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.