Balustrade-to-wall junction

By - , Build 166

This quick overview of saddle flashings at an enclosed balustrade-to-wall junction provides useful tips on correct detailing and installation.

ONE OF the trickiest flashing details to design and construct correctly is a balustrade-to-wall junction flashing. The junction where the capping of an enclosed balustrade meets the face of the main exterior wall of a building – typically at the end of a deck – can be a risky location for weathertightness failure.

Where a metal cap flashing is used along the top of the balustrade, designs to Building Code Acceptable Solution E2/AS1 require a fabricated metal saddle flashing to make these junctions weathertight. However, MBIE is aware that metal saddle flashings are often positioned incorrectly.

Different – saddle flashing at front of cavity

Figure 12 of E2/AS1 requires these saddle flashings to be positioned at the front of the cavity (immediately behind the outer cladding) – see note (1) and detail (c) in Figure 12. Placing these flashings at the front of the cavity reduces the likelihood of water entering the cavity where the flashing passes through it.

Importantly, this approach is different to most other cavity flashing details in E2/AS1. The narrow width of the balustrade means that only a very small volume of water could enter the cavity of the main wall above, so a different approach is acceptable.

Any such water will run down to the flexible flashing tape where the sloped packer meets the main wall underlay, then be diverted to the adjacent cavity beside the balustrade and eventually drain out its base.

Getting it right

E2/AS1 has several specific requirements for parapets and enclosed balustrades:

  • No penetrations are allowed in the top surfaces of parapets and enclosed balustrade walls. Where rails are required on balustrades, they must be side-fixed through the cladding into the framing as per E2/AS1 Figure 19 (on page 58 of the E2/AS1 document).
  • The sides of cappings must cover the cladding on both sides as per E2/AS1 Table 7 (on page 40 of E2/AS1) situation 2 or 3:
    • 70 mm overlap plus kick-out (or bird’s beak for inside edge of enclosed balustrades as per E2/AS1 Figure 5 on page 38) for low, medium, high and very high wind zones
    • 90 mm overlap plus kick-out or bird’s beak for extra high wind zone.
  • All claddings on parapets and enclosed balustrades must be installed over drained cavities, except vertical corrugated steel.
  • In extra high wind zones, all claddings must be installed over a rigid wall underlay, consisting at a minimum of 7 mm H3 treated plywood or 6 mm fibre-cement sheet, overfixed with a wall underlay.

The references to E2/AS1 above can be found on www.building.govt.nz.

More detail in flashings supplement

BRANZ has published step-by-step diagrams showing the installation sequence for the components to these junctions in the recent Build supplement – Flashings. As with the installation of any flashing, sequencing of installation steps is key to a good outcome. The balustrade-to-wall junction can be found in section 4.5 of the supplement.

This key resource provides a comprehensive overview of construction sequencing for most common residential flashing applications and explains the steps in the installation process.

Quiz

1. What is the minimum slope allowed by E2/AS1 for the top of a metal saddle flashing to a parapet or enclosed balustrade?
a. 15°.
b. 5°.
c. Depends on the wind zone and average rainfall at location.

2. Using E2/AS1, can you penetrate the upper surface of a parapet or enclosed balustrade saddle flashing?
a. No.
b. Yes, but it depends on the wind zone.
c. Sometimes.
d. Only if the homeowner signs a disclaimer.

3. What cover is required by E2/AS1 to the sides of a saddle flashing in a VH wind zone?
a. 70 mm.
b. 25 mm.
c. 90 mm.

Answers: 1. b 2. a 3. a

For more

To download or read E2/AS1, visit www.building.govt.nz, and for the Build supplement – Flashings, visit www.buildmagazine.org.nz/articles/show/flashing-supplement.

Download the PDF

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Articles are correct at the time of publication but may have since become outdated.

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