RC122 JanFeb 2026 - Magazine - Page 34
CONSTRUCTION
SAVING A STUNNING SKYLIGHT
Mitigating water infiltration at Yorkdale Subway Station
by Jason Paulos and Hamid Vossoughi
Y
Jason Paulos is a
Façade Project Manager
with WSP in Canada.
Hamid Vossoughi is a
Senior Façade Engineering
Specialist for WSP in
Canada.
Implementing the skylight
The skylight system at Yorkdale Station was originally built
as a barrier system in the 1970s, utilizing an aluminum
frame with single-pane wired glass panels. During the
retro昀椀t in the mid-1990s, the Toronto Transit Commission
introduced a concealed drainage system to manage rainwater more e昀昀ectively. This system included new extrusions
and concealed gutters within the expansion joint system.
The existing gutters were lined with a membrane to prevent
water back昀氀ow and ensure that any rainwater that penetrated the joints was properly channeled away from the
structure. This updated system incorporated single-pane
wired glass that was structurally bonded with silicone to
a clear anodized aluminum frame, along with reusing the
existing mechanical glass retainers at each corner.
The skylight system includes nine expansion joints
that manage thermal expansion and contraction across
the length of the system. These joints, along with weather
seals and metal 昀氀ashings, were designed to manage potential water penetration and mitigate damage from Toronto’s
variable climate. Louvers are located at the base of the
skylight system to provide ventilation to the station and
34—RENEW CANADA – JANUARY/FEBRUARY 2026
alleviate the impact of the train entry to the station and the
imposed piston e昀昀ect/air pressure on the skylight system.
Additionally, the original design of the skylight featured two access systems for maintenance and repair: an
A-frame platform on a guide rail for interior maintenance
and a mobile curved ladder on an exterior guide rail. Both
systems were designed to allow maintenance workers to
perform cleaning and minor repairs as required. However,
neither system had been serviced or certi昀椀ed in the recent
past, making them unreliable and/or practical to use.
The balance of the station structural shell consists of
precast concrete panels positioned in an inverted “V”
shape along the platform below the skylight. These panels,
positioned at the height of the train cars, are protected by
stainless steel cladding to shield them from environmental
elements.
Assessing the situation
A 2013 evaluation identi昀椀ed widespread leakage, mainly
from degraded seals between the skylight and precast
shelter—accounting for nearly 75 per cent of leaks. Expansion joints had visibly degraded, and corrosion was noted
on steel support.
The station’s access systems also presented challenges.
Both interior and exterior access setups had become di昀케cult to use over time due to limited mobility and outdated
designs. Neither system had been maintained or upgraded
since their installation, making them ine昀昀ective for reaching all parts of the skylight for necessary repairs.
The TTC faced several challenges in executing maintenance on the skylight system due to its age, operational
constraints, lack of access for maintenance and or report,
and limited budget. Given Yorkdale Station’s status as an
active transit hub, it was essential for the station to remain
fully operational during the retro昀椀t. This required all work
to be conducted during overnight closures, imposing
signi昀椀cant constraints on the available work hours each
night. Furthermore, the platform’s design as a suspended
slab introduced additional complexity, as any interior scaffolding would require shoring underneath, a task complicated by con昀椀ned spaces.
Yorkdale Subway Station’s most prominent feature is a 600-foot
barrel-vaulted glass skylight that spans nearly the entire length of
the central platform.
RENEWCANADA.NET
WSP
ORKDALE SUBWAY STATION in Toronto stands as an architectural icon within the city’s transit network.
Originally designed by Arthur Erickson Architects
in 1974 and completed in 1978, the station is a
multi-leveled concrete and steel structure set in
the median of the Allen Road expressway. Its most
prominent feature is a 600-foot (183 metre) barrel-vaulted
glass skylight that spans nearly the entire length of the
central platform. Supported by a curved structural steel
framing system, this skylight not only provides essential
daylight to the station’s platform but also serves as a visually memorable landmark, connecting transit users to the
Yorkdale Shopping Centre.
Over the years, however, the skylight has faced persistent water leakage issues that have created safety hazards,
particularly by making the platform slippery during rain
events. This leakage has not only posed risks to transit users but has also presented ongoing maintenance challenges. Major restoration work in the mid-1990s was implemented to address these issues by introducing a concealed
drainage system into the skylight. However, after 30 years
of service, water intrusion has become a concern once
again, and water leakage has continued to compromise the
station’s operational safety and aesthetic integrity.
