Figures 1 and 2 in ‘Timber windows in a cavity’ on page 26 of Build 149 has details for timber window installation. However, there is no comment on whether these details are appropriate for all wind zones.
The absence of sealant between the outer face of the timber and the underside of the head flashings appears to be an omission, particularly in higher wind zone situations given:
● timber’s tendency to distort
● the use of head flashings similar to those used on aluminium joinery
● the likelihood of gaps opening.
The addition of the bead and extending the downward leg of the flashing to 20 mm in Figure 1 to form a true drip edge would provide more appropriate protection.
PAUL PROBETT: TAURANGA
Comment These details are based on window sections in NZS 3610:1979 (section SJ9 for the sill) and traditional flashing installations. They have had decades of successful performance in a range of situations.
However, your suggestion of increasing the flashing cover and installing sealant is a good one if a designer wants to increase the margin of safety.
I must say well said to Mike Fox for his very good well written opinion piece in Build 149 August/September 2015.
It needs to be sent to most of the local New Zealand councils for the planners to read and consider.
Common sense decisions and actions will help New Zealand move forward and get out of the handcuffs that is the PC red tape.
RICHARD HOADLEY: BY EMAIL
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