Holes in floor joists for waste pipes

[Vicdiy]

If you have to run a basin or shower waste perpendicular to the joists I understand that you need to make the hole in the middle of the joists.My question is how big a hole can you make without affecting the structural integrity of the joist and how can you put a fall on the pipe if you have to go through several joists and the hole has to be in the middle of the joist?

 

[townfanjon]

Not good practice at all but we have all been there.
If memory serves I think you can notch up to 1/8 th of the depth of the joist and hole upto a 1/4 of the depth , however there is a measument on where in the joist the hole or notch can be made , this is in relation to where the joist is supported i.e let into the wall . Sorry I cannot remember it . ( dont assume its anywhere you want ) somebody will be along soon no doubt to confirm.

 

[Scott_D]

The maximum hole size will depend on the joist size

 

[snowhead]

From here; Cutting holes and notches in solid timber joists - advice and guidance from NICEIC

 

[Vicdiy]

View attachment 35025

View attachment 35026


From here; Cutting holes and notches in solid timber joists - advice and guidance from NICEIC

Thank you very detailed reply. How do you get a fall, or do you just lay them flat?

 

[chris watkins]

Thank you very detailed reply. How do you get a fall, or do you just lay them flat?

You don't normally install them running through the joists.
Try using boxing either above or below the ceiling.

 

[snowhead]

How do you get a fall, or do you just lay them flat?

As above , avoid it at all possible.
The only way to see if you can get any fall is to work out the maximum sized hole you can get it the centre of the joist, deduct pipe size and see it the fall works over the length.

e.g if max hole is 65mm and pipe is to be 40mm then you have 25mm fall over the run to play with.
It that fall works then it's either 65mm holes all the way and pack the pipe up at each hole to get the fall.
Or carefully calculate the smaller hole positions and drill accordingly.
Bear in mind you need space to play with to actually get the pipe in.

What will wreck the whole thing is if there are already notches and or holes being used.

 

[SimonG]

Or go with joists and sort it outside. But be careful of run lengths against pipe size.

 

[Vicdiy]

Or go with joists and sort it outside. But be careful of run lengths against pipe size.

There are a lot of the nearly flat shower trays without an upstand being installed now so I think a lot of plumbers must be running pipes through the joists.

 

[Scott_D]

Drop through to room below and box in