Waste through joists

[koibloke]

Fitting a shower tray directly onto 9'' x 3'' joists. Am I OK taking the 1½'' waste through the joists to couple to existing waste pipe. Sound advice much appreciated.

 

[uug197h]

If you are cutting a hole in the joist then its best if you screw a block of wood under the hole about 8" long and put nogins in (wood from 1 joist to the other) i also put a metel strap on the top of the joist better safe than sorry

 

[Matty A]

I would advise checkin how many other holes are in the same joist that are near to where you are going to put your waste as not to weaken too much in one place.

If there are too many holes in then you can cut a lengh of 18mm pine ply 9" wide then glue and screw to the joist then drill your hole through the ply as well also brace between joists wi noggins ( as uug197h) said..

 

[nick penfold]

building regs state that holes in joists should be no more than one quarter the depth of the joist.

 

[TerryH]

Koibloke,
The figures I have are different to Nick's.
To notch into the joist you should be between 7% and 25% of the lenght of the joist away from the wall. The notch should be no more than 1/8th of the depth of the joist.

Obviously a difference of opinion there!
Terry.

 

[ajs heating]

yes as you say 7 - 25 of the length. depending on span of joist.
max depth of notch will give you 28.75mm
max size bored hole will give you 57.50mm

 

[nick penfold]

yes yes guys you are right. notches no more than one eighth etc but we were TALKING about HOLES. If your drilling a hole through the joist, it must be no more in diamater than one quarter the depth of the joist.

Sorry if i confused people with the previous post )

 

[pt44]

Hi

I've posted elsewhere about this - but this thread is very similar to my problem.

I have joists which are 165mm deep. I need to run a 40mm bath & basin waste through them. It needs to go over a 2mt distance.

Therefore - to get a drop of say 20mm over 1mt distance. I calculate that I need to start the 1st hole approx 40mm from the top of the joist (centre of hole would be at 60mm. But that leaves only 40mm (2 inches) at the top point - is this a little too thin? The same would apply at the end joist, where it would be 40mm lower, therefore the centre would be at 100mm meaning the bottom of the hole would be at 120mm - which is again 40mm from the edge of the joist.

Is this within limits? Or should I make the drop shallower - if so, how shallow can I go? Currently, the previous plumber put zero drop in. He just notched the joist at the top with no drop.

Paul

 

[sonray ltd]

how do you plan on getting the waste pipe through the holes.

 

[pt44]

how do you plan on getting the waste pipe through the holes.

Did you have to ask that? Damn. Good question. Hadn't got to that one. I have no idea. I suppose I could make lots of short sections and join them all with straight connectors. A pain, but a solution. How would one do this normally? I can't believe I've been lucky enough to have avoided ever having to do this before now.

 

[sonray ltd]

1, i've never put a waste through a joist.
2, or notched a joist like the last person.
3, if it can't run along the joist or under a joist it go's above floor level
where it probably was originally.

 

[pt44]

1, i've never put a waste through a joist.
2, or notched a joist like the last person.
3, if it can't run along the joist or under a joist it go's above floor level
where it probably was originally.

makes sense. I do know that the current owners moved the doorway. Which in turn means that they must have moved the bath - as its now where the door once was. So originally - who knows where the waste was. I suppose I could possibly suggest turning the bath around. This would mean that I could run the waste above floor level - going into the floor - along the same wall as the stack. Would make life easier for me - I must agree and would save drilling through joists.

 

[sonray ltd]

i thought someting had been altered in the past, waste or as you say the bath.

 

[Lee_H20]

cant u run the waste pipework unda tha joists an clip it to the joists???

 

[pt44]

cant u run the waste pipework unda tha joists an clip it to the joists???

Not unless I wished to rip out the ceiling below and have a waste pipe going under their downstairs ceiling

Might look a tad ugly, to say the least.

