Remuera two-storey alteration case study — the inter-storey flashing detail caught in shop drawings
Updated: Jul 9
A Remuera two-storey alteration's inter-storey flashing detail was correct on the architectural section but ambiguous on the cladding shop drawings. Caught at shop-drawing review, the clarification prevented a weathertightness defect at the storey junction.
By Steve Parker · Trueworks · NZ construction estimation · 5 min
Shop drawings are the last document where a cladding detail can be corrected before fabrication. A junction that reads one way on the architect's section and another on the cladding shop drawing is a junction that will be built to whichever the trade is holding on the day.
By Steve Parker · Trueworks · NZ construction estimation · 5 min
What you'll learn in this case study
The inter-storey flashing detail ambiguity in shop drawings
The E2/AS1 §9.5 resolution that closed it
The cost-of-catching-it-later table from shop drawing through to defects liability
Quick answer: On a Remuera two-storey alteration, the inter-storey flashing at the floor-junction between level 1 and level 2 cladding was correctly detailed on the architectural section as a Z-flashing with a kick-out at the head of the level-1 sheet. The cladding subcontractor's shop drawing showed a single-fold tray flashing without the kick-out, omitting the upstand into the level-2 cladding cavity. E2/AS1 §9.5 sets the inter-storey detail. Caught at shop drawing review the resolution cost a re-issue. Caught at defects liability or a year-3 leak it would have run $18-32k in cladding strip-back, framing dry-out, and re-clad.
The build
A Remuera large modern alteration: a two-storey rear addition to a 1960s timber-framed dwelling, with a contemporary fibre-cement panel cladding palette to the rear elevations and a render-finish to the lower-floor plinth. Head contract sat in the $1.8-2.4M envelope on a fixed-price NZS 3910 head contract. The architect was the CA, the cladding subcontractor was a specialist panel installer with shop-drawing-based delivery.
The cladding shop drawings landed for approval seven days after the order was placed. Standard CA practice is to review and either approve, approve-with-comments, or reject with reasons within ten working days.
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What we found in the quote
The architectural cladding details at A-30.05 (typical inter-storey junction) showed a precision-folded Z-flashing with a 75 mm cover-flange to the level-1 sheet head, an 80 mm horizontal kick-out at the storey-line, a 20 mm drip edge, and a 90 mm upstand into the level-2 cladding cavity behind the lower edge of the level-2 sheet. The detail was correctly drawn to E2/AS1 §9.5 with all the dimensions noted.
The cladding subcontractor's shop drawing landed showing the same flashing region. Three differences from the architectural detail. First, the upstand into the level-2 cavity was 50 mm not 90 mm. Second, the kick-out was 60 mm not 80 mm. Third, the drip edge was implied (not dimensioned). The cover-flange and the basic Z-fold were correctly drawn.
On a single-storey cladding job those differences might pass inspection. On an inter-storey junction with a level-1 cladding face above 2.4 m of vertical drop, the difference is the difference between a junction that sheds wind-driven rain and a junction that catches the runoff in the cavity below.
E2/AS1 §9.5 is specific about the inter-storey detail. The clause sets the minimum upstand into the upper cladding cavity, the kick-out projection, the drip edge dimensions, and the lap arrangement at the flashing ends. The architect's detail was at the §9.5 standard; the cladding shop drawing was below it on three dimensions.
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How the code resolves it
E2/AS1 §9.5 covers inter-storey junctions, parapet and balustrade junctions, and other horizontal cladding-to-cladding transitions where one cladding plane sits above another. Figure 79 of E2/AS1 shows the canonical inter-storey detail with named dimensions: minimum 75 mm horizontal kick-out (extended for higher wind zones), minimum 90 mm vertical upstand into the upper cavity, minimum 15 mm drip-edge return, and minimum 25 mm head-of-lower-sheet cover.
The clause is performance-and-deemed-to-comply. A detail that meets the §9.5 dimensions is deemed to comply. A detail that does not requires either an alternative-solution position with engineer-of-design backing, or an amendment.
NZS 3604 §4 covers wind-zone classification for residential framing. Remuera sits in Auckland Wind Zone Medium typically (subject to specific site assessment for elevated or exposed sites). The §9.5 dimensions in E2/AS1 are baseline for Medium wind zone; higher zones (High, Very High, Extra High) require increased kick-out and upstand.
