Direct-fix window installation

By - , Build 128

Recent changes to E2/AS1 mean that the construction sequence for openings in walls with direct-fix claddings must now be done differently.

Steps 4–8.
Figure 1: Sill tray flashing.
Steps 1–2.
Step 3.
Steps 9–14 for sill.
Steps 11–15 for window head.

Major changes have recently been made to a number of Building Code documents including the Acceptable Solution E2/AS1. Under the changes, direct-fix claddings are not permitted in the EH wind zone, parapets or enclosed balcony walls. One area of change for designs following E2/AS1 concerns openings in walls with direct-fix claddings, particularly:

  • the sill tray flashing design
  • installation of jamb battens
  • head flashing sealant at each end of the window.

Sill tray flashing

Windows installed in openings with direct-fix wall claddings must have a sill tray flashing as shown in Figure 1. It must:

  • extend for the full width of the opening between trimming studs
  • have an 8 mm back upstand
  • have tapered end upstands
  • provide 35 mm minimum cover to the cladding.

The sill tray can be flat – the 5° slope required in previous versions of E2/AS1 is removed.

The window must be supported on frame support blocks (supplied by the joinery manufacturer) and have a minimum 8 mm flange cover over the sill tray flashing downturn (previously, this was a 10 mm minimum cover) with a 5 mm unsealed air gap.

The jamb flanges must have a 10 mm minimum cover, and if not protected by a scriber or plug, the gap must be sealed (unchanged from previously). The changes mean that the packers underneath the timber reveal to the sill need to be a minimum of 8 mm – measure with the flashing in place to get the correct height.

Figure 1: Sill tray flashing.

Jamb battens

Window openings with direct-fix wall claddings now require two 45 × 20 mm vertical jamb battens to be fixed to the face of the trimming stud on each side of the opening:

  • The inside batten must be fitted between the lintel and the sill trimmer.
  • The outside batten is fitted to the underside of the lintel but is stopped 20–40 mm short of the sill trimmer. This allows the sill flashing to extend along the full length of the sill trimmer between trimming studs without requiring stud notching.

The battens are installed after the timber-framed opening has been protected by folding the wall underlay back around the frame opening, then covering the corners and the full length of the sill trimmer with flexible flashing tape (this is unchanged from previously).

The cladding is fixed and trimmed to the battens, not the studs. The window opening width should be measured after the sill battens and the sill tray have been installed.

Head flashing sealant

A 50 mm long bead of sealant must be installed between the cladding and each end of the head flashing to prevent water tracking around the end of the flashing.

Compliance from 1 February 2012

These changes aim to simplify the installation of windows and doors and improve their weathertightness.

The amended E2/AS1 (Amendment 5) came into effect on 1 August 2011, and from 1 February 2012 this will be the only version of the document that can be used as a means of compliance.

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

Steps 4–8.
Figure 1: Sill tray flashing.
Steps 1–2.
Step 3.
Steps 9–14 for sill.
Steps 11–15 for window head.

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