Luckily, I've since solved this dilemma. I ran the bath waste around the wall above floor level, which I need to box in. It dips under the floor at the last minute to join the stack at its original point. The basin waste, I ran along the existing route, notched into the joists, but I notched them out just a bit more, couple of mm's, so that it had some drop over the 1mt distance it had to travel.

Paul

 

[andekoch]

notches are in the top (or bottom of a joist) while holes are in the centre of a joist (ie the centre of the hole must be on the centre line of the joist.
So a notch can only be from 0.7 to 0.25 of the span length and 0.125 times the depth of the joist.
A hole can be in the area 0.25 to 0.4 of the span and 0.25 times the depth, also cant have holes closer than 3 times diameter from the next so watch for other pipes and cables.

With a hole being on the centre line of a joist it means that a pipe will not have a fall (unless this can be achieved by different size holes or using a 40 mm pipe and drilling 50mm holes and then packing the bottom to get the required slope.

Easier to find a solution that does not cross joists.

 

[Mike Jackson]

The job's probably complete by now the last post before yours was 5 months ago.

 

[pt44]

The job's probably complete by now the last post before yours was 5 months ago.

Nah, I'm still drilling the holes

Just kidding. All finished months ago. Had no choice in the end but to go through the joists. Luckily they were thick deep joists and it was a basin waste so only 32mm. Just made a gentle slope over about 5-6 joists. The holes were already there, about 40mm in size. So just made sure it was wedged, to keep the slope. Not much of a drop, but considering the previous installer had an upward slope (yep, not even a drop) it was an improvement.

Paul

 

[andekoch]

hmmm, perhaps I should check the dates on the posts more closely. Was relying on the recent posts feature.

 

[jono44]

Not sure I'd like to spend the rest of my life sleeping/living in the room below that bathroom!
I've seen some crazy stuff done to joists - some people don't realise they form an important part of the structure of the building.

 

[pt44]

Not sure I'd like to spend the rest of my life sleeping/living in the room below that bathroom!
I've seen some crazy stuff done to joists - some people don't realise they form an important part of the structure of the building.

I think you may be worrying a little too much there. Perhaps you have seen scary holes in joists, but the situation as I listed it - is far from scary and completely within reasonable limits. In fact, I could probably have made the holes bigger. (not to mention that there is no bedroom under the bathroom).

http://tileyourworld.com/construction/JoistBoringGuide.pdf

Good guide here, found from a quick google. 1/3 size of depth of joist is max hole size. And hole must not be closer than 2" from the edge. Sounds perfectly reasonable and sensible to me. I had a similar conversation with an architect and builder when I was having my house done. Absolutely no problem going through the centre of joists with holes. So long you follow that guide.

Paul

 

[ocentric]

I wouldn't follow that guide unless you're in the USA! The post in this thread from Andekoch a few days ago has the definitive guide for England & Wales...

 

[pt44]

I wouldn't follow that guide unless you're in the USA! The post in this thread from Andekoch a few days ago has the definitive guide for England & Wales...

I'm not going to argue guides - as I'm certainly no pro on the matter. However, I would point out the obvious. If I'm in the UK - how on earth does the recommendation differ from the US?

Are you saying our timber is different?

Otherwise, if the timber joist is the same - then the recommendations are the same. Regardless of what part of the planet you reside on. As for rules and regulations? I have no idea. But guides are guides, surely.

 

[helpsy]

Checkout Building Regulation Part A(Structure)

 

[dontknowitall]

I onc had a job putting 12 meters of 110 soil pipe through the house and through the joists. Boy that was fun! Subsequent fitting of two 40mm/50mm shower wastes were a doddle in comparison.

Perfectly possible to do - but I did employ a structural engineer and carpenter had some steel braces made for it as a result.

If you're in doubt, I'd get a suitably qualified structural engineer - once you make a start (according to his recommendations) while it's not easy, it's not that difficult to do.

 

[mogwai]

Hi
Been plumbing now for some 37 years. would just like to say that i never had to cut or drill joists for waste pipe. Waste always goes surface, only below boards if it is running parallell with the joists