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Ten NCC pushbacks every building designer gets, and the clause that settles each one

Every building designer has the same ten arguments. Not the same jobs, the same arguments. The glazier who says a bathroom window is not a door so it does not need safety glass. The certifier who wants a barrier the whole way round a deck that only drops a metre at one corner. The client who wants a bedroom in an attic that rakes to nothing.

The argument is rarely about who is right. It is about who can put the clause on the table first. These are ten real questions building designers asked DatumDesk, each answered with the verdict, the clause and the page. Some side with the certifier. Some do not. All of them end the argument.

Sarah-Jane Kavanagh, DatumDesk · Updated 13 October 2026

How to read each one. The question as it was asked, the verdict, and the citation in the form Document, Clause, Page. Every item links to the full published answer with all of its sources. Adoption differs by state, so confirm with your state building authority.
  1. 01

    Bathroom glazing is about height, not whether it is a door.

    This one catches experienced people because the instinct is door or not door. The Housing Provisions do not care. In a bathroom the test is the height of the lowest sight line above the floor, the bath or the shower base, and a full-height window beside a bath is as caught as the shower screen. If the glazier's quote says annealed, send it back with the clause attached.

    WAClass 1NCC 2025 (NCC 2022 electable)
    The questionOur Bunbury bathroom has a full-height window beside the bath and a glass shower screen. The glazier says ordinary annealed glass is fine for the window because it is not a door. When does bathroom glazing have to be safety glass?

    The answer. The glazier is wrong. In a bathroom, the safety glazing rule is triggered by height, not by whether the glass is a door: any glazing, including windows, with its lowest sight line less than 2.0 m above the floor, the bottom of the bath or the shower base must be safety glass. A full-height window beside a bath is caught, and so is the shower screen.

    ABCB Housing Provisions Standard (NCC 2025), 8.4.6(1) Kitchen, bathroom, ensuite, spa room and splash-back glazing, p. 204

    Read the full answer with every source
  2. 02

    The 1 m barrier trigger is measured point by point along the deck edge, not for the deck as a whole.

    The deck on a sloping block is the classic over-call, because a barrier the whole way round is simpler to certify than a partial one. The Standard measures the fall at each point along the edge, so the barrier is required where the drop reaches a metre and not where it does not. Draw the ground line at the corners, mark where the metre is crossed, and ask which clause requires the rest.

    QLDClass 1aNCC 2022
    The questionOur deck on a sloping Brisbane block sits 800 mm above ground at the house and about 1.3 m at the far corner. The certifier wants a barrier the whole way round. Where exactly does the 1 m trigger bite?

    The answer. The 1 m fall test is measured at each point along the deck edge, not across the deck as a whole, so a barrier is required along the far sections and not at the 800 mm house end. Ask the certifier to name the clause behind a whole-of-perimeter call.

    ABCB Housing Provisions Standard (NCC 2022), 11.3.3(1) and Figure 11.3.3a, p. 301

    Read the full answer with every source
  3. 03

    Horizontal rails are only banned as climbable where the fall is more than 4 m.

    Horizontal rails get called climbable on reflex. The ban on climbable elements between 150 and 760 mm only applies where the fall is more than 4 m. At 3 m it does not. What still applies is the 125 mm opening rule and the 40 mm edge gap, so check the rail spacing before you argue the other point, and do not offer a solid bottom panel as the fix, because the Standard does not define it as one.

    QLDClass 1NCC 2022
    The questionOur Toowoomba first-floor balcony has a horizontal-rail balustrade, and the certifier says the rails make it climbable. The drop is about 3 m. What does the code say about climbable elements, and does a solid panel at the bottom fix it?

    The answer. Not at 3 m, on the deemed-to-satisfy rules: the ban on climbable horizontal elements between 150 mm and 760 mm above the floor only applies where the fall is more than 4 m, measured to the surface beneath. The 125 mm opening and 40 mm edge gap rules still apply, and a solid bottom panel is not a defined fix in the Standard.

    ABCB Housing Provisions Standard (NCC 2022), 11.3.3(1) Barriers to prevent falls, p. 301

    Read the full answer with every source
  4. 04

    A door onto more than three risers needs a threshold landing, and the Standard gives the size.

    A laundry door that opens straight onto a run of external steps is a detail nobody draws on purpose. More than three risers, or more than 570 mm, and a threshold landing is required: at least 750 mm long, the full width of the doorway, no steeper than 1:50. It is a cheap fix on the drawing and an expensive one in concrete.

    VICClass 1NCC 2025
    The questionOur Bendigo design has the laundry door opening straight onto a four-riser external stair down to the yard. The building surveyor wants a landing at the door. When is a threshold landing required, and how big does it need to be?

