E2/AS1 §9.5 inter-storey junction — the 35mm upstand the NZ cladding installer keeps missing (2026)

sp8002
May 30
7 min read

E2/AS1 §9.5 sets the inter-storey junction detail on multi-storey cladding. The 35mm vertical upstand and the head-flashing return are the two items most commonly missed on NZ residential. The re-work cost on a partly-clad two-storey runs $14-32k plus 2 weeks.

By Steve Parker · Trueworks · NZ construction estimation · 6 min

§9.5 of E2/AS1 is the deemed-to-comply solution for the inter-storey junction in two-storey cladding. The 35mm minimum vertical upstand to the flashing, combined with the §9.1.5 head-flashing detail at storey junctions, is the line between a weathertight build and a leaky-building remediation invoice.

By Steve Parker · Trueworks · NZ construction estimation · 6 min

What you'll learn in this post

What E2/AS1 §9.5 and §9.1.5 actually require at the inter-storey junction
The three failure modes that produce leaky inter-storey details
The 5-item check before signing off the cladding quote

Quick answer: E2/AS1 §9.5 sets the deemed-to-comply detail for inter-storey junctions in two-storey direct-fixed and cavity cladding. The detail requires a minimum 35mm vertical upstand on the storey-junction flashing, with the head-flashing principles from §9.1.5 applied. Miss the 35mm upstand on a Very High wind zone or in a high-rainfall climate zone, and the assembly fails the deemed-to-comply path under E2/AS1. The retro-fix on a partly-clad two-storey runs $14-32k plus 2 weeks, with consent amendment exposure under §45 of the Building Act.

E2/AS1 is the acceptable solution for external moisture under Building Code clause E2. It sets out the geometrical and material requirements for cladding, flashings, junctions, and penetrations that, if followed, deem the assembly to comply with E2. §9 is the part of E2/AS1 covering wall-cladding junctions and penetrations. §9.5 specifically covers the inter-storey junction — where the cladding on the lower storey terminates and the upper-storey cladding begins.

This post reads §9.5 alongside §9.1.5 (the head-flashing principles) and identifies the three most common failure modes on NZ residential two-storey work.

What §9.5 actually says

§9.5.1 — application

§9.5 applies to inter-storey junctions on direct-fixed and cavity-fixed wall claddings. The clause sets out the deemed-to-comply detail for the junction between the lower-storey cladding (terminating at the inter-storey flashing) and the upper-storey cladding (starting above the flashing).

§9.5.2 — the geometric requirements

§9.5.2 sets the minimum dimensions:

35mm minimum vertical upstand from the top of the inter-storey flashing to the bottom of the upper-storey cladding
15mm minimum cover of the inter-storey flashing under the upper-storey cladding
Drip-edge on the flashing extending past the lower-storey cladding face
Continuous head-flashing principles per §9.1.5 — minimum 15° slope, end-stops, anti-capillary breaks

§9.1.5 — head-flashing principles

§9.1.5 is the upstream clause that §9.5 incorporates by reference. §9.1.5 requires:

Head flashing extends 50mm past each side of the opening
Slope of not less than 15°
Upstand against the wall sheathing
End-stops to prevent water tracking sideways
Anti-capillary break under the upper-cladding lap

The inter-storey junction is functionally a head flashing the width of the building elevation. Every §9.1.5 principle applies.

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How the inter-storey junction fails on NZ residential

1. The 35mm upstand compressed to 20-25mm. The detail is drawn correctly on the architectural set, but on site the upper-storey cladding gets fixed lower than the drawn line. The installer wants a "tight" visual line, or the framing has been set at a height that doesn't leave room for the upstand. The 35mm requirement is non-negotiable under §9.5.2. Below 35mm, the deemed-to-comply path is broken. The Building Code clause E2 (weathertightness) still has to be met, but now by alternative-solution route — meaning specific design, evidence, and BCA acceptance.

2. The end-stops omitted on the inter-storey flashing. §9.1.5 requires end-stops to prevent water tracking sideways behind the cladding. On long elevations, the inter-storey flashing is sometimes installed as a continuous run without end-stops returning into the corner detail. Water tracks along the back of the flashing, gets behind the corner, finds its way into the cavity. This is one of the leaky-building patterns from the 2000s and it still recurs.

3. The anti-capillary break missing under the upper-cladding lap. The lower edge of the upper-storey cladding needs an anti-capillary break — typically a 5mm minimum gap between the back of the upper cladding and the face of the flashing. Without it, water held in capillary action between the two surfaces tracks up under the cladding and into the building paper. §9.1.5(c) addresses this. The detail is often drawn correctly and installed incorrectly because the cavity batten or pack creating the gap is the wrong thickness.

