8" x 2" Floor joist - safe to cut a 4" diamet

[JackSpratt]

I am installing a shower fan duct in a basement that will run through the ceiling above and ideally I need to go across two consecutive floor joists of 8" x 2" with a 4" hole - my instinct says this is unwise ! Should I do this or find an alternative route ? Thanks

 

[big-all]

fairly sure its 25% max along the centre line and within prescribe boundaries

 

[JackSpratt]

Is that a don't do it ? (being that 25% of 8" = 2")

 

[big-all]

Is that a don't do it ? (being that 25% of 8" = 2")

its a definite don't do it as you need 4mm clearance as well taking it to 51%

the only thing i would add is if the span was very small [say 0.9 m] it may still have enough strength all depends on maximum load above

also you may be able to sister joists on small spans to bring it close to the regs if not fully within

another thought could you not use flat section venting thats about 2" and install a false ceiling you would only loose about 3" head height

 

[JackSpratt]

Many thanks big-all.