I want to drill some holes in some 50 x 170mm joists, that I am
installing in a first floor, for wiring to go through. The joists are
3.6m long and the holes will be not far off the middle of the span.

Can anyone tell me what is the biggest hole I am allowed/advised to
drill, and how far down the joist it should be?

Thanks
Richard

On Nov 10, 2:29 pm, geraldthehamster wrote:
I want to drill some holes in some 50 x 170mm joists, that I am
installing in a first floor, for wiring to go through. The joists are
3.6m long and the holes will be not far off the middle of the span.

Can anyone tell me what is the biggest hole I am allowed/advised to
drill, and how far down the joist it should be?

Thanks
Richard

I believe that the cables must be a minimum of 50mm both from the
finished floor level and the finished ceiling level. So that should
give you the area within which the hole can be made.

Regarding the max hole dia. that depends on loading factors and you
would need to consult a contruction engineer for an acurate figure.
That said if you're talking typically house wiring then I would drill
the size needed to allow the cable to pass without chaffing and
certainly no single hole larger than 25mm.

ac1951 wrote:
On Nov 10, 2:29 pm, geraldthehamster wrote:
I want to drill some holes in some 50 x 170mm joists, that I am
installing in a first floor, for wiring to go through. The joists are
3.6m long and the holes will be not far off the middle of the span.

Can anyone tell me what is the biggest hole I am allowed/advised to
drill, and how far down the joist it should be?


I believe that the cables must be a minimum of 50mm both from the
finished floor level and the finished ceiling level. So that should
give you the area within which the hole can be made.

But the holes should still ideally be made on the centre line of the
joist, which minimises weakening of its strength.

David

On Nov 10, 2:50 pm, Lobster wrote:
ac1951 wrote:
On Nov 10, 2:29 pm, geraldthehamster wrote:
I want to drill some holes in some 50 x 170mm joists, that I am
installing in a first floor, for wiring to go through. The joists are
3.6m long and the holes will be not far off the middle of the span.

Can anyone tell me what is the biggest hole I am allowed/advised to
drill, and how far down the joist it should be?

I believe that the cables must be a minimum of 50mm both from the
finished floor level and the finished ceiling level. So that should
give you the area within which the hole can be made.

But the holes should still ideally be made on the centre line of the
joist, which minimises weakening of its strength.

David

and also in line with the centre of a floor board to minimise the risk
of someone driving a 3" nail through to the cables.

Typically a 22mm hole is sufficient for house rewires.


"ac1951" wrote in message
ps.com...
On Nov 10, 2:50 pm, Lobster wrote:
ac1951 wrote:
On Nov 10, 2:29 pm, geraldthehamster wrote:
I want to drill some holes in some 50 x 170mm joists, that I am
installing in a first floor, for wiring to go through. The joists are
3.6m long and the holes will be not far off the middle of the span.

Can anyone tell me what is the biggest hole I am allowed/advised to
drill, and how far down the joist it should be?

I believe that the cables must be a minimum of 50mm both from the
finished floor level and the finished ceiling level. So that should
give you the area within which the hole can be made.

But the holes should still ideally be made on the centre line of the
joist, which minimises weakening of its strength.

David

and also in line with the centre of a floor board to minimise the risk
of someone driving a 3" nail through to the cables.

"geraldthehamster" wrote in

Can anyone tell me what is the biggest hole I am allowed/advised to
drill,

Rather than go big, drill 2 or 3 smaller
--
Vass

Approved Document A (old 1992 edition)

"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 diameters (centre to centre) apart; and should be located between
0.25 and 0.4 times the span from the support"

i.e. not at mid span!

geraldthehamster wrote:
I want to drill some holes in some 50 x 170mm joists, that I am
installing in a first floor, for wiring to go through. The joists are
3.6m long and the holes will be not far off the middle of the span.

Can anyone tell me what is the biggest hole I am allowed/advised to
drill, and how far down the joist it should be?

The literal answer (at centre of span) is zero.

The rules a

- between 7% and 25% of the span, measured from either end, you can
notch the top edge, up to one-eighth of the depth of the joist;

- between 25% and 40% of the span you can drill on the centre line with
a max. hole diameter of one-quarter of the depth;

- multiple holes should be spaced 3 diameters apart.

These apply without any need for structural design input.

NB: notches are for plumbing & heating pipework, they're too shallow to
use for running electric cables.

--
Andy

On 10 Nov, 16:08, " wrote:
Approved Document A (old 1992 edition)

"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 diameters (centre to centre) apart; and should be located between
0.25 and 0.4 times the span from the support"

i.e. not at mid span!

Thanks all

Regards
Richard

in my new old house
there are big notches
with wires and pipes going through them,
more than in your building regualtions,
what shall i do?

cover them up and forget them?
strengthen them somehow?

[g]

On 10 Nov, 17:13, "
wrote:
in my new old house
there are big notches
with wires and pipes going through them,
more than in your building regualtions,
what shall i do?

cover them up and forget them?
strengthen them somehow?

[g]

Dear diceg
If there is room, I suggest you use pinned, sliding wedges in the gap
above the services to strenthen up the compression zone and enable
the couple (with the tension zone) to be more effective.
In practical terms - measure the distance you can "fill" the notch
without affecting the services - get some boarding that thickness -
make a two angled timbers out of a rectangle by cutting at an
appropriate angle say of 5 or 10 degrees - put in some glue and
hammer the two together in the gap until it is tight and pin it
(carefully) . you will need longer bits than the gap to do this
practically
Chris G

On 10 Nov, 17:13, "
wrote:
in my new old house
there are big notches
with wires and pipes going through them,
more than in your building regualtions,
what shall i do?

cover them up and forget them?
strengthen them somehow?

[g]

It's an interesting question. I want to do mine "properly" because the
BCO will be up there some time soon on another matter, and I don't
want to risk problems if he twigs the floor's new. However, being done
to regulations and being safe aren't necessarily the same thing. I
wonder how far you can really mutilate joists before a floor actually
becomes dangerous?

"Andy Wade" wrote in message
...
geraldthehamster wrote:
I want to drill some holes in some 50 x 170mm joists, that I am
installing in a first floor, for wiring to go through. The joists are
3.6m long and the holes will be not far off the middle of the span.

Can anyone tell me what is the biggest hole I am allowed/advised to
drill, and how far down the joist it should be?

The literal answer (at centre of span) is zero.

The rules a

- between 7% and 25% of the span, measured from either end, you can notch
the top edge, up to one-eighth of the depth of the joist;

- between 25% and 40% of the span you can drill on the centre line with a
max. hole diameter of one-quarter of the depth;

- multiple holes should be spaced 3 diameters apart.

These apply without any need for structural design input.

NB: notches are for plumbing & heating pipework, they're too shallow to
use for running electric cables.

--
Andy

Tip: I am eternally grateful to my builder for marking the floor where there
are pipes or cables below. It helped me to understand how things were routed
(as well as making sure I avoid nailing)

John wrote:

Tip: I am eternally grateful to my builder for marking the floor where there
are pipes or cables below. It helped me to understand how things were routed
(as well as making sure I avoid nailing)

I always mark positions of services on the floor myself when I've had
the boards up for some reason or another - but have to say I'd never
rely on such markings done by somebody else.

Apart from anything else, I've noticed that plumbers in particular seem
to have a bizarre propensity for putting floorboards back in the "wrong"
place (and then wonder why they are left at the end with a hole in the
floor which can't be filled with any combination of the bits of board
remaining...)

I'm also slowly building up a digital photo-library of the house in
different states of repair, both for interest's sake plus to help with
future project planning / problem diagnosis etc).

David