The cladding shop drawing's 50 mm upstand and 60 mm kick-out are below the §9.5 deemed-to-comply baseline. The detail as drawn is not an alternative solution — it's a non-compliant detail.
Under the cladding sub-contract and the CA role under NZS 3910 §6, the architect-as-CA's response to a shop drawing that departs from the contract documents is to reject the shop drawing with reasons and require a re-issue. The shop drawing is not the binding document — the architectural set is. The shop drawing is the trade's interpretation of the architectural set, submitted for approval.
What it would have cost if caught later
| Stage caught | Cost range (ex GST) | Why | |---|---|---| | Shop drawing review (where we caught it) | $0-1k | Written rejection with comments, one round of re-issue, no programme effect | | Pre-fabrication (cladding panels cut against bad shop drawings) | $3-5k | Panel re-fabrication or modification at the lower-edge return, programme shift of 1-2 days | | Mid-install (level-1 cladding done, level-2 starting) | $8-12k | Standdown of cladding crew, strip-back of the storey-junction zone, refit of flashing to correct detail, sheet re-fix | | Practical completion to year 2 | $14-22k | Detail installed and concealed; remediation requires partial strip-back of both storeys' cladding around the junction, including paint touch-up | | Year 3-5 weathertightness leak | $18-32k | Targeted intrusive investigation, framing dry-out, replacement of saturated insulation, junction re-build, internal wall remediation |
The bottom row is the realistic worst case if the leak is localised. A widespread inter-storey leak across multiple elevations multiplies the row by 1.5x to 2x.
The clarification we recommended
A one-page shop-drawing comment sheet to the cladding subcontractor, structured as a §6 CA instruction. The sheet listed the three §9.5 dimension departures with the architectural set reference (A-30.05) and the E2/AS1 §9.5 reference. The instruction was clear: resubmit shop drawing with kick-out at 80 mm minimum, upstand at 90 mm minimum, drip-edge dimensioned at 15 mm minimum, lap arrangement at the flashing ends noted.
The cladding sub re-issued within four days. The revised shop drawing matched the architectural detail. The architect approved.
Cost effect: nil on the build. The cladding sub absorbed the shop-drawing revision in their own design fee. The flashing fabrication was unchanged because the order had not gone to the metal fabricator yet. Programme effect: nil.
What other Remuera two-storey alteration shop-drawing reviews should check
Inter-storey flashing dimensions against E2/AS1 §9.5 Figure 79 — kick-out, upstand, drip-edge, cover all named
Wind-zone classification per NZS 3604 §4 with the dimensions adjusted upward for High or higher
Lap arrangement at the flashing ends and the junction with vertical cladding-trim flashings
Cladding-cavity continuity through the inter-storey junction — the cavity must not be broken at the storey line in a way that prevents drainage to a kick-out
The cladding sub's shop drawing reviewed against the architectural set within the CA's ten-working-day window, with comments returned in writing
FAQ — inter-storey flashing detail review on Remuera two-storey alterations
Q1: Why does E2/AS1 §9.5 matter more on a two-storey than a single-storey? The inter-storey junction is the horizontal transition where the upper cladding sheds water onto the lower cladding's flashing. On a single storey there is no such transition. On a two-storey alteration the §9.5 detail is the primary defence against wind-driven rain entering the cavity. A bad detail on a single storey will not leak; a bad detail at the inter-storey will.
Q2: Can the shop drawing depart from the architectural set if the cladding manufacturer's standard detail is different? Only as an alternative solution with the engineer of design or the architect's written acceptance. The cladding manufacturer's standard detail is often a baseline detail for a different wind zone or a different cladding system. The Remuera detail must be confirmed against the specific wind zone and the specific architectural set.
Q3: Who owns the shop-drawing review under NZS 3910? The CA (architect or QS as appointed) owns the review under §6. The CA is required to either approve, approve-with-comments, or reject with reasons within a reasonable time — typically ten working days. The trade is bound by the CA's response.
Q4: What's the typical wind zone for a Remuera site? Most Remuera sites sit in Auckland Wind Zone Medium per NZS 3604 §4. Elevated sites on the ridgeline or sites with significant local terrain exposure can shift to High. A site-specific wind assessment is required where the zone is borderline.
Q5: How long should a cladding shop drawing review take on a typical Remuera alteration? Five to seven working days for a competent review against the architectural set, the specification, and E2/AS1. The CA has ten working days under typical sub-contract terms. Cutting the review short to keep the trade rhythm is the false economy that catches details like this.
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