Our Darwin builder says door seals and draught stripping are only for cold climates, but the energy assessor has them on the spec. Do the building sealing rules apply to a climate zone 1 house in the NT?

The builder is wrong about what switches the rule on. In the Northern Territory, building sealing is triggered by air-conditioning, not by climate. The NT has its own Part 13.4, and it requires a seal on each edge of an external door, openable window and other such opening when serving a conditioned space. [3] There is no climate-zone limb in the NT version at all. [2] [3] So if the Darwin house is air-conditioned and the elemental provisions are being used, the assessor's spec is right.

Where the "cold climates" idea comes from. The national Part 13.4 has two triggers: serving a conditioned space, or serving a habitable room in climate zones 4, 5, 6, 7 and 8. [6] The second limb is the cold-climate one. In the NT that whole Part is replaced by NT Part 13.4, which keeps only the conditioned-space trigger. [2] [6] Climate zone 1 does not get you out.

Two compliance routes, and only one of them uses this Part. Under the deemed-to-satisfy provisions, the thermal performance requirement is met by either: [1]

• a house energy rating of 5 stars or more, using house energy rating software; or
• the elemental provisions: NT Part 13.2 (building fabric), NT Part 13.3 (external glazing and shading), NT Part 13.4 (building sealing) and NT Part 13.5 (air movement).

On the elemental route, NT Part 13.4 is mandatory. On the 5-star route, it is not a separate checklist, but the seals on the spec may be part of how the assessor got the rating. Ask which route they used before anyone deletes them.

When the NT sealing rules do not apply. NT Part 13.4 does not apply to: [2]

• a building where the only means of air-conditioning is an evaporative cooler (in the NT this applies in any climate zone);
• a permanent ventilation opening needed for the safe operation of a gas appliance;
• a Class 10a building used for the accommodation of vehicles.

What the seals have to be. [3]

• Every edge of the external door or openable window, not just the bottom.
• The seal may be a foam or rubber compressible strip, fibrous seal or the like.
• Not required: external louvre doors, louvre windows or other such openings, and windows that meet the maximum air infiltration rates in AS 2047.

The detail southern specs get wrong. The national clause demands a draft protection device at the bottom edge of a door and also catches the internal door between the house and an unconditioned garage. [6] The NT clause names neither: it asks for a seal on each edge of external doors and windows, and a compressible strip or fibrous seal will do. [3] A spec copied from a Melbourne job can over-ask in Darwin.

The rest of NT Part 13.4. Where serving a conditioned space: exhaust fans need a sealing device such as a self-closing damper or filter, and roof lights must be sealed or capable of being sealed. [4] Ceilings, walls, floors and frames forming the external fabric of a conditioned space must be built to minimise air leakage, with close-fitting linings or sealed junctions. [5] An evaporative cooler serving a heated space needs a self-closing damper. [5]

Practical next step. Ask the assessor two things: which compliance route (5-star rating or elemental), and which rooms are air-conditioned. On the elemental route, every external door and openable window to those rooms gets a seal on each edge, unless it is a louvre or an AS 2047 rated window. Specify the seal as a compressible strip or fibrous seal, not a southern draft-stopper detail.

NT edition note. NCC 2022 with NT variations is the operative edition. NCC 2025 has no effect in the NT: it was disapplied from 1 May 2026 until the next NCC edition is published, and no NT adoption date has been announced. [7]