Drilling 42mm holes through joist for shower tray drain

5 Aug 2009
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United Kingdom
Hi, I am just about to replace the shower tray in my en-suite and will be relacing the old tray with legs for a stone cast one that sit flush to the floor boarding (chipboard). The existing drain runs above the floor and down through the floor next to the wall from where it runs parallel to the joists into the soil stack. I will now need to take the drain (and the sink drain as this also ran under the shower tray) under the floor and this will mean drilling 2 off 42mm hole through the joists (near to the wall end of the joist)

Is this a bad idea from the point of view of weakening the joist (~180mm wide)??

Plan B would be to drop both drains straight down the utilities room wall below, T together, and plumb through the outside wall into the outside grid, alongside the utility sink/washing machine drain. Is this a better option??
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