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Old 04-05-2019, 04:29 PM   #1
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Drilling Dryer Vent Hole Through Floor Joist


As part of my bathroom renovation, I am setting up a laundry area in the bathroom. Unfortunately, the only sane place to put it, will put the dryer vent tube itself down into the same floor joist bay as the main sewer drain and vent. So I'd have to go through that pipe to get to the exterior wall.

There is an easy solution to this, I can cut a hole in the floor joists and run the dyer vent into the next bay. Then it's a clean shot, smooth sailing to the outside of the house.

My concern is with the hold I need to drill. I wanted to get some opinions on doing it. This is a 1 bedroom ranch with 2" x 8" floor joists. They are space very roughly at 12" on center. The one I need to drill through is actually a double beam because its under a non-weight-bearing interior wall.

It's about 7 1/8" of actual wood. And the hole I'll be drilling will be about 4 1/8". That will leave me 1.5" of wood above and below the hole. A knowledgable friend suggested I buy another 6' or so 2" x 8" and sandwich it up there with fasteners and liquid nail adhesive as extra support and drill through all three. This seems like a good plan to me, I just want more opinions.

The alternatives to doing it this way are not ideal. If I go up into the attic then out the side, it would be a VERY long way to go. I can't go out the roof because it's covered in solar panels, so I'd have to go about 40 feet total to go up into the Attic and then out the side of the house.

Alternately, I could drop down, go under the floor joist, and then go up into the bay. I prefer the drilling method to this because this method will make a big low-spot in the vent where things can build up over time, particles and cold air. Also it will be in a spot in the basement that will make it inconvenient to have it hanging that low. In other words, you'll have to duck under it.

So I'd prefer to do it the original way, drilling through the floor joists. What do you think?
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Old 04-05-2019, 04:57 PM   #2
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Re: Drilling Dryer Vent Hole Through Floor Joist


A 2 ply floor joist may be considered a beam and likely should be considered as carrying a load.
I would like to see a sketch of the layout of the bathroom.
What is the ceiling height in the bathroom?
Do you have a path for the bathroom ceiling fan duct?
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Old 04-05-2019, 05:29 PM   #3
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Re: Drilling Dryer Vent Hole Through Floor Joist


You don't want to denigrate the viability of the joist by drilling through it. Eating over half of the joist will weaken it. You, likewise don't want to go down and then back up. You will be forming a ptrap and moist air will condensate and fill the hose, eventually stopping the air flow. Straight out, down and straight out are the best options. Going up also presents backwash of lint, so you will have to anticipate that and put a tee cleanout in the end.
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Old 04-05-2019, 05:40 PM   #4
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Re: Drilling Dryer Vent Hole Through Floor Joist


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Originally Posted by chandler48 View Post
You don't want to denigrate the viability of the joist by drilling through it. Eating over half of the joist will weaken it. You, likewise don't want to go down and then back up. You will be forming a ptrap and moist air will condensate and fill the hose, eventually stopping the air flow. Straight out, down and straight out are the best options. Going up also presents backwash of lint, so you will have to anticipate that and put a tee cleanout in the end.
Down and straight out is preferred but the only way I can do that is by drilling a hole in the joist.
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Old 04-05-2019, 05:46 PM   #5
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Re: Drilling Dryer Vent Hole Through Floor Joist


Is this an electric dryer?

Are you aware that you can use an indoor dryer vent kit? Makes a lot of sense in the winter, not so much in the summer.

https://www.amazon.com/BetterVent-In...SIN=B00Q4X2FSM

As for drilling a hole, 2-3/8" is the max. allowable diameter for a 2x8 floor joist and that's only if you aren't near the midspan of the joist.
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Drilling Dryer Vent Hole Through Floor Joist-floor-joist-hole-sizes.jpg  
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Last edited by HenryMac; 04-05-2019 at 05:53 PM.
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Old 04-05-2019, 06:00 PM   #6
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Re: Drilling Dryer Vent Hole Through Floor Joist


Make your lateral move into the next stud bay before you go down thru the floor.
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Old 04-06-2019, 01:02 AM   #7
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Re: Drilling Dryer Vent Hole Through Floor Joist


