WINDOWS Magazine Spring 2017 | Page 26

WINDOWS | CASE STUDY 02 END DAMS A DAM TIRESOME TOPIC 01 SIMON OWEN Associate Director, Building Diagnostics, Jackson Teece Architects D espite prescriptive instructions in window system manufacturers’ literature, and warnings in entry-level manuals aimed at building investigators, the lack of correct installation of dams at the ends of aluminium-framed window system subsills is a defect which is still encountered so frequently as to no longer be surprising. This article illustrates the outcomes of the omission or poor installation of end dams and also discusses the potential merits of applying the principle of the end dam to window head flashings. SUBSILL END DAMS Figure 02 is a doctored extract from an Australian aluminium framing system manufacturer’s manual from the 1980s. The author has encountered numerous creative substitutions for the required 24 Spring 2017 03 Despite instruction and warnings, incorrect installation of s ubsill end dams in aluminium-framed window systems is a frequently encountered defect. This article illustrates the outcomes of poor installation or missing end dams and the application of this principle to head flashings. purpose-made components that are needed to prevent water collected in subsills from spilling over the subsills end and wetting finishes - from deformed and repurposed soft drink cans to pieces of torn denim - but by far the most popular substitution has been elastomeric sealant applied in quantities varying from pointlessly scant to absurd in its gratuitousness (image 03). During recent investigative work, Jackson Teece Building Diagnostics were asked to justify why elastomeric sealant was not a sound alternative to the fitting of purpose- made end dams. A window assembly was located where the sealant ‘dam’ appeared intact and was gently hose-tested. Within minutes this exercise demonstrated the folly of reliance upon sealant alone (images 04 to 07). Manufacturers of window systems that incorporate subsills generally supply purpose-made end dams. When these are properly fitted to subsills, no further work is needed to prevent water leakage from the window system at the ends of subsills. Reliance on sealant caulking between the ends of subsills and the adjoining wall construction is reckless due to the following reasons: 1. The number of variables which lead to the decline in sealant joint performance is high. 2. The success of a sealant joint relies heavily upon substrate preparation and sealant application. The responsibility for this rests wholly with the sealant applicator. 3. Whether a substrate has been adequately prepared to receive a sealant cannot be readily verified after application of the sealant.