    The answer. The building surveyor is right. A doorway that opens onto a stair of more than 3 risers or more than 570 mm needs a threshold landing at least 750 mm long, the full width of the doorway, with a gradient no steeper than 1:50.

    ABCB Housing Provisions Standard (NCC 2025), 11.2.5(1) and (2) Landings; Figures 11.2.5a and 11.2.5b, p. 311

    Read the full answer with every source
  5. 05

    Winders are allowed, and the going is measured in the middle, not at the inside edge.

    Winders are allowed, up to three in place of a quarter landing. The going is not measured at the inside edge, where it will always look too narrow, but at the middle of a stair up to a metre wide, or 400 mm in from each side on a wider one, and it has to be at least 240 mm there. If the certifier is measuring at the string, this is the clause to send.

    SAClass 1NCC 2022
    The questionOur Adelaide Hills staircase turns with three winders, and the certifier says the going is too narrow on the inside. How are goings measured on winders, and is a winder even allowed in a Class 1 house?

    The answer. Winders are allowed: up to 3 in lieu of a quarter landing, so a three-winder turn is fine in principle. The going is not tested at the narrow inside edge but at the middle of the stair (up to 1 m wide) or 400 mm in from each side (over 1 m wide), and it must be at least 240 mm there.

    ABCB Housing Provisions Standard (NCC 2022), 11.2.2(3)(a) and (b), 11.2.2(4)(a)(i) and (ii), p. 291

    Read the full answer with every source
  6. 06

    A window within 900 mm of the boundary does not count for natural light.

    Natural light has a boundary rule most people discover when it fails. A window closer than 900 mm to an adjoining allotment does not count at all, so 700 mm is not nearly there, it is out. Glazing under an open alfresco can count toward the ten per cent. Enclose the alfresco and the stricter borrowed-light test applies instead.

    WAClass 1NCC 2025 (NCC 2022 electable)
    The questionOur Perth two-storey design has the living room window 700 mm off the side boundary, and the only other glazing opens under the covered alfresco. The certifier says the room fails natural light. Does the side window count at all, and does light through the alfresco count?

    The answer. The side window cannot count: a window providing natural light must be at least 900 mm from an adjoining allotment boundary, so 700 mm is 200 mm short. Glazing under the alfresco can count toward the 10% of floor area needed if the alfresco is an open verandah or the like, and if it is enclosed, the stricter borrowed light test applies instead.

    ABCB Housing Provisions Standard (NCC 2025), 10.5.1(1), (2) and (3) Natural light, p. 275

    Read the full answer with every source
  7. 07

    Roof lights need 900 mm from a separating wall or boundary, and together no more than 20 per cent of the roof.

    Skylights near a party wall are a fire separation question before they are a daylight one. A combustible roof light needs 900 mm from the vertical projection of the separating wall and 900 mm from a side boundary, and all of them together can take up no more than 20 per cent of the roof. On a terrace that usually means one fewer skylight than the client asked for.

    SAClass 1NCC 2022
    The questionOur Adelaide terrace design has three skylights in a roof that runs to within a metre of the party wall, and the certifier has raised fire separation. How close to a boundary or separating wall can a roof light sit, and how much of the roof can they take up?

    The answer. The certifier is right to raise it. A combustible roof light must sit at least 900 mm from the vertical projection of a separating wall and 900 mm from a side boundary, and all the roof lights together can take up no more than 20% of the roof or part of the roof.

    ABCB Housing Provisions Standard (NCC 2022), 9.3.3 Roof lights, p. 232

    Read the full answer with every source
  8. 08

    An attic bedroom needs 2.2 m over two thirds of the floor, and anything under 1.5 m does not count.

    The bedroom under a 2.4 m ridge is a rite of passage. An attic habitable room needs 2.2 m over two thirds of its floor area, with anything under 1.5 m left out of the count, and a ceiling that rakes straight down from 2.4 m gets nowhere near that. A flat section or a dormer might. Model it before you promise it.

    TASClass 1NCC 2022
    The questionWe want to turn a Hobart attic into a bedroom. The ceiling is 2.4 m at the ridge but rakes down steeply on both sides. The designer says it can still comply. How is ceiling height measured under a sloping roof?

    The answer. An attic bedroom needs at least 2.2 m of ceiling height over two-thirds of its floor area, with anything under 1.5 m left out of the count. A ceiling that rakes straight down from a 2.4 m ridge gets nowhere near that, so the designer is only right if the ceiling has a flat section or a different profile.

    ABCB Housing Provisions Standard (NCC 2022), 10.3.1(1)(e)(i)(A), (1)(e)(i)(B), (1)(e)(ii) and 10.3.1(2), p. 263

    Read the full answer with every source
  9. 09

    Every storey needs a smoke alarm, bedrooms or not, and more than one means interconnected.

