CASE STUDY | WINDOWS
04
4. The ends of subsills must be fully
dammed by the abutting wall materials.
5. The damming wall material must be
waterproof.
05
6. The cross-sectional shape of subsills
is complex and ensuring that a viscous
sealant has fully closed the junction of
the subsill and abutting surface is difficult.
7. Sealants require maintenance. The only
means of gaining adequate access to the
ends of subsills is to disassemble the
window or door system.
LESSON: Put in subsill end dams. It is
actually easier than trying to substitute them.
06
07
HEAD FLASHING END DAMS – A
DAM LUNATIC TALKING?
British Standard BS 5628 Part 3 – Use of
Masonry was revised in 1985 which led the
Building Research Establishment (BRE)
Housing Defects Prevention Unit in the
United Kingdom to revise its own Defect
Action Sheet number 15 (1983) as DAS 98
in 1987. Both Defect Action Sheets dealt
with the penetration of water into buildings
around windows. The revised Defect Action
Sheet included a requirement from the
newly-updated British Standard that cavity
trays at window heads, known as head
flashing in Australia, include stop-ends to
prevent accumulated water from spilling
over the ends and wetting the inside skins of
cavity walls, cavity ties, mortar dags or cavity
insulation (not often encountered here), or
due to sagging of the head flashing, creating
a discharge point near or at the vertical face
of the inside skin of the wall (figures 08 and
09).
The current Australian Standard does not
require such a measure but it presumes that
cavities will be clear and not bridged with
mortar or debris, that flexible flashings will
be installed and forever keep the shape
in which they are shown on architects’
wall sections (which are usually prepared
by people who have never had to handle,
position, fold, join and clean lengths of
bitumen-coated aluminium foil to a deadline)
and that weepholes will be installed in the
correct course and intelligently positioned.
Given the likelihood that cavities can
be bridged, weepholes can be poorly-
formed and then easily become clogged,
and that flexible flashing materials can
sag with the passing of time, I present
the Brits’ improvement on things for your
consideration. It might be about time we
stopped waiting to be told how to improve
what we do.
08
01
The intersection of the bounding wall,
floor, and glazed aluminium-framed
balcony sliding door assembly in a
Sydney fringe residential apartment
building. The predictable deterioration
due to missing, poorly-installed or
substituted subsill end dams is evident
in the dampness and growth of mould
emanating from the interface of the
subsill and wall. Other symptoms, not
visible in this image, include dampness of
the carpet and underlay, and corrosion
of the carpet stretcher fasteners and
prongs. This is most severe in the corner
formed by the glazed assembly and wall.
02
03
Extract from the Alcan fabricator’s
manual (1980s). End dams, here called
stop-ends, are clearly shown screw-fixed
to and sealed against each end of the
subsill.
Clear silicone sealant pumped into the
junction between an anodised aluminium
subsill and precast concrete wall panel
failed to adhere to the concrete which
was not properly prepared to receive the
sealant.
04–07 Images captured at one-minute intervals
during hose-testing of the aluminium-
framed window assembly. As image 05
shows, water penetration commenced
09
within one minute and steadily continued
(images 06 and 07).
08 A generic and compliant head flashing
arrangement and its possible downfall in
allowing water collected by the window
head flashing to be diverted to the
interior leaf of a cavity wall. Diagram by
Danielle Hynard.
09 The British solution to overcome the
issue in image 08. Diagram by Danielle
Hynard.
Simon Owen is Associate Director of Building
Diagnostics at Jackson Teece Architecture.
WINDOWS MAGAZINE 25