Drilling joists and other supporting structure.

[andreas]

I need to pass a 15mm pipe through a 175 x 50 joist, then through a 175 x 80 trimmer joist perpendicular to the first joist. There is no other possible route for it to take. 

I have read guidance on drilling through joists but none of them mention if that is all types of joists, or if it is different with trimmer joists?

Also when they discuss the span, does it mean any individual span where a single joist spans several supports? The 175 x 50 starts on one wall, rests on a second wall 2.2m away, then a third wall 0.9m further on, then finally supported by the trimmer joist 0.3m further on. I need the hole ideally to go between the second and third wall, so do I just calculate the position based on a span of 0.9m, or on the total span?

[ProDave]

I would say 15mm is pretty insignificant for a 175mm joist.  The important point is drill the hole on the centreline.

[MikeSharp01]

17 minutes ago, ProDave said:

I would say 15mm is pretty insignificant for a 175mm joist.  The important point is drill the hole on the centreline.

And avoid getting too close to the ends of the beam, as in stay several depths from the end EG 400mm plus if they are wooden joists the supplier will have a drilling chart you can use.

[George]

You should do it based on the individual spans. 

 

But given it's a 900mm span a 15mm hole isn't really going to make any odds to a 175mm deep joist.

[saveasteading]

All the above are correct. The mid height of a timber has very little effect on strength. Hole sizes are covered in the building regs, so it is official.

[bmj1]

I got a shock when our sparky drilled some decent size holes in our structural steel beams holding up the 2nd floor.

 

Checked with our SE, and it was all fine. These holes were 30mm diameter.

[saveasteading]

5 hours ago, bmj1 said:

Checked with our SE, and it was all fine

similar logic to that of mid timber. the top and bottom flanges are doing the work in tension and compression, and should not normally be cut, but the web is mostly just holding the flanges apart and together.

[Temp]

Google where to drill joists. Should find a drawing showing zones where you can drill from the ends and hole sizes...

 

Edited November 12, 2023 by Temp