Commercial
Old and new
FACT FILE
Hylo, Bunhill Row,
London
Main client: CIT
Architect:
Horden Cherry Lee
Main contractor: Mace
Structural engineer:
AKT II
Steelwork contractor:
Bourne Steel
Steel tonnage: 870t
24 NSC
Jun 20
Located a short distance from Old
Street underground station, just north
of the City of London, a high-rise
development with a difference is
taking shape in Islington.
A 16-storey office block, built in the
1960s, is being reinvented by Mace, who are
stripping back the original concrete frame and
adding 13 new steel-framed floors to enlarge
the structure into a 29-storey edifice.
The works also include enlarging the two
podiums that sit adjacent to the building,
removing and replacing the existing two cores
as well as some substantial strengthening
works to the existing columns to allow them
to support extra loadings.
When viewing this construction project,
the obvious question is why not demolish the
old building and start afresh?
The answer is simple, according to AKT
II Associate, Michael Hynd. “The primary
driver was minimising the embodied carbon
of the scheme and being as environmentallyfriendly
as possible through reusing the
inherent capacity in the existing structure.
“It is more sustainable to refurbish
and enhance the building as opposed to
undertaking a large demolition programme,
which was something the local authority and
the client was keen to avoid.”
For this reason, main contractor Mace
decided on a cut-and-carve approach,
whereby as much of the original structure
is being retained, some existing floor plates
enlarged and the top of the building extended
with new floors.
The end product of this work will result
in Hylo being converted into what CIT
describes as a design-led work and lifestyle
office development comprising 29 floors with
25,800m2 of office and retail space.
Steve Riddell, Managing Director
Developments, CIT says: “As the line
between corporate and creative becomes
more integrated, our aim is to provide a
workplace solution that offers flexible spaces
that embrace collaboration and connectivity
at the same time. We are excited for Hylo to
become the defining destination in the Old
Street district.”
The choice of structural steelwork for
the new upper floors was made due to the
material’s lightweight attributes compared to
other framing solutions.
“The original building had residual
capacity within the floor slabs, which
were believed to have been designed to
accommodate printing works on some floors,”
says Mr Hynd.
“It’s fair to say the large diameter underream
piles had some free capacity which we’ve
used up with the new steel floors, however, no
other framing solution would have allowed
us to re-use the existing foundations, while
achieving the desired spans and floor zones in
the extension floors.”
Paul Fairhurst, Mace’s Project Director
at Hylo agrees and says: “We chose steel to
transform the Hylo structure because it is a
lighter material than concrete. This meant that
the original and new foundations did not have
to be as deep. We therefore had the knockon
benefit of cost efficiency and savings to
foundation design and installation.
“Secondly, steel is typically quicker to
erect and install than a traditional reinforced
concrete structure.”
Prior to Bourne Steel erecting the steelwork
and installing the metal deck flooring
for 13 new levels of the structure, a lot of
work had to be undertaken to the existing
frame. An extensive surveying programme
was completed in order to determine the
condition of the concrete. The results proved
to be very welcome as the frame was in good
order.
However, the two cores were too small
for the needs of the enlarged building and so
they were replaced with two new ones that
extended to the full new height of the building
A 1960s office block in central London is being given a new lease
of life with the addition of 13 new steel-framed floors.
Thirteen new steel
floors are extending the
structure up to 29 levels
/Multi-storey_office_buildings
/Braced_frames
/Construction
/Life_cycle_assessment_and_embodied_carbon#What_is_embodied_carbon.3F
/Multi-storey_office_buildings#Flexibility_and_adaptability
/The_case_for_steel
/The_case_for_steel#Take_a_load_off_your_foundations
/Construction#Installation_of_metal_decking