Grate Designs

Oi Uncle, new BPC note out on balconies — SD 02. Everyone’s shouting. But here’s what got me: they’ve drawn a typical detail. An actual picture, from the regulator. Figure 1(b). Am I allowed to just build that? /Shonky

---

My dear Shonky,

Sit down. Pour something. You’ve just asked the best question of your career, and you’re not going to enjoy the answer.

Start with the word that does the work. The regulator has published a note on balconies. Very tidy, mobile-friendly. Count the musts. The plumber must obtain a copy of the approved design before commencing. Any variation must be assessed by the surveyor and the permit amended before work proceeds. Above-ground stormwater piping from balconies must be classified as roofing stormwater work. It must be installed by an accredited person under a licensed plumber. The overflow invert must sit not less than 20 mm below the adjacent internal floor substrate. The substrate must have a fall of 1:80.

Firm as a plumb bob. Now here’s the sentence carrying the whole load.

Typically responsible for design

“The architect, designer or engineer are typically responsible for the preparation of balcony designs.”

Typically.

Not must. Not shall. Not “is responsible”. Typically — the word you use for weather, not duty. It’s the one place in the document where somebody had to be named as the author, and that’s exactly where the voice goes soft and sits down. See the pattern and you can’t unsee it: must turns up wherever the obligation already exists in the Act, the Regulations or the Code, and the note simply repeats it and takes credit for the firmness. Typically turns up at the single point where the law says nothing, so there’s nothing to repeat.

The note says the architect, designer or engineer typically prepares the design. Under the Regulations, design work is a licensed plumber’s function, and this is roofing (stormwater) work. The one man whose licence includes designing it is the one told to fetch a copy of it.

Go figure the figure

And that’s what makes your question so beautiful, son, they’ve drawn you a picture, talk about leadership by example! If you lodged it, it’d bounce. Since they published it, we frame it.

Behold it. Figure 1(b). Typical Overflow Detail. Straight from the regulator. Not a manufacturer’s brochure, not some consultant’s PDF — the Commission’s own drawing, on the Commission’s own website.

If that’s the detail in the approved design, you build it. Exactly. Tile for tile, fillet for fillet. If a TikTok inspector squints at your balcony, you point at the webpage and say: that’s the detail, and it isn’t mine. Don’t add a skirting tile they didn’t draw. Don’t add a reglet they didn’t draw. Don’t dimension anything they left undimensioned. You didn’t design it, you built it, and any variation would have needed the surveyor’s blessing and a permit amendment anyway — the note says so in the imperative.

That’s your shield, Shonky. Now let me show you the hinges on it.

Look at what’s drawn. The waterproofing turns up and terminates beneath something — a flange, a flashing, nobody’s labelled it. Over the membrane: no cover tiles, no protection, nothing. Who, in the whole history of this trade, leaves a membrane exposed in the weather without skirting tiles and where a bloke with a broom comes past twice a year?

And here’s the one that’ll keep you awake. Have a hard look at what that membrane is sitting on. Go on — try. There’s a tile, there’s a couple of grey bands, and not a label between them. The Code is now very particular about this: the membrane goes directly onto the structural substrate, concrete to AS 3600, and a tile bed or a screed doesn’t count. So which is it in the picture? Nobody can tell you. It’s a typical detail that declines to identify the one layer the Code cares most about.

Then look at what the membrane’s doing. They’ve labelled “Fillet” twice on that drawing. One’s where a fillet belongs, at the foot of the wall, then folded the membrane through a dead 90° at the junction. The other’s at the top of the upstand, exactly where the waterproofing standard’s own detail puts a sealant bead under a mechanically fixed flashing. So either they’ve called the sealant a fillet, or they’ve terminated the membrane with a fillet and no sealant.

Even the picture can’t follow its own advice. The membrane runs up the wall, wrapping right round the inside of the hole and out the far side, lining the whole aperture like wallpaper. Every other trade on earth stops the membrane at a flange and lets the flange do the talking — a made thing, clamped, testable, replaceable. Not here. Here the watertightness of a plumbing component hangs on how well a bloke with a brush dressed a membrane into a hole at the wettest, tightest, most awkward spot on the balcony.

The best part? The same note lists “incorrect use of leak control flanges” as one of the reasons balconies fail. Names the villain on page one, then leaves him out of the picture entirely.

