Tile waterproofing in NZ: AS 3740, E3/AS2 and what to keep on file

Is AS 3740 required in New Zealand?

No. AS 3740 (Waterproofing of domestic wet areas) is an Australian standard. BRANZ describes the 2010 edition as not mandatory and not referenced in Acceptable Solution E3/AS1, though good practice to follow. A lot of NZ product literature, supplier training and older web pages still refer to it, which is why the search term is so common. The pathway that gives you a deemed-to-comply route is E3/AS2, an Acceptable Solution effective from 5 November 2020. It says that work installed to sections 1 to 4 of the Waterproof Membrane Association of NZ (WMAI) Code of Practice for Internal Wet Area Membrane Systems, as modified by paragraph 2.0 of E3/AS2, complies with Building Code clauses E3.3.2 to E3.3.6. AS/NZS 4858 (wet-area membranes) is the product standard that the Code of Practice calls up for the membrane itself. Use AS 3740 as a reference for detailing if your supplier does, but write “E3/AS2 and the WMAI Code of Practice” on your records.

What E3 actually asks of a wet area

Clause E3 Internal Moisture is performance-based. Floors of spaces containing sanitary fixtures must be impervious, surfaces must be easy to clean, and splash from showers and baths must not damage the linings or framing. A floor waste is only required where accidental overflow could damage an adjoining household unit or other property. Tiles and grout are not the waterproofing, because water passes through grout. The membrane behind and under the tiles is the barrier, and the tile is a wearing surface. That is why the membrane has to be right before the first tile is stuck down.

Membrane heights and extents in the WMAI Code of Practice

The extents come from section 4.0.6 of the Code of Practice (4th edition, August 2020, the copy published on building.govt.nz). In a shower, the membrane on the walls extends to the higher of 300 mm above the shower rose or 1800 mm above the shower floor or tray, and horizontally to the line of any fixed screen or door, 300 mm beyond the line of any curtain, 1500 mm beyond a fixed rose in an open shower, or 600 mm beyond the length of a hand-held rose in an open shower. The whole floor of an enclosed wet room is covered and contained by a water-stop at edges where an upstand cannot be formed. Walls behind and around fixtures with water supplies, such as vanities, get membrane that extends at least 150 mm beyond the cabinet or fixture, and elsewhere there is a minimum 75 mm upstand at floor-to-wall junctions. The older “rose height plus 50 mm” rule of thumb comes from the Australian standard and can leave you well short above a high rose. Check which edition of the Code of Practice the current E3/AS2 cites on the MBIE Building Code Hub, because it is updated periodically, and write the edition on your record.

Toolie’s wet-area register for tilers has a shower rose height field and a membrane height field. It calculates the higher of 1800 mm or 300 mm above the rose, and warns when the height you recorded is below that.

Flood tests, applicators and who is responsible

Every membrane system should be visually inspected and flood tested after it has fully cured and before it is covered by tiles. The Code of Practice sets out the method: bung the outlet, put a temporary water-stop at any threshold that lacks one, fill with water from an external source (not the shower rose) up to the lowest threshold, check for loss after 12 hours, check adjacent rooms and any room below for staining, and sign off a minimum 12-hour full-area test. It also recommends photographic evidence. If water loss shows up, the membrane is repaired or re-applied as the supplier requires and tested again. The code expects the applicator and installer to be certified by the membrane supplier and says the applicator should provide a PS3. On many jobs the tiler is not the applicator, so agree in writing who applies the membrane, who flood tests it, and who signs off. If you tile over someone else’s membrane without a flood test record, you have taken on a risk that you cannot see.

Do tilers need a licence or a consent?

Tiling is not an LBP licence class. The classes are Design, Carpentry, Roofing, Bricklaying and Blocklaying, External Plastering, Foundations and Site. Interior wet-area work is generally not restricted building work, and MBIE lists new sanitary fixtures among work that does not affect structure or weathertightness. Consent depends on the work. Replacing tiles like for like, in the same place, is covered by the Schedule 1 exemption for repair and replacement with comparable materials. That exemption does not cover repair or replacement (other than maintenance) of something that has failed the Building Code’s durability provisions, which includes a shower that leaks, and it does not cover sanitary plumbing. A new shower with new or relocated plumbing or drainage, or a structural change, needs a consent, and then the waterproofing becomes an inspected item for the Code Compliance Certificate. When in doubt, ask the council before you start.

Tile installation standards: movement joints and flat substrates

AS/NZS 3958.1 is the installation guide for ceramic tiles, and it deals with movement joints and with substrate flatness. Large-format and rectified tiles are unforgiving: tight joints show every lippage problem, and a floor with no movement joints will eventually crack. Read the Standard and the tile manufacturer’s instructions for the spacing and tolerance values rather than relying on a rule of thumb from the web, because we have deliberately not reproduced them here. Whatever values you work to, measure the substrate before you tile, correct it if it is out, and write the numbers down.

Toolie’s tiler pack flags when a job is a wet area, and adds a movement joint record and a substrate flatness assessment for large-format, rectified and commercial work. Where the Standard sets a value, Toolie cites the clause and leaves the number for you to enter.

The wet-area record: what to write down

A record that fits on one page is more useful than a binder. For each wet area, note the client, address and room, the consent number if there is one, the membrane brand and product with the AS/NZS 4858 reference from the data sheet, who applied it and their supplier certification, whether bond breakers were used at junctions, shower rose and membrane heights, that falls to the waste were checked, each flood test (date, area, water depth, duration, result, who witnessed it), and whether photos were taken before tiling. Add your own workmanship warranty and the date you finished.

That is the layout of Toolie’s wet-area register. Each flood test is a row with date, depth, hours and result, and the record warns you about missing photos, unchecked falls and unchecked movement joints. The photos box is a tick that records that you took them; the images stay on your phone or in your own filing. You can print the record to hand over with the job.

Sources

Official sources this guide relies on. Rules change, so check the current version before relying on a date or threshold.

• E3/AS2 Internal moisture, first edition — MBIE Building Code Hub
• Code of Practice for Internal Wet Area Membrane Systems (4th ed., Aug 2020) — building.govt.nz
• BRANZ Bulletin BU591: Waterproofing tiled showers
• Restricted building work — building.govt.nz (MBIE)
• Building Act 2004 (Schedule 1) — legislation.govt.nz

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