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Old 07-24-2012, 01:28 PM   #1
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Floor Joist and bathroom venting


So I want to install a bathroom fan in my already finished basement bathroom. The only thing is that the floor joists are running perpendicular to the shortest route (about 4' of run). Meaning I'll have to drill 4-1/8" diamater through my 2x8 floor joists.

Coincidentally, the upstairs bathroom is directly above my downstairs bathrrom as well.

Would there be any problem drilling this size hole in about 4-5' worth of floor joists?

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Old 07-24-2012, 01:41 PM   #2
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Floor Joist and bathroom venting


[quote=bates;973155

Would there be any problem drilling this size hole in about 4-5' worth of floor joists?[/quote]


There certainly would be a problem. On an 8" deep joist, 2 1/2" is about the most you should do.

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Old 07-24-2012, 01:43 PM   #3
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Originally Posted by tony.g View Post
There certainly would be a problem. On an 8" deep joist, 2 1/2" is about the most you should do.

How am I to route the vent then?
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Old 07-24-2012, 02:33 PM   #4
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How am I to route the vent then?
That's your problem; you asked if it would be OK to drill a 4" + hole through an 8" deep joist.

You have to work another way round for the ducting. Sorry, but you cannot compromise the structure for ease of getting a duct through.
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Old 07-24-2012, 02:53 PM   #5
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Floor Joist and bathroom venting


If that is only a half bath, you may have more options for venting the fan.
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Old 07-24-2012, 03:23 PM   #6
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If it's a short run to the outside, will your Code let you use a smaller duct, (say 2") or has it got to be 4"?
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Old 07-24-2012, 04:26 PM   #7
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Draw us a picture. Why can't you go the longer route that is parallel/in between the joists?

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Old 07-24-2012, 04:40 PM   #8
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laugh if you'd like at my quick drawing. At work where I don't draw so I had to be quick. Anyways, oddly enough the joist run the same direction as the lines on the paper.

Top picture is an overview layout of the master bed/bath

Bottom picture shows the change in ceiling height between the bathroom and bedroom (same height) compared to inside the closet height.
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Old 07-24-2012, 04:49 PM   #9
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Can you get hold of flat, rectangular ducting of the equivalent cross-sectional area? Something like 2" deep by 8" across would do.
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Old 07-24-2012, 04:55 PM   #10
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Can you get hold of flat, rectangular ducting of the equivalent cross-sectional area? Something like 2" deep by 8" across would do.


I'd have to give a look around, sounds like it's not an everyday home depot item?
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Old 07-24-2012, 05:12 PM   #11
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Have a look at this, particularly diagram 3 on p2, showing the flat ducting (it looks to be 4" x approx 2"). There are adaptors from round to rectangular.

(its a UK firm, but your hd or lowes will have something similar; if the pic. doesn't come through, I can scan it and upload).

http://www.wickes.co.uk/content/ebiz...ges/gil/93.pdf
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Old 07-24-2012, 05:22 PM   #12
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I'd have to give a look around, sounds like it's not an everyday home depot item?
I found the round to rectangular ductwork at one of those stores HD or Lowes. Please don't bore 4 inch holes in 8 inch joists.You will probably sell that house someday and whomever buys it will inherit that mess and curse you in effigy when they discover it.
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Old 07-24-2012, 07:30 PM   #13
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^
Assuming the upstairs tub doesn't come down on top of you first. ...
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Old 07-25-2012, 02:05 AM   #14
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If its any help to get some extra clearance, you can notch the underside of the floor joists to get the ducting a bit higher up. This is allowable if the notch is not too far in from the ends of the joists, and not too deep.
See this;

http://arch.umd.edu/Tech/Structural_..._Guide_A11.pdf

Most Codes have prescriptive rules for this - check yours. If you decide to notch them, don't go mad with it - you have a bathroom upstairs as well.
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Old 07-25-2012, 09:58 AM   #15
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Is the basement totally below ground level?
Is the bathroom on an outside wall?

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