Screeds on balconies. What NCC 2025 changes.

You may have heard that screeds are no longer allowed outside. That is not what the code says. The change is narrower, and it is about where the fall is made and where the membrane sits.

What NCC 2025 changed

For Class 2 to 9 buildings (apartments, hotels, offices and the like), NCC 2025 Volume One adds three rules for concrete roofs, balconies and podiums:

• The fall is in the slab. The structural slab is graded at least 1:80. A screed, topping or tile bed does not count as the structural slab. The one exception is inside a planter box.
• The membrane goes on the slab. On concrete, the membrane is applied directly to the structural slab.
• The finish drains or is fixed down. The finish over the membrane is either self-draining, such as pavers on pedestals, or fixed directly to the membrane.

Put together, a screed laid to falls with the membrane on top of it no longer fits the deemed-to-satisfy path on these buildings. It can still be done, but it needs a Performance Solution agreed with the certifier.

Where it does not apply

Houses (Class 1)

Unchanged. AS 4654.2 still lets the fall be made in a screed on the structure.

Jobs under NCC 2022

Unchanged. Fall location is left to AS 4654.2.

Planter boxes

A screed may form the 1:80 fall inside the planter.

Tiled or metal roofs, timber decks

Outside these clauses.

NCC 2025 starts on different dates in different states. Ask your certifier which edition your job is under before you price the balcony.

A screed over the membrane

A screed or tile bed above the membrane is still part of AS 4654.2 and AS 3958:

• A bonded topping needs enough movement joints, placed over the joints in the structure.
• An unbonded screed sits on a double slip sheet, so it never touches the membrane.
• AS 3958 sets an unbonded site-mixed screed at 40 mm or more, reinforced. AS 4654.2's guide figure is 50 mm with light mesh.

Under NCC 2025, a floating screed over the membrane is neither clearly self-draining nor directly fixed. Treat it as at risk and confirm it with the certifier before work starts. Tiles fixed with adhesive straight to the membrane, and pedestal pavers, sit inside the deemed-to-satisfy options.

What to do on your next balcony

1. Confirm the NCC edition and the building class.
2. On a Class 2 to 9 job under NCC 2025, ask the engineer for the 1:80 fall in the slab.
3. Put the membrane on the slab, then choose the finish: direct-stick tiles, pedestals, or a screed the certifier has accepted.
4. Send FORSPEC the drawings if the slab is already poured flat. We will set out the options.

A revision of AS 4654.2 is also out for public comment this month. FORSPEC will report what it says once the final text is published.