Edge detailing for membrane roofs

By - , Build 130

Don’t be misled into thinking that rubber roofing membranes can do without edge detailing. It’s required in E2/AS1, and omitting it can lead to stained walls.

Figure 2: Anti-spill edge details for roof membranes from BRANZ Weathertight Solutions Volume 6 Membrane Roofing.
Figure 1: Anti-spill edge or water check to prevent water spillage, from BRANZ Good Practice Guide Membrane Roofing (1999).

Recently, Consumer magazine issue 521 highlighted an issue with the staining of wall claddings. Water from synthetic rubber roofing membrane was running down a wall surface and leaving noticeable staining on the surface of the wall. This staining can appear worse with a texture-coated finish due to the dirt trapped on the textured surface.

Over time, synthetic rubber roofing membrane surfaces will oxidise due to UV exposure. It is this oxidation, removed and carried by the roof water, that causes the wall staining when edge details preventing spillage have not been incorporated into the roof or deck construction. The photos in the Consumer article do not clearly show the roof edge detail used but they do not appear to include any form of anti-spill edge.

Figure 1: Anti-spill edge or water check to prevent water spillage, from BRANZ Good Practice Guide Membrane Roofing (1999).
Figure 2: Anti-spill edge details for roof membranes from BRANZ Weathertight Solutions Volume 6 Membrane Roofing.

Anti-spill edge detail needed

Edge detailing to synthetic rubber roofs and decks that prevents water running off the roof and down over the walls has been required for some time. Since 2005, using E2/AS1 (Figure 61) as a means of compliance has required these edge details – one option is shown in Figure 1.

BRANZ also specifies edge details in:

  • BRANZ Good Practice Guide Membrane Roofing published in November 1999 (Section 2.13). This also highlights the consequences of uncontrolled water spillage off roofs, for example, staining of walls, and recommends incorporating a detail, such as Figure 1, to prevent it.
  • BRANZ Weathertight Solutions Volume 6 Membrane Roofing published in 2008 (see Figure 2).

As well, both major suppliers recommend edge detailing to prevent spillage occurring.

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Figure 2: Anti-spill edge details for roof membranes from BRANZ Weathertight Solutions Volume 6 Membrane Roofing.
Figure 1: Anti-spill edge or water check to prevent water spillage, from BRANZ Good Practice Guide Membrane Roofing (1999).

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