Waste pipe through joists

[McArthur 94]

I am fitting a shower tray upstairs. I want to run 42mm shower waste pipe for a run of 1. 6m. The problem I have is that I would have to drill a hole 45mm in a 120mm joist. These joists I don't think are structural as they run from rsj to rsj. I would have to go through 3 joists. Is this acceptable or should I drop pipe into kitchen underneath and run in pipe box.

 

[ShaunCorbs]

How deep are the joists ?

TBH I would box them in

 

[Aire]

Your only allowed to drill 1/4 of the total depth of a joist. So in your case, 30mm is maximum

 

[McArthur 94]

Joist are only 125 mm thick as really for floorboards /plasterboard as the rsj are the structural element. Just wasn't sure if the hole will still be a bit too big

 

[Aire]

Joist are only 125 mm thick as really for floorboards /plasterboard as the rsj are the structural element. Just wasn't sure if the hole will still be a bit too big

Doesn't matter, 30mm is your max

 

[Ric2013]

Hmm. I'm going to look at this a different way that some may disagree with.

The Approved Documents state that drilling a hole more than a quarter of a joist in diameter is unacceptable. Given that the Approved Documents are only guidelines on ways to satisfy the requirements of the building regulations, then the hole size is presumably based on the joist depth being also in accordance with the Approved Documents.

In a very old house like mine, where a 10' span is covered by a 6" (152mm in French measures) joist that bounces like a trampoline, I would hesistate to even drill a quarter height diameter hole, even if the Approved Document says its usually fine: the Approved Document presumably already considers my joists to be undersized.

In the OP's house, we do not know what the OP means by the joists are non-structural, or the length of the span they cover. It may well be that they could safely be drilled as the OP suggests, but we cannot possibly say that they are based on the limited information given.

I would say, though, that if the joists can be reinforced in some way that makes up for any loss in rigidity or strength resultant from the boring, then surely it would not matter that they have large holes bored in them?

My point being made very nicely by Stafford Council:

We appreciate there may be alternative ways of complying with the requirements to those shown. You are therefore under no obligation to adopt any particular solution shown in an Approved Document if you prefer to meet the requirements in some other way. If an alternative method is used, sufficient evidence will be required to show that the alternative approach is at least equivalent to that shown in the Approved Documents.

Which isn't to say I'm saying the OP should go ahead, merely that if the OP really wants to put the pipe under the floor, there may be a way to do it safely. FWIW though, OP, joists generally are there just to support the floorboards and the plaster ceiling, so unless your span between supports is very short, you would seriously need to consider how you can make good the weakening that 45mm holes will cause.

 

[Jones82]

Can you run in the joists then take the pipe outside and into an external drain, possibly around the corner of the building?.

The problem with running through joists is the fall required, 23mm a meter on waste pipes.

Holes should be drilled in the centre of joists which often means no fall and problems in the "long run" Pun intended

 

[Ric2013]

Can you run in the joists then take the pipe outside and into an external drain, possibly around the corner of the building?.

The problem with running through joists is the fall required, 23mm a meter on waste pipes.

Holes should be drilled in the centre of joists which often means no fall and problems in the "long run" Pun intended

23mm a meter? I though anything between 18 and 90 was generally accepted, but not by a textbook right now...

 

[McArthur 94]

Cannot run pipe with joists as house is mid terraced, span is 2 meters from rsj to rsj. I know it’s not ideal as 18mm/m drop on a 1.6m run would be about 30 mm drop plus 45mm hole. Would mean I would be near bottom /top at either end instead of being in middle. May be best with pipe box in kitchen was just hoping that it could all be hidden away

 

[Rob Foster]

Before you close up the floor on this job, and after you have tested watertightness its a good idea to pack plenty if the quilt type insulation under the shower tray. Down stairs the drumming noise of the shower water hitting the shower tray can be very annoying. Rob Foster aka centralheatking

 

[Jones82]

Think I remember 23mm a meter from my above ground waste level 3 exam... it was about 12 years ago mind!

 

[hammers4spanner]

Any Any waste pope through a joist should be banned imho void house insurance . Get so fed up with this low level tray nonsense from customers its getting daft now.

 

[McArthur 94]

Forgive me if I'm being silly but how would raising the tray solve this issue. As the holes would still be too late to drill in joists

 

[Riley]

I think he’s implying the pipe can be run above floor

 

[Chuck]

May be best with pipe box in kitchen was just hoping that it could all be hidden away

If you make a half-decent job of the boxing nobody will notice it's there after a couple of days.

 

[Tea-Break]

Put simply: British Standards are advise in how to do a job properly, to thus comply with Building Regulations. As the name suggests Regulations are
Legally enforceable in a court.
Standard timber joists (as previously stated) should be drill in there centre axis ‘no greater than 0.25 (1/4) of their depth. In this case 30mm. With the correct gradient 18-90mm per m. In this case an alternative route or a different location are needed.
Posting the question, demonstrates your commitment to doing your work professionally.
I hope you are able to come up with a suitable solution for this problem.

 

[Tim Court]

I have a lot of experience in the commercial field and getting services into ceiling voids is a big issue and we often resort to passing services through structural beams with the addition of local stiffening (designed by the structural engineer). For a timber joist the principle would be the same...
Under load the bottom of the joist is in tension and the top in compression so adding a length of steel strap to the underside of the joist might suffice, or worst case two straps below the hole and two straps above, on the sides of the joist.
If you are not sure and must go this route I would recommend you find an independent local structural engineer who can advise for a reasonable cost. Your local building control can point you in the right direction if you ask them very nicely (they are not allowed to recommend but will give you a couple of names who do domestic!)

 

[Ric2013]

Put simply: British Standards are advise in how to do a job properly, to thus comply with Building Regulations. As the name suggests Regulations are
Legally enforceable in a court.
Standard timber joists (as previously stated) should be drill in there centre axis ‘no greater than 0.25 (1/4) of their depth. In this case 30mm. With the correct gradient 18-90mm per m. In this case an alternative route or a different location are needed.
Posting the question, demonstrates your commitment to doing your work professionally.
I hope you are able to come up with a suitable solution for this problem.

The Approved Documents are not British Standards nor are they building regulations. They are purely a way to satisfy the requirements of the building regulations without needing any specialist knowledge. If the Approved Documents were all you could do, then it would be illegal to build a house in straw bale, rammed earth, etc. If you choose to work outside of the approved documents you really need to know what you are doing, possibly get some form of engineer to check what you doing works etc - and I cannot see that drilling a large hole in a 5 inch joist spanning over 6 feet is a good idea now I have heard further details about this proposal.

My point was that if a pair of very thick metal plates, for instance, were made to reinforce the holed joist, this would probably mean that the building regulations would be met even though the Approved Document probably doesn't have specific guidelines for reinforcing joists using metal plates.