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Old 12-08-2012, 11:26 AM   #1
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Reinforcing floor joist for vent pipes

Hello everyone,
I am in need of ideas/ expertise on how it would be possible to reinforce my floor joist to run (2) 4" pipes and (1) 3" pipe to the out side. I am installing an exhaust fan in my bathroom downstairs and there is no good way to run the ducting parallel to to the joist and dropping a bulkhead down to run the pipe under the joist would take away too much headroom. I would have to go through about (15) 2x10 joist spanning roughly 15 feet at 16"oc. After reading some other post about reinforcing joist I was wondering if the following senario would be an addiquate reinforcement: Ripping a 2x4x14' select structural SPF board down to 3", cutting an inch and a half wide dato 3/4" deep to create a T-joist, then adding 3/4" plywood to each side of the 2x10 above the T, glueing and screw the crap out of it, and then adding 1/2" plywood on top of that going to the bottom of the T, glueing and screwing the crap out of that, making a 4" thick beam. I would then drill a 4 1/8" hole or 4 1/2" hole, which ever one will let me get a 4" pipe through without being too tight, about 4-5' from the wall on one side and then drill another hole for a 4" pipe about 3' from the other wall for the dryer vent and a 3" hole in the middle for the fresh air intake for the boiler. Is this over kill? Not enough? I would like to do without adding the 2x4 to the bottom and save on headroom because I am already planning on raising the floor 2" by installing a hydronic infloor heating system and the ceiling is dropping an inch because I am installing 1/2" sound stop board under the 1/2" Sheetrock that I am using for the ceiling, bring the demensions to 87" of head room without the added T-joist.


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Old 12-08-2012, 09:15 PM   #2
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Perhaps you could draw up your plan??? There are specific sizes, quantities, and locations for allowed holes in dimensional lumber. See if a local lumber company has that info for you, or Google it; best bet is to see a structural engineer.


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Old 12-09-2012, 07:31 AM   #3
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If these are just vent pipes why so many?
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Old 12-09-2012, 08:57 AM   #4
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Well, after thinking it over and talking to my brother I think I'll end up just doing the (2) 4" pipes and not the fresh air intake. One is for the bathroom fan, there was not one before, just a window, which caused a lot of mold to start growing and tiles falling off the walls which was the condition when I bought the house. I don't want to go out over the window because that is right by the back door and under a 4' over hang, the other way runs into the front door and I want to get the moisture out and away from the house as fast as possible so I want to make the ducting run as short as possible. The other 4" vent pipe is for the washer and dryer that I want to install in the basement, again wanting to keep the ducting run as short as possible and as straight as possible so it is easy to clean any lint build up in the pipes. The fresh air intake I don't really think it matters how long the ducting run is and it is not carrying any moisture or lint out so I can run that one as long as I want and avoid cutting into any joist.
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Old 12-17-2012, 11:35 AM   #5
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