Pipe under joists

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Hi I am having to shift my kitchen. The waste pipe which I believe has to be 35mm is going to have to go under a joist (or through). If go under the joist, I lose the slope required to take away waste. If I go through it do I breach building regs ? The joist runs parallel to an interior wall (old tenement flat) about 10cm away. I'm in Edinburgh dont know if regs vary with location. Thanx in advance. Dave.
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an
A 32 mm hole through the joist is OK if you can keep it nearer the top of the joist than in the middle. Just try to keep the hole size to the minimum needed to pass the pipe through.
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On Thu, 09 Oct 2003 21:27:26 GMT, "BigWallop"

Apologies for raising a concern, but surely it isn't acceptable to chop a 32mm hole in a joist? Wouldn't that seriously weaken the joist to the point of possible failure?
Please note that I am not basing my query on knowledge or fact, it just seems unlikely to take out that much material without there being an adverse effect.
PoP
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On Thu, 9 Oct 2003 21:54:49 UTC, PoP

I'm not sure either, but I do know that the hole should be round; no corners, as they are a bad thing.
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I think square corners were the cause of the first jetliners mysteriously and randomly responding to gravity back in the 50's. Eventually they figured that cracked were raking out from the window corners, destroying the aircraft frame.
PoP
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On Fri, 10 Oct 2003 01:44:45 UTC, PoP

There have been nasty examples on ships, too. (seen in that wonderful book on structures mentioned a while back...)
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Bob Eager wrote:

yes. Liberty ships or summat.
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wrote:

With Liberty ships the key problem was the previously unknown problem of brittle fracture: normal steel becomes brittle about freezing point and then if overstressed will fracture rather than yield.
http://www.disastercity.com/titanic/index.shtml
The Comet problem was to do with metal fatigue, with the square corners windows causing concentration of stresses.
To get back on topic, good practice for notching joists is to drill and cut, though of course it depends how much one is taking out the joist.
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PoP wrote:

Fatigue and stress concentration. Relevant to a metal stressed skin aircraft - less so to a wooden beam.
Most issues with square holes are to do with introducing stress concentrations, but I don;t think its seriously significant in te current case. A couple of holes and a pad saw will make a decent slot for two pipes, but arguably two separate holes are better.

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wrote:

Hi
I think it was Comets that suffered from this particularly, messing up what was otherwise seen as a pretty sucessful aircraft.
Although it discusses ships and hatch shapes rather than airplanes the book 'The New Science of Strong Materials: Or Why You Don't Fall Through the Floor' by J.E. Gordon covers this behaviour, called Griffith cracking, IIRC. The 'magic' of these things is that once you reach a critical crack size catastrophic failure is inevitable.
One story in there is about a ship that had a crack developing. One of the galley crew (because this is where the crack was, IIRC) took to marking the progression of the crack by dating the tip of the crack periodically.
Eventually the ship split and sank. Luckily (for science) the recovered the half of the ship with the marks on it. These marks become the first record of a Griffith crack 'in the field' and showed that the ship had carried on sailing for years whilst the crack was below the critical size, but once it reached the theoretical failure point the next heavy seas took her down.
I may have elements of that wrong, but I think the gist is right. The book quite a good read for other material stuff you've probably always wondered about too.
IanC
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PoP wrote:

Yes, it weakens it. Its not necessarily serious tho, because joists are rather crude atructural devices. They are engineered not to not break, but not to bend too much. As such they are well over strength for loading.
Putting a hole through them at one spotonly slightly reduces their stiffness. It DOES reduce strenght, particularly in teh center of a long span. but on a short span or at the edges, its not serious.

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BigWallop wrote:

Actually middle is better, but don't worry.

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be
to
of
minimum
Now that's what I thought, but a joiner told me to try and keep a hole of that size nearer the top of the joist. I didn't ask him to elaborate to much on it at the time, I just did what he said because I tought he knew better. I might just go and ask him why now.
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Middle sounds better - if the joist flexes, there is wood at the top and bottom to take the stresses, remove one or other of these, and its a bit like the way you chop down a tree, isnt it?
--
Richard Faulkner

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to
parallel
dont
top
Yep, also what I thought, but then, when the joiner told me to put the holes nearer the top of the joist, my thought was that maybe the floor board being screwed back down across the space would have something to do with giving the joist some reinforcement. But I have to admit that I to thought the holes were better in the middle of the joists.
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On Fri, 10 Oct 2003 01:09:44 GMT, "BigWallop"

I have to admit to being quietly amazed by this discussion!
A joist might be what - 100mm in height? And you drill out 32mm, thus removing about 30% of the strength of the joist. That joist might have an inconvenient knot around about that area to further weaken the structure. And even if the joist was 200mm in height that would still represent a 15% loss of strength overall - which in my book sounds pretty significant.
Doesn't add up for me, however I am happy to bow to the combined expertise of others on this matter!
PoP
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Hi guys
Building regs state:
Holes should be no greater diameter than 0.25 times the depth of the joist; should be drilled at the neutral axis; should be not less than 3 dimeters (centre to centre) apart; and should be located between 0.25 and 0.4 times the span from the support.
HTH Gordon
BTW The neutral axis means the centre of the joist. Notches may only be 0.125 times the depth of the joist.
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Gordon wrote:

A simple rule for carpenters.
In practice, you can break it, but an understanding of structural theory is necessary :-)
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wrote:

I think I'll go with gut feel :)
PoP
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PoP wrote:

Gut feel is OK if like many many craftsmen, you have been using the materials for years and have experienced failures in them.
Otherwise, stick to someone esses rules, or do the (very complex) calculations, or take the engineering route, and put the structures in a machine and stress them till they break.
:-)

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