Floor Joists notched onto wall, where to drill a hole?

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Hi Folks,

I would like to make a hole through my joist for a small pipe.

I've reviews the building regulations on the location of notches and holes, but I'm confused about how tall my joists are, so don't know where the middle of the joist is.

The sit on metal plates on top of the breeze block of the cavity wall but the bottom 7cm(out of 18cm) of the joist has been notched to fit the breeze block. All the joists are like this.

has this reduced the effective height of the joist to the top 12cm?
Is it normal to do this to joists? Is it a problem?

So where do I drill my hole, in the middle of the joist at 9cm or in the middle of top section at 6cm from the top?

I've attached a diagram and a photo of the notched ends.

The hole I need to drill, is under the bath, so I don't what to weaken the joist further if this end notching is a problem.

Thanks.
 

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You're not supposed to drill holes near the end. You should notch, only between 1/4 and 2/5 of the span, and only 1/8th of the depth of the joust.
If you really want to drill through the neutral axis, you must do that in the middle 1/5 of the span.

Having said that, a significant proportion of plumbers and other tradesmen see joists as a mere obstruction rather than a structural element, and you hear more people on here worrying about excessive notching than people dropping though the floor.
 
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Thanks for your reply John, I've seen the advice on where to notch and drill in relation to the span between supports.

The top notch in the photo was already there on that joist, but some of the other joists don't have any path through for my pipe!

So where is the neutral strain point of the joist for drilling a new hole? It seemed simple, until I noticed the end of the joist was notched at the bottom when the house was constructed. Could this end notch on the bottom have weakened the joist and changed where the neutral strain point depth is in the joist?

i.e. is the joist still effectively 18cm deep, or is the neutral strain point now in the top section of the joist?
 
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Good grief, there's only about 2 inches of that joist left, and right on a knot too.

So, given that your house hasn't fallen down yet, and you have an apparently unused notch in your joist, why not just reuse it?
 
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You have a point Cjard, the house hasn't fallen down yet and it has probably been like that with a top notch and notched end for 60 years! I do plan to use that notch, I don't know what it was for originally.

But, further along the house, under the bath and next to an internal brick wall(stood on the joist) those other joists have no notch or hole, so I have to decide where to notch or hole, and where. Under the bath it just feels more critical with 150kg of water plus 80kg of me, plus maybe the misses, when the occasion arises.

There doesn't seem to be any sign of splitting or weakness in the joists. I think the wood is extremely hard and strong. Similar wood in the loft was exposed to the weather for years and is still as good as new. so maybe I'm overthinking it. Wouldn't be the first time!
 
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Trades people have different priorities to home owners. A bit of time spent doing things properly can make your house more comfortable and cheaper to run in many cases. Don't worry about over thinking, it means you'll do a better job!
 
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Thanks John, speaking of which, I'm planning on pluging the hurricane coming through the joist ends, with a sheet of plasterboard and foam, I can't see any downside and I noticed some similar advice on the house builders federation website.

I think that draft is just unwanted ventilation?
 
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You could do but it's possible it's actually keeping things dry there. If you want to get rid of 90% of the draft that will work well, although if you really want 100% you'll need some thing flexible that sticks to the joists and wall.
 
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I did notice that there seemed to be companies online performing this kind of draft proofing, so I thought it would be OK, but then after a bit more thought I was worried about damp, but there doesn't seem to be any, hard to assess the effect of blocking off the draft, and I hopefully wouldn't be under the floor for another 20 years to check, perhaps it is best to lag the heating pipe and leave the draft?
 
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It's your choice! Personally I've got a damp meter so I'd get it on the joists and if they're dry I'd go for it! Draughts are the enemy of damp, but the friend of large heating bills!
 

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