Waste pipe through joists

[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.