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Posted By Topic: drilling through studs

Mar 14 2019 18:39

on a job today and the builder tells me the building inspector doesn't 'like' holes to be drilled through triple and more studs, ie if there's three studs grouped together, or more then he says it's a no-no.
i love how he uses the word like, i like some things too like moa beer and toast in bed....
what i need to know is what i am allowed to and not allowed to do in terms of drilling through this to bring a cable through.

Mar 14 2019 19:00

In that case you need NZS 3604.
(Only several hundred dollars; from SNZ or maybe from some builders' supplies outlets)

My copy is somewhat out of date, so I can't be certain; but I doubt the inspector can find any rule that supports his "like"

Mar 14 2019 20:27

There are several clauses in the timber framed building standard (which I don't have handy at the moment) about the maximum size, number, and the position of holes and notches in studs and nogs.
Until recently the building inspectors did not worry too much, but now they are rejecting some work and insisting on backing timber in some cases.
This also affects plumbers who often need bigger holes than sparkys do.

Mar 15 2019 08:46

Amazing what a few court judgements against various Councils for failing to adequately inspect leaky homes has done for the eagerness of building inspectors. Pity some are still pig-ignorant even in their own field. Just like some of our trade's Inspectors, I suppose.

All the limits on drilling that I am aware of relate to size and / or placement of holes in relation to the size & function of the timber framing in question.
For studs there's a max size (25 mm for 100 mm studs; 19 mm for 75 mm studs), and can be either in the centre or notched into the edge. But in 1990 edition there's no restriction on how many can be drilled at those sizes.(separately or together). I very much doubt that's changed in latest edition.

However there are a couple of Exceptions, allowing the holes / notches to be bigger.
19 mm notches can be enlarged to 22mm for purpose of fitting diagonal braces (does anyone still use timber diagonals?); while 25 mm holes / notches can go up to 35 mm provided no more than 3 consecutive studs are drilled / notched.

Trimming studs(eg beside a window opening) must not have holes, notches, checks, or cuts in the middle third of their length

A trimming stud made up from 2 bits of timber nailed together is certainly only one trimming stud, not two.
And as long as the trimming stud has the right thickness; the one beside it, that supports the lintel, is not a "stud" but a "jack stud"; and "the provisions of this clause do not apply to this jackstud".

Where an opening's lintel comes below 350 mm from top plate, there will be a double stud at full height, plus a jack stud. So these 3 bits of timber count as one stud for holes / notches go.

In my view, "3 consecutive studs" is NOT where they are doubled up, as with trimming studs beside actual studs. It's 3 separate studs; either at full stud spacing, or closer around openings and corners.

If you keep your hole size down to 25 mm, and keep them in the middle, it would be very difficult to breach the framing rules.


Mar 15 2019 09:46

thanks Aleck, it's a long time since a 100mm stud was used on a new build, wonder what they specify for 90mm.........,

Mar 15 2019 12:19

later (1999)edition refers to "90 x 45" & "70 x 45" instead of 100 x 50 & 75 x 50 (I only have the top plate page from that).
Though 100 mm is still the nominal size when you buy timber.

Latest appears to be 2011; costing $279 for PDF

Mar 15 2019 12:37

A way round this is to install a metal plate to strengthen the top plate or stud you’ve cut out. These can be purchased through Heatcraft or Realcold or any murchant.

I use them when I cut a large hole for penetrations pair coil to feed through for heat pumps.

Plumbers cut and hack out huge holes for waste and sewer pipes all the time.

Mar 15 2019 15:00

I'm aware of several such products, and a method using checked-in timber; but only applicable to top plates
I don't know of anything similar that's allowed for studs.

Mar 16 2019 12:13

There is at least one supplier who makes a device for fitting to studs to allow holes greater than 25 mm diameter to be used.

Mar 18 2019 00:39

Typically the only time you have to drill through triple studs is to mount a light switch near a door. If you follow 3000 the switch has to be 150 from the edge anyway so you shouldn't need to drill into the stud. What generally happens is someone does take this into account and jams a pantry so close to the door frame and the customer still wants the light switch there. Holes in bracing components get the chippies wild too if you start roughing out before the get it signed off and the inspector has a moan


Mar 18 2019 08:26

"If you follow 3000 the switch has to be 150 from the edge"

Where did you get that idea?

Mar 18 2019 09:16

Possibly referring to not being allowed to cut holes less than 100mm from the edge of bracing sheets.

Mar 18 2019 15:21

One of my guys cost me $500 in hardware a couple of week back. He simply did a double 25mm slot along 15 floor joists that where about 140mm wide. Building inspector pulled it up. And my guy knew it was not allowed but habit got the better of him. Anyway see image for building code 3604 referring to floor joists. Sorry don't know about studs.

Mar 18 2019 18:37

The 150 mm rule is for braceline gib .

Mar 18 2019 20:52

Just to explain Sam1234's drawing - You are allowed holes only in the centre of joists - up to 1/5th of the depth in size, or 32mm. Whichever is the lesser. But they must be separated by a distance equal to the depth of the joist. (Depth is the joist height).

For Peters comment. It's not 150mm. Small openings up to 90x90mm must be no closer than 90mm from the edge of the sheet. Larger openings, like switchboards, must be in the centre 1/3rd of the (total) bracing element size, and be no larger than 1/3rd of the height of the bracing element in either direction (height or width).


Mar 19 2019 08:27

Bracing can get very complicated, mostly because there are so many ways of achieving the required number of bracing elements per wall. But also generally easy to solve, as if something reduces the effectiveness of one bracing element can usually just add another bracing element to that wall.

Point being that each trade has it's special knowledge, so we can't just waltz in and do our thing without regard for other trades. We need to be aware of what else is going on around us. While there can be complications getting all the respective rules / restrictions for each trade dealt with; a little bit of discussion / co-operation before ripping into it can manage most of them.