BRANZ weathertightness poster

, Build 81

In the August/September 2002 edition of Build you would have received the BRANZ weathertightness poster. This column takes a detail from the poster and provides a ‘good practice’ solution to it.

Figure 2: Prefabricated flanges on meter box.
Figure 1: Flange seal to small-diameter penetration.

Risk factor 7 on the weathertightness poster ‘Penetrations’ highlighted the detail shown below.

A small but significant area of concern with the weathertightness of wall claddings is where the weatherskin is punctured by a pipe, meter box, handrail stanchion or structural or decorative support.

Ideally designers should aim to eliminate penetrations through the cladding. If they are unavoidable, then they should be in a sheltered or protected situation, such as under the eaves or, for meter boxes, within a sheltered porch. Always show penetration locations on drawings.

Small penetrations

Small-diameter penetrations, such as an overflow pipe or a hot-water cylinder drain, can be routed through the foundation to exit below the cladding. Existing penetrations, or those where repositioning is not possible, can be dealt with relatively easily using a circular flange sealed to both the penetrating item and the cladding (see Figure 1 on the opposite page). Large circular items, such as an air extractor or clothes dryer vent, should ideally exit through a soffit. Where there is no soffit, they must be fitted with a weatherprotective cowl sealed to the cladding.

Large penetrations

Larger penetrations, such as structural supports and meter boxes, require more attention to detail. Flanges and/or flashings are advised in all but the most protected situations.

One option for a meter box is to have it fabricated with flashing flanges, as shown in Figure 2 opposite. Other options include locating the meter behind a viewing window or in a weather-protected part of the building. This allows the meter to be read and simplifies the weatherproofing details.

Pergola or deck structures are best erected separately from the building so that no penetration through the cladding is required. Penetrations that are solely decorative should be avoided completely.

Figure 1: Flange seal to small-diameter penetration.
Figure 2: Prefabricated flanges on meter box.

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Figure 2: Prefabricated flanges on meter box.
Figure 1: Flange seal to small-diameter penetration.

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