Joist drilling

[NickB_99]

Hi,

I need to run some 2.5mm T&E in an upstairs bedroom.

The floor joists are 200mm deep, 50mm wide, 4240mm span and spaced approx 470mm.

The floor board I have easy access to is about 200mm from the span end and best placed for where the sockets will be.

I was thinking I only need to drill a smallish hole (e.g. 12mm dia) on the joist centre line, to thread the T&E through.
But reading the LABC guide fragment I found on the net, on where to make holes, seems you need to be much further away from the edge when drilling holes as opposed to making a notch. But the hole I need is much smaller than their 50mm max dia for this depth.

I'd prefer not to have to lift up another 2 or 3 boards - hoping for some advice from the experienced!

 

[conny]

Think you may be getting confused. 50mm is the minimum distance from the top and bottom of the joist to drill the hole. This is to try and avoid someone banging a nail too far into the joist and damaging the cable.

If you are running a single 2.5mm cable I would make the hole 20mm diameter to make it easy to pull through with less chance of damage. As for distance from the end of the span I've not heard of that one.

No doubt if I am wrong someone will correct me.

 

[tony1851]

Your floor joists are actually a little over the recommended maxiumum span, so as above, no more than 20mm max. diameter hole.

 

[NickB_99]

Thanks for the prompt feedback.

Had taken guidance from http://niceic.com/Uploads/File3777.pdf

Good suggestion for 20mm to ease cable pulling. Won't go over this.

Bit concerned to hear the joists are above maximum recommended span.
House was built in the 60s. Any idea if the rules changed?

 

[tony1851]

Bit concerned to hear the joists are above maximum recommended span.
House was built in the 60s. Any idea if the rules changed?

There have never been any fixed rules - it's just been guidance as to the most economic and workable joist-size for particulars spans, spacing and loading.

Your floor certainly won't collapse, but under certain loading conditions (say a kid's party or similar) you might get a bit of bounce and higher- than normal deflection.

Just don't go drilling too much, and if you have tradesmen in to do jobs (plumbers etc), be alert to how these people can sometimes not be aware of where and how to notch or drill.