Holes in floor joists for waste pipes

[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!

 

[gmartine]

I just don't agree that it is something you should completely avoid doing otherwise why issue guidelines in the first place if it can't be done safely? The calculations have been made and they're issued because it can just like many other aspects of our trade.

 

[gmartine]

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

In hindsight not much in it strength/stiffness wise but it might be more representative as to how it might be used when access is limited or say it was a floor joist when you wouldn't want to uneven the top surface of the joist.

 

[Rob Foster]

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.

Slightly off topic but when you put these flat floor level shower trays in after you have tested it pack as much cheap insulation underneath in between the joists, everywhere. The drumming sound of water from the shower can be awesome downstairs as we found out a few years ago, it drowned out there telly...we were lucky cause the customers were a partltbdeaf couple who let it go ! Rob Foster aka centralheatking