E2/AS1 §10 membrane deck upstand — the 150mm rule that voids the warranty on NZ residential (2026)

sp8002
May 30
7 min read

E2/AS1 §10 sets the deemed-to-comply detail for membrane decks; §9.1.6.5 sets the 150mm minimum upstand at door thresholds. Below 150mm and the membrane manufacturer voids warranty. The retro-fix on a finished deck-with-door runs $18-55k.

By Steve Parker · Trueworks · NZ construction estimation · 7 min

§10 of E2/AS1 covers exterior membrane decks and their junctions. §9.1.6.5 sets the 150mm minimum upstand at door thresholds opening onto the deck. The 150mm rule is the single most-disputed deck detail on NZ residential. Below it, the deemed-to-comply path closes and the membrane manufacturer voids warranty.

By Steve Parker · Trueworks · NZ construction estimation · 7 min

What you'll learn in this post

What E2/AS1 §10 and §9.1.6.5 actually require for membrane decks
How the 150mm upstand fails on NZ residential
The 5-item check before signing the membrane deck quote

Quick answer: E2/AS1 §10 sets out deemed-to-comply requirements for exterior decks with waterproof membrane systems. §9.1.6.5 sets the 150mm minimum upstand of the membrane above the finished deck level at thresholds, walls, and penetrations. The 150mm rule is the architectural detail most often "value-engineered" off NZ residential and the single most common cause of voided membrane warranties. The retro-fix on a finished deck-with-door — lifting the door threshold and re-membraning — runs $18-55k depending on door scale and finish. Manufacturers' CodeMark appraisals echo and sometimes exceed the 150mm requirement.

§10 of E2/AS1 is the wet end of the standard — exterior decks, balconies, and other elements where horizontal waterproofing is the line between dry interior and bad-weather day. §9.1.6.5 is the upstream clause governing wall and threshold upstands. The two together set the geometric envelope every NZ residential membrane deck must hold.

This post reads them together and identifies why the 150mm upstand keeps being compressed on NZ residential builds, and what the retro-fix actually costs.

What §10 and §9.1.6.5 actually say

§10 — membrane decks generally

§10 of E2/AS1 covers exterior decks with a waterproof membrane system. The deemed-to-comply pathway requires:

A continuous, fully-bonded membrane over the substrate
Falls to drains of not less than 1:60 (1.66% — per §10.1.3)
Membrane carried up walls, parapets, and thresholds to defined upstand heights
Drains and outlets detailed per §10.5
Threshold details per §9.1.6 and §9.1.6.5

§9.1.6.5 — threshold upstands

§9.1.6.5 sets the upstand requirement at door thresholds opening onto exterior decks:

150mm minimum upstand of the membrane above the finished deck level
35mm minimum upstand of the door threshold above the finished deck level
Stop-end / sill flashing at the door head and jambs
Membrane lap onto the threshold flashing with anti-capillary detail

The 150mm number is the dimension that's most often compressed in residential design — clients want flush-threshold doors, level-access decks, "no step" walk-out balconies. Every one of those is a compromise of §9.1.6.5.

The level-threshold alternative

E2/AS1 anticipates this and provides an alternative for level thresholds in some scenarios — but only with specific drainage provisions, a covered deck, and an alternative-solution route demonstrating equivalent performance. Most NZ residential level-threshold details are not detailed correctly under this alternative.

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How the 150mm rule fails on NZ residential

1. The level-threshold "feature" priced as a standard detail. The architect specifies a level-threshold door from interior floor to deck for aesthetic reasons. The builder prices the deck on standard rates, not on alternative-solution rates. At consent, the BCA queries the detail. The architect either redesigns to a 150mm upstand (which kills the aesthetic) or commissions an alternative-solution package including drainage gully, overflow, covered overhang, and supporting evidence. The supporting package adds $8-20k and 2-4 weeks programme.

2. The membrane installed correctly at 150mm, then the deck tiles raised on the slab. The membrane installer leaves a clean 150mm upstand. The tiler then installs deck tiles on a 30mm bedding screed, reducing the effective upstand at the threshold to 120mm. The membrane is fine; the assembly is not. The CCC inspection picks it up; remediation requires removing the tiles, lowering the bedding, re-tiling. Cost: $8-15k.

3. The "we'll just add a drain" mistake at finished-floor level. The builder thinks they can address a sub-150mm threshold by adding a linear drain on the deck. The drain doesn't substitute for the upstand under §9.1.6.5 — it only adds capacity. The deemed-to-comply path still requires the 150mm upstand. The alternative-solution route requires drainage capacity calculations, redundancy, and BCA acceptance. The half-measure of "add a drain" leaves the assembly in a non-compliant zone.