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Make your lateral move into the next stud bay before you go down thru the floor.
That's not possible. I'd have a dryer hose coming out of the wall of the bedroom and going down into a hole in the floor. The only bay the vent could possibly come down into is this "wrong" one. I'll try to sketch out a floor plan so it makes more sense, but me no draw good....
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Old 04-06-2019, 01:17 AM   #8
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Re: Drilling Dryer Vent Hole Through Floor Joist


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That's not possible. I'd have a dryer hose coming out of the wall of the bedroom and going down into a hole in the floor. The only bay the vent could possibly come down into is this "wrong" one. I'll try to sketch out a floor plan so it makes more sense, but me no draw good....
We build drops and boxes for those kind of things all the time. Could you cheat the corner of the bedroom with a 8x8 box floor to ceiling?
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Old 04-06-2019, 03:16 AM   #9
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Re: Drilling Dryer Vent Hole Through Floor Joist


Ok it's visual aide time.

First, the floorplan. The orange lines are the floor joists. And the big one at the bottom is the centerbeam. I can't see any possible way to make it so the vent comes down in any bay but the bay that is blocked by sewer pipes.

Next, a photo of this side of the bathroom, with blue square where the washer and dryer go.

Then a view of the bathroom from the basement. The blue squares are approximate because it's hard to draw accurately.

And last, a view looking down the bays, towards the back wall of the house. The washer and dryer would be above this and facing towards our left.

So the "idea" has evolved from sistering a short 3rd 2x8, lagging it in place, and drilling through all three... from that, to sandwiching three strips of half inch plywood, liquid nailed and bolted in place, about 6' long, then drilling the hole through all that material. I know this is still not ideal and I'm not saying that I'm actually going to go through with it. But I would prefer to do it that way, given the alternatives.
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Drilling Dryer Vent Hole Through Floor Joist-floorplan.png   Drilling Dryer Vent Hole Through Floor Joist-washer-dryer-location.jpg   Drilling Dryer Vent Hole Through Floor Joist-basement-view.jpg   Drilling Dryer Vent Hole Through Floor Joist-img_7540.jpg  
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Old 04-06-2019, 04:53 AM   #10
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Re: Drilling Dryer Vent Hole Through Floor Joist


Why not come down and turn laterally with the joists and exit through the sill? It only appears to be less than 8 feet.
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Old 04-06-2019, 05:05 AM   #11
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Re: Drilling Dryer Vent Hole Through Floor Joist


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Originally Posted by chandler48 View Post
Why not come down and turn laterally with the joists and exit through the sill? It only appears to be less than 8 feet.
Because the sewer pipes block the bay the vent comes down in to. That's the whole problem, unless i'm not understanding your suggestion.
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Old 04-06-2019, 05:17 AM   #12
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Re: Drilling Dryer Vent Hole Through Floor Joist


I understand. OK, plan B. Since your walls are opened up, why not a rear exit from the dryer into the wall cavity, turn right and exit out the exterior wall? You can buy wall pans to accomplish this since you probably only have 3 1/2". https://www.homedepot.com/p/Dundas-J...D48S/202449700
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Old 04-06-2019, 05:18 AM   #13
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Re: Drilling Dryer Vent Hole Through Floor Joist


Turning right goes into the rest of the house. I'd have to turn left and I'd hit that same sewer pipe and vent.
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Old 04-06-2019, 06:58 AM   #14
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Re: Drilling Dryer Vent Hole Through Floor Joist


Take another look ti see if it is possible to squeeze the dryer line past the drain. A 4" alum. dryer vent can collapse a bit into a oval if needed. Might want to pick up 2' length and try to position it in there.

I really would avoid popping a 4" hole, mid way thru a 8" floor joist. Not a good plan.
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Old 04-06-2019, 08:15 AM   #15
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So you already have that blue wire dropping down, what 3" below the beam? Is an extra 1" really going to be that inconvenient?
Though that will still result in your vent going down and then back up to go out unless you're going through concrete...

So, looking at your picture, the joist to the left of the beam looks to be about 12" from the double, while the rest look to be 16" on center. I might think about seeing if that single joist can be moved over enough (2-4") to accommodate the vent going past the sewage drain pipe. At most, that joist would still only be 16" from the double beam, which should still be able to carry the load without issue.

A lot of work for a stupid dryer vent? Yes.
Compromising structural integrity? No.
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