Reinforcing floor joist for vent pipes

11 years ago

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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Comments (8)

PeterH2
11 years ago
Can you put the boiler air intake near one end or the other? So long as there is a decent web between the holes, that will be a lot stronger than right in the middle, where there is most stress.

Is it impossible to sister in additional 2x10 joists instead of trying to fabricate something so complex?
worthy
11 years ago
Once you exceed the Code permissable notches, most homemade fixes are structurally inadequate, no matter how much you glue and screw the crap out of them.

Not only are you risking structural problems with your home, it's all but certain that the fan won't move air that distance anyway.

See below for illustrated Guide to notching based on current Codes. Credit: City of Grand Island, Nebraska
insomniac243
Original Author
11 years ago
Thanks for the advice, I guess I'll try and think of something else
brickeyee
11 years ago
An acual engineered repair is not all that hard, it just needs to be analyzed and stamped off.

There are repair kits available for at least a few joist sizes.
They are made of formed metal and have a correct 'listing' that satisfies the code.

One is linked below.

Here is a link that might be useful: Metwood

This post was edited by brickeyee on Mon, Dec 10, 12 at 11:17
don92
11 years ago
Can you run a small chase somewhere through the main floor? Go up a few inches and then out.
sombreuil_mongrel
11 years ago
In cases where the joist must be cut beyond the approved notch size, the joist must be headed off; supported by the adjacent joists which must be doubled/sistered. Use joist hangers.
Casey
lazypup
11 years ago
Rather than do all that complicated work on the joists, why not just run the line parallel to the joists and exit out through a side wall instead of the end wall?
brickeyee
11 years ago
"In cases where the joist must be cut beyond the approved notch size..."

Or use an approved joist reinforcer.

They get you up to 6 inches.

This post was edited by brickeyee on Thu, Dec 13, 12 at 16:58