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The reference table

| §9.5 requirement | Dimension | Why it matters | Failure mode on NZ residential | |---|---|---|---| | Vertical upstand to inter-storey flashing | 35mm minimum | Stops splash and wind-driven water reaching cladding back | Compressed to 20-25mm for visual line | | Flashing cover under upper cladding | 15mm minimum | Maintains continuous water-shedding plane | Cover lost at lap-and-fix detail | | Flashing slope | 15° minimum (per §9.1.5) | Drains water clear of the building | Flat or near-flat flashing installed | | End-stops to inter-storey flashing | At corners and terminations | Prevents lateral water tracking | Continuous run, no end-stops | | Anti-capillary break | 5mm gap minimum | Stops capillary lift behind upper cladding | Wrong pack thickness, gap closed | | Drip-edge past lower cladding | 5-10mm projection | Water drips clear, not down lower-cladding face | Drip-edge omitted, water tracks down |

Worked example

A two-storey alteration in a coastal Auckland suburb. Cavity-fixed direct-applied fibre-cement cladding both storeys. The architect's detail correctly shows 35mm upstand to the inter-storey flashing, end-stops at corners, and an 8mm anti-capillary gap. The cladding installer fixes the upper-storey first storey of cladding at a height that leaves 22mm between the top of the flashing and the bottom of the upper cladding sheet.

The defensible response: site stop-work on the upper-storey cladding. The installer claims the visual line was the architect's preference. The architect produces the drawn detail at 35mm. The contractor pushes back on cost. The Engineer or CA determines: §9.5.2 is non-negotiable on a deemed-to-comply route. The fix: strip the upper-storey first run of cladding (2-3 hours), reposition the bottom edge 13mm higher, re-fix.

The expensive version: cladding completed both storeys at 22mm upstand. Pre-line BCA inspection picks it up. Remediation now requires stripping the upper-storey cladding to expose the inter-storey junction, replacing the flashing if it has been damaged, re-cladding. Cost: $14-32k depending on elevation length and cladding type. Programme: 2 weeks. Plus consent amendment if the BCA requires it documented under §45 of the Building Act.

What to check before signing the cladding quote

Five items, every time:

The cladding quote names E2/AS1 §9.5 as the inter-storey detail — and the framing schedule accommodates the 35mm upstand
The architectural detail at storey junctions matches §9.5.2 dimensions — 35mm upstand, 15mm cover, 15° slope
End-stops are specified and ordered — the flashing schedule should name them
The cavity-batten or pack thickness creates the 5mm anti-capillary break — and matches the cladding manufacturer's installation guide
The drip-edge projection is detailed — typically 5-10mm past the lower cladding face

If those five items are present and tracked through to installation, §9.5 holds and the inter-storey junction is on the deemed-to-comply route. If they're missing, the assembly is on an alternative-solution route by accident, which is the most common path to a leaky-building dispute.

FAQ — E2/AS1 §9.5 inter-storey junction on NZ residential

Q1: Can the 35mm upstand be reduced if the upper cladding is heavy or impervious? Not on the deemed-to-comply route. §9.5.2 is fixed at 35mm minimum. A reduced upstand can be designed as an alternative solution under E2, with supporting evidence, but it requires BCA acceptance and is usually more expensive in evidence than just achieving the 35mm.

Q2: Does §9.5 apply to all cladding types? §9.5 applies to direct-fixed and cavity-fixed wall claddings within the scope of E2/AS1. Specific cladding systems (some metal claddings, some proprietary panel systems) have their own manufacturer's CodeMark or appraisal details that may override the §9.5 generic detail.

Q3: What's the BCA inspection trigger point for §9.5? The pre-line / pre-cladding inspection picks up junction details. On most Council inspection regimes, the inter-storey flashing must be inspected before the upper-storey cladding is installed — once the upper cladding is fixed, the detail is concealed.

Q4: Does the §9.5 detail apply to a single-storey with parapet or attic? The inter-storey detail is specifically for a junction between two cladding planes at a storey change. A single-storey with parapet uses different §9 details (parapet capping under §9.4) and roof-to-wall junctions under §9.3. Don't apply §9.5 outside its scope.

Q5: What's the warranty implication if §9.5 isn't followed? Most cladding manufacturers' warranties require installation per E2/AS1 or per their own appraisal details, whichever is more stringent. A §9.5 deficiency typically voids the cladding warranty and the membrane / building-paper warranty for the affected area.

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