Reinforcing floor joist for vent pipes
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.