Drilling through joist, regulations. Waste pipe.

[Skiny]

What's the regulation regarding drilling through joists?

I want to put a shower in a small alcove upstairs, in between the front wall of the house and the stairs. Because of the stairs, the waste pipe can't just run between the joists. The drainage on the shower is right in the centre of the tray, so I would only need to cross one joist (which has in fact been tripled up, as I put a staircase to the loft and wanted extra strength).

What are the regulations regarding this?

Joist size is 7x2 with a span of about 4m or less. As I say, the joist has 2 new ones next to it (both ends supported, not just bolted together), so we have 3 in total next to one another. I'll post a drawing below, to show the layout.

Thanks

 

[^woody^]

There are no regulations, you can do what you like.

Obviously, you just need to ensure that the joist is not weakened by the cut, else if it is, a suitable strengthener is fitted

 

[Skiny]

Oh? I'm very surprised at that.

Any notch/hole in the wood is going to cause some weakness, so surely there must be some sort of standard/requirement? I expected something like a maximum percentage of the wood that can be removed, or something?

 

[REEMS]

Diameter of the hole is to be no more than a quarter of the depth of the timber.
Andy.

 

[clifford1]

A hole near the top of a beam is less weakening than one near the bottom.

 

[bernardgreen]

Drill the hole halfway down from the top of the joist, ( or halfway up from the bottom ).

The bottom of the joist is being stretched and the top compacted as the joist tries to bend under the load it is carrying. The middle is just keeping top and bottom apart.

Don't make holes this big in wooden beams / joists but in steel these beams with large holes are almost as strong as the same beam without holes.

 

[garyo]

I'm sure I've seen guidance in something like Part A - if you search you may find it. For instance this LABC guidance from Hertfordshire - only notch near the edges of beams (within 25% of the span), but drilling holes can be done at any point along the span : https://www.dacorum.gov.uk/docs/def...-of-joists-may2011.pdf?Status=Master&sfvrsn=0

 

[^woody^]

Oh? I'm very surprised at that.

Any notch/hole in the wood is going to cause some weakness, so surely there must be some sort of standard/requirement? I expected something like a maximum percentage of the wood that can be removed, or something?

Nah

 

[noseall]

He's called Woody because he eats wood. Just look at the bite he took out of that joist beneath the shower tray.

 

[bernardgreen]

Also as you are drilling through a triplex of joists do not make the pipe a tight fit in the hole. Allow a few millimetres of space around the pipe to allow for any movement of one piece of timber relative to the others. If it is a tight fit and there is movement then the pipe might be damaged.

 

[JohnD]

Nah

Most of the forces are taken by the top and bottom surfaces. The rest is just to hold them together.

 

[Skiny]

Thanks very much for the replies, guys. I'll be sure to make it just over 40mm to allow for movement/expansion, halfway down.