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

 

[Vicdiy]

Drop through to room below and box in

It could look very ugly having a boxing in a living room!

 

[Scott_D]

It could look very ugly having a boxing in a living room!

Raised tray or boxing
Sometimes customers need to realise they have to compromise

 

[gmartine]

If you're worried about joist integrity reinforce it....3/4 ply either side to sandwich joist.

 

[SimonG]

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.

Not this one!

 

[chris watkins]

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.

Not this one! either

If you're worried about joist integrity reinforce it....3/4 ply either side to sandwich joist.

say the structural engineer who fully "understands bending moments"

 

[gmartine]

Not this one! either say the structural engineer who fully "understands bending moments"

I think I can recall my first year statics course at Uni...
The bending moments acting on a beam haven't changed just because it has holes drilled in it but it's ability to resist them has been compromised. Cutting holes can initiate cracks that can propagate when beams are loaded, mostly because of low tension strength perpendicular to grain of timber. Crack propagation changes the failure mechanism of beams, and fracture can occur at considerably lower than predicted loads therefore reinforcing the area to avoid it is a fairly common sense solution.

 

[SimonG]

I like that steel, but would like it maybe 12" longer on either side.

 

[gmartine]

It's pretty strong SimonG, those J bends make it effectively act like a box section of steel by increasing the stiffness no end.

 

[chris watkins]

I think I can recall my first year statics course at Uni...
The bending moments acting on a beam haven't changed just because it has holes drilled in it but it's ability to resist them has been compromised. Cutting holes can initiate cracks that can propagate when beams are loaded, mostly because of low tension strength perpendicular to grain of timber. Crack propagation changes the failure mechanism of beams, and fracture can occur at considerably lower than predicted loads therefore reinforcing the area to avoid it is a fairly common sense solution.

Great, so you could make an informed decision if you wanted to drilling holes in joists.
My point was/is, should we be encouraging those who don't have your knowledge to be cutting hole, thinking that screwing lumps of ply to each side will make things all right?

 

[gmartine]

The OP had already been given the advice on hole size and position to which I simply added that they could also reinforce the beam to which you decided to snidely take umbrage with. Report it or wind your neck in.

 

[chris watkins]

The OP had already been given the advice on hole size and position to which I simply added that they could also reinforce the beam to which you decided to snidely take umbrage with. Report it.

Sorry you feel the way gmartine but its not OP I am so worried about it is all the other muppets who come along afterwards read this thread & think that bits of ply on each side repairs a cut joist.
You of all people would know the dangers in that surely.

 

[ShaunCorbs]

isnt that the wrong way eg the tabs under the timber?

 

[gmartine]

Sorry you feel the way gmartine but its not OP I am so worried about it is all the other muppets who come along afterwards read this thread & think that bits of ply on each side repairs a cut joist.
You of all people would know the dangers in that surely.

On the contrary, although I wasn't specific as to how a beam should be sandwiched (I'd also bond it) if you almost double the beam width around the area of a hole and just use screws it is still very effective and I'd rather reinforce a beam than not.
How many times have you seen a beam failure because of an overzealous plumber or DIY'er? I haven't but on the rare occasion I've often wondered how it's managed to stay up there is so little left. The truth is that the size of holes drilled by plumbers lets say an average of around 50mm won't catastrophically compromise the average house beam and it doesn't especially if guidelines are adhered to.



@Shaun...by having the tabs that way around you increase the overall effective cross-section of the beam and therefore stiffness, like an I-beam/RSJ

 

[AWheating]

The answer is avoid running wastes through joists.

 

[Jim Goodenough]

The answer is avoid running wastes through joists.

If at all possible I might add!