up well, they only need to be 2-1/2", but 2-3/4" leaves room for error.

    I started doing this years ago for running wires, and have found that it can be adopted to plumbing just as easily.

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    DIY Junior Member jpb123's Avatar
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    Thanks so much cacher_chick. That helped a lot!

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