    A lower floor with no bedrooms still needs a smoke alarm, because the rule is one per storey, not one per sleeping area. Once there is more than one they have to be interconnected, mains powered where mains power is supplied, and to AS 3786. The certifier is right on this one every time, so draw it in before they ask.

    NSWClass 1NCC 2022
    The questionOur two-storey Sydney house has bedrooms upstairs and the living areas downstairs. The certifier wants an extra smoke alarm on the lower floor even though there are no bedrooms there. Where do smoke alarms have to go in a new Class 1a house, and do they need to be interconnected?

    The answer. The certifier is right. In a Class 1a house every storey needs a smoke alarm, including a storey with no bedrooms, and once there is more than one alarm they must all be interconnected, mains powered where mains power is supplied, and comply with AS 3786.

    ABCB Housing Provisions Standard (NCC 2022), Schedule 5 New South Wales, NSW 9.5.1 Smoke and heat alarm requirements, p. 477

    Read the full answer with every source
  10. 10

    The step-free entry exemption has two limbs, and you need both.

    The step-free entry exemption on a sloping block is real, and narrower than the way it gets described at the counter. You need both limbs: no step-free route via the garage, carport or parking space, and a site condition such as an average slope steeper than 1:14. It switches off the access path clause and nothing else in the Standard.

    ACTClass 1aNCC 2025 (electable in the ACT to 30 April 2027)
    The questionOur sloping Canberra block makes a step-free entry very hard. The certifier mentioned the livable housing provisions have an out for exactly this. When is step-free entry required and what relief exists?

    The answer. The certifier is right that there is an exemption, but it has two limbs and you need both: no step-free route via a garage, carport or parking space, and a site condition such as an average slope steeper than 1:14. It only switches off the access path clause; everything else in the Livable Housing Design Standard still applies.

    NCC 2025 Volume Two, Building Code of Australia, H8P1, p. 157

    Read the full answer with every source
The pattern

What these have in common.

Seven of the ten side with the certifier or the Standard. Three do not, and those three are worth the most, because a barrier the whole way round, a balustrade replaced at a 3 m fall and a staircase rebuilt to an inside-edge measurement are real money on a residential job.

The habit that saves it is the same either way. Before the next site meeting, have the clause open, not the recollection of it. A certifier agrees with a page number faster than with a designer who is pretty sure.

Where these came from

Every answer above was produced by DatumDesk.

DatumDesk answers Australian National Construction Code (NCC) compliance questions with clause citations, drawing on NCC 2022 and NCC 2025, state and territory variations, and ABCB handbooks. The commentary on this page is ours. The question, the verdict and the citation on each item are the published answer, verbatim, and the full answer with every source is one click away.

Browse all published answersCheck which edition applies in your state
Questions building designers ask

Before you rely on any of this.

Do these answers apply in my state?

Each answer names its jurisdiction and the edition it was answered under. Most Housing Provisions clauses are national, but the edition and the state schedule can change the detail, so check the tags on each item and read the full answer for the state variation. Adoption differs by state, so confirm with your state building authority.

Why do some answers say the certifier asked for too much?

Because the deemed-to-satisfy provision sometimes stops short of what was requested. Those answers set out exactly where it stops and suggest asking which clause supports the request. That is a question, not a fight.

Which NCC edition applies in my state right now?

It depends on the state and, in some, on the lodgement date. Victoria and Western Australia are on NCC 2025, with Western Australia allowing an election for NCC 2022 until 30 April 2027. The ACT allows either edition until the same date. New South Wales, Queensland, South Australia (for building work) and Tasmania move on 1 May 2027. The Northern Territory has disapplied NCC 2025 until the next edition. DatumDesk keeps a per-state status page at datumdesk.ai/ncc-2025 and every answer leads with the edition operative in your jurisdiction. Adoption differs by state, so confirm with your state building authority.

How are DatumDesk answers checked?

Answers are generated only from an indexed corpus of the NCC volumes, the Housing Provisions, state and territory variations, ABCB handbooks and referenced regulation. Every numeric value is cited to a document, clause and page. Practice notes are labelled as interpretive. Licensed Australian Standards are named and deferred to, never reproduced. Where the corpus does not hold the answer, DatumDesk says so instead of guessing.

Does DatumDesk replace a building surveyor or certifier?

No. The certifier makes the call and carries the authority. DatumDesk makes sure you arrive at that conversation with the clause, the edition and the page already in hand, and that your question is on the record.

What does DatumDesk cost?

DatumDesk Pro is AU$19 a month or AU$190 a year, per practitioner, with every feature on both. The first 14 days are free. Cancel any time from your account.

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