Extra raking window head detail

By - , Build 163

Raking window head details can be a little tricky to design. This design solution can be used when a raked window head is directly under a soffit.

Figure 1 Raked window head directly under soffit.
Figure 2 High end of raking window head.

IN BUILD 158, Soffit detail at gable verge described detailing requirements to prevent wind-driven rain from penetrating the junction between the soffit and the wall cladding at a gable verge.

Raking window head detail in Build 162 outlined the design and installation of a raked window incorporating a window head flashing under a gable soffit.

What if no space for window head flashing?

What about the situation where the window head is directly underneath a raking soffit, leaving no room for a window head flashing? Gable walls present two weathertightness issues when installing windows:

  • They tend to be higher and therefore more likely to leave the window head exposed to wind and rain.
  • The sloping head means that, if water penetrates the junction between the top of the window frame and the soffit, it will drain to the low end of the window head and potentially behind the wall cladding if not detailed to allow that water to drain.
Figure 1 Raked window head directly under soffit.

Design solution

As there is no room to incorporate a window head flashing, use a 40+ × 18 mm timber trim fitted and sealed against the junction between the soffit and window frame head. This is based on detail 8A(f) in Acceptable Solution E2/AS1 to New Zealand Building Code clause E2 External moisture.

Additionally, BRANZ suggests that the timber trim:

  • is rebated over the face of the window flange (see Figures 1 and 2)
  • is sealed to both the window flange and the soffit
  • extends at least 50 mm beyond the window head at both ends.
Figure 2 High end of raking window head.

For more

The Build articles mentioned are available free from www.buildmagazine.org.nz.

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Figure 1 Raked window head directly under soffit.
Figure 2 High end of raking window head.

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