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The reference table

| §10 / §9.1.6.5 requirement | Dimension / value | Why it matters | Common compromise | |---|---|---|---| | Threshold upstand (membrane) | 150mm minimum | Stops water ingress under driving rain | Compressed to 70-100mm for level-access aesthetic | | Threshold upstand (door sill) | 35mm minimum above finished deck | Stops splash and snow over the sill | Removed entirely on "flush threshold" specifications | | Deck fall to outlet | 1:60 minimum (1.66%) | Drains standing water away | Flat or near-flat decks on visual-line specifications | | Number of outlets / overflows | Per §10.5 — outlets plus overflow scupper | Redundancy if primary outlet blocks | Single outlet, no overflow, blockage risk | | Membrane lap onto threshold flashing | Continuous, sealed | Stops water entering threshold cavity | Membrane terminated short of flashing | | Wall upstand (vertical surfaces) | 100mm minimum per §10 | Stops splash up walls and parapets | Lost when wall finish installed over membrane |

Worked example

A two-storey alteration with an upper-level membrane deck off the master bedroom. Architect's drawings show level threshold to the bi-fold door. Deck area approximately 28m². No drainage gully, no overflow scupper on the architectural set.

The consent-stage save: the architect is challenged on the level threshold by the QS during quote review. The architect either (a) raises the deck level to provide the 150mm upstand at the threshold, which means raising the door head and lintel by 150mm, or (b) commits to an alternative-solution detail with drainage gully at the threshold, overflow scupper at the deck edge, and a covered deck under the upper-level eaves. The alternative-solution route adds $7-12k to the deck cost but preserves the level-threshold aesthetic.

The CCC-inspection-finds-it version: the deck is built with a 90mm upstand at the threshold, no drainage gully, no overflow. CCC inspection rejects the assembly. Remediation requires lifting the bi-fold door, raising the threshold by 60mm to achieve 150mm upstand, re-flashing, re-membraning at the threshold, replacing the threshold flashing, replacing the bi-fold sill brush seal, re-fitting the door. Cost: $22k. Programme: 11 working days.

The membrane-warranty-voided version: the deck passes CCC because of a missed item, but the membrane manufacturer's appraisal requires the 150mm upstand. Three years later, water tracks under the threshold and damages the bedroom floor below. The owner claims under the membrane warranty. The manufacturer voids on inspection because the upstand was 90mm. Remediation cost falls on the contractor (if within Building Act §362I 10-year liability) or the owner.

What to check before signing the membrane deck quote

Five items, every time:

The architectural detail at deck thresholds shows 150mm upstand explicitly — measured from finished deck level to top of membrane
If level-threshold is specified, the alternative-solution package is named — drainage gully, overflow, covered overhang, supporting evidence
The deck fall is 1:60 or steeper and shown on the level-survey set-out — not just labelled "to drain"
At least two outlets or one outlet plus an overflow scupper are specified — per §10.5 redundancy
The membrane manufacturer's appraisal upstand requirements are checked against the architectural detail — some manufacturers require 175mm or more

If those five items are clean, the deck is on the deemed-to-comply path and the membrane warranty holds. If they're not, the next decision-maker on the file is either the BCA at inspection or the membrane manufacturer at warranty claim.

FAQ — E2/AS1 §10 and §9.1.6.5 on NZ residential

Q1: Can the 150mm upstand be reduced if the deck is covered by a roof above? Under an alternative-solution route, a reduced upstand may be acceptable on a covered deck with appropriate evidence. The deemed-to-comply route under §9.1.6.5 requires 150mm regardless of cover. Most BCA's want evidence the reduced upstand has been engineered, not just argued.

Q2: What if the deck membrane is a liquid-applied versus a sheet membrane? The §9.1.6.5 upstand applies to both. The manufacturer's appraisal will specify the membrane termination detail, but the 150mm vertical upstand from finished deck level is a Building Code requirement on the deemed-to-comply path.

Q3: Does the 35mm door-sill upstand apply to bi-fold and slider doors? Yes — §9.1.6.5 applies to door thresholds generally. The 35mm sill upstand is challenging on bi-fold and slider doors because the manufacturers' standard threshold heights are sometimes lower. Specific door / threshold systems with CodeMark appraisals provide the path through this.

Q4: What's the cost of moving from deemed-to-comply to alternative-solution on a deck threshold? On a residential deck, the alternative-solution package — drainage gully, overflow, covered overhang, designer's certificate, supporting evidence — typically adds $5-15k to the build cost and 2-4 weeks programme through consent. It's a real cost, but often less than the cost of a redesign that lifts the door 150mm.

Q5: Who's liable if the deck leaks five years after Practical Completion? Under Building Act 2004 §362I, the contractor's residential warranty runs 10 years. If the leak is the result of a §9.1.6.5 non-compliance the contractor signed off on, the contractor is exposed. The membrane manufacturer's warranty may also have been voided by the non-compliance.

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