The caption is my favourite part. “Pipe or slot Overflow designed as per AS 3500.3 clause 3.8, 1% AEP.” Go and read clause 3.8. It gives you the storm event for the design, and not one word on the overflow itself: how high, how wide, how high the freeboard sits so the spill meets the hydraulic capacity for the 1% AEP. For that you’re told to use the roof provisions, and when you turn to them there’s a note waiting: vertical piped overflow outlets and covered overflow devices are not covered by this document.

The certificate isn’t yours

And where drainage doesn’t comply with the deemed-to-satisfy clause, the Code says you need a performance solution — which, per the very same note, must be attached to the plumber’s compliance certificate. Now, you’ll be feeling clever about one thing: the compliance certificate isn’t yours. The plumber signs that, and it’s backed by his insurance, and if the pipe’s wrong you’ve got someone to chase. Enjoy the feeling. It lasts about as long as the first phone call.

Because the owner doesn’t sue the plumber, son. The owner sues you. Every domestic contract carries a warranty that the work complies with all laws and legal requirements, including the Building Act and its regulations. You can’t write that out of a contract, it follows the building to the next owner, and — here’s the sting — a claim pleaded that way isn’t apportionable. No carving it four ways with the architect, the surveyor and the plumber. You wear the whole thing, and then you go hunting for contribution from a bloke with fifty grand of cover and a company he can dissolve before Christmas.

And when they come for you, the questions are already written. The SD 02 note itself lists what decides the water-carrying capacity of a pipe: diameter, length, internal roughness, hydraulic head, gradient, and the number and type of bends and fittings. No method with them, no worked example, no acceptance criteria. That’s not a standard, son. It’s a cross-examination script — six numbered items, each a separate question you either answered or didn’t:

Factor	Who actually controls it	Where it’s decided
Pipe diameter	Hydraulic designer / plumber	Design, if anyone designs it
Pipe length	Architect’s riser strategy	Permit drawings
Internal roughness	Plumber’s material choice	Procurement
Hydraulic head	Architect and RBS — set by overflow and floor levels	Permit drawings
Pipe gradient	Plumber, constrained by slab depth	On site
Number and type of bends	Builder’s structure and services coordination	On site, after the pour

And what will they say failed? The fall in the slab. The seventy-mill step. The hob. The joint that should have been on the high point. The substrate the membrane was supposed to sit on. Read that list again. Not one of them is plumbing. Every single one is yours, poured on a Thursday, by your concreter, off a drawing nobody dimensioned.

Six factors, four parties, one certificate — and none of it saves you. The plumber signs the paper. You just build the puddle.

And where did the maths behind all this come from? I went looking. The note says a handbook contains an informative note allowing you to use roof drainage principles on balconies, and it’s true — I found it. It’s a NOTE at the end of the scope clause of an installation code for metal roof and wall cladding. It says roof principles “may also be utilised” for drains from balconies, patios “and the like”.

That’s the foundation, son. One “may”, in the scope of a roof sheeting manual.

The man holding the calculator

And here’s the question nobody’s asked. Who, exactly, is supposed to do the sum?

The note names three: the architect, the designer, or the engineer. So take it seriously and follow both roads, because there are only two, and they land in the same hole.

Road one — a design professional does it. Which one? The architect draws a square with a cross in it. The designer picks the tile. And the engineer? Victoria prescribes five kinds — fire safety, civil, structural, electrical, mechanical. Go on, son. Find the hydraulic one. It isn’t there and never has been.

Mind you, the note knows hydraulic design exists. It wants it “coordinated” with the architectural layout, the structural interfaces and the waterproofing. It just never says who does it.

Road two — the plumber does it. And here the note is perfectly clear. No building permit? “The plumber is responsible for the balcony stormwater design and the installation of the drainage system”. Not typically. Responsible. Elsewhere it puts it beyond doubt: without a permit, the design must be undertaken and, where required, certified by appropriately registered or licensed plumbers within their own authorisations and limitations. He works it out, he installs it, he signs it, and the State takes his word for the lot — that’s what self-certification has meant in this jurisdiction for years.

Now put a building permit on the same balcony and watch what happens to that man. Same trade. Same licence. Same six variables, same physics, same rain. And he goes from author to recipient: he must obtain a copy of the approved design before commencing work.

Ask yourself what changed, Shonky. Not his competence — nobody re-tested him. Not the balcony. Not the arithmetic. Somebody lodged a form. That’s the entire difference. On Tuesday the licensed drainage plumber is fit to design a balcony drain from first principles; on Wednesday, because a surveyor has a folder open, he’s fit only to fetch someone else’s calculations — and that someone else belongs to a discipline the State never got round to giving a category.

So you’d think somebody has to put their hand up. And here’s the thing, son — there’s a form for it. Regulation 126. Certificate of compliance for proposed building work (BPC link). Go and look at the tick-boxes: structural, sewerage, water, drainage, mechanical including hydraulic services. And a line underneath that says I prepared the design, or part of the design. Part of. They thought of it. Somebody sat down and understood that one drawing set has several authors, and built a box to write their names in.

Now find the licensed plumber’s name on it. You can’t. Design certificates come from a prescribed engineer in the relevant class. The one man who can do the arithmetic can’t sign the form that records he did it.

And the surveyor can’t save you either. His Code of Conduct forbids him from participating in design, from suggesting a solution, from arranging design services on the applicant’s behalf. He can’t ring the plumber and ask. All he can do is request a certificate from somebody entitled to give one — and if he relies on it, he has to write down why he thought that person was competent. Competent at hydraulics. In a state that doesn’t register hydraulic engineers.

There’s your ‘novation’, Shonky. A form with a box for the author, a designer who can’t sign it, a surveyor forbidden to ask, and nothing anywhere that makes anyone fill it in. The design doesn’t get novated. It gets orphaned.

The Hole That Wept Backwards

Now let me tell you how this actually kills a building, son.

Somebody sits down and calculates. Fifty mill. And here’s the part you won’t like — the arithmetic might even work. The people who model this for a living say so themselves: in small catchments a fifty-mill pipe can shift the water. They still won’t use it. It isn’t in their computer models at all, and their minimum stays at ninety, because a pipe that size blocks.

That’s the whole argument, son, and it was settled before the note existed. In March 2025 the president of the Association of Hydraulic Services Consultants wrote to his members about exactly this — fifty-mill cast-in balcony outlets offered up as Performance Solutions in place of the ninety the Standard nominates. Not a blog post. A review conducted through the Victorian Building Authority’s own Plumbing Technical Advisory Panel.

His findings, in his words: the fifty-mill drains block with silt on a regular basis, the balcony ponds, and water is drawn under the membrane at the submerged clamp of the outlet. Every solution reviewed would be highly unlikely to demonstrate compliance if challenged. Any that leaned on “self-cleansing velocity” was technically compromised and unsupported by any recognised research. And the association went further than criticism — it declared it would not support, defend or provide technical assistance to any member involved in facilitating fifty-millimetre cast-in balcony drainage.

Because none of that is a matter of taste. The Victorian variation doesn’t treat blockage as housekeeping. VIC E3P4 makes it a Performance Requirement: access for maintenance and clearing blockages, and no loss of amenity from blockages and uncontrolled discharge. A pipe cast flat between two layers of steel, unreachable for the life of the building, doesn’t argue with that clause. It simply fails it. And the deemed-to-satisfy road runs out behind it — VIC E3D2 calls up the Standard and the handbook together, and where they conflict, the Standard prevails. The Standard nominates ninety.

So a year before SD 02, through the regulator’s own technical panel, the industry had already said what happens when you put fifty in a slab. Then the note arrived. It acknowledged there was no prescribed sizing method, reached sideways to an informative note in a roof-cladding handbook, and left the door open behind it. The argument was never whether the answer is twenty-five or fifty, son. It’s that once the calculator prints anything below ninety, somebody can call it an approved design without ever having the conversation about blockage that the Performance Solution process exists to force.

Cast it. And here’s what nobody drew: a pipe laid dead flat between two layers of steel doesn’t stay dead flat. It sags between the chairs, it lifts where the vibrator found it, and by the time the concrete’s off the truck you’ve got a low spot. Now you own a fifty-mill trough that never quite empties, sitting under the one component the whole balcony depends on.

And then the puddle flange betrays you. Not because it’s wrong — because it’s right. Those weep holes are there to let water out of the screed and into the waste. That’s their job, that’s why the good detail has them. Fill the waste instead, and the water comes back up the same holes, into the bed, and stays on the membrane. Eventually, a continuously wet membrane leaks whether or not you put a hole in it.

Anybody could have prepared the design. Everybody was going to be coordinated at permit stage. Somebody would have certified it if the surveyor had asked. Nobody had to do the sum.

Somebody’s problem, nobody’s business

And now the part that should have been the whole point.

There’s a woman in that apartment. She didn’t read the note. She’s never heard of clause 3.8, she couldn’t tell a puddle flange from a park bench, and she paid nine hundred thousand dollars for a two-bedroom with a balcony because the photo had a chair on it. She is, by the regulator’s own description, the entire reason the office exists. Protecting consumers and raising standards. First thing the new Commissioner published was a policy statement, and it said two things: consumers first, all tools used.

So let’s use the tools, son. Let’s see what the single front door does for her.

A rectification order — ten years after occupancy now, and that’s genuinely new, genuinely better. It goes to the builder. It does not go to whoever typed fifty. The first-resort warranty? Up to three storeys. She’s on level nine. The developer bond, two per cent, held back so there’s money to fix defects after occupancy — doesn’t apply if the permit issued before July 2027. Her building was permitted last winter.

So the door opens, and it’s the same room. Her, an owners corporation, a special levy, and a builder being ordered to rectify a defect that was decided by an arithmetic nobody was required to perform, off a drawing nobody was required to dimension, certified on a form nobody was required to request.

Laser-focused on the consumer. They mean it, too — that’s the maddening part. Three new tools, real money, real teeth, all of it pointed at the far end of the pipe. And not one line anywhere that makes somebody, before the pour, write down their name next to a number.

They built a front door, Shonky. They just never checked whether the drain fell to the outlet.

The note may be wrong; to ignore it is Wrongs

Here’s something for the back pocket, and know exactly what each is worth.

Go and read RP 01 — Roof Plumbing, Regulatory Framework, version 2.0, published 4 May 2023, still on the same website today. Under what is not roofing stormwater plumbing work, in black and white: “the surface drainage of a balcony.” The regulator’s own current note says your balcony isn’t roof plumbing. Its newest note says it is. Neither mentions the other.

And SD 02 arrives with almost no badges at all. No plumbing header. No audience boxes. No sector, no topic, no document number. It does carry a version and a date — version 1.0, published 10 August 2026 — but you’ll find them in a grey box below “Other resources,” at the bottom of the page, after you’ve read the whole thing . Its own predecessor SD 01 said “Building Practice Note” across the front, and RP 01 puts PLUMBING PRACTICE NOTE at the top of page one, then ticks nine boxes telling you who it’s for — plumbers among them. And no “superseded” line either — because it’s version 1.0 of something new, not an update to the version 2.0 plumbing note it happens to contradict. So how was a man to know this was official stuff, let alone that it was aimed at him? “SD. Storm drainage, I assumed your honour.”

Enjoy that, then put it down gently. It’s worth something at sentencing and nothing on liability. If the Regulations make it roofing stormwater work, it was roofing stormwater work before anybody built a webpage, and not having read the webpage never made a single job compliant. Play it at your own peril.

Don’t go thinking the missing badges save you. The Wrongs Act 1958 never asks whether a document had a version number, an author, or a header saying what it was. It asks what you knew, or ought to have known, and whether a sensible operator would have done something about it. A webpage published by the regulator answers that question just fine — no letterhead required. They can spell grate as gate, print the same warning twice and forget to sign it, and it will still walk into a hearing room and tell everyone what a competent bloke in your position was supposed to be aware of in 2026. Unsigned guidance can’t be appealed, can’t be prosecuted, and can’t be argued with. It can only be quoted back at you.

So feed that URL to the Wayback Machine tonight. Not out of civic duty — because that detail will be quietly redrawn the moment someone with a scale rule looks hard at it, and the page will carry on as though it always looked that way. And when they ask in 2031 why you built it wrong, you’ll be the only man in the room who can prove what they were showing you at the time.

And I’ll give them this, because your uncle is fair when it suits him. The NCC 2025 Water Management provisions did real work this edition — falls in the pour, hobs, step downs, joints on the high point, membranes on concrete, self-draining finishes. That’s genuine. The one thing it left soft was how to size the pipe, and the office that could have settled it with a binding determination — the real instrument, the one with legal effect — wrote typically on an unsigned webpage and drew you a picture instead.

Build the picture, son. Just don’t stand under it.

Your loving uncle,

Dodgy Bilda

---

Disclaimer: This article is a work of fiction and satire, it is not legal advice — seek your own professional counsel before acting on anything you read here. The author used AI tools for assistance but takes full responsibility for the content. See Preface for